WO2022210125A1 - Steel wire for mechanical structural component and manufacturing method therefor - Google Patents
Steel wire for mechanical structural component and manufacturing method therefor Download PDFInfo
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- WO2022210125A1 WO2022210125A1 PCT/JP2022/013277 JP2022013277W WO2022210125A1 WO 2022210125 A1 WO2022210125 A1 WO 2022210125A1 JP 2022013277 W JP2022013277 W JP 2022013277W WO 2022210125 A1 WO2022210125 A1 WO 2022210125A1
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Images
Classifications
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
- C21D1/26—Methods of annealing
- C21D1/32—Soft annealing, e.g. spheroidising
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/06—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of rods or wires
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
- C21D9/52—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for wires; for strips ; for rods of unlimited length
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/60—Ferrous alloys, e.g. steel alloys containing lead, selenium, tellurium, or antimony, or more than 0.04% by weight of sulfur
Definitions
- the present disclosure relates to a steel wire for machine structural parts and a manufacturing method thereof.
- spheroidizing annealing is usually performed for the purpose of imparting cold workability to bar steel including hot-rolled wire rods. Then, the steel wire obtained by the spheroidizing annealing is subjected to cold working, and then subjected to machining such as cutting to form a predetermined component shape. Further, quenching and tempering are performed to adjust the final strength, and the mechanical structural parts are manufactured.
- Patent Document 1 As a method for obtaining a softened steel wire, for example, in Patent Document 1, as a method for producing a medium carbon steel with excellent cold forgeability, heating to an austenitizing temperature range two or more times in a spheroidizing annealing treatment is disclosed. shown to do. According to the manufacturing method of Patent Document 1, it is indicated that a steel for cold forging having a hardness of 83 HRB or less after spheroidizing annealing and a spheroidal carbide ratio in the structure of 70% or more can be obtained.
- Patent Document 2 discloses a steel material having low deformation resistance after spheroidizing annealing and excellent cold forgeability, and a method for manufacturing the same.
- steel satisfying a predetermined chemical composition is hot-worked, cooled to room temperature, then heated to a temperature range of A1 point to A1 point + 50 ° C., and after the temperature rise, the A1 After holding for 0 to 1 hour in the temperature range from point to A1 point +50 ° C, the temperature range from the temperature range from A1 point to A1 point +50 ° C to A1 point -100 ° C to A1 point -30 ° C is 10 to 200 ° C.
- the temperature is raised to the temperature range of A1 point to A1 point + 30 ° C. and held in the temperature range of A1 point to A1 point + 30 ° C.
- the temperature range from the A1 point to the A1 point + 30 ° C. until the A1 point is reached.
- the residence time is 10 minutes to 2 hours, and the cooling temperature range from the temperature range of A1 point to A1 point +30 ° C to A1 point -100 ° C to A1 point -20 ° C is an average cooling rate of 10 to 100 ° C/hr. After cooling at , it is shown to be held in the cooling temperature range for 10 minutes to 5 hours and then further cooled.
- Patent Document 3 describes a steel wire for machine structural parts that can exhibit excellent cold workability by reducing deformation resistance during cold working and improving crack resistance.
- a steel wire for machine structural parts is disclosed, in which the metallographic structure of the steel is composed of ferrite and cementite, and the number ratio of cementite present in ferrite grain boundaries is 40% or more of the total number of cementite.
- the manufacturing conditions for the rolled wire rod subjected to spheroidizing annealing are finish rolling at 800°C or higher and 1050°C or lower, first cooling at an average cooling rate of 7°C/sec or higher, and average cooling rate of 1°C.
- the end and the start of the second cooling are performed within the range of 700 to 750 ° C.
- the end of the second cooling and the start of the third cooling are performed within the range of 600 to 650 ° C.
- the end of the third cooling is performed. It is indicated that it is preferable to set the temperature to 400° C. or lower.
- wire rod and “steel bar” refer to wire-shaped and rod-shaped steel materials obtained by hot rolling, and are not subjected to heat treatment such as spheroidizing annealing or wire drawing.
- steel refers to steel.
- steel wire refers to a wire rod or steel bar subjected to at least one of heat treatment such as spheroidizing annealing and wire drawing.
- the wire rod, steel bar and steel wire are collectively referred to as "long steel”.
- Aspect 1 of the present invention is C: 0.05% by mass to 0.60% by mass, Si: 0.005% by mass to 0.50% by mass, Mn: 0.30% by mass to 1.20% by mass, P: more than 0% by mass, 0.050% by mass or less, S: more than 0% by mass, 0.050% by mass or less, Al: 0.001% by mass to 0.10% by mass, Cr: more than 0% by mass, 1.5% by mass or less, and N: more than 0% by mass, 0.02% by mass or less, containing, the balance consisting of iron and inevitable impurities,
- the half width of the X-ray diffraction peak on the (211) plane of the ferrite grain is 0.500° or less
- Steel for machine structural parts, wherein the average equivalent circle diameter of all cementite is (1.863-2.13 [C]) ⁇ m or less when the amount of C (% by mass) in the steel is represented by [C] is a line.
- Aspect 2 of the present invention is Furthermore, Cu: more than 0% by mass, 0.25% by mass or less, Ni: more than 0% by mass, 0.25% by mass or less, Mo: more than 0% by mass, 0.50% by mass or less and B: more than 0% by mass, 0.01% by mass or less for machine structural parts according to aspect 1, containing one or more selected from the group consisting of Steel wire.
- Aspect 3 of the present invention is Furthermore, Ti: more than 0% by mass, 0.2% by mass or less, The machine according to aspect 1 or 2, containing one or more selected from the group consisting of Nb: more than 0% by mass and 0.2% by mass or less, and V: more than 0% by mass and 0.5% by mass or less Steel wire for structural parts.
- Aspect 4 of the present invention is Furthermore, Mg: more than 0% by mass, 0.02% by mass or less, Ca: more than 0% by mass, 0.05% by mass or less, Li: more than 0 mass%, 0.02 mass% or less, and REM: more than 0 mass%, containing one or more selected from the group consisting of 0.05 mass% or less, any one of aspects 1 to 3 1.
- Aspect 5 of the present invention is 5.
- Aspect 6 of the present invention is A long steel satisfying the chemical composition according to any one of aspects 1 to 4, A method for producing a steel wire for machine structural parts according to any one of aspects 1 to 5, which includes a step of performing spheroidizing annealing including the following steps (1) to (3). (1) After heating to a temperature T1 of (A1 + 8 ° C.) to (A1 + 31 ° C.), heating and holding at the temperature T1 for more than 1 hour and 6 hours or less, (2) Cooling to a temperature T2 exceeding 650 ° C.
- A1 is calculated by the following formula (1).
- A1 (° C.) 723+29.1 ⁇ [Si] ⁇ 10.7 ⁇ [Mn]+16.9 ⁇ [Cr] ⁇ 16.9 ⁇ [Ni] (1)
- [element] represents the content (% by mass) of each element, and the content of elements not included is zero.
- Aspect 7 of the present invention is Aspect 6.
- FIG. 4 is a diagram illustrating conditions for spheroidizing annealing in the method for manufacturing a steel wire for machine structural parts according to the present embodiment.
- 1 is a diagram illustrating a heat treatment process in the prior art
- Fig. 3 is a diagram illustrating a heat treatment process in another prior art
- Fig. 3 is a diagram illustrating a heat treatment process in another prior art
- the present inventors have made extensive studies from various angles in order to realize a steel wire for machine structural parts that has both excellent cold workability and hardenability.
- the hardness of the steel after spheroidizing annealing can be reduced and the cold workability is improved.
- the present inventors focused on the idea that the rod-shaped cementite generated in the cooling process during spheroidizing contains a large amount of interfacial strain. We thought that it would be possible to reduce the Furthermore, the present inventors thought that by reducing the size of all cementite, it is possible to reduce the amount of cementite that remains undissolved during high-temperature holding in the quenching process, thereby improving the hardenability.
- the present inventors have found that, particularly in the metal structure, the half-value width of the X-ray diffraction peak in the (211) plane of the ferrite grain, which is an indicator of the amount of strain in ferrite, is set to a certain value or less.
- the inventors found that the average equivalent circle diameter of all cementite should be set to a certain value or less according to the amount of C in the steel material.
- the present inventors set the chemical composition within a certain range, and performed spheroidizing annealing under particularly specified conditions in the method of manufacturing the steel wire for machine structural parts. I found that it is effective.
- the metal structure of the steel wire for machine structural parts according to the present embodiment will be described first.
- the half width of the X-ray diffraction peak on the (211) plane of the ferrite grains is 0.500° or less.
- the half width of the ferrite peak in X-ray diffraction indicates the degree of strain introduction related to the dislocation density. A smaller half-value width of the peak indicates a smaller strain in the steel. Therefore, the smaller the peak half-value width, the smaller the strain in the steel. As a result, the hardness of the steel is lowered and the cold workability is improved.
- the peak half-value width of the (211) plane of ferrite which can clearly grasp the tendency, is defined as a representative.
- the peak half width is preferably 0.495° or less, more preferably 0.493° or less.
- the lower limit of the peak half-value width is not particularly limited, but considering the component composition and production conditions according to the embodiment of the present invention, it is approximately 0.100°.
- the average equivalent circle diameter of all cementite is (1.863-2.13 [C]) ⁇ m or less when the amount of C (% by mass) in the steel material is represented by [C]] If the cementite is excessively coarsened, the cementite will not be sufficiently dissolved during the high temperature hold in the quenching treatment step after cold working, and a sufficiently high hardness cannot be obtained by quenching. Therefore, in the present embodiment, when the amount of C (% by mass) in the steel material is represented by [C], the average circle equivalent diameter of all cementite is set to (1.863-2.13 [C]) ⁇ m or less. . Preferably, it is (1.858-2.13 [C]) ⁇ m or less.
- the average equivalent circle diameter of all cementite is preferably (1.668-2.13 [C]) ⁇ m or more.
- the average equivalent circle diameter of all cementite is more preferably (1.669-2.13 [C]) ⁇ m or more.
- the form of all cementite is not particularly limited, and includes spherical cementite as well as rod-shaped cementite with a large aspect ratio.
- the aspect ratio is the ratio (major axis/minor axis) of the longest diameter of cementite particles to the longest diameter in the direction perpendicular to the long diameter.
- the standard for the size of cementite to be measured is not limited, the size of cementite that can be determined by the method of measuring the average circle equivalent diameter of all cementites, which will be described later, is the minimum size. Specifically, cementite particles having an equivalent circle diameter of 0.3 ⁇ m or more are to be measured.
- the metal structure of the steel wire for machine structural parts according to the present embodiment is a spheroidized structure having spheroidized cementite, and is obtained by, for example, performing spheroidizing annealing, which will be described later, on a steel bar that satisfies the chemical composition described later. be able to.
- the metal structure of the steel wire for machine structural parts of this embodiment is substantially composed of ferrite and cementite.
- substantially means that the area ratio of ferrite in the metal structure of the steel wire for machine structural parts of the present embodiment is 90% or more, and the area ratio of rod-shaped cementite having an aspect ratio of 3 or more is 5% or less. If the adverse effect on cold workability is small, it means that the area ratio of nitrides such as AlN and inclusions other than nitrides is allowed to be less than 3%. Further, the area ratio of the ferrite may be 95% or more.
- the term “ferrite” refers to a portion whose crystal structure is the bcc structure, and includes ferrite in pearlite, which is a layered structure of ferrite and cementite.
- the "ferrite grains” that are the object of measurement of the "ferrite grain size” include grains containing rod-shaped cementite that is insufficiently spheroidized and generated during spheroidizing annealing. Crystal grains containing rod-shaped cementite (pearlite grains) that may remain before annealing are excluded.
- crystal grains without cementite present in the grains can be confirmed when observed at 1000 times using an optical microscope. It means “crystal grains in which cementite is present in the grains and the shape of the cementite can be observed (that is, the boundary between cementite and ferrite can be clearly observed)". Crystal grains in which the shape of cementite cannot be observed at a magnification of 1000 using the optical microscope (that is, the boundary between cementite and ferrite cannot be clearly observed) are not subject to judgment in the present embodiment, and "ferrite crystal grains” exclude.
- the average value of the ferrite crystal grain size in the metal structure is 30 ⁇ m or less.
- the average ferrite grain size is more preferably 25 ⁇ m or less, still more preferably 20 ⁇ m or less. The smaller the average ferrite crystal grain size, the better, but the lower limit can be about 2 ⁇ m, considering possible production conditions and the like.
- the steel wire for machine structural parts according to the present embodiment which satisfies the following chemical composition and has the metal structure described above, can achieve both a low hardness that enables good cold working and a high hardness after quenching treatment. .
- HV Hardness (after spheroidizing annealing) ⁇ 91([C]+[Cr]/9+[Mo]/2)+91 (2) Hardness after quenching treatment (HV) > 380 ln ([C]) + 1010 (3)
- C is an element that controls the strength of steel materials, and the strength after quenching and tempering increases as the content increases.
- the lower limit of the amount of C was set to 0.05% by mass.
- the amount of C is preferably 0.10% by mass or more, more preferably 0.15% by mass or more, and still more preferably 0.20% by mass or more.
- the upper limit of the amount of C was set at 0.60% by mass.
- the amount of C is preferably 0.55% by mass or less, more preferably 0.50% by mass or less.
- Si 0.005% by mass to 0.50% by mass
- Si is used as a deoxidizer during smelting and contributes to strength improvement.
- the lower limit of the amount of Si was set to 0.005% by mass.
- the amount of Si is preferably 0.010% by mass or more, more preferably 0.050% by mass or more.
- Si contributes to solid-solution strengthening of ferrite and has the effect of considerably increasing the strength after spheroidizing annealing. If the Si content is excessive, the cold workability deteriorates due to the above effect, so the upper limit of the Si content was made 0.50% by mass.
- the amount of Si is preferably 0.40% by mass or less, more preferably 0.35% by mass or less.
- Mn 0.30% by mass to 1.20% by mass
- Mn is an element that effectively acts as a deoxidizer and contributes to the improvement of hardenability.
- the lower limit of the amount of Mn was set to 0.30% by mass.
- the Mn content is preferably 0.35% by mass or more, more preferably 0.40% by mass or more.
- the upper limit of the amount of Mn was set to 1.20% by mass.
- the Mn content is preferably 1.10% by mass or less, more preferably 1.00% by mass or less. From the viewpoint of further suppressing a decrease in toughness, the content may be less than 0.50% by mass, and may be 0.45% by mass or less.
- P more than 0% by mass, 0.050% by mass or less
- P phosphorus
- the amount of P was set to 0.050% by mass or less.
- the P content is preferably 0.030% by mass or less, more preferably 0.020% by mass or less. Although the P content is preferably as small as possible, it is usually contained in an amount of 0.001% by mass or more.
- S more than 0% by mass, 0.050% by mass or less
- S sulfur
- the amount of S is set to 0.050% by mass or less.
- the S content is preferably 0.030% by mass or less, more preferably 0.020% by mass or less.
- the amount of S is preferably as small as possible, it is usually contained in an amount of 0.001% by mass or more.
- Al 0.001% by mass to 0.10% by mass
- Al is an element contained as a deoxidizing agent, and has the effect of reducing impurities accompanying deoxidizing. In order to exhibit this effect, the lower limit of the amount of Al was set to 0.001% by mass.
- the Al content is preferably 0.005% by mass or more, more preferably 0.010% by mass or more.
- the upper limit of the amount of Al was set to 0.10% by mass.
- the Al content is preferably 0.08% by mass or less, more preferably 0.05% by mass or less.
- Cr more than 0% by mass, 1.5% by mass or less
- Cr is an element that has the effect of improving the hardenability of steel and increasing the strength, and also has the effect of promoting spheroidization of cementite. Specifically, Cr dissolves in cementite and delays the dissolution of cementite during heating for spheroidizing annealing. Since the cementite does not dissolve and partially remains during heating, rod-shaped cementite having a large aspect ratio is less likely to form during cooling, making it easier to obtain a spheroidized structure. Therefore, the Cr content is more than 0% by mass, preferably 0.01% by mass or more. Further, it may be 0.05% by mass or more, and even more preferably 0.10% by mass or more.
- the content can be more than 0.30% by mass, and can also be more than 0.50% by mass. If the amount of Cr is excessive, the diffusion of elements including carbon is delayed, and the dissolution of cementite is delayed more than necessary, making it difficult to obtain a spheroidized structure. As a result, the hardness reduction effect of the present invention may be reduced. Therefore, the Cr content is 1.50% by mass or less, preferably 1.40% by mass or less, and more preferably 1.25% by mass or less. From the viewpoint of accelerating the diffusion of the elements, the Cr content can be set to 1.00% by mass or less, 0.80% by mass or less, or 0.30% by mass or less.
- N is an impurity that is inevitably contained in steel, but when a large amount of solid-solution N is contained in steel, it causes an increase in hardness and a decrease in ductility due to strain aging, and deteriorates cold workability. Therefore, the N content is 0.02% by mass or less, preferably 0.015% by mass or less, and more preferably 0.010% by mass or less.
- the balance is iron and unavoidable impurities.
- unavoidable impurities trace elements (for example, As, Sb, Sn, etc.) brought in depending on the conditions of raw materials, materials, manufacturing equipment, etc. are allowed.
- elements such as P and S, whose content is generally preferably as low as possible and thus are unavoidable impurities, but whose composition range is separately defined as described above.
- the term "inevitable impurities" constituting the balance is a concept excluding elements whose composition range is separately defined.
- the steel wire for machine structural parts according to the present embodiment only needs to contain the above elements in its chemical composition.
- the optional elements described below may not be contained, but by containing them together with the above elements as necessary, it is possible to more easily ensure hardenability and the like.
- the selected elements are described below.
- Cu, Ni, Mo and B are all effective elements for increasing the strength of the final product by improving the hardenability of the steel material, and may be contained alone or in combination of two or more. The effect of these elements increases as their content increases.
- a preferable lower limit for effectively exhibiting the above effects is more than 0% by mass, more preferably 0.02% by mass or more, and still more preferably 0.05% by mass or more for each of Cu, Ni, and Mo.
- the content of each of Cu and Ni is 0.22% by mass or less, more preferably 0.20% by mass or less, and the content of Mo is more preferably 0.40% by mass or less, and further preferably It is preferably 0.35% by mass or less, and the B content is more preferably 0.007% by mass or less, still more preferably 0.005% by mass or less.
- Ti, Nb and V form a compound with N and reduce solid solution N to exhibit the effect of reducing deformation resistance.
- the effect of these elements increases as their content increases.
- the preferable lower limit for effectively exhibiting the above effects for any element is more than 0% by mass, more preferably 0.03% by mass or more, and still more preferably 0.05% by mass or more.
- the compounds formed may lead to an increase in deformation resistance, which may rather deteriorate the cold workability.
- the V content is preferably 0.5% by mass or less.
- the content of each of Ti and Nb is more preferably 0.18% by mass or less, more preferably 0.15% by mass or less, and the V content is more preferably 0.45% by mass or less, further preferably It is 0.40% by mass or less.
- Mg more than 0% by mass, 0.02% by mass or less
- Ca more than 0% by mass, 0.05% by mass or less
- Li more than 0% by mass, 0.02% by mass or less
- rare earth elements Rare Earth Metal :REM
- Mg, Ca, Li and REM are elements effective in spheroidizing sulfide-based inclusions such as MnS and improving the deformability of steel. These effects increase as the content increases.
- the content of Mg, Ca, Li and REM is preferably more than 0% by mass, more preferably 0.0001% by mass or more, and still more preferably 0.0005% by mass or more. be. However, even if it is contained excessively, the effect is saturated, and the effect corresponding to the content cannot be expected. , more preferably 0.015% by mass or less, and the content of Ca and REM is preferably 0.05% by mass or less, more preferably 0.045% by mass or less, and still more preferably 0.040% by mass or less. is.
- each of Mg, Ca, Li and REM may be contained alone, or two or more kinds thereof may be contained. Content is fine.
- the REM is meant to include lanthanoid elements (15 elements from La to Lu), Sc (scandium) and Y (yttrium).
- the shape of the steel wire for machine structural parts according to this embodiment is not particularly limited. For example, those having a diameter of 5.5 mm to 60 mm can be used.
- the spheroidizing annealing conditions should be appropriately controlled as described below in manufacturing the steel wire for machine structural parts. is preferred.
- the hot rolling process for producing a wire rod or steel bar to be subjected to spheroidizing annealing is not particularly limited, and a conventional method may be followed.
- wire drawing may be applied before spheroidizing annealing.
- the diameter of the wire rod, steel wire, and steel bar to be subjected to spheroidizing annealing is not particularly limited.
- FIG. 1 shows an example of a diagram explaining the conditions of spheroidizing annealing in the manufacturing method according to the embodiment of the present invention, and the number of repetitions of the cooling-heating process is not limited to this FIG.
- a method for manufacturing a steel wire for machine structural parts includes a spheroidizing annealing step including steps (1) to (3) below.
- A1 is calculated by the following formula (1).
- A1 (° C.) 723+29.1 ⁇ [Si] ⁇ 10.7 ⁇ [Mn]+16.9 ⁇ [Cr] ⁇ 16.9 ⁇ [Ni] (1)
- [element] represents the content (% by mass) of each element, and the content of elements not included is zero.
- the temperature T1 must be A1+8° C. or higher.
- the temperature T1 is preferably A1+15° C. or higher, more preferably A1+20° C. or higher.
- the temperature T1 was set to A1+31° C. or lower.
- the temperature T1 is preferably A1+30° C. or lower, more preferably A1+29° C. or lower.
- the heating and holding time (t1) at the temperature T1 is too short, rod-shaped cementite with large interfacial strain remains in the ferrite crystal grains, the hardness increases, and the cold workability decreases.
- the heating holding time (t1) should be more than 1 hour and 6 hours or less.
- the heating and holding time (t1) is preferably 1.5 hours or longer, more preferably 2.0 hours or longer. If the heating holding time (t1) is too long, the heat treatment time will be long and the productivity will be lowered. Therefore, the heating and holding time (t1) is 6 hours or less, preferably 5 hours or less, and more preferably 4 hours or less. Note that the average heating rate during heating ([1] in FIG.
- the temperature (T1) from (A1 + 8 ° C.) to (A1 + 31 ° C.) does not affect the steel material properties, so the temperature can be raised at an arbitrary rate. .
- the temperature may be raised at a rate of 30° C./hour to 100° C./hour.
- the temperature at point A1 is calculated by the following formula (1) described on page 273 of Leslie Iron and Steel Materials Science (Maruzen).
- A1 (° C.) 723+29.1 ⁇ [Si] ⁇ 10.7 ⁇ [Mn]+16.9 ⁇ [Cr] ⁇ 16.9 ⁇ [Ni] (1)
- [element] represents the content (% by mass) of each element, and the content of elements not included is zero.
- Cooling to a temperature T2 exceeding 650 ° C. and not exceeding (A1-17 ° C.) and heating to a heating temperature higher than the temperature T2 and not exceeding (A1 + 60 ° C.) Perform a total of 2 to 6 times of the cooling-heating process. ([7] in Fig. 1)] Subsequently, the cooling-heating step of cooling to a temperature T2 above 650° C. to (A1-17° C.) and heating to a heating temperature higher than the temperature T2 (A1+60° C.) or less is performed 2 to 6 times in total. Each step of the cooling-heating process is described in detail below.
- the average cooling rate is preferably 100° C./hour or less.
- the average cooling rate is more preferably 90° C./hour or less, still more preferably 80° C./hour or less.
- the average cooling rate is preferably 1° C./hour or more, more preferably 3° C./hour or more, and even more preferably 5° C./hour or more.
- the ultimate temperature (T2) is too low, the annealing time will be prolonged. Therefore, the ultimate temperature (T2) of cooling needs to exceed 650°C. According to the manufacturing method according to the present embodiment, even if the ultimate cooling temperature (T2) exceeds 650° C., the cementite can be controlled into a desired form without long-term annealing.
- the cooling temperature (T2) is preferably 670° C. or higher.
- the ultimate cooling temperature (T2) is too high, excessive reprecipitation of rod-shaped cementite with a large interfacial strain will increase the amount of strain in the ferrite and lower the cold workability.
- the ultimate temperature (T2) of cooling needs to be lower than the A1 point by a certain amount or more. Therefore, the upper limit of the cooling temperature (T2) was set to A1-17°C.
- the ultimate temperature (T2) of cooling is preferably A1-18° C. or lower. Further, if the temperature is maintained after reaching the ultimate cooling temperature (T2), the heat treatment time will be prolonged. Therefore, it is better not to hold from these points of view. However, in order to equalize temperature variations in the furnace, it may be held for a short period of time.
- the holding time at the cooling reaching temperature T2 is preferably within 1 hour.
- the steel is heated from the ultimate temperature (T2) of the cooling.
- the ultimate temperature of heating as shown in [6] in FIG. 1, that is, the heating temperature (T3) may be any temperature within the temperature range higher than the temperature T2 and not higher than (A1+60° C.).
- the heating temperature is preferably A1° C. or higher from the viewpoint of sufficiently remelting the rod-shaped cementite having a large interfacial strain generated in the step (2-i).
- the heating temperature (T3) is preferably A1+57° C. or lower.
- the average temperature increase rate from the cooling temperature (T2) to the heating temperature (T3) as shown in [5] of FIG. 1 is not particularly limited.
- the average temperature increase rate is, for example, 200° C./ It may be less than an hour. Further, for example, from the viewpoint of sufficiently suppressing coarsening of the cementite generated by this heating and further enhancing hardenability, the heating rate can be set to 5° C./hour or more.
- the holding time is set to 1 hour or less to suppress redissolution of spherical cementite generated in the step of cooling to the temperature T2.
- the magnitude relationship between the heating temperature (T3) and the temperature T1 is not particularly limited.
- the heating temperature (T3) may be the same temperature as the temperature T1, or the heating temperature (T3) may be It may be higher than the temperature T1.
- the cooling-heating step of (2-i) cooling and (2-ii) heating is repeated multiple times, but each time, the temperature T2 and the temperature T3 satisfy the above ranges. There is a need.
- the number of cooling-heating steps was set to 6 or less.
- the number of times of the above cooling (2-i) and the above heating (2-ii) is four.
- the temperature (T2) reached by each cooling may be different within a defined range.
- the average cooling rate in the cooling-heating process refers to the average cooling rate from the temperature T1 to the cooling target temperature (T2) in the first cooling-heating process, and from the heating temperature (T3) after the second time. It means the average cooling rate up to the cooling ultimate temperature (T2).
- the ultimate cooling temperature (T4) is preferably (A1-250°C) or higher, more preferably (A1-200°C) or higher, and even more preferably (A1-150°C) or higher, from the viewpoint of shortening the annealing time. be.
- the average cooling rate (R3) must be 20°C/hour or less in order to suppress the reprecipitation of rod-shaped cementite with a large amount of interfacial strain and reduce the amount of strain in ferrite.
- the average cooling rate (R3) is preferably 18°C/hour or less, more preferably 15°C/hour or less. If the average cooling rate (R3) is too slow, the cementite is excessively coarsened, and the cementite is not sufficiently dissolved during the high temperature holding in the quenching process, resulting in a decrease in hardness after quenching, that is, deterioration of hardenability. . Further, the annealing time is lengthened, resulting in a decrease in productivity. Therefore, the lower limit of the average cooling rate (R3) was set at 5°C/hour.
- the average cooling rate (R3) is preferably 10°C/hour or more.
- the ultimate cooling temperature (T4) may be any temperature as long as it is less than (A1-30° C.). Cooling below the arbitrary temperature is not particularly limited, and may be air cooling, for example.
- the above spheroidizing annealing may be repeated once or multiple times. From the viewpoint of suppressing excessive coarsening of cementite and securing productivity, for example, it is preferably 4 times or less, more preferably 3 times or less.
- the spheroidizing annealing is repeated multiple times, it may be repeated under the same conditions or under different conditions within the above specified range.
- wire drawing may be added between the spheroidizing annealing. For example, wire drawing before spheroidizing annealing to be described later ⁇ first spheroidizing annealing ⁇ wire drawing ⁇ second spheroidizing annealing can be performed in this order.
- processes other than the spheroidizing annealing process are not particularly limited.
- a step of wire drawing with a reduction in area of preferably 15% or less may be included for the purpose of adjusting dimensions.
- the area reduction rate is more preferably 10% or less, still more preferably 8% or less, and even more preferably 5% or less.
- the area reduction rate is more preferably 10% or more, still more preferably 15% or more, and even more preferably 20% or more.
- the area reduction rate is preferably 50% or less.
- Annealing was performed using the above wire or steel wire using a laboratory furnace.
- the wire or steel wire was heated to T1 shown in Table 2 and held for t1.
- 5 ° C. / hour was heated to the temperature T2 in Table 2
- 5 ° C. / hour was heated to a heating temperature higher than the temperature T2 in Table 2 (A1 + 60 ° C.) or less Heating was performed at an average heating rate of 100°C/hour.
- This cooling and heating process was repeated for the number of cooling-heating cycles shown in Table 2.
- the material was cooled to temperature T4 at an average cooling rate R3 in Table 2.
- manufacturing conditions G1, G2, T and U do not repeat the cooling-heating process. Specifically, for example, under the manufacturing conditions G1, the temperature was raised to 740° C., held for 5 hours, cooled to 640° C. at an average cooling rate of 10° C./hour, and then air-cooled.
- the heat treatment conditions that satisfy the manufacturing conditions of Patent Document 3, specifically, the conditions indicated as SA2 in the example of Patent Document 3 are performed as the manufacturing conditions H, that is, the heat treatment process shown in FIG. 2 is repeated five times. rice field.
- Sample No. shown in Table 3. 17 as the manufacturing condition L, the heat treatment conditions satisfying the manufacturing conditions of Patent Document 1; The fifth spheroidizing annealing condition in 1 was performed, ie the heat treatment step shown in FIG. 3 was repeated three times.
- As manufacturing conditions M heat treatment conditions satisfying the manufacturing conditions of Patent Document 2, specifically condition c in Table 2 of Patent Document 2, that is, heat treatment in the pattern shown in FIG. 4 was performed.
- the annealing parameters listed in Table 2 are the set temperatures of the heat treatment furnace.
- a thermocouple was attached to the steel material to test the difference between the actual temperature of the steel material and the set temperature.
- the average value of the ferrite crystal grain size, the average equivalent circle diameter of all cementite, and the half-value width of the X-ray diffraction peak on the (211) plane of the ferrite grains. sought as follows.
- the hardness after spheroidizing annealing and the hardness after quenching treatment were measured and evaluated by the following methods.
- the ferrite grain size was measured as follows.
- the test piece was etched using nital (2% by volume of nitric acid, 98% by volume of ethanol) to expose the structure. Then, with an optical microscope, the structure of the test piece in which the above structure is exposed is observed at a magnification of 400 times, and ferrite grains of an average size representing the structure of the entire steel wire can be observed within the evaluation surface.
- the half-value width of the X-ray diffraction peak in ferrite grains was obtained by measuring the half-value width of the X-ray diffraction peak in the (211) plane of ferrite at the D/4 position (D: diameter) of the steel wire after spheroidizing annealing. .
- the test piece was embedded in resin so that the cross section of the steel wire after spheroidizing annealing could be observed, and was subjected to Emily polishing, diamond buffing, and electropolishing to remove strain on the evaluation surface introduced during sample preparation. provided.
- the hardness after spheroidizing annealing is determined by the amount of C (% by mass), the amount of Cr (% by mass), and the amount of Mo (% by mass) in the steel [C], [Cr], and [Mo], respectively. (elements not included are zero mass%), the case where the following formula (2) is satisfied is evaluated as "OK” as being excellent in cold workability, and the following formula (2) is not satisfied The case was evaluated as "NG” as being inferior in cold workability.
- each sample after hardening treatment was measured as follows. First, as a sample for quenching treatment, each sample after spheroidizing annealing is processed so that the thickness (t), which is the length in the rolling direction, is 5 mm so that quenching can be sufficiently performed in the quenching treatment. did. As a quenching treatment, the sample was held at a high temperature of A3+ (30 to 50° C.) for 5 minutes, and then water-cooled after the high temperature holding. A3 is a value derived from the following formula (5). Also, the high temperature holding time here was the time after the furnace temperature reached the set temperature.
- A3 (°C) 910 - 203 x ⁇ ([C]) - 14.2 x [Ni] + 44.7 x [Si] + 104 x [V] + 31.5 x [Mo] + 13.1 x [W] - 30 ⁇ [Mn] ⁇ 11 ⁇ [Cr] ⁇ 20 ⁇ [Cu]+700 ⁇ [P]+400 ⁇ [Al]+120 ⁇ [As]+400 ⁇ [Ti] (5)
- [element] represents the content (% by mass) of each element, and an element not contained is calculated as 0%.
- No. No. 13 is an example in which annealing is performed under the annealing conditions SA2 of Patent Document 3 as the manufacturing condition H that satisfies the manufacturing conditions shown in Patent Document 3. Under these manufacturing conditions, the cementite was excessively coarsened by annealing, and the hardness after quenching treatment was lower than the reference value, resulting in poor hardenability.
- T1 is 730 ° C., which is lower than A1 + 8 ° C., so the amount of strain in ferrite increases due to rod-shaped cementite with a large amount of interfacial strain remaining from before annealing, and the half-value width of the X-ray diffraction peak was over 0.500°. Therefore, the hardness after spheroidizing annealing was higher than the reference value, resulting in poor cold workability.
- the average cooling rate R3 is as high as 21 ° C./hour, so the rod-shaped cementite with a large interface strain generated in the step [8] in FIG.
- the price range exceeded 0.500°. Therefore, the hardness after spheroidizing annealing was higher than the reference value, resulting in poor cold workability.
- T2 is as high as 710° C., so the amount of strain in the ferrite increases due to rod-shaped cementite with a large interface strain generated in the step [3] of FIG. over 500°. Therefore, the hardness after spheroidizing annealing was higher than the reference value, resulting in poor cold workability.
- No. No. 17 is an example in which annealing is performed under manufacturing condition L, which satisfies the manufacturing conditions shown in Patent Document 1. Under these manufacturing conditions, t1 is not maintained, etc., and due to rod-shaped cementite with a large amount of interfacial strain remaining from before annealing, the amount of strain in the ferrite increases, and the half-value width of the X-ray diffraction peak exceeds 0.500°. rice field. Therefore, the hardness after spheroidizing annealing was higher than the reference value, resulting in poor cold workability.
- No. No. 18 is an example in which annealing is performed under the condition c of Patent Document 2 as the manufacturing condition M that satisfies the manufacturing conditions shown in Patent Document 2.
- the amount of strain in the ferrite increased due to rod-shaped cementite with a large amount of interfacial strain remaining from before annealing, and the half width of the X-ray diffraction peak exceeded 0.500°. Therefore, the hardness after spheroidizing annealing was higher than the reference value, resulting in poor cold workability.
- the steel wire for machine structural parts according to the present embodiment has low deformation resistance at room temperature when manufacturing various machine structural parts, and can suppress abrasion and breakage of jigs and tools for plastic working such as molds. It exhibits excellent cold workability, such as suppressing the occurrence of cracks during forging. Furthermore, since it is excellent in hardenability, high hardness can be secured by hardening treatment after cold working. For these reasons, the steel wire for machine structural parts according to the present embodiment is useful as a steel wire for cold working machine structural parts.
- the steel wire for machine structural parts according to the present embodiment can be subjected to cold working such as cold forging, cold heading, and cold rolling to obtain various machine structures such as parts for automobiles and parts for construction machinery. Used to manufacture parts.
- mechanical structural parts include bolts, screws, nuts, sockets, ball joints, inner tubes, torsion bars, clutch cases, cages, housings, hubs, covers, cases, receiving washers, tappets, saddles, bulks, Inner cases, clutches, sleeves, outer races, sprockets, cores, stators, anvils, spiders, rocker arms, bodies, flanges, drums, joints, connectors, pulleys, metal fittings, yokes, mouthpieces, valve lifters, spark plugs, pinion gears, steering Examples include mechanical parts such as shafts and common rails, electrical parts, and the like.
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Abstract
Provided is a steel wire for a mechanical structural component, said steel wire containing 0.05 mass%-0.60 mass% of C, 0.005 mass%-0.50 mass% of Si, 0.30 mass%-1.20 mass% of Mn, more than 0 mass% but no more than 0.050 mass% of P, more than 0 mass% but no more than 0.050 mass% of S, 0.001 mass%-0.10 mass% of Al, more than 0 mass% but no more than 1.5 mass% of Cr, and more than 0 mass% but no more than 0.02 mass% of N, the remainder thereof comprising iron and unavoidable impurities, wherein the x-ray diffraction peak half width in the (211) plane of ferrite grains is 0.500° or less, and the average circle-equivalent diameter of all cementite, when the quantity (mass%) of C in the steel is represented as [C], is (1.863-2.13[C]) μm or less.
Description
本開示は、機械構造部品用鋼線およびその製造方法に関する。
The present disclosure relates to a steel wire for machine structural parts and a manufacturing method thereof.
自動車用部品、建設機械用部品等の各種機械構造用部品を製造するにあたっては、通常、熱間圧延線材を含む条鋼に冷間加工性を付与する目的で球状化焼鈍が施される。そして、球状化焼鈍して得られた鋼線に、冷間加工を施し、その後切削加工などの機械加工を施すことによって、所定の部品形状に成形される。さらに、焼入れ焼戻しを行い最終的な強度調整が行われて、機械構造用部品が製造される。
In the manufacture of various machine structural parts such as automobile parts and construction machinery parts, spheroidizing annealing is usually performed for the purpose of imparting cold workability to bar steel including hot-rolled wire rods. Then, the steel wire obtained by the spheroidizing annealing is subjected to cold working, and then subjected to machining such as cutting to form a predetermined component shape. Further, quenching and tempering are performed to adjust the final strength, and the mechanical structural parts are manufactured.
近年、冷間加工工程において、鋼材の割れの防止や金型寿命を向上させるため、従来よりも更に軟質化された鋼線が望まれている。
In recent years, there has been a demand for steel wires that are even softer than before in order to prevent cracks in the steel material and improve mold life in the cold working process.
軟質化された鋼線を得る方法として、例えば特許文献1には、冷間鍛造性に優れた中炭素綱の製造方法として、球状化焼鈍処理において2回以上のオーステナイト化温度域への加熱を行うことが示されている。特許文献1の製造方法によれば、球状化焼鈍後の硬さが83HRB以下でかつ組織中の球状炭化物比率が70%以上である冷間鍛造用鋼が得られると示されている。
As a method for obtaining a softened steel wire, for example, in Patent Document 1, as a method for producing a medium carbon steel with excellent cold forgeability, heating to an austenitizing temperature range two or more times in a spheroidizing annealing treatment is disclosed. shown to do. According to the manufacturing method of Patent Document 1, it is indicated that a steel for cold forging having a hardness of 83 HRB or less after spheroidizing annealing and a spheroidal carbide ratio in the structure of 70% or more can be obtained.
特許文献2には、球状化焼鈍後の変形抵抗が低く冷間鍛造性に優れた特性を有する鋼材、およびその製造方法が開示されている。該製造方法として、所定の成分組成を満足する鋼を、熱間加工処理した後、室温まで冷却し、その後、A1点~A1点+50℃の温度域に昇温して、昇温後に前記A1点~A1点+50℃の温度域で0~1hr保持してから、前記A1点~A1点+50℃の温度域からA1点-100℃~A1点-30℃までの温度域を10~200℃/hrの平均冷却速度で冷却する焼鈍処理を2回以上行った後、A1点~A1点+30℃の温度域に昇温して前記A1点~A1点+30℃の温度域で保持してから冷却するにあたり、昇温の際にA1点に達してからA1点~A1点+30℃の温度域に保持した後に冷却する際、A1点に達するまでの前記A1点~A1点+30℃の温度域滞在時間を10分 ~2時間とし、前記A1点~A1点+30℃の温度域からのA1点-100℃~A1点-20℃までの冷却温度域を10~100℃/hrの平均冷却速度で冷却した後、当該冷却温度域で10分~5時間保持してから更に冷却することが示されている。
Patent Document 2 discloses a steel material having low deformation resistance after spheroidizing annealing and excellent cold forgeability, and a method for manufacturing the same. As the manufacturing method, steel satisfying a predetermined chemical composition is hot-worked, cooled to room temperature, then heated to a temperature range of A1 point to A1 point + 50 ° C., and after the temperature rise, the A1 After holding for 0 to 1 hour in the temperature range from point to A1 point +50 ° C, the temperature range from the temperature range from A1 point to A1 point +50 ° C to A1 point -100 ° C to A1 point -30 ° C is 10 to 200 ° C. After performing the annealing treatment for cooling at an average cooling rate of /hr twice or more, the temperature is raised to the temperature range of A1 point to A1 point + 30 ° C. and held in the temperature range of A1 point to A1 point + 30 ° C. When cooling, after reaching the A1 point when the temperature is raised, when cooling after holding in the temperature range from the A1 point to the A1 point + 30 ° C., the temperature range from the A1 point to the A1 point + 30 ° C. until the A1 point is reached. The residence time is 10 minutes to 2 hours, and the cooling temperature range from the temperature range of A1 point to A1 point +30 ° C to A1 point -100 ° C to A1 point -20 ° C is an average cooling rate of 10 to 100 ° C/hr. After cooling at , it is shown to be held in the cooling temperature range for 10 minutes to 5 hours and then further cooled.
特許文献3には、冷間加工時における変形抵抗の低減と共に、耐割れ性の向上を図り、優れた冷間加工性を発揮できる機械構造部品用鋼線として、所定の成分組成を有し、鋼の金属組織が、フェライトおよびセメンタイトより構成され、フェライト結晶粒界に存在するセメンタイトの数割合が、全セメンタイト数に対して40%以上である機械構造部品用鋼線が開示されている。特許文献3では、球状化焼鈍に供する圧延線材の製造条件を、800℃以上、1050℃以下で仕上げ圧延し、平均冷却速度が7℃/秒以上の第1冷却と、平均冷却速度が1℃/秒以上、5℃/秒以下の第2冷却と、平均冷却速度が前記第2冷却よりも速くかつ5℃/秒以上である第3冷却とを、この順で行い、前記第1冷却の終了と前記第2冷却の開始を700~750℃の範囲内で行い、前記第2冷却の終了と前記第3冷却の開始を600~650℃の範囲内で行い、前記第3冷却の終了を400℃以下にすることが好ましいと示されている。
Patent Document 3 describes a steel wire for machine structural parts that can exhibit excellent cold workability by reducing deformation resistance during cold working and improving crack resistance. A steel wire for machine structural parts is disclosed, in which the metallographic structure of the steel is composed of ferrite and cementite, and the number ratio of cementite present in ferrite grain boundaries is 40% or more of the total number of cementite. In Patent Document 3, the manufacturing conditions for the rolled wire rod subjected to spheroidizing annealing are finish rolling at 800°C or higher and 1050°C or lower, first cooling at an average cooling rate of 7°C/sec or higher, and average cooling rate of 1°C. / sec or more and 5 ° C./sec or less, and third cooling whose average cooling rate is faster than the second cooling and 5 ° C./sec or more are performed in this order, and the first cooling is performed. The end and the start of the second cooling are performed within the range of 700 to 750 ° C., the end of the second cooling and the start of the third cooling are performed within the range of 600 to 650 ° C., and the end of the third cooling is performed. It is indicated that it is preferable to set the temperature to 400° C. or lower.
しかしながら、特許文献1~3に開示されている従来の技術では、球状化焼鈍後の硬さを十分に低減できず、球状化焼鈍後に行われる冷間加工での加工性に劣るか、冷間加工後に行う焼入れ処理で硬さを十分に高めることができない、すなわち焼入れ性に劣る場合があった。つまり、従来、冷間加工性と焼入性の双方を高めることに着目した技術はなかった。
However, in the conventional techniques disclosed in Patent Documents 1 to 3, the hardness after spheroidizing annealing cannot be sufficiently reduced, and the workability in cold working performed after spheroidizing annealing is poor, or cold working is performed. In some cases, the hardness cannot be sufficiently increased by the quenching treatment performed after working, that is, the quenchability is poor. That is, conventionally, there has been no technique focused on improving both cold workability and hardenability.
本開示は、このような状況に鑑みてなされたものであり、その目的は、硬さが十分に低く冷間加工性に優れ、かつ焼入れ処理により高い硬さの得られる、すなわち焼入れ性に優れた、機械構造部品用鋼線と、上記機械構造部品用鋼線を比較的短時間で製造できる、機械構造部品用鋼線の製造方法とを提供することにある。
The present disclosure has been made in view of such circumstances, and an object of the present disclosure is to provide sufficiently low hardness, excellent cold workability, and high hardness by quenching treatment, that is, excellent quenchability. Another object of the present invention is to provide a steel wire for machine structural parts and a method for producing the steel wire for machine structural parts, which can produce the steel wire for machine structural parts in a relatively short period of time.
本明細書において、「線材」「棒鋼」とはそれぞれ、熱間圧延して得られた線状、棒状の鋼材であって、球状化焼鈍などの熱処理と伸線加工のいずれも施されていない鋼材をいう。また「鋼線」とは、線材または棒鋼に、球状化焼鈍などの熱処理と伸線加工の少なくとも一つが施されたものをいう。本明細書では、上記線材、棒鋼および鋼線を総称して「条鋼」という。
In this specification, the terms "wire rod" and "steel bar" refer to wire-shaped and rod-shaped steel materials obtained by hot rolling, and are not subjected to heat treatment such as spheroidizing annealing or wire drawing. Refers to steel. The term "steel wire" refers to a wire rod or steel bar subjected to at least one of heat treatment such as spheroidizing annealing and wire drawing. In this specification, the wire rod, steel bar and steel wire are collectively referred to as "long steel".
本発明の態様1は、
C :0.05質量%~0.60質量%、
Si:0.005質量%~0.50質量%、
Mn:0.30質量%~1.20質量%、
P :0質量%超、0.050質量%以下、
S :0質量%超、0.050質量%以下、
Al:0.001質量%~0.10質量%、
Cr:0質量%超、1.5質量%以下、および
N: 0質量%超、0.02質量%以下、
を含有し、残部が鉄および不可避不純物からなり、
フェライト粒の(211)面におけるX線回折ピークの半価幅が0.500°以下であり、
全セメンタイトの平均円相当直径が、鋼中のC量(質量%)を[C]で表したときに、(1.863-2.13[C])μm以下である、機械構造部品用鋼線である。Aspect 1 of the present invention is
C: 0.05% by mass to 0.60% by mass,
Si: 0.005% by mass to 0.50% by mass,
Mn: 0.30% by mass to 1.20% by mass,
P: more than 0% by mass, 0.050% by mass or less,
S: more than 0% by mass, 0.050% by mass or less,
Al: 0.001% by mass to 0.10% by mass,
Cr: more than 0% by mass, 1.5% by mass or less, and N: more than 0% by mass, 0.02% by mass or less,
containing, the balance consisting of iron and inevitable impurities,
The half width of the X-ray diffraction peak on the (211) plane of the ferrite grain is 0.500° or less,
Steel for machine structural parts, wherein the average equivalent circle diameter of all cementite is (1.863-2.13 [C]) μm or less when the amount of C (% by mass) in the steel is represented by [C] is a line.
C :0.05質量%~0.60質量%、
Si:0.005質量%~0.50質量%、
Mn:0.30質量%~1.20質量%、
P :0質量%超、0.050質量%以下、
S :0質量%超、0.050質量%以下、
Al:0.001質量%~0.10質量%、
Cr:0質量%超、1.5質量%以下、および
N: 0質量%超、0.02質量%以下、
を含有し、残部が鉄および不可避不純物からなり、
フェライト粒の(211)面におけるX線回折ピークの半価幅が0.500°以下であり、
全セメンタイトの平均円相当直径が、鋼中のC量(質量%)を[C]で表したときに、(1.863-2.13[C])μm以下である、機械構造部品用鋼線である。
C: 0.05% by mass to 0.60% by mass,
Si: 0.005% by mass to 0.50% by mass,
Mn: 0.30% by mass to 1.20% by mass,
P: more than 0% by mass, 0.050% by mass or less,
S: more than 0% by mass, 0.050% by mass or less,
Al: 0.001% by mass to 0.10% by mass,
Cr: more than 0% by mass, 1.5% by mass or less, and N: more than 0% by mass, 0.02% by mass or less,
containing, the balance consisting of iron and inevitable impurities,
The half width of the X-ray diffraction peak on the (211) plane of the ferrite grain is 0.500° or less,
Steel for machine structural parts, wherein the average equivalent circle diameter of all cementite is (1.863-2.13 [C]) μm or less when the amount of C (% by mass) in the steel is represented by [C] is a line.
本発明の態様2は、
更に、
Cu:0質量%超、0.25質量%以下、
Ni:0質量%超、0.25質量%以下、
Mo:0質量%超、0.50質量%以下および
B :0質量%超、0.01質量%以下よりなる群から選択される1種以上を含有する、態様1に記載の機械構造部品用鋼線である。Aspect 2 of the present invention is
Furthermore,
Cu: more than 0% by mass, 0.25% by mass or less,
Ni: more than 0% by mass, 0.25% by mass or less,
Mo: more than 0% by mass, 0.50% by mass or less and B: more than 0% by mass, 0.01% by mass or less for machine structural parts according toaspect 1, containing one or more selected from the group consisting of Steel wire.
更に、
Cu:0質量%超、0.25質量%以下、
Ni:0質量%超、0.25質量%以下、
Mo:0質量%超、0.50質量%以下および
B :0質量%超、0.01質量%以下よりなる群から選択される1種以上を含有する、態様1に記載の機械構造部品用鋼線である。
Furthermore,
Cu: more than 0% by mass, 0.25% by mass or less,
Ni: more than 0% by mass, 0.25% by mass or less,
Mo: more than 0% by mass, 0.50% by mass or less and B: more than 0% by mass, 0.01% by mass or less for machine structural parts according to
本発明の態様3は、
更に、
Ti:0質量%超、0.2質量%以下、
Nb:0質量%超、0.2質量%以下、および
V :0質量%超、0.5質量%以下よりなる群から選択される1種以上を含有する、態様1または2に記載の機械構造部品用鋼線である。Aspect 3 of the present invention is
Furthermore,
Ti: more than 0% by mass, 0.2% by mass or less,
The machine according to aspect 1 or 2, containing one or more selected from the group consisting of Nb: more than 0% by mass and 0.2% by mass or less, and V: more than 0% by mass and 0.5% by mass or less Steel wire for structural parts.
更に、
Ti:0質量%超、0.2質量%以下、
Nb:0質量%超、0.2質量%以下、および
V :0質量%超、0.5質量%以下よりなる群から選択される1種以上を含有する、態様1または2に記載の機械構造部品用鋼線である。
Furthermore,
Ti: more than 0% by mass, 0.2% by mass or less,
The machine according to
本発明の態様4は、
更に、
Mg:0質量%超、0.02質量%以下、
Ca:0質量%超、0.05質量%以下、
Li:0質量%超、0.02質量%以下、および
REM:0質量%超、0.05質量%以下よりなる群から選択される1種以上を含有する、態様1~3のいずれか1つに記載の機械構造部品用鋼線である。Aspect 4 of the present invention is
Furthermore,
Mg: more than 0% by mass, 0.02% by mass or less,
Ca: more than 0% by mass, 0.05% by mass or less,
Li: more than 0 mass%, 0.02 mass% or less, and REM: more than 0 mass%, containing one or more selected from the group consisting of 0.05 mass% or less, any one ofaspects 1 to 3 1. The steel wire for machine structural parts according to 1.
更に、
Mg:0質量%超、0.02質量%以下、
Ca:0質量%超、0.05質量%以下、
Li:0質量%超、0.02質量%以下、および
REM:0質量%超、0.05質量%以下よりなる群から選択される1種以上を含有する、態様1~3のいずれか1つに記載の機械構造部品用鋼線である。
Furthermore,
Mg: more than 0% by mass, 0.02% by mass or less,
Ca: more than 0% by mass, 0.05% by mass or less,
Li: more than 0 mass%, 0.02 mass% or less, and REM: more than 0 mass%, containing one or more selected from the group consisting of 0.05 mass% or less, any one of
本発明の態様5は、
フェライト結晶粒径の平均値が30μm以下である、態様1~4のいずれか1つに記載の機械構造部品用鋼線である。Aspect 5 of the present invention is
5. The steel wire for machine structural parts according to any one ofaspects 1 to 4, wherein the average ferrite grain size is 30 μm or less.
フェライト結晶粒径の平均値が30μm以下である、態様1~4のいずれか1つに記載の機械構造部品用鋼線である。
5. The steel wire for machine structural parts according to any one of
本発明の態様6は、
態様1~4のいずれか1つに記載の化学成分組成を満たす条鋼に、
下記(1)~(3)の工程を含む球状化焼鈍を施す工程を含む、態様1~5のいずれか1つに記載の機械構造部品用鋼線の製造方法である。
(1)(A1+8℃)~(A1+31℃)の温度T1に加熱した後に、該温度T1で1時間超、6時間以下で加熱保持し、
(2)650℃超、(A1-17℃)以下の温度T2まで冷却し、次いで、温度T2よりも高く(A1+60℃)以下の加熱温度まで加熱する、冷却-加熱工程を、合計2回~6回実施し、
(3)5℃/時間~20℃/時間の平均冷却速度で(A1-30℃)未満の温度まで冷却する。
ここで、A1は、下記式(1)で算出される。
A1(℃)=723+29.1×[Si]-10.7×[Mn]+16.9×[Cr]-16.9×[Ni]・・・(1)
ただし、[元素]は、各元素の含有量(質量%)を表し、含まれない元素の含有量はゼロとする。Aspect 6 of the present invention is
A long steel satisfying the chemical composition according to any one ofaspects 1 to 4,
A method for producing a steel wire for machine structural parts according to any one ofaspects 1 to 5, which includes a step of performing spheroidizing annealing including the following steps (1) to (3).
(1) After heating to a temperature T1 of (A1 + 8 ° C.) to (A1 + 31 ° C.), heating and holding at the temperature T1 for more than 1 hour and 6 hours or less,
(2) Cooling to a temperature T2 exceeding 650 ° C. and not exceeding (A1-17 ° C.), and then heating to a heating temperature higher than the temperature T2 and not exceeding (A1 + 60 ° C.), a total of 2 or more cooling-heating steps 6 times,
(3) Cool to a temperature below (A1-30°C) at an average cooling rate of 5°C/hr to 20°C/hr.
Here, A1 is calculated by the following formula (1).
A1 (° C.)=723+29.1×[Si]−10.7×[Mn]+16.9×[Cr]−16.9×[Ni] (1)
However, [element] represents the content (% by mass) of each element, and the content of elements not included is zero.
態様1~4のいずれか1つに記載の化学成分組成を満たす条鋼に、
下記(1)~(3)の工程を含む球状化焼鈍を施す工程を含む、態様1~5のいずれか1つに記載の機械構造部品用鋼線の製造方法である。
(1)(A1+8℃)~(A1+31℃)の温度T1に加熱した後に、該温度T1で1時間超、6時間以下で加熱保持し、
(2)650℃超、(A1-17℃)以下の温度T2まで冷却し、次いで、温度T2よりも高く(A1+60℃)以下の加熱温度まで加熱する、冷却-加熱工程を、合計2回~6回実施し、
(3)5℃/時間~20℃/時間の平均冷却速度で(A1-30℃)未満の温度まで冷却する。
ここで、A1は、下記式(1)で算出される。
A1(℃)=723+29.1×[Si]-10.7×[Mn]+16.9×[Cr]-16.9×[Ni]・・・(1)
ただし、[元素]は、各元素の含有量(質量%)を表し、含まれない元素の含有量はゼロとする。
A long steel satisfying the chemical composition according to any one of
A method for producing a steel wire for machine structural parts according to any one of
(1) After heating to a temperature T1 of (A1 + 8 ° C.) to (A1 + 31 ° C.), heating and holding at the temperature T1 for more than 1 hour and 6 hours or less,
(2) Cooling to a temperature T2 exceeding 650 ° C. and not exceeding (A1-17 ° C.), and then heating to a heating temperature higher than the temperature T2 and not exceeding (A1 + 60 ° C.), a total of 2 or more cooling-
(3) Cool to a temperature below (A1-30°C) at an average cooling rate of 5°C/hr to 20°C/hr.
Here, A1 is calculated by the following formula (1).
A1 (° C.)=723+29.1×[Si]−10.7×[Mn]+16.9×[Cr]−16.9×[Ni] (1)
However, [element] represents the content (% by mass) of each element, and the content of elements not included is zero.
本発明の態様7は、
前記条鋼は、線材に、5%超の減面率で伸線加工を施して得られた鋼線である、態様6に記載の機械構造部品用鋼線の製造方法である。Aspect 7 of the present invention is
Aspect 6. The method for producing a steel wire for machine structural parts according to aspect 6, wherein the steel bar is a steel wire obtained by drawing a wire with a reduction in area of more than 5%.
前記条鋼は、線材に、5%超の減面率で伸線加工を施して得られた鋼線である、態様6に記載の機械構造部品用鋼線の製造方法である。
本開示によれば、冷間加工性に優れるとともに焼入れ性に優れた機械構造部品用鋼線と、該機械構造部品用鋼線の製造方法を提供できる。
According to the present disclosure, it is possible to provide a steel wire for machine structural parts that is excellent in cold workability and hardenability, and a method for manufacturing the steel wire for machine structural parts.
本発明者らは、優れた冷間加工性と焼入性を兼備した機械構造部品用鋼線を実現すべく、様々な角度から鋭意検討した。
The present inventors have made extensive studies from various angles in order to realize a steel wire for machine structural parts that has both excellent cold workability and hardenability.
球状化焼鈍後のフェライト中のひずみ量が低いと、球状化焼鈍後の鋼の硬さを低減でき、冷間加工性が向上する。本発明者らは、球状化焼鈍中の冷却過程で生成される棒状セメンタイトは界面ひずみを多く含むといった着想に焦点をあて、冷却過程で生成される棒状セメンタイトを低減すれば、フェライト中のひずみ量の低減を図ることができると考えた。さらに、本発明者らは、全セメンタイトのサイズを小さくすることで、焼入れ処理工程の高温保持中に未溶解となるセメンタイトを低減でき、焼入性を向上させることができると考えた。
When the amount of strain in the ferrite after spheroidizing annealing is low, the hardness of the steel after spheroidizing annealing can be reduced and the cold workability is improved. The present inventors focused on the idea that the rod-shaped cementite generated in the cooling process during spheroidizing contains a large amount of interfacial strain. We thought that it would be possible to reduce the Furthermore, the present inventors thought that by reducing the size of all cementite, it is possible to reduce the amount of cementite that remains undissolved during high-temperature holding in the quenching process, thereby improving the hardenability.
そこで、本発明者らは、更に鋭意検討した結果、特に金属組織において、フェライト中のひずみ量の指標となるフェライト粒の(211)面におけるX線回折ピークの半価幅を一定値以下にすると共に、全セメンタイトの平均円相当直径を、鋼材中のC量に応じて一定値以下にすればよいことを見出した。また、本発明者らは、更に上記金属組織を実現するには、化学成分組成を一定範囲内とするとともに、機械構造部品用鋼線の製造方法において、特に規定の条件で球状化焼鈍を行うことが有効であることを見出した。以下、まず本実施形態に係る機械構造部品用鋼線について、該機械構造部品用鋼線の金属組織から説明する。
Therefore, as a result of further intensive studies, the present inventors have found that, particularly in the metal structure, the half-value width of the X-ray diffraction peak in the (211) plane of the ferrite grain, which is an indicator of the amount of strain in ferrite, is set to a certain value or less. In addition, the inventors found that the average equivalent circle diameter of all cementite should be set to a certain value or less according to the amount of C in the steel material. Further, in order to further realize the above metal structure, the present inventors set the chemical composition within a certain range, and performed spheroidizing annealing under particularly specified conditions in the method of manufacturing the steel wire for machine structural parts. I found that it is effective. Hereinafter, the metal structure of the steel wire for machine structural parts according to the present embodiment will be described first.
1.金属組織
[フェライト粒の(211)面におけるX線回折ピークの半価幅が0.500°以下]
本実施形態の機械構造部品用鋼線は、フェライト粒の(211)面におけるX線回折ピークの半価幅が0.500°以下である。X線回折におけるフェライトのピークの半価幅は、転位密度と関係するひずみの導入度合いを示す。ピーク半価幅が小さいことは、鋼中のひずみが小さいことを表している。そのため、ピーク半価幅が小さいほど、鋼中のひずみが小さくなる。その結果、鋼の硬さが低下し、冷間加工性が向上する。フェライトのいずれの結晶方位を測定してもほぼ同じ傾向を示すが、本開示では、傾向を明確に把握できるフェライトの(211)面のピーク半価幅を代表的に規定することとした。ピーク半価幅は、好ましくは0.495°以下であり、より好ましくは0.493°以下である。ピーク半価幅の下限は、特に限定されないが、本発明の実施形態に係る成分組成および製造条件を考慮すれば、おおむね0.100°程度である。 1. Metal structure [X-ray diffraction peak half width of 0.500° or less in (211) plane of ferrite grain]
In the steel wire for machine structural parts of the present embodiment, the half width of the X-ray diffraction peak on the (211) plane of the ferrite grains is 0.500° or less. The half width of the ferrite peak in X-ray diffraction indicates the degree of strain introduction related to the dislocation density. A smaller half-value width of the peak indicates a smaller strain in the steel. Therefore, the smaller the peak half-value width, the smaller the strain in the steel. As a result, the hardness of the steel is lowered and the cold workability is improved. Almost the same tendency is shown by measuring any crystal orientation of ferrite, but in the present disclosure, the peak half-value width of the (211) plane of ferrite, which can clearly grasp the tendency, is defined as a representative. The peak half width is preferably 0.495° or less, more preferably 0.493° or less. The lower limit of the peak half-value width is not particularly limited, but considering the component composition and production conditions according to the embodiment of the present invention, it is approximately 0.100°.
[フェライト粒の(211)面におけるX線回折ピークの半価幅が0.500°以下]
本実施形態の機械構造部品用鋼線は、フェライト粒の(211)面におけるX線回折ピークの半価幅が0.500°以下である。X線回折におけるフェライトのピークの半価幅は、転位密度と関係するひずみの導入度合いを示す。ピーク半価幅が小さいことは、鋼中のひずみが小さいことを表している。そのため、ピーク半価幅が小さいほど、鋼中のひずみが小さくなる。その結果、鋼の硬さが低下し、冷間加工性が向上する。フェライトのいずれの結晶方位を測定してもほぼ同じ傾向を示すが、本開示では、傾向を明確に把握できるフェライトの(211)面のピーク半価幅を代表的に規定することとした。ピーク半価幅は、好ましくは0.495°以下であり、より好ましくは0.493°以下である。ピーク半価幅の下限は、特に限定されないが、本発明の実施形態に係る成分組成および製造条件を考慮すれば、おおむね0.100°程度である。 1. Metal structure [X-ray diffraction peak half width of 0.500° or less in (211) plane of ferrite grain]
In the steel wire for machine structural parts of the present embodiment, the half width of the X-ray diffraction peak on the (211) plane of the ferrite grains is 0.500° or less. The half width of the ferrite peak in X-ray diffraction indicates the degree of strain introduction related to the dislocation density. A smaller half-value width of the peak indicates a smaller strain in the steel. Therefore, the smaller the peak half-value width, the smaller the strain in the steel. As a result, the hardness of the steel is lowered and the cold workability is improved. Almost the same tendency is shown by measuring any crystal orientation of ferrite, but in the present disclosure, the peak half-value width of the (211) plane of ferrite, which can clearly grasp the tendency, is defined as a representative. The peak half width is preferably 0.495° or less, more preferably 0.493° or less. The lower limit of the peak half-value width is not particularly limited, but considering the component composition and production conditions according to the embodiment of the present invention, it is approximately 0.100°.
[全セメンタイトの平均円相当直径が、鋼材中のC量(質量%)を[C]で表したときに、(1.863-2.13[C])μm以下]
セメンタイトが粗大化しすぎると、冷間加工後の焼入れ処理工程で高温保持時に、セメンタイトが十分溶解せず、焼入れで十分高い硬さを得ることができない。よって、本実施形態では、鋼材中のC量(質量%)を[C]で表したときに、全セメンタイトの平均円相当直径を(1.863-2.13[C])μm以下とした。好ましくは、(1.858-2.13[C])μm以下である。 [The average equivalent circle diameter of all cementite is (1.863-2.13 [C]) μm or less when the amount of C (% by mass) in the steel material is represented by [C]]
If the cementite is excessively coarsened, the cementite will not be sufficiently dissolved during the high temperature hold in the quenching treatment step after cold working, and a sufficiently high hardness cannot be obtained by quenching. Therefore, in the present embodiment, when the amount of C (% by mass) in the steel material is represented by [C], the average circle equivalent diameter of all cementite is set to (1.863-2.13 [C]) μm or less. . Preferably, it is (1.858-2.13 [C]) μm or less.
セメンタイトが粗大化しすぎると、冷間加工後の焼入れ処理工程で高温保持時に、セメンタイトが十分溶解せず、焼入れで十分高い硬さを得ることができない。よって、本実施形態では、鋼材中のC量(質量%)を[C]で表したときに、全セメンタイトの平均円相当直径を(1.863-2.13[C])μm以下とした。好ましくは、(1.858-2.13[C])μm以下である。 [The average equivalent circle diameter of all cementite is (1.863-2.13 [C]) μm or less when the amount of C (% by mass) in the steel material is represented by [C]]
If the cementite is excessively coarsened, the cementite will not be sufficiently dissolved during the high temperature hold in the quenching treatment step after cold working, and a sufficiently high hardness cannot be obtained by quenching. Therefore, in the present embodiment, when the amount of C (% by mass) in the steel material is represented by [C], the average circle equivalent diameter of all cementite is set to (1.863-2.13 [C]) μm or less. . Preferably, it is (1.858-2.13 [C]) μm or less.
一方、鋼中のセメンタイト量が一定の場合、セメンタイトのサイズが大きくなるほど、セメンタイトの数密度は減少して、セメンタイト間の距離が長くなる。鋼材中のセメンタイト間の距離が長いほど析出強化し難く、その結果、球状化焼鈍後の硬さをより低減できる。これらの観点から、全セメンタイトの平均円相当直径を、(1.668-2.13[C])μm以上とすることが好ましい。全セメンタイトの平均円相当直径は、より好ましくは(1.669-2.13[C])μm以上である。
On the other hand, when the amount of cementite in the steel is constant, the larger the cementite size, the lower the number density of cementite and the longer the distance between cementite. The longer the distance between cementites in the steel material, the more difficult the precipitation strengthening, and as a result, the hardness after spheroidizing annealing can be further reduced. From these points of view, the average equivalent circle diameter of all cementite is preferably (1.668-2.13 [C]) μm or more. The average equivalent circle diameter of all cementite is more preferably (1.669-2.13 [C]) μm or more.
上記全セメンタイトについて、形態は特に限定されず、球状のセメンタイトの他、アスペクト比の大きい棒状セメンタイトが含まれる。上記アスペクト比は、セメンタイト粒子の最長長さである長径と、長径に垂直な方向における最長長さである短径との比(長径/短径)である。尚、測定対象となるセメンタイトの大きさの基準は限定されないが、後述する全セメンタイトの平均円相当直径の測定方法によって判別できるセメンタイトのサイズが最小サイズとなる。具体的には、円相当直径が0.3μm以上のセメンタイト粒子が測定対象となる。
The form of all cementite is not particularly limited, and includes spherical cementite as well as rod-shaped cementite with a large aspect ratio. The aspect ratio is the ratio (major axis/minor axis) of the longest diameter of cementite particles to the longest diameter in the direction perpendicular to the long diameter. Although the standard for the size of cementite to be measured is not limited, the size of cementite that can be determined by the method of measuring the average circle equivalent diameter of all cementites, which will be described later, is the minimum size. Specifically, cementite particles having an equivalent circle diameter of 0.3 μm or more are to be measured.
本実施形態に係る機械構造部品用鋼線の金属組織は、球状化したセメンタイトを有する球状化組織であり、後述する化学成分組成を満たす条鋼に、例えば、後述する球状化焼鈍を施すことによって得ることができる。
The metal structure of the steel wire for machine structural parts according to the present embodiment is a spheroidized structure having spheroidized cementite, and is obtained by, for example, performing spheroidizing annealing, which will be described later, on a steel bar that satisfies the chemical composition described later. be able to.
本実施形態の機械構造部品用鋼線の金属組織は、実質フェライトおよびセメンタイトより構成される。上記「実質」とは、本実施形態の機械構造部品用鋼線の金属組織に占めるフェライトが面積率で90%以上であり、アスペクト比が3以上の棒状セメンタイトが面積率で5%以下と、冷間加工性に及ぼす悪影響が小さければ、AlN等の窒化物と、窒化物以外の介在物を面積率で3%未満とを許容することを意味する。前記フェライトの面積率は、更には95%以上であってもよい。
The metal structure of the steel wire for machine structural parts of this embodiment is substantially composed of ferrite and cementite. The above-mentioned "substantial" means that the area ratio of ferrite in the metal structure of the steel wire for machine structural parts of the present embodiment is 90% or more, and the area ratio of rod-shaped cementite having an aspect ratio of 3 or more is 5% or less. If the adverse effect on cold workability is small, it means that the area ratio of nitrides such as AlN and inclusions other than nitrides is allowed to be less than 3%. Further, the area ratio of the ferrite may be 95% or more.
本明細書において、「フェライト」とは、結晶構造がbcc構造である部分を指し、フェライトとセメンタイトの層状組織であるパーライト中のフェライトも含む。
また、「フェライト結晶粒径」の測定対象である「フェライト結晶粒」とは、球状化が不十分で球状化焼鈍中に生成される棒状セメンタイトを含む結晶粒も評価対象であるが、球状化焼鈍前から残存し得る棒状セメンタイトを含む結晶粒(パーライト結晶粒)は対象外である。具体的には、ナイタール(硝酸2体積%、エタノール98体積%)を用いてエッチング後に、光学顕微鏡を用いて1000倍で観察したときに確認できる、「セメンタイトが粒内に存在しない結晶粒」と「セメンタイトが粒内に存在し、セメンタイトの形状が観察できる(すなわち、セメンタイトとフェライトの境界が明瞭に観察できる)結晶粒」をいう。上記光学顕微鏡を用いて1000倍ではセメンタイトの形状を観察できない(すなわち、セメンタイトとフェライトの境界が明瞭に観察できない)結晶粒は、本実施形態では判断対象外であり、「フェライト結晶粒」には含めない。 As used herein, the term “ferrite” refers to a portion whose crystal structure is the bcc structure, and includes ferrite in pearlite, which is a layered structure of ferrite and cementite.
In addition, the "ferrite grains" that are the object of measurement of the "ferrite grain size" include grains containing rod-shaped cementite that is insufficiently spheroidized and generated during spheroidizing annealing. Crystal grains containing rod-shaped cementite (pearlite grains) that may remain before annealing are excluded. Specifically, after etching using nital (nitric acid 2% by volume, ethanol 98% by volume), "crystal grains without cementite present in the grains" can be confirmed when observed at 1000 times using an optical microscope. It means "crystal grains in which cementite is present in the grains and the shape of the cementite can be observed (that is, the boundary between cementite and ferrite can be clearly observed)". Crystal grains in which the shape of cementite cannot be observed at a magnification of 1000 using the optical microscope (that is, the boundary between cementite and ferrite cannot be clearly observed) are not subject to judgment in the present embodiment, and "ferrite crystal grains" exclude.
また、「フェライト結晶粒径」の測定対象である「フェライト結晶粒」とは、球状化が不十分で球状化焼鈍中に生成される棒状セメンタイトを含む結晶粒も評価対象であるが、球状化焼鈍前から残存し得る棒状セメンタイトを含む結晶粒(パーライト結晶粒)は対象外である。具体的には、ナイタール(硝酸2体積%、エタノール98体積%)を用いてエッチング後に、光学顕微鏡を用いて1000倍で観察したときに確認できる、「セメンタイトが粒内に存在しない結晶粒」と「セメンタイトが粒内に存在し、セメンタイトの形状が観察できる(すなわち、セメンタイトとフェライトの境界が明瞭に観察できる)結晶粒」をいう。上記光学顕微鏡を用いて1000倍ではセメンタイトの形状を観察できない(すなわち、セメンタイトとフェライトの境界が明瞭に観察できない)結晶粒は、本実施形態では判断対象外であり、「フェライト結晶粒」には含めない。 As used herein, the term “ferrite” refers to a portion whose crystal structure is the bcc structure, and includes ferrite in pearlite, which is a layered structure of ferrite and cementite.
In addition, the "ferrite grains" that are the object of measurement of the "ferrite grain size" include grains containing rod-shaped cementite that is insufficiently spheroidized and generated during spheroidizing annealing. Crystal grains containing rod-shaped cementite (pearlite grains) that may remain before annealing are excluded. Specifically, after etching using nital (
[フェライト結晶粒径の平均値:30μm以下]
本実施形態に係る機械構造部品用鋼線は、前記金属組織におけるフェライト結晶粒径の平均値が30μm以下であることが好ましい。フェライト結晶粒径の平均値が30μm以下であれば、機械構造部品用鋼線の延性を向上でき、冷間加工時の割れ発生を更に抑制することができる。フェライト結晶粒径の平均値は、より好ましくは25μm以下であり、更に好ましくは20μm以下である。フェライト結晶粒径の平均値は、小さければ小さいほど好ましいが、可能な製造条件等を考慮すれば、下限はおおよそ2μmとなりうる。 [Average value of ferrite crystal grain size: 30 μm or less]
In the steel wire for machine structural parts according to the present embodiment, it is preferable that the average value of the ferrite crystal grain size in the metal structure is 30 μm or less. When the average ferrite grain size is 30 μm or less, the ductility of the steel wire for machine structural parts can be improved, and cracking during cold working can be further suppressed. The average ferrite crystal grain size is more preferably 25 μm or less, still more preferably 20 μm or less. The smaller the average ferrite crystal grain size, the better, but the lower limit can be about 2 μm, considering possible production conditions and the like.
本実施形態に係る機械構造部品用鋼線は、前記金属組織におけるフェライト結晶粒径の平均値が30μm以下であることが好ましい。フェライト結晶粒径の平均値が30μm以下であれば、機械構造部品用鋼線の延性を向上でき、冷間加工時の割れ発生を更に抑制することができる。フェライト結晶粒径の平均値は、より好ましくは25μm以下であり、更に好ましくは20μm以下である。フェライト結晶粒径の平均値は、小さければ小さいほど好ましいが、可能な製造条件等を考慮すれば、下限はおおよそ2μmとなりうる。 [Average value of ferrite crystal grain size: 30 μm or less]
In the steel wire for machine structural parts according to the present embodiment, it is preferable that the average value of the ferrite crystal grain size in the metal structure is 30 μm or less. When the average ferrite grain size is 30 μm or less, the ductility of the steel wire for machine structural parts can be improved, and cracking during cold working can be further suppressed. The average ferrite crystal grain size is more preferably 25 μm or less, still more preferably 20 μm or less. The smaller the average ferrite crystal grain size, the better, but the lower limit can be about 2 μm, considering possible production conditions and the like.
(特性)
下記の化学成分組成を満たし、かつ上述した金属組織を有する本実施形態に係る機械構造部品用鋼線は、冷間加工を良好に実施できる低硬度と、焼入れ処理後の高硬度とを両立できる。本実施形態では、鋼中のC量(質量%)、Cr量(質量%)、Mo量(質量%)を各々[C]、[Cr]、[Mo]で表したときに(含まれない元素はゼロ質量%とする)、硬さ、後述する実施例では球状化焼鈍後の硬さが、下記式(2)を満たすと共に、焼入れ処理後の硬さが下記式(3)を満たす場合に、硬さが十分低く冷間加工性に優れると共に、焼入れ処理後の高硬度を達成、すなわち焼入れ性に優れると判定した。
(球状化焼鈍後の)硬さ(HV)<91([C]+[Cr]/9+[Mo]/2)+91 ・・・(2)
焼入れ処理後の硬さ(HV)>380ln([C])+1010 ・・・(3) (Characteristic)
The steel wire for machine structural parts according to the present embodiment, which satisfies the following chemical composition and has the metal structure described above, can achieve both a low hardness that enables good cold working and a high hardness after quenching treatment. . In this embodiment, when the amount of C (% by mass), the amount of Cr (% by mass), and the amount of Mo (% by mass) in the steel are represented by [C], [Cr], and [Mo], respectively (not included element is zero mass %), hardness, and in the examples described later, the hardness after spheroidizing annealing satisfies the following formula (2), and the hardness after quenching satisfies the following formula (3) Secondly, it was judged that the hardness is sufficiently low and the cold workability is excellent, and high hardness after quenching treatment is achieved, that is, the quenchability is excellent.
Hardness (HV) (after spheroidizing annealing) <91([C]+[Cr]/9+[Mo]/2)+91 (2)
Hardness after quenching treatment (HV) > 380 ln ([C]) + 1010 (3)
下記の化学成分組成を満たし、かつ上述した金属組織を有する本実施形態に係る機械構造部品用鋼線は、冷間加工を良好に実施できる低硬度と、焼入れ処理後の高硬度とを両立できる。本実施形態では、鋼中のC量(質量%)、Cr量(質量%)、Mo量(質量%)を各々[C]、[Cr]、[Mo]で表したときに(含まれない元素はゼロ質量%とする)、硬さ、後述する実施例では球状化焼鈍後の硬さが、下記式(2)を満たすと共に、焼入れ処理後の硬さが下記式(3)を満たす場合に、硬さが十分低く冷間加工性に優れると共に、焼入れ処理後の高硬度を達成、すなわち焼入れ性に優れると判定した。
(球状化焼鈍後の)硬さ(HV)<91([C]+[Cr]/9+[Mo]/2)+91 ・・・(2)
焼入れ処理後の硬さ(HV)>380ln([C])+1010 ・・・(3) (Characteristic)
The steel wire for machine structural parts according to the present embodiment, which satisfies the following chemical composition and has the metal structure described above, can achieve both a low hardness that enables good cold working and a high hardness after quenching treatment. . In this embodiment, when the amount of C (% by mass), the amount of Cr (% by mass), and the amount of Mo (% by mass) in the steel are represented by [C], [Cr], and [Mo], respectively (not included element is zero mass %), hardness, and in the examples described later, the hardness after spheroidizing annealing satisfies the following formula (2), and the hardness after quenching satisfies the following formula (3) Secondly, it was judged that the hardness is sufficiently low and the cold workability is excellent, and high hardness after quenching treatment is achieved, that is, the quenchability is excellent.
Hardness (HV) (after spheroidizing annealing) <91([C]+[Cr]/9+[Mo]/2)+91 (2)
Hardness after quenching treatment (HV) > 380 ln ([C]) + 1010 (3)
2.化学成分組成
本実施形態に係る機械構造部品用鋼線の化学成分組成について説明する。 2. Chemical Component Composition The chemical component composition of the steel wire for machine structural parts according to the present embodiment will be described.
本実施形態に係る機械構造部品用鋼線の化学成分組成について説明する。 2. Chemical Component Composition The chemical component composition of the steel wire for machine structural parts according to the present embodiment will be described.
[C:0.05質量%~0.60質量%]
Cは、鋼材の強度を支配する元素であり、含有量を増加させるほど焼入れ焼き戻し後の強度が高くなる。上記の効果を有効に発揮させるため、C量の下限は、0.05質量%とした。C量は、好ましくは0.10質量%以上であり、より好ましくは0.15質量%以上、更に好ましくは0.20質量%以上である。しかし、C量が過剰であると、球状化焼鈍後の組織において球状セメンタイトの数が過剰となり、硬さが増加するため冷間加工性が低下する。そこで、C量の上限は、0.60質量%と定めた。C量は、好ましくは0.55質量%以下であり、より好ましくは0.50質量%以下である。 [C: 0.05% by mass to 0.60% by mass]
C is an element that controls the strength of steel materials, and the strength after quenching and tempering increases as the content increases. In order to effectively exhibit the above effects, the lower limit of the amount of C was set to 0.05% by mass. The amount of C is preferably 0.10% by mass or more, more preferably 0.15% by mass or more, and still more preferably 0.20% by mass or more. However, if the amount of C is excessive, the number of spheroidal cementites becomes excessive in the structure after spheroidizing annealing, and the hardness increases, resulting in deterioration of cold workability. Therefore, the upper limit of the amount of C was set at 0.60% by mass. The amount of C is preferably 0.55% by mass or less, more preferably 0.50% by mass or less.
Cは、鋼材の強度を支配する元素であり、含有量を増加させるほど焼入れ焼き戻し後の強度が高くなる。上記の効果を有効に発揮させるため、C量の下限は、0.05質量%とした。C量は、好ましくは0.10質量%以上であり、より好ましくは0.15質量%以上、更に好ましくは0.20質量%以上である。しかし、C量が過剰であると、球状化焼鈍後の組織において球状セメンタイトの数が過剰となり、硬さが増加するため冷間加工性が低下する。そこで、C量の上限は、0.60質量%と定めた。C量は、好ましくは0.55質量%以下であり、より好ましくは0.50質量%以下である。 [C: 0.05% by mass to 0.60% by mass]
C is an element that controls the strength of steel materials, and the strength after quenching and tempering increases as the content increases. In order to effectively exhibit the above effects, the lower limit of the amount of C was set to 0.05% by mass. The amount of C is preferably 0.10% by mass or more, more preferably 0.15% by mass or more, and still more preferably 0.20% by mass or more. However, if the amount of C is excessive, the number of spheroidal cementites becomes excessive in the structure after spheroidizing annealing, and the hardness increases, resulting in deterioration of cold workability. Therefore, the upper limit of the amount of C was set at 0.60% by mass. The amount of C is preferably 0.55% by mass or less, more preferably 0.50% by mass or less.
[Si:0.005質量%~0.50質量%]
Siは、溶製時に脱酸材として用いられる他、強度の向上に寄与する。該効果を有効に発揮させるため、Si量の下限は0.005質量%とした。Si量は、好ましくは0.010質量%以上であり、より好ましくは0.050質量%以上である。しかし、Siは、フェライトの固溶強化に寄与し、球状化焼鈍後の強度をかなり高める作用を有する。Si含有量が過剰であると、上記作用により冷間加工性が劣化するため、Si量の上限は0.50質量%とした。Si量は、好ましくは0.40質量%以下であり、より好ましくは0.35質量%以下である。 [Si: 0.005% by mass to 0.50% by mass]
Si is used as a deoxidizer during smelting and contributes to strength improvement. In order to effectively exhibit this effect, the lower limit of the amount of Si was set to 0.005% by mass. The amount of Si is preferably 0.010% by mass or more, more preferably 0.050% by mass or more. However, Si contributes to solid-solution strengthening of ferrite and has the effect of considerably increasing the strength after spheroidizing annealing. If the Si content is excessive, the cold workability deteriorates due to the above effect, so the upper limit of the Si content was made 0.50% by mass. The amount of Si is preferably 0.40% by mass or less, more preferably 0.35% by mass or less.
Siは、溶製時に脱酸材として用いられる他、強度の向上に寄与する。該効果を有効に発揮させるため、Si量の下限は0.005質量%とした。Si量は、好ましくは0.010質量%以上であり、より好ましくは0.050質量%以上である。しかし、Siは、フェライトの固溶強化に寄与し、球状化焼鈍後の強度をかなり高める作用を有する。Si含有量が過剰であると、上記作用により冷間加工性が劣化するため、Si量の上限は0.50質量%とした。Si量は、好ましくは0.40質量%以下であり、より好ましくは0.35質量%以下である。 [Si: 0.005% by mass to 0.50% by mass]
Si is used as a deoxidizer during smelting and contributes to strength improvement. In order to effectively exhibit this effect, the lower limit of the amount of Si was set to 0.005% by mass. The amount of Si is preferably 0.010% by mass or more, more preferably 0.050% by mass or more. However, Si contributes to solid-solution strengthening of ferrite and has the effect of considerably increasing the strength after spheroidizing annealing. If the Si content is excessive, the cold workability deteriorates due to the above effect, so the upper limit of the Si content was made 0.50% by mass. The amount of Si is preferably 0.40% by mass or less, more preferably 0.35% by mass or less.
[Mn:0.30質量%~1.20質量%]
Mnは、脱酸材として有効に作用すると共に、焼入れ性の向上に寄与する元素である。該効果を十分に発揮させるため、Mn量の下限は、0.30質量%とした。Mn量は、好ましくは0.35質量%以上であり、より好ましくは0.40質量%以上である。しかし、Mn量が過剰であると、偏析が起こり易くなり、靱性が低下する。そのため、Mn量の上限は、1.20質量%とした。Mn量は、好ましくは1.10質量%以下であり、より好ましくは1.00質量%以下である。靱性の低下をより抑制する観点から、更に0.50質量%未満、更に0.45質量%以下にすることもできる。 [Mn: 0.30% by mass to 1.20% by mass]
Mn is an element that effectively acts as a deoxidizer and contributes to the improvement of hardenability. In order to sufficiently exhibit the effect, the lower limit of the amount of Mn was set to 0.30% by mass. The Mn content is preferably 0.35% by mass or more, more preferably 0.40% by mass or more. However, if the amount of Mn is excessive, segregation tends to occur and the toughness decreases. Therefore, the upper limit of the amount of Mn was set to 1.20% by mass. The Mn content is preferably 1.10% by mass or less, more preferably 1.00% by mass or less. From the viewpoint of further suppressing a decrease in toughness, the content may be less than 0.50% by mass, and may be 0.45% by mass or less.
Mnは、脱酸材として有効に作用すると共に、焼入れ性の向上に寄与する元素である。該効果を十分に発揮させるため、Mn量の下限は、0.30質量%とした。Mn量は、好ましくは0.35質量%以上であり、より好ましくは0.40質量%以上である。しかし、Mn量が過剰であると、偏析が起こり易くなり、靱性が低下する。そのため、Mn量の上限は、1.20質量%とした。Mn量は、好ましくは1.10質量%以下であり、より好ましくは1.00質量%以下である。靱性の低下をより抑制する観点から、更に0.50質量%未満、更に0.45質量%以下にすることもできる。 [Mn: 0.30% by mass to 1.20% by mass]
Mn is an element that effectively acts as a deoxidizer and contributes to the improvement of hardenability. In order to sufficiently exhibit the effect, the lower limit of the amount of Mn was set to 0.30% by mass. The Mn content is preferably 0.35% by mass or more, more preferably 0.40% by mass or more. However, if the amount of Mn is excessive, segregation tends to occur and the toughness decreases. Therefore, the upper limit of the amount of Mn was set to 1.20% by mass. The Mn content is preferably 1.10% by mass or less, more preferably 1.00% by mass or less. From the viewpoint of further suppressing a decrease in toughness, the content may be less than 0.50% by mass, and may be 0.45% by mass or less.
[P:0質量%超、0.050質量%以下]
P(リン)は、不可避不純物であり、鋼中で粒界偏析を起こして鍛造性および靱性に悪影響を及ぼす有害元素である。よって、P量は、0.050質量%以下とした。P量は、好ましくは0.030質量%以下であり、より好ましくは0.020質量%以下である。P量は、少なければ少ないほど好ましいが、通常0.001質量%以上含まれる。 [P: more than 0% by mass, 0.050% by mass or less]
P (phosphorus) is an unavoidable impurity and a harmful element that causes grain boundary segregation in steel and adversely affects forgeability and toughness. Therefore, the amount of P was set to 0.050% by mass or less. The P content is preferably 0.030% by mass or less, more preferably 0.020% by mass or less. Although the P content is preferably as small as possible, it is usually contained in an amount of 0.001% by mass or more.
P(リン)は、不可避不純物であり、鋼中で粒界偏析を起こして鍛造性および靱性に悪影響を及ぼす有害元素である。よって、P量は、0.050質量%以下とした。P量は、好ましくは0.030質量%以下であり、より好ましくは0.020質量%以下である。P量は、少なければ少ないほど好ましいが、通常0.001質量%以上含まれる。 [P: more than 0% by mass, 0.050% by mass or less]
P (phosphorus) is an unavoidable impurity and a harmful element that causes grain boundary segregation in steel and adversely affects forgeability and toughness. Therefore, the amount of P was set to 0.050% by mass or less. The P content is preferably 0.030% by mass or less, more preferably 0.020% by mass or less. Although the P content is preferably as small as possible, it is usually contained in an amount of 0.001% by mass or more.
[S:0質量%超、0.050質量%以下]
S(硫黄)は、不可避不純物であり、鋼中でMnSを形成し、延性を劣化させるので、冷間加工性には有害な元素である。そこで、S量は、0.050質量%以下とした。S量は、好ましくは0.030質量%以下であり、より好ましくは0.020質量%以下である。S量は、少なければ少ないほど好ましいが、通常0.001質量%以上含まれる。 [S: more than 0% by mass, 0.050% by mass or less]
S (sulfur) is an unavoidable impurity, forms MnS in steel, and deteriorates ductility, so it is an element harmful to cold workability. Therefore, the amount of S is set to 0.050% by mass or less. The S content is preferably 0.030% by mass or less, more preferably 0.020% by mass or less. Although the amount of S is preferably as small as possible, it is usually contained in an amount of 0.001% by mass or more.
S(硫黄)は、不可避不純物であり、鋼中でMnSを形成し、延性を劣化させるので、冷間加工性には有害な元素である。そこで、S量は、0.050質量%以下とした。S量は、好ましくは0.030質量%以下であり、より好ましくは0.020質量%以下である。S量は、少なければ少ないほど好ましいが、通常0.001質量%以上含まれる。 [S: more than 0% by mass, 0.050% by mass or less]
S (sulfur) is an unavoidable impurity, forms MnS in steel, and deteriorates ductility, so it is an element harmful to cold workability. Therefore, the amount of S is set to 0.050% by mass or less. The S content is preferably 0.030% by mass or less, more preferably 0.020% by mass or less. Although the amount of S is preferably as small as possible, it is usually contained in an amount of 0.001% by mass or more.
[Al:0.001質量%~0.10質量%]
Alは脱酸材として含まれる元素であり、脱酸に伴って不純物を低減する効果がある。この効果を発揮させるため、Al量の下限は、0.001質量%とした。Al量は、好ましくは0.005質量%以上であり、より好ましくは0.010質量%以上である。しかし、Al量が過剰であると、非金属介在物が増加し、靱性が低下する。そのため、Al量の上限は、0.10質量%と定めた。Al量は、好ましくは0.08質量%以下であり、より好ましくは0.05質量%以下である。 [Al: 0.001% by mass to 0.10% by mass]
Al is an element contained as a deoxidizing agent, and has the effect of reducing impurities accompanying deoxidizing. In order to exhibit this effect, the lower limit of the amount of Al was set to 0.001% by mass. The Al content is preferably 0.005% by mass or more, more preferably 0.010% by mass or more. However, if the amount of Al is excessive, nonmetallic inclusions increase and the toughness decreases. Therefore, the upper limit of the amount of Al was set to 0.10% by mass. The Al content is preferably 0.08% by mass or less, more preferably 0.05% by mass or less.
Alは脱酸材として含まれる元素であり、脱酸に伴って不純物を低減する効果がある。この効果を発揮させるため、Al量の下限は、0.001質量%とした。Al量は、好ましくは0.005質量%以上であり、より好ましくは0.010質量%以上である。しかし、Al量が過剰であると、非金属介在物が増加し、靱性が低下する。そのため、Al量の上限は、0.10質量%と定めた。Al量は、好ましくは0.08質量%以下であり、より好ましくは0.05質量%以下である。 [Al: 0.001% by mass to 0.10% by mass]
Al is an element contained as a deoxidizing agent, and has the effect of reducing impurities accompanying deoxidizing. In order to exhibit this effect, the lower limit of the amount of Al was set to 0.001% by mass. The Al content is preferably 0.005% by mass or more, more preferably 0.010% by mass or more. However, if the amount of Al is excessive, nonmetallic inclusions increase and the toughness decreases. Therefore, the upper limit of the amount of Al was set to 0.10% by mass. The Al content is preferably 0.08% by mass or less, more preferably 0.05% by mass or less.
[Cr:0質量%超、1.5質量%以下]
Crは、鋼の焼入れ性を向上させ強度を高める効果を有するとともに、セメンタイトの球状化を促進する効果を有する元素である。具体的には、Crは、セメンタイトに固溶して球状化焼鈍の加熱時にセメンタイトの溶解を遅延させる。加熱時にセメンタイトが溶解せずに一部残存することで、アスペクト比が大きい棒状セメンタイトが冷却時に生成しにくくなり、球状化組織を得やすくなる。そのため、Cr量は、0質量%超とし、0.01質量%以上とすることが好ましい。更に0.05質量%以上としてもよく、より更には0.10質量%以上としてもよい。セメンタイトの球状化をより促進させる観点からは、更に0.30質量%超とすることができ、更に0.50質量%超とすることもできる。Cr量が過剰であると、炭素を含む元素の拡散が遅延し、セメンタイトの溶解を必要以上に遅延させて、球状化組織が得られにくくなる。その結果、本発明による硬さ低減の効果が低下し得る。そのため、Cr量は、1.50質量%以下、好ましくは1.40質量%以下、より好ましくは1.25質量%以下である。Cr量は、元素の拡散をより早める観点からは、更に1.00質量%以下、更に0.80質量%以下、更に0.30質量%以下にすることができる。 [Cr: more than 0% by mass, 1.5% by mass or less]
Cr is an element that has the effect of improving the hardenability of steel and increasing the strength, and also has the effect of promoting spheroidization of cementite. Specifically, Cr dissolves in cementite and delays the dissolution of cementite during heating for spheroidizing annealing. Since the cementite does not dissolve and partially remains during heating, rod-shaped cementite having a large aspect ratio is less likely to form during cooling, making it easier to obtain a spheroidized structure. Therefore, the Cr content is more than 0% by mass, preferably 0.01% by mass or more. Further, it may be 0.05% by mass or more, and even more preferably 0.10% by mass or more. From the viewpoint of further promoting cementite spheroidization, the content can be more than 0.30% by mass, and can also be more than 0.50% by mass. If the amount of Cr is excessive, the diffusion of elements including carbon is delayed, and the dissolution of cementite is delayed more than necessary, making it difficult to obtain a spheroidized structure. As a result, the hardness reduction effect of the present invention may be reduced. Therefore, the Cr content is 1.50% by mass or less, preferably 1.40% by mass or less, and more preferably 1.25% by mass or less. From the viewpoint of accelerating the diffusion of the elements, the Cr content can be set to 1.00% by mass or less, 0.80% by mass or less, or 0.30% by mass or less.
Crは、鋼の焼入れ性を向上させ強度を高める効果を有するとともに、セメンタイトの球状化を促進する効果を有する元素である。具体的には、Crは、セメンタイトに固溶して球状化焼鈍の加熱時にセメンタイトの溶解を遅延させる。加熱時にセメンタイトが溶解せずに一部残存することで、アスペクト比が大きい棒状セメンタイトが冷却時に生成しにくくなり、球状化組織を得やすくなる。そのため、Cr量は、0質量%超とし、0.01質量%以上とすることが好ましい。更に0.05質量%以上としてもよく、より更には0.10質量%以上としてもよい。セメンタイトの球状化をより促進させる観点からは、更に0.30質量%超とすることができ、更に0.50質量%超とすることもできる。Cr量が過剰であると、炭素を含む元素の拡散が遅延し、セメンタイトの溶解を必要以上に遅延させて、球状化組織が得られにくくなる。その結果、本発明による硬さ低減の効果が低下し得る。そのため、Cr量は、1.50質量%以下、好ましくは1.40質量%以下、より好ましくは1.25質量%以下である。Cr量は、元素の拡散をより早める観点からは、更に1.00質量%以下、更に0.80質量%以下、更に0.30質量%以下にすることができる。 [Cr: more than 0% by mass, 1.5% by mass or less]
Cr is an element that has the effect of improving the hardenability of steel and increasing the strength, and also has the effect of promoting spheroidization of cementite. Specifically, Cr dissolves in cementite and delays the dissolution of cementite during heating for spheroidizing annealing. Since the cementite does not dissolve and partially remains during heating, rod-shaped cementite having a large aspect ratio is less likely to form during cooling, making it easier to obtain a spheroidized structure. Therefore, the Cr content is more than 0% by mass, preferably 0.01% by mass or more. Further, it may be 0.05% by mass or more, and even more preferably 0.10% by mass or more. From the viewpoint of further promoting cementite spheroidization, the content can be more than 0.30% by mass, and can also be more than 0.50% by mass. If the amount of Cr is excessive, the diffusion of elements including carbon is delayed, and the dissolution of cementite is delayed more than necessary, making it difficult to obtain a spheroidized structure. As a result, the hardness reduction effect of the present invention may be reduced. Therefore, the Cr content is 1.50% by mass or less, preferably 1.40% by mass or less, and more preferably 1.25% by mass or less. From the viewpoint of accelerating the diffusion of the elements, the Cr content can be set to 1.00% by mass or less, 0.80% by mass or less, or 0.30% by mass or less.
[N:0質量%超、0.02質量%以下]、
Nは、鋼に不可避的に含まれる不純物であるが、鋼中に固溶Nが多く含まれていると、ひずみ時効による硬度上昇、延性低下を招き、冷間加工性が劣化する。したがって、N含有量は、0.02質量%以下であり、好ましくは0.015質量%以下、より好ましくは0.010質量%以下である。 [N: more than 0% by mass, 0.02% by mass or less],
N is an impurity that is inevitably contained in steel, but when a large amount of solid-solution N is contained in steel, it causes an increase in hardness and a decrease in ductility due to strain aging, and deteriorates cold workability. Therefore, the N content is 0.02% by mass or less, preferably 0.015% by mass or less, and more preferably 0.010% by mass or less.
Nは、鋼に不可避的に含まれる不純物であるが、鋼中に固溶Nが多く含まれていると、ひずみ時効による硬度上昇、延性低下を招き、冷間加工性が劣化する。したがって、N含有量は、0.02質量%以下であり、好ましくは0.015質量%以下、より好ましくは0.010質量%以下である。 [N: more than 0% by mass, 0.02% by mass or less],
N is an impurity that is inevitably contained in steel, but when a large amount of solid-solution N is contained in steel, it causes an increase in hardness and a decrease in ductility due to strain aging, and deteriorates cold workability. Therefore, the N content is 0.02% by mass or less, preferably 0.015% by mass or less, and more preferably 0.010% by mass or less.
[残部]
残部は、鉄および不可避不純物である。不可避不純物としては、原料、資材、製造設備等の状況によって持ち込まれる微量元素(例えば、As、Sb、Snなど)の混入が許容される。なお、例えば、PおよびSのように、通常、含有量が少ないほど好ましく、従って不可避不純物であるが、その組成範囲について上記のように別途規定している元素がある。このため、本明細書において、残部を構成する「不可避不純物」という場合は、別途その組成範囲が規定されている元素を除いた概念である。 [Remainder]
The balance is iron and unavoidable impurities. As unavoidable impurities, trace elements (for example, As, Sb, Sn, etc.) brought in depending on the conditions of raw materials, materials, manufacturing equipment, etc. are allowed. For example, there are elements, such as P and S, whose content is generally preferably as low as possible and thus are unavoidable impurities, but whose composition range is separately defined as described above. For this reason, in this specification, the term "inevitable impurities" constituting the balance is a concept excluding elements whose composition range is separately defined.
残部は、鉄および不可避不純物である。不可避不純物としては、原料、資材、製造設備等の状況によって持ち込まれる微量元素(例えば、As、Sb、Snなど)の混入が許容される。なお、例えば、PおよびSのように、通常、含有量が少ないほど好ましく、従って不可避不純物であるが、その組成範囲について上記のように別途規定している元素がある。このため、本明細書において、残部を構成する「不可避不純物」という場合は、別途その組成範囲が規定されている元素を除いた概念である。 [Remainder]
The balance is iron and unavoidable impurities. As unavoidable impurities, trace elements (for example, As, Sb, Sn, etc.) brought in depending on the conditions of raw materials, materials, manufacturing equipment, etc. are allowed. For example, there are elements, such as P and S, whose content is generally preferably as low as possible and thus are unavoidable impurities, but whose composition range is separately defined as described above. For this reason, in this specification, the term "inevitable impurities" constituting the balance is a concept excluding elements whose composition range is separately defined.
本実施形態に係る機械構造部品用鋼線は、化学成分組成において、上記元素を含んでいればよい。下記に述べる選択元素は、含まれていなくてもよいが、上記元素と共に必要に応じて含有させることにより、焼入れ性等の確保をより容易に達成させることができる。以下、選択元素について述べる。
The steel wire for machine structural parts according to the present embodiment only needs to contain the above elements in its chemical composition. The optional elements described below may not be contained, but by containing them together with the above elements as necessary, it is possible to more easily ensure hardenability and the like. The selected elements are described below.
[Cu:0質量%超、0.25質量%以下、Ni:0質量%超、0.25質量%以下、Mo:0質量%超、0.50質量%以下、およびB:0質量%超、0.01質量%以下よりなる群から選択される1種以上]
Cu、Ni、MoおよびBは、いずれも鋼材の焼入れ性を向上させることによって最終製品の強度を増加させるのに有効な元素であり、必要によって単独または2種以上が含有される。これらの元素による効果はその含有量が増加するにつれて大きくなる。上記効果を有効に発揮させるための好ましい下限は、Cu、Ni、Moの各々では0質量%超、より好ましくは0.02質量%以上、更に好ましくは0.05質量%以上であり、Bでは0質量%超、より好ましくは0.0003質量%以上、更に好ましくは0.0005質量%以上である。
一方、これらの元素の含有量が過剰になると、強度が高くなり過ぎ、冷間加工性が劣化し得るので、上記のように夫々の好ましい上限を定めた。より好ましくは、Cu,Niの各々の含有量は、0.22質量%以下、更に好ましくは0.20質量%以下であり、Moの含有量は、より好ましくは0.40質量%以下、更に好ましくは0.35質量%以下であり、B含有量は、より好ましくは0.007質量%以下、更に好ましくは0.005質量%以下である。 [Cu: more than 0% by mass, 0.25% by mass or less, Ni: more than 0% by mass, 0.25% by mass or less, Mo: more than 0% by mass, 0.50% by mass or less, and B: more than 0% by mass , one or more selected from the group consisting of 0.01% by mass or less]
Cu, Ni, Mo and B are all effective elements for increasing the strength of the final product by improving the hardenability of the steel material, and may be contained alone or in combination of two or more. The effect of these elements increases as their content increases. A preferable lower limit for effectively exhibiting the above effects is more than 0% by mass, more preferably 0.02% by mass or more, and still more preferably 0.05% by mass or more for each of Cu, Ni, and Mo. It is more than 0% by mass, more preferably 0.0003% by mass or more, and still more preferably 0.0005% by mass or more.
On the other hand, if the content of these elements becomes excessive, the strength becomes too high and the cold workability may deteriorate. More preferably, the content of each of Cu and Ni is 0.22% by mass or less, more preferably 0.20% by mass or less, and the content of Mo is more preferably 0.40% by mass or less, and further preferably It is preferably 0.35% by mass or less, and the B content is more preferably 0.007% by mass or less, still more preferably 0.005% by mass or less.
Cu、Ni、MoおよびBは、いずれも鋼材の焼入れ性を向上させることによって最終製品の強度を増加させるのに有効な元素であり、必要によって単独または2種以上が含有される。これらの元素による効果はその含有量が増加するにつれて大きくなる。上記効果を有効に発揮させるための好ましい下限は、Cu、Ni、Moの各々では0質量%超、より好ましくは0.02質量%以上、更に好ましくは0.05質量%以上であり、Bでは0質量%超、より好ましくは0.0003質量%以上、更に好ましくは0.0005質量%以上である。
一方、これらの元素の含有量が過剰になると、強度が高くなり過ぎ、冷間加工性が劣化し得るので、上記のように夫々の好ましい上限を定めた。より好ましくは、Cu,Niの各々の含有量は、0.22質量%以下、更に好ましくは0.20質量%以下であり、Moの含有量は、より好ましくは0.40質量%以下、更に好ましくは0.35質量%以下であり、B含有量は、より好ましくは0.007質量%以下、更に好ましくは0.005質量%以下である。 [Cu: more than 0% by mass, 0.25% by mass or less, Ni: more than 0% by mass, 0.25% by mass or less, Mo: more than 0% by mass, 0.50% by mass or less, and B: more than 0% by mass , one or more selected from the group consisting of 0.01% by mass or less]
Cu, Ni, Mo and B are all effective elements for increasing the strength of the final product by improving the hardenability of the steel material, and may be contained alone or in combination of two or more. The effect of these elements increases as their content increases. A preferable lower limit for effectively exhibiting the above effects is more than 0% by mass, more preferably 0.02% by mass or more, and still more preferably 0.05% by mass or more for each of Cu, Ni, and Mo. It is more than 0% by mass, more preferably 0.0003% by mass or more, and still more preferably 0.0005% by mass or more.
On the other hand, if the content of these elements becomes excessive, the strength becomes too high and the cold workability may deteriorate. More preferably, the content of each of Cu and Ni is 0.22% by mass or less, more preferably 0.20% by mass or less, and the content of Mo is more preferably 0.40% by mass or less, and further preferably It is preferably 0.35% by mass or less, and the B content is more preferably 0.007% by mass or less, still more preferably 0.005% by mass or less.
[Ti:0質量%超、0.2質量%以下、Nb:0質量%超、0.2質量%以下、およびV:0質量%超、0.5質量%以下よりなる群から選択される1種以上]
Ti,NbおよびVは、Nと化合物を形成し、固溶Nを低減することで、変形抵抗低減の効果を発揮するため、必要によって単独でまたは2種以上を含有させることができる。これらの元素による効果はその含有量が増加するにつれて大きくなる。いずれの元素についても上記効果を有効に発揮させるための好ましい下限は0質量%超、より好ましくは0.03質量%以上、更に好ましくは0.05質量%以上である。しかしながら、これらの元素の含有量が過剰になると、形成される化合物が変形抵抗の上昇を招き、却って冷間加工性が低下し得るので、TiおよびNbの各々の含有量は0.2質量%以下、Vの含有量は0.5質量%以下とすることが好ましい。TiおよびNbの各々の含有量は、より好ましくは0.18質量%以下、更に好ましくは0.15質量%以下であり、V含有量は、より好ましくは0.45質量%以下、更に好ましくは0.40質量%以下である。 [Ti: more than 0% by mass, 0.2% by mass or less, Nb: more than 0% by mass, 0.2% by mass or less, and V: more than 0% by mass, selected from the group consisting of 0.5% by mass or less 1 or more]
Ti, Nb and V form a compound with N and reduce solid solution N to exhibit the effect of reducing deformation resistance. The effect of these elements increases as their content increases. The preferable lower limit for effectively exhibiting the above effects for any element is more than 0% by mass, more preferably 0.03% by mass or more, and still more preferably 0.05% by mass or more. However, if the content of these elements becomes excessive, the compounds formed may lead to an increase in deformation resistance, which may rather deteriorate the cold workability. Hereinafter, the V content is preferably 0.5% by mass or less. The content of each of Ti and Nb is more preferably 0.18% by mass or less, more preferably 0.15% by mass or less, and the V content is more preferably 0.45% by mass or less, further preferably It is 0.40% by mass or less.
Ti,NbおよびVは、Nと化合物を形成し、固溶Nを低減することで、変形抵抗低減の効果を発揮するため、必要によって単独でまたは2種以上を含有させることができる。これらの元素による効果はその含有量が増加するにつれて大きくなる。いずれの元素についても上記効果を有効に発揮させるための好ましい下限は0質量%超、より好ましくは0.03質量%以上、更に好ましくは0.05質量%以上である。しかしながら、これらの元素の含有量が過剰になると、形成される化合物が変形抵抗の上昇を招き、却って冷間加工性が低下し得るので、TiおよびNbの各々の含有量は0.2質量%以下、Vの含有量は0.5質量%以下とすることが好ましい。TiおよびNbの各々の含有量は、より好ましくは0.18質量%以下、更に好ましくは0.15質量%以下であり、V含有量は、より好ましくは0.45質量%以下、更に好ましくは0.40質量%以下である。 [Ti: more than 0% by mass, 0.2% by mass or less, Nb: more than 0% by mass, 0.2% by mass or less, and V: more than 0% by mass, selected from the group consisting of 0.5% by mass or less 1 or more]
Ti, Nb and V form a compound with N and reduce solid solution N to exhibit the effect of reducing deformation resistance. The effect of these elements increases as their content increases. The preferable lower limit for effectively exhibiting the above effects for any element is more than 0% by mass, more preferably 0.03% by mass or more, and still more preferably 0.05% by mass or more. However, if the content of these elements becomes excessive, the compounds formed may lead to an increase in deformation resistance, which may rather deteriorate the cold workability. Hereinafter, the V content is preferably 0.5% by mass or less. The content of each of Ti and Nb is more preferably 0.18% by mass or less, more preferably 0.15% by mass or less, and the V content is more preferably 0.45% by mass or less, further preferably It is 0.40% by mass or less.
[Mg:0質量%超、0.02質量%以下、Ca:0質量%超、0.05質量%以下、Li:0質量%超、0.02質量%以下、および希土類元素(Rare Earth Metal:REM):0質量%超、0.05質量%以下よりなる群から選択される1種以上]
Mg、Ca、LiおよびREMは、MnS等の硫化化合物系介在物を球状化させ、鋼の変形能を向上させるのに有効な元素である。こうした作用はその含有量が増加するにつれて増大する。上記効果を有効に発揮させるには、Mg、Ca、LiおよびREMの含有量は夫々、好ましくは0質量%超、より好ましくは0.0001質量%以上、更に好ましくは0.0005質量%以上である。しかし過剰に含有させてもその効果は飽和し、含有量に見合う効果が期待できないので、MgおよびLiの含有量は夫々、好ましくは0.02質量%以下、より好ましくは0.018質量%以下、更に好ましくは0.015質量%以下であり、CaとREMの含有量は夫々、好ましくは0.05質量%以下、より好ましくは0.045質量%以下、更に好ましくは0.040質量%以下である。なお、Mg、Ca、LiおよびREMは、夫々、単独で含有させてもよいし、2種以上を含有させてもよく、また2種以上を含有させる場合の含有量は夫々上記範囲で任意の含有量でよい。前記REMとは、ランタノイド元素(LaからLuまでの15元素)、Sc(スカンジウム)およびY(イットリウム)を含む意味である。 [Mg: more than 0% by mass, 0.02% by mass or less, Ca: more than 0% by mass, 0.05% by mass or less, Li: more than 0% by mass, 0.02% by mass or less, and rare earth elements (Rare Earth Metal :REM): One or more selected from the group consisting of more than 0% by mass and 0.05% by mass or less]
Mg, Ca, Li and REM are elements effective in spheroidizing sulfide-based inclusions such as MnS and improving the deformability of steel. These effects increase as the content increases. In order to effectively exhibit the above effects, the content of Mg, Ca, Li and REM is preferably more than 0% by mass, more preferably 0.0001% by mass or more, and still more preferably 0.0005% by mass or more. be. However, even if it is contained excessively, the effect is saturated, and the effect corresponding to the content cannot be expected. , more preferably 0.015% by mass or less, and the content of Ca and REM is preferably 0.05% by mass or less, more preferably 0.045% by mass or less, and still more preferably 0.040% by mass or less. is. Incidentally, each of Mg, Ca, Li and REM may be contained alone, or two or more kinds thereof may be contained. Content is fine. The REM is meant to include lanthanoid elements (15 elements from La to Lu), Sc (scandium) and Y (yttrium).
Mg、Ca、LiおよびREMは、MnS等の硫化化合物系介在物を球状化させ、鋼の変形能を向上させるのに有効な元素である。こうした作用はその含有量が増加するにつれて増大する。上記効果を有効に発揮させるには、Mg、Ca、LiおよびREMの含有量は夫々、好ましくは0質量%超、より好ましくは0.0001質量%以上、更に好ましくは0.0005質量%以上である。しかし過剰に含有させてもその効果は飽和し、含有量に見合う効果が期待できないので、MgおよびLiの含有量は夫々、好ましくは0.02質量%以下、より好ましくは0.018質量%以下、更に好ましくは0.015質量%以下であり、CaとREMの含有量は夫々、好ましくは0.05質量%以下、より好ましくは0.045質量%以下、更に好ましくは0.040質量%以下である。なお、Mg、Ca、LiおよびREMは、夫々、単独で含有させてもよいし、2種以上を含有させてもよく、また2種以上を含有させる場合の含有量は夫々上記範囲で任意の含有量でよい。前記REMとは、ランタノイド元素(LaからLuまでの15元素)、Sc(スカンジウム)およびY(イットリウム)を含む意味である。 [Mg: more than 0% by mass, 0.02% by mass or less, Ca: more than 0% by mass, 0.05% by mass or less, Li: more than 0% by mass, 0.02% by mass or less, and rare earth elements (Rare Earth Metal :REM): One or more selected from the group consisting of more than 0% by mass and 0.05% by mass or less]
Mg, Ca, Li and REM are elements effective in spheroidizing sulfide-based inclusions such as MnS and improving the deformability of steel. These effects increase as the content increases. In order to effectively exhibit the above effects, the content of Mg, Ca, Li and REM is preferably more than 0% by mass, more preferably 0.0001% by mass or more, and still more preferably 0.0005% by mass or more. be. However, even if it is contained excessively, the effect is saturated, and the effect corresponding to the content cannot be expected. , more preferably 0.015% by mass or less, and the content of Ca and REM is preferably 0.05% by mass or less, more preferably 0.045% by mass or less, and still more preferably 0.040% by mass or less. is. Incidentally, each of Mg, Ca, Li and REM may be contained alone, or two or more kinds thereof may be contained. Content is fine. The REM is meant to include lanthanoid elements (15 elements from La to Lu), Sc (scandium) and Y (yttrium).
本実施形態に係る機械構造部品用鋼線の形状等は特に限定されない。例えば直径が5.5mm~60mmのものが挙げられる。
The shape of the steel wire for machine structural parts according to this embodiment is not particularly limited. For example, those having a diameter of 5.5 mm to 60 mm can be used.
3.製造方法
本発明の実施形態に係る機械構造部品用鋼線の金属組織を得るには、該機械構造部品用鋼線を製造するにあたり、球状化焼鈍条件を以下に説明の通り適切に制御することが好ましい。球状化焼鈍に供する線材又は棒鋼を製造するための、熱間圧延工程に関しては特に限定されず、定法に従えば良い。後述の通り、球状化焼鈍前に伸線加工を付与してもよい。球状化焼鈍に供する条鋼である線材、鋼線、棒鋼の直径は特に限定されず、線材と鋼線の場合は、例えば5.5mm~60mm、棒鋼の場合は、例えば18mm~105mmである。 3. Manufacturing Method In order to obtain the metal structure of the steel wire for machine structural parts according to the embodiment of the present invention, the spheroidizing annealing conditions should be appropriately controlled as described below in manufacturing the steel wire for machine structural parts. is preferred. The hot rolling process for producing a wire rod or steel bar to be subjected to spheroidizing annealing is not particularly limited, and a conventional method may be followed. As will be described later, wire drawing may be applied before spheroidizing annealing. The diameter of the wire rod, steel wire, and steel bar to be subjected to spheroidizing annealing is not particularly limited.
本発明の実施形態に係る機械構造部品用鋼線の金属組織を得るには、該機械構造部品用鋼線を製造するにあたり、球状化焼鈍条件を以下に説明の通り適切に制御することが好ましい。球状化焼鈍に供する線材又は棒鋼を製造するための、熱間圧延工程に関しては特に限定されず、定法に従えば良い。後述の通り、球状化焼鈍前に伸線加工を付与してもよい。球状化焼鈍に供する条鋼である線材、鋼線、棒鋼の直径は特に限定されず、線材と鋼線の場合は、例えば5.5mm~60mm、棒鋼の場合は、例えば18mm~105mmである。 3. Manufacturing Method In order to obtain the metal structure of the steel wire for machine structural parts according to the embodiment of the present invention, the spheroidizing annealing conditions should be appropriately controlled as described below in manufacturing the steel wire for machine structural parts. is preferred. The hot rolling process for producing a wire rod or steel bar to be subjected to spheroidizing annealing is not particularly limited, and a conventional method may be followed. As will be described later, wire drawing may be applied before spheroidizing annealing. The diameter of the wire rod, steel wire, and steel bar to be subjected to spheroidizing annealing is not particularly limited.
図1を参照しながら、本発明の実施形態に係る機械構造部品用鋼線の製造方法における球状化焼鈍条件について説明する。図1は、本発明の実施形態に係る製造方法における球状化焼鈍の条件を説明するダイアグラムの一例を示すものであり、冷却-加熱工程の繰り返し回数等について、この図1に限定されない。
The spheroidizing annealing conditions in the method for manufacturing a steel wire for machine structural parts according to the embodiment of the present invention will be described with reference to FIG. FIG. 1 shows an example of a diagram explaining the conditions of spheroidizing annealing in the manufacturing method according to the embodiment of the present invention, and the number of repetitions of the cooling-heating process is not limited to this FIG.
本発明の実施形態に係る機械構造部品用鋼線の製造方法は、下記(1)~(3)の工程を含む球状化焼鈍工程を含む。
(1)(A1+8℃)~(A1+31℃)の温度T1に加熱した後に、該温度T1で1時間超、6時間以下で加熱保持し、
(2)650℃超、(A1-17℃)以下の温度T2まで冷却し、温度T2よりも高く(A1+60℃)以下の加熱温度まで加熱する、冷却-加熱工程を合計2回~6回実施し、
(3)5℃/時間~20℃/時間の平均冷却速度で(A1-30℃)未満の温度まで冷却する。
ここで、A1は、下記式(1)で算出される。
A1(℃)=723+29.1×[Si]-10.7×[Mn]+16.9×[Cr]-16.9×[Ni]・・・(1)
ただし、[元素]は、各元素の含有量(質量%)を表し、含まれない元素の含有量はゼロとする。 A method for manufacturing a steel wire for machine structural parts according to an embodiment of the present invention includes a spheroidizing annealing step including steps (1) to (3) below.
(1) After heating to a temperature T1 of (A1 + 8 ° C.) to (A1 + 31 ° C.), heating and holding at the temperature T1 for more than 1 hour and 6 hours or less,
(2) Cooling to a temperature T2 exceeding 650 ° C. and not exceeding (A1-17 ° C.) and heating to a heating temperature higher than the temperature T2 and not exceeding (A1 + 60 ° C.), performing a total of 2 to 6 times of the cooling-heating process. death,
(3) Cool to a temperature below (A1-30°C) at an average cooling rate of 5°C/hr to 20°C/hr.
Here, A1 is calculated by the following formula (1).
A1 (° C.)=723+29.1×[Si]−10.7×[Mn]+16.9×[Cr]−16.9×[Ni] (1)
However, [element] represents the content (% by mass) of each element, and the content of elements not included is zero.
(1)(A1+8℃)~(A1+31℃)の温度T1に加熱した後に、該温度T1で1時間超、6時間以下で加熱保持し、
(2)650℃超、(A1-17℃)以下の温度T2まで冷却し、温度T2よりも高く(A1+60℃)以下の加熱温度まで加熱する、冷却-加熱工程を合計2回~6回実施し、
(3)5℃/時間~20℃/時間の平均冷却速度で(A1-30℃)未満の温度まで冷却する。
ここで、A1は、下記式(1)で算出される。
A1(℃)=723+29.1×[Si]-10.7×[Mn]+16.9×[Cr]-16.9×[Ni]・・・(1)
ただし、[元素]は、各元素の含有量(質量%)を表し、含まれない元素の含有量はゼロとする。 A method for manufacturing a steel wire for machine structural parts according to an embodiment of the present invention includes a spheroidizing annealing step including steps (1) to (3) below.
(1) After heating to a temperature T1 of (A1 + 8 ° C.) to (A1 + 31 ° C.), heating and holding at the temperature T1 for more than 1 hour and 6 hours or less,
(2) Cooling to a temperature T2 exceeding 650 ° C. and not exceeding (A1-17 ° C.) and heating to a heating temperature higher than the temperature T2 and not exceeding (A1 + 60 ° C.), performing a total of 2 to 6 times of the cooling-heating process. death,
(3) Cool to a temperature below (A1-30°C) at an average cooling rate of 5°C/hr to 20°C/hr.
Here, A1 is calculated by the following formula (1).
A1 (° C.)=723+29.1×[Si]−10.7×[Mn]+16.9×[Cr]−16.9×[Ni] (1)
However, [element] represents the content (% by mass) of each element, and the content of elements not included is zero.
[(1)(A1+8℃)~(A1+31℃)の温度T1に加熱した後に、該温度T1で1時間超、6時間以下で加熱保持(図1の[1]および[2])]
(A1+8℃)~(A1+31℃)の温度(T1)に加熱することによって、圧延の段階で生成した、アスペクト比が大きく、界面ひずみの多い棒状セメンタイトの溶解を促進させる。温度T1が低過ぎると、加熱保持時に界面ひずみの多い棒状セメンタイトが溶解されず、フェライト中に残存しつづけ、硬さが増加し、冷間加工性が低下する。十分に軟質化された鋼線を得るには、温度T1を、A1+8℃以上にする必要がある。温度T1は、好ましくはA1+15℃以上であり、より好ましくはA1+20℃以上である。一方、温度T1が高過ぎると、結晶粒が粗大になり過ぎて、次工程の冷却過程でフェライト結晶粒界に球状セメンタイトが析出し難くなり、棒状セメンタイトが増加して、硬さが増加し、冷間加工性が低下する。そのため、温度T1はA1+31℃以下とした。温度T1は、好ましくはA1+30℃以下であり、より好ましくはA1+29℃以下である。 [(1) After heating to a temperature T1 of (A1 + 8 ° C.) to (A1 + 31 ° C.), heating and holding at the temperature T1 for more than 1 hour and 6 hours or less ([1] and [2] in FIG. 1)]
Heating to a temperature (T1) of (A1+8° C.) to (A1+31° C.) accelerates the dissolution of the rod-shaped cementite having a large aspect ratio and a large interfacial strain generated in the rolling stage. If the temperature T1 is too low, the rod-shaped cementite, which has a large interfacial strain, is not dissolved during heating and holding, and remains in the ferrite, increasing the hardness and degrading the cold workability. To obtain a sufficiently softened steel wire, the temperature T1 must be A1+8° C. or higher. The temperature T1 is preferably A1+15° C. or higher, more preferably A1+20° C. or higher. On the other hand, if the temperature T1 is too high, the crystal grains become too coarse, making it difficult for spherical cementite to precipitate at the ferrite crystal grain boundaries in the cooling process of the next step, increasing rod-like cementite, increasing hardness, Cold workability deteriorates. Therefore, the temperature T1 was set to A1+31° C. or lower. The temperature T1 is preferably A1+30° C. or lower, more preferably A1+29° C. or lower.
(A1+8℃)~(A1+31℃)の温度(T1)に加熱することによって、圧延の段階で生成した、アスペクト比が大きく、界面ひずみの多い棒状セメンタイトの溶解を促進させる。温度T1が低過ぎると、加熱保持時に界面ひずみの多い棒状セメンタイトが溶解されず、フェライト中に残存しつづけ、硬さが増加し、冷間加工性が低下する。十分に軟質化された鋼線を得るには、温度T1を、A1+8℃以上にする必要がある。温度T1は、好ましくはA1+15℃以上であり、より好ましくはA1+20℃以上である。一方、温度T1が高過ぎると、結晶粒が粗大になり過ぎて、次工程の冷却過程でフェライト結晶粒界に球状セメンタイトが析出し難くなり、棒状セメンタイトが増加して、硬さが増加し、冷間加工性が低下する。そのため、温度T1はA1+31℃以下とした。温度T1は、好ましくはA1+30℃以下であり、より好ましくはA1+29℃以下である。 [(1) After heating to a temperature T1 of (A1 + 8 ° C.) to (A1 + 31 ° C.), heating and holding at the temperature T1 for more than 1 hour and 6 hours or less ([1] and [2] in FIG. 1)]
Heating to a temperature (T1) of (A1+8° C.) to (A1+31° C.) accelerates the dissolution of the rod-shaped cementite having a large aspect ratio and a large interfacial strain generated in the rolling stage. If the temperature T1 is too low, the rod-shaped cementite, which has a large interfacial strain, is not dissolved during heating and holding, and remains in the ferrite, increasing the hardness and degrading the cold workability. To obtain a sufficiently softened steel wire, the temperature T1 must be A1+8° C. or higher. The temperature T1 is preferably A1+15° C. or higher, more preferably A1+20° C. or higher. On the other hand, if the temperature T1 is too high, the crystal grains become too coarse, making it difficult for spherical cementite to precipitate at the ferrite crystal grain boundaries in the cooling process of the next step, increasing rod-like cementite, increasing hardness, Cold workability deteriorates. Therefore, the temperature T1 was set to A1+31° C. or lower. The temperature T1 is preferably A1+30° C. or lower, more preferably A1+29° C. or lower.
また、温度T1での加熱保持時間(t1)が短過ぎると、界面ひずみの多い棒状セメンタイトがフェライト結晶粒内に残存し、硬さが増加し、冷間加工性が低下する。十分に軟質化された鋼線を得るには、加熱保持時間(t1)は、1時間超、6時間以下にする必要がある。好ましい加熱保持時間(t1)は、1.5時間以上であり、より好ましくは2.0時間以上である。加熱保持時間(t1)が長過ぎると、熱処理時間が長くなり生産性が低下する。そのため、加熱保持時間(t1)は、6時間以下であり、好ましくは5時間以下であり、より好ましくは4時間以下である。なお、(A1+8℃)~(A1+31℃)の温度(T1)まで加熱時(図1の[1])の平均昇温速度は鋼材特性に影響しないので、任意の速度で昇温を行えばよい。例えば、30℃/時間~100℃/時間で昇温すればよい。
On the other hand, if the heating and holding time (t1) at the temperature T1 is too short, rod-shaped cementite with large interfacial strain remains in the ferrite crystal grains, the hardness increases, and the cold workability decreases. In order to obtain a sufficiently softened steel wire, the heating holding time (t1) should be more than 1 hour and 6 hours or less. The heating and holding time (t1) is preferably 1.5 hours or longer, more preferably 2.0 hours or longer. If the heating holding time (t1) is too long, the heat treatment time will be long and the productivity will be lowered. Therefore, the heating and holding time (t1) is 6 hours or less, preferably 5 hours or less, and more preferably 4 hours or less. Note that the average heating rate during heating ([1] in FIG. 1) to the temperature (T1) from (A1 + 8 ° C.) to (A1 + 31 ° C.) does not affect the steel material properties, so the temperature can be raised at an arbitrary rate. . For example, the temperature may be raised at a rate of 30° C./hour to 100° C./hour.
なお、上記A1点の温度は、レスリー鉄鋼材料学(丸善)の第273頁に記載の下記式(1)で算出される。
A1(℃)=723+29.1×[Si]-10.7×[Mn]+16.9×[Cr]-16.9×[Ni]・・・(1)
ただし、[元素]は、各元素の含有量(質量%)を表し、含まれない元素の含有量はゼロとする。 The temperature at point A1 is calculated by the following formula (1) described on page 273 of Leslie Iron and Steel Materials Science (Maruzen).
A1 (° C.)=723+29.1×[Si]−10.7×[Mn]+16.9×[Cr]−16.9×[Ni] (1)
However, [element] represents the content (% by mass) of each element, and the content of elements not included is zero.
A1(℃)=723+29.1×[Si]-10.7×[Mn]+16.9×[Cr]-16.9×[Ni]・・・(1)
ただし、[元素]は、各元素の含有量(質量%)を表し、含まれない元素の含有量はゼロとする。 The temperature at point A1 is calculated by the following formula (1) described on page 273 of Leslie Iron and Steel Materials Science (Maruzen).
A1 (° C.)=723+29.1×[Si]−10.7×[Mn]+16.9×[Cr]−16.9×[Ni] (1)
However, [element] represents the content (% by mass) of each element, and the content of elements not included is zero.
[(2)650℃超、(A1-17℃)以下の温度T2まで冷却し、温度T2よりも高く(A1+60℃)以下の加熱温度まで加熱する冷却-加熱工程を合計2回~6回実施(図1の[7])]
続いて、650℃超~(A1-17℃)の温度T2まで冷却し、温度T2よりも高く(A1+60℃)以下の加熱温度まで加熱する冷却-加熱工程を合計2回~6回実施する。冷却-加熱工程の各工程について、以下に詳細に説明する。 [(2) Cooling to a temperature T2 exceeding 650 ° C. and not exceeding (A1-17 ° C.) and heating to a heating temperature higher than the temperature T2 and not exceeding (A1 + 60 ° C.) Perform a total of 2 to 6 times of the cooling-heating process. ([7] in Fig. 1)]
Subsequently, the cooling-heating step of cooling to a temperature T2 above 650° C. to (A1-17° C.) and heating to a heating temperature higher than the temperature T2 (A1+60° C.) or less is performed 2 to 6 times in total. Each step of the cooling-heating process is described in detail below.
続いて、650℃超~(A1-17℃)の温度T2まで冷却し、温度T2よりも高く(A1+60℃)以下の加熱温度まで加熱する冷却-加熱工程を合計2回~6回実施する。冷却-加熱工程の各工程について、以下に詳細に説明する。 [(2) Cooling to a temperature T2 exceeding 650 ° C. and not exceeding (A1-17 ° C.) and heating to a heating temperature higher than the temperature T2 and not exceeding (A1 + 60 ° C.) Perform a total of 2 to 6 times of the cooling-heating process. ([7] in Fig. 1)]
Subsequently, the cooling-heating step of cooling to a temperature T2 above 650° C. to (A1-17° C.) and heating to a heating temperature higher than the temperature T2 (A1+60° C.) or less is performed 2 to 6 times in total. Each step of the cooling-heating process is described in detail below.
<(2-i)650℃超~(A1-17℃)の温度T2まで冷却(図1の[3]および[4])>
界面ひずみの少ない球状セメンタイトの析出を促進させるために冷却する。温度T1からの平均冷却速度を遅くすると、界面ひずみの多い棒状セメンタイトが過剰に再析出することを抑制し、フェライト中のひずみ量が低減し、冷間加工性をより高めることができる。そのため、平均冷却速度は、100℃/時間以下とするのが好ましい。平均冷却速度は、より好ましくは90℃/時間以下であり、更により好ましくは80℃/時間以下である。一方、平均冷却速度を速めると、冷却時に生成したセメンタイトが過剰に粗大化することを抑制し、その結果、焼入れ処理工程の高温保持中にセメンタイトが十分に溶解し、焼入れ処理後の硬さがより向上、すなわち焼入れ性をより高めることができる。更に焼鈍時間を短くすることができ、生産性が向上する。従って、平均冷却速度は、1℃/時間以上とすることが好ましく、より好ましくは3℃/時間以上、更により好ましくは5℃/時間以上である。 <(2-i) Cooling to temperature T2 from over 650° C. to (A1-17° C.) ([3] and [4] in FIG. 1)>
Cool to promote the precipitation of spherical cementite with less interfacial strain. When the average cooling rate from temperature T1 is slowed down, excessive reprecipitation of rod-shaped cementite with a large interfacial strain can be suppressed, the amount of strain in ferrite can be reduced, and cold workability can be further improved. Therefore, the average cooling rate is preferably 100° C./hour or less. The average cooling rate is more preferably 90° C./hour or less, still more preferably 80° C./hour or less. On the other hand, when the average cooling rate is increased, excessive coarsening of the cementite formed during cooling is suppressed, and as a result, the cementite is sufficiently dissolved during the high temperature holding of the quenching process, and the hardness after quenching is reduced. Further improvement, that is, the hardenability can be further enhanced. Furthermore, the annealing time can be shortened, improving productivity. Therefore, the average cooling rate is preferably 1° C./hour or more, more preferably 3° C./hour or more, and even more preferably 5° C./hour or more.
界面ひずみの少ない球状セメンタイトの析出を促進させるために冷却する。温度T1からの平均冷却速度を遅くすると、界面ひずみの多い棒状セメンタイトが過剰に再析出することを抑制し、フェライト中のひずみ量が低減し、冷間加工性をより高めることができる。そのため、平均冷却速度は、100℃/時間以下とするのが好ましい。平均冷却速度は、より好ましくは90℃/時間以下であり、更により好ましくは80℃/時間以下である。一方、平均冷却速度を速めると、冷却時に生成したセメンタイトが過剰に粗大化することを抑制し、その結果、焼入れ処理工程の高温保持中にセメンタイトが十分に溶解し、焼入れ処理後の硬さがより向上、すなわち焼入れ性をより高めることができる。更に焼鈍時間を短くすることができ、生産性が向上する。従って、平均冷却速度は、1℃/時間以上とすることが好ましく、より好ましくは3℃/時間以上、更により好ましくは5℃/時間以上である。 <(2-i) Cooling to temperature T2 from over 650° C. to (A1-17° C.) ([3] and [4] in FIG. 1)>
Cool to promote the precipitation of spherical cementite with less interfacial strain. When the average cooling rate from temperature T1 is slowed down, excessive reprecipitation of rod-shaped cementite with a large interfacial strain can be suppressed, the amount of strain in ferrite can be reduced, and cold workability can be further improved. Therefore, the average cooling rate is preferably 100° C./hour or less. The average cooling rate is more preferably 90° C./hour or less, still more preferably 80° C./hour or less. On the other hand, when the average cooling rate is increased, excessive coarsening of the cementite formed during cooling is suppressed, and as a result, the cementite is sufficiently dissolved during the high temperature holding of the quenching process, and the hardness after quenching is reduced. Further improvement, that is, the hardenability can be further enhanced. Furthermore, the annealing time can be shortened, improving productivity. Therefore, the average cooling rate is preferably 1° C./hour or more, more preferably 3° C./hour or more, and even more preferably 5° C./hour or more.
また、冷却の到達温度(T2)が低すぎると、焼鈍時間の長時間化につながる。従って、冷却の到達温度(T2)は、650℃超とする必要がある。本実施形態に係る製造方法によれば、冷却の到達温度(T2)が650℃超であっても、長時間の焼鈍を行うことなくセメンタイトを所望の形態に制御することができる。冷却の到達温度(T2)は、好ましくは670℃以上である。一方、冷却の到達温度(T2)が高すぎると、界面ひずみの多い棒状セメンタイトが過剰に再析出し、フェライト中のひずみ量が増加し、冷間加工性が低下する。そのため、冷却の到達温度(T2)はA1点より一定以上低い値にする必要がある。従って、冷却の到達温度(T2)の上限は、A1-17℃とした。冷却の到達温度(T2)は、好ましくはA1-18℃以下である。また、冷却の到達温度(T2)に達した後、保持すると、熱処理時間の長時間化を招く。よって、これらの観点から保持しない方がよい。しかし、炉内の温度ばらつきを均一にするため、短時間であれば保持してもよい。冷却の到達温度T2での保持時間は、1時間以内とするのが好ましい。
Also, if the ultimate cooling temperature (T2) is too low, the annealing time will be prolonged. Therefore, the ultimate temperature (T2) of cooling needs to exceed 650°C. According to the manufacturing method according to the present embodiment, even if the ultimate cooling temperature (T2) exceeds 650° C., the cementite can be controlled into a desired form without long-term annealing. The cooling temperature (T2) is preferably 670° C. or higher. On the other hand, if the ultimate cooling temperature (T2) is too high, excessive reprecipitation of rod-shaped cementite with a large interfacial strain will increase the amount of strain in the ferrite and lower the cold workability. Therefore, the ultimate temperature (T2) of cooling needs to be lower than the A1 point by a certain amount or more. Therefore, the upper limit of the cooling temperature (T2) was set to A1-17°C. The ultimate temperature (T2) of cooling is preferably A1-18° C. or lower. Further, if the temperature is maintained after reaching the ultimate cooling temperature (T2), the heat treatment time will be prolonged. Therefore, it is better not to hold from these points of view. However, in order to equalize temperature variations in the furnace, it may be held for a short period of time. The holding time at the cooling reaching temperature T2 is preferably within 1 hour.
<(2-ii)温度T2よりも高く(A1+60℃)以下の加熱温度まで加熱(図1の[5]および[6])>
上記(2-i)の工程で析出した界面ひずみの多い棒状セメンタイトを再溶解させるために、上記冷却の到達温度(T2)から加熱する。図1の[6]に示す様な加熱の到達温度、すなわち加熱温度(T3)は、温度T2よりも高く(A1+60℃)以下の温度範囲における任意の温度であればよい。前記加熱温度は、上記(2-i)の工程で生成した界面ひずみの多い棒状セメンタイトを十分に再溶解させる観点からは、A1℃以上であることが好ましい。また、フェライト結晶粒界上の球状セメンタイトの再溶解を抑制して、球状化焼鈍後の硬さ増加を抑制する観点からは、加熱温度(T3)は、A1+57℃以下であることが好ましい。 <(2-ii) Heating to a heating temperature higher than temperature T2 (A1 + 60 ° C.) or less ([5] and [6] in FIG. 1)>
In order to re-dissolve the rod-shaped cementite having a large interfacial strain precipitated in the step (2-i), the steel is heated from the ultimate temperature (T2) of the cooling. The ultimate temperature of heating as shown in [6] in FIG. 1, that is, the heating temperature (T3) may be any temperature within the temperature range higher than the temperature T2 and not higher than (A1+60° C.). The heating temperature is preferably A1° C. or higher from the viewpoint of sufficiently remelting the rod-shaped cementite having a large interfacial strain generated in the step (2-i). Moreover, from the viewpoint of suppressing remelting of spherical cementite on ferrite grain boundaries and suppressing an increase in hardness after spheroidizing annealing, the heating temperature (T3) is preferably A1+57° C. or lower.
上記(2-i)の工程で析出した界面ひずみの多い棒状セメンタイトを再溶解させるために、上記冷却の到達温度(T2)から加熱する。図1の[6]に示す様な加熱の到達温度、すなわち加熱温度(T3)は、温度T2よりも高く(A1+60℃)以下の温度範囲における任意の温度であればよい。前記加熱温度は、上記(2-i)の工程で生成した界面ひずみの多い棒状セメンタイトを十分に再溶解させる観点からは、A1℃以上であることが好ましい。また、フェライト結晶粒界上の球状セメンタイトの再溶解を抑制して、球状化焼鈍後の硬さ増加を抑制する観点からは、加熱温度(T3)は、A1+57℃以下であることが好ましい。 <(2-ii) Heating to a heating temperature higher than temperature T2 (A1 + 60 ° C.) or less ([5] and [6] in FIG. 1)>
In order to re-dissolve the rod-shaped cementite having a large interfacial strain precipitated in the step (2-i), the steel is heated from the ultimate temperature (T2) of the cooling. The ultimate temperature of heating as shown in [6] in FIG. 1, that is, the heating temperature (T3) may be any temperature within the temperature range higher than the temperature T2 and not higher than (A1+60° C.). The heating temperature is preferably A1° C. or higher from the viewpoint of sufficiently remelting the rod-shaped cementite having a large interfacial strain generated in the step (2-i). Moreover, from the viewpoint of suppressing remelting of spherical cementite on ferrite grain boundaries and suppressing an increase in hardness after spheroidizing annealing, the heating temperature (T3) is preferably A1+57° C. or lower.
図1の[5]に示す様な、冷却の到達温度(T2)から加熱温度(T3)までの平均昇温速度も特に限定されない。平均昇温速度は、例えば、上記(2-i)の工程で生成した界面ひずみの多い棒状セメンタイトを更に十分に再溶解させ、球状化焼鈍後の硬さを更に抑制する観点から、200℃/時間以下としてもよい。また、例えば、この加熱で生成したセメンタイトの粗大化を十分抑制し、焼入れ性をより高める観点等から、5℃/時間以上とすることができる。
The average temperature increase rate from the cooling temperature (T2) to the heating temperature (T3) as shown in [5] of FIG. 1 is not particularly limited. The average temperature increase rate is, for example, 200° C./ It may be less than an hour. Further, for example, from the viewpoint of sufficiently suppressing coarsening of the cementite generated by this heating and further enhancing hardenability, the heating rate can be set to 5° C./hour or more.
上記加熱温度(T3)に達した後、該加熱温度での保持の有無は問わない。該加熱温度で保持する場合には、例えば、保持時間を1時間以内とし、上記温度T2まで冷却する工程で生成した球状セメンタイトの再溶解を抑制することが挙げられる。
After reaching the above heating temperature (T3), it does not matter whether or not the heating temperature is maintained. In the case of holding at the heating temperature, for example, the holding time is set to 1 hour or less to suppress redissolution of spherical cementite generated in the step of cooling to the temperature T2.
なお、上記加熱温度(T3)と上記温度T1との大小関係は、特に限定されず、例えば、上記加熱温度(T3)を上記温度T1と同じ温度としてもよいし、上記加熱温度(T3)を上記温度T1よりも高くしてもよい。
The magnitude relationship between the heating temperature (T3) and the temperature T1 is not particularly limited. For example, the heating temperature (T3) may be the same temperature as the temperature T1, or the heating temperature (T3) may be It may be higher than the temperature T1.
本実施形態に係る製造方法では、上記(2-i)冷却と上記(2-ii)加熱の冷却-加熱工程を複数回繰り返すが、各回において、温度T2および温度T3が上記範囲を満たしている必要がある。
In the manufacturing method according to the present embodiment, the cooling-heating step of (2-i) cooling and (2-ii) heating is repeated multiple times, but each time, the temperature T2 and the temperature T3 satisfy the above ranges. There is a need.
<(2-iii)冷却-加熱工程を合計2回~6回実施(図1の[7])>
上記(2-i)の工程で析出する界面ひずみの多い棒状セメンタイトの析出を抑制するには、上記(1)の工程で温度T1に加熱保持した後、上記(2-i)および上記(2-ii)の冷却-加熱工程を合計2~6回行う必要がある。この冷却-加熱工程を繰り返し行わない場合、フェライト中のひずみ量が増大するため、球状化焼鈍後の硬さが増大する。よって、上記冷却-加熱工程を2回以上行う。好ましくは3回以上である。実施回数を多くする程硬さが低減されるが、実施回数が多過ぎてもその効果は飽和する。また、焼鈍時間の長時間化につながり、生産性を低下させる。従って、冷却-加熱工程の実施回数は6回以下とした。なお、図1の場合、上記(2-i)の冷却と上記(2-ii)の加熱の実施回数は、4回である。また、各回の冷却の到達温度(T2)は、それぞれ規定する範囲内で異なっていてもよい。また、冷却-加熱工程における平均冷却速度は、1回目の冷却-加熱工程では、温度T1から冷却の到達温度(T2)までの平均冷却速度をいい、2回目以降は、加熱温度(T3)から冷却の到達温度(T2)までの平均冷却速度をいう。 <(2-iii) Performing the cooling-heating step a total of 2 to 6 times ([7] in FIG. 1)>
In order to suppress the precipitation of rod-shaped cementite with a large interfacial strain that precipitates in the step (2-i), after heating and holding at the temperature T1 in the step (1), the above (2-i) and the above (2) It is necessary to perform the cooling-heating step of -ii) a total of 2 to 6 times. If this cooling-heating process is not repeated, the amount of strain in the ferrite increases, resulting in an increase in hardness after spheroidizing annealing. Therefore, the cooling-heating process is performed twice or more. It is preferably three times or more. The hardness is reduced as the number of times of implementation is increased, but the effect is saturated even if the number of times of implementation is too large. In addition, the annealing time is lengthened and the productivity is lowered. Therefore, the number of cooling-heating steps was set to 6 or less. In the case of FIG. 1, the number of times of the above cooling (2-i) and the above heating (2-ii) is four. Also, the temperature (T2) reached by each cooling may be different within a defined range. In addition, the average cooling rate in the cooling-heating process refers to the average cooling rate from the temperature T1 to the cooling target temperature (T2) in the first cooling-heating process, and from the heating temperature (T3) after the second time. It means the average cooling rate up to the cooling ultimate temperature (T2).
上記(2-i)の工程で析出する界面ひずみの多い棒状セメンタイトの析出を抑制するには、上記(1)の工程で温度T1に加熱保持した後、上記(2-i)および上記(2-ii)の冷却-加熱工程を合計2~6回行う必要がある。この冷却-加熱工程を繰り返し行わない場合、フェライト中のひずみ量が増大するため、球状化焼鈍後の硬さが増大する。よって、上記冷却-加熱工程を2回以上行う。好ましくは3回以上である。実施回数を多くする程硬さが低減されるが、実施回数が多過ぎてもその効果は飽和する。また、焼鈍時間の長時間化につながり、生産性を低下させる。従って、冷却-加熱工程の実施回数は6回以下とした。なお、図1の場合、上記(2-i)の冷却と上記(2-ii)の加熱の実施回数は、4回である。また、各回の冷却の到達温度(T2)は、それぞれ規定する範囲内で異なっていてもよい。また、冷却-加熱工程における平均冷却速度は、1回目の冷却-加熱工程では、温度T1から冷却の到達温度(T2)までの平均冷却速度をいい、2回目以降は、加熱温度(T3)から冷却の到達温度(T2)までの平均冷却速度をいう。 <(2-iii) Performing the cooling-heating step a total of 2 to 6 times ([7] in FIG. 1)>
In order to suppress the precipitation of rod-shaped cementite with a large interfacial strain that precipitates in the step (2-i), after heating and holding at the temperature T1 in the step (1), the above (2-i) and the above (2) It is necessary to perform the cooling-heating step of -ii) a total of 2 to 6 times. If this cooling-heating process is not repeated, the amount of strain in the ferrite increases, resulting in an increase in hardness after spheroidizing annealing. Therefore, the cooling-heating process is performed twice or more. It is preferably three times or more. The hardness is reduced as the number of times of implementation is increased, but the effect is saturated even if the number of times of implementation is too large. In addition, the annealing time is lengthened and the productivity is lowered. Therefore, the number of cooling-heating steps was set to 6 or less. In the case of FIG. 1, the number of times of the above cooling (2-i) and the above heating (2-ii) is four. Also, the temperature (T2) reached by each cooling may be different within a defined range. In addition, the average cooling rate in the cooling-heating process refers to the average cooling rate from the temperature T1 to the cooling target temperature (T2) in the first cooling-heating process, and from the heating temperature (T3) after the second time. It means the average cooling rate up to the cooling ultimate temperature (T2).
[(3)5℃/時間~20℃/時間の平均冷却速度で(A1-30℃)未満の温度まで冷却(図1の[8]および[9])]
冷却-加熱工程の最終回の加熱温度(T3)から冷却する。冷却到達温度(T4)が(A1-30℃)以上になると、界面ひずみの多い棒状セメンタイトが再析出し、フェライト中のひずみが増加し、冷間加工性が低下する。そのため、冷却到達温度(T4)を(A1-30℃)未満とした。好ましくは、(A1-35℃)以下、より好ましくは(A1-40℃)以下である。冷却到達温度(T4)は、焼鈍時間を短縮化する観点から、好ましくは(A1-250℃)以上、より好ましくは(A1-200℃)以上、さらにより好ましくは(A1-150℃)以上である。 [(3) cooling to a temperature below (A1-30°C) at an average cooling rate of 5°C/h to 20°C/h ([8] and [9] in Figure 1)]
Cool from the final heating temperature (T3) of the cooling-heating process. When the ultimate cooling temperature (T4) is (A1-30° C.) or higher, rod-shaped cementite with a large interfacial strain reprecipitates, strain in ferrite increases, and cold workability deteriorates. Therefore, the ultimate cooling temperature (T4) was set to less than (A1-30°C). It is preferably (A1-35°C) or less, more preferably (A1-40°C) or less. The ultimate cooling temperature (T4) is preferably (A1-250°C) or higher, more preferably (A1-200°C) or higher, and even more preferably (A1-150°C) or higher, from the viewpoint of shortening the annealing time. be.
冷却-加熱工程の最終回の加熱温度(T3)から冷却する。冷却到達温度(T4)が(A1-30℃)以上になると、界面ひずみの多い棒状セメンタイトが再析出し、フェライト中のひずみが増加し、冷間加工性が低下する。そのため、冷却到達温度(T4)を(A1-30℃)未満とした。好ましくは、(A1-35℃)以下、より好ましくは(A1-40℃)以下である。冷却到達温度(T4)は、焼鈍時間を短縮化する観点から、好ましくは(A1-250℃)以上、より好ましくは(A1-200℃)以上、さらにより好ましくは(A1-150℃)以上である。 [(3) cooling to a temperature below (A1-30°C) at an average cooling rate of 5°C/h to 20°C/h ([8] and [9] in Figure 1)]
Cool from the final heating temperature (T3) of the cooling-heating process. When the ultimate cooling temperature (T4) is (A1-30° C.) or higher, rod-shaped cementite with a large interfacial strain reprecipitates, strain in ferrite increases, and cold workability deteriorates. Therefore, the ultimate cooling temperature (T4) was set to less than (A1-30°C). It is preferably (A1-35°C) or less, more preferably (A1-40°C) or less. The ultimate cooling temperature (T4) is preferably (A1-250°C) or higher, more preferably (A1-200°C) or higher, and even more preferably (A1-150°C) or higher, from the viewpoint of shortening the annealing time. be.
界面ひずみの多い棒状セメンタイトの再析出を抑制し、フェライト中のひずみ量を低減するため、平均冷却速度(R3)は、20℃/時間以下とする必要がある。平均冷却速度(R3)は、好ましくは18℃/時間以下であり、より好ましくは15℃/時間以下である。平均冷却速度(R3)が遅すぎると、セメンタイトが過剰に粗大化し、焼入れ処理工程の高温保持中にセメンタイトが十分に溶解されず、焼入れ処理後の硬さが低下、すなわち焼入れ性の劣化を招く。更に焼鈍時間の長時間化につながり、生産性が低下する。従って、平均冷却速度(R3)の下限は、5℃/時間と定めた。平均冷却速度(R3)は、好ましくは10℃/時間以上である。
The average cooling rate (R3) must be 20°C/hour or less in order to suppress the reprecipitation of rod-shaped cementite with a large amount of interfacial strain and reduce the amount of strain in ferrite. The average cooling rate (R3) is preferably 18°C/hour or less, more preferably 15°C/hour or less. If the average cooling rate (R3) is too slow, the cementite is excessively coarsened, and the cementite is not sufficiently dissolved during the high temperature holding in the quenching process, resulting in a decrease in hardness after quenching, that is, deterioration of hardenability. . Further, the annealing time is lengthened, resulting in a decrease in productivity. Therefore, the lower limit of the average cooling rate (R3) was set at 5°C/hour. The average cooling rate (R3) is preferably 10°C/hour or more.
(A1-30℃)未満の温度域では、界面のひずみの多い棒状セメンタイトの析出は生じない。そのため、冷却到達温度(T4)は、(A1-30℃)未満であれば、任意の温度でよい。該任意の温度以下の冷却は、特に限定されず、例えば空冷としてもよい。
In a temperature range of less than (A1-30°C), precipitation of highly strained rod-shaped cementite at the interface does not occur. Therefore, the ultimate cooling temperature (T4) may be any temperature as long as it is less than (A1-30° C.). Cooling below the arbitrary temperature is not particularly limited, and may be air cooling, for example.
上記のような球状化焼鈍((1)~(3)の工程)を1回または複数回繰り返し行ってもよい。セメンタイトの過剰な粗大化の抑制と、生産性確保の観点からは、例えば、4回以下とすることが好ましく、より好ましくは3回以下である。上記球状化焼鈍を複数回繰り返す場合、上記規定の範囲内で、同じ条件で繰り返しても良く、異なる条件で繰り返しても良い。また、上記球状化焼鈍を複数回繰り返す場合、球状化焼鈍間に伸線加工を加えてもよい。例えば、後述する球状化焼鈍前の伸線加工→1回目の球状化焼鈍→伸線加工→2回目の球状化焼鈍の順に実施することができる。
The above spheroidizing annealing (steps (1) to (3)) may be repeated once or multiple times. From the viewpoint of suppressing excessive coarsening of cementite and securing productivity, for example, it is preferably 4 times or less, more preferably 3 times or less. When the spheroidizing annealing is repeated multiple times, it may be repeated under the same conditions or under different conditions within the above specified range. Further, when the spheroidizing annealing is repeated multiple times, wire drawing may be added between the spheroidizing annealing. For example, wire drawing before spheroidizing annealing to be described later→first spheroidizing annealing→wire drawing→second spheroidizing annealing can be performed in this order.
本実施形態に係る機械構造部品用鋼線の製造方法において、上記球状化焼鈍工程以外の工程は特に限定されない。例えば、球状化焼鈍後に、寸法を調整する目的で減面率が好ましくは15%以下の伸線加工を施す工程を含めてもよい。減面率を15%以下とすることで、冷間加工前の硬さ増加を抑制できる。減面率は、より好ましくは10%以下であり、更に好ましくは8%以下、より更により好ましくは5%以下である。
In the method for manufacturing a steel wire for machine structural parts according to the present embodiment, processes other than the spheroidizing annealing process are not particularly limited. For example, after spheroidizing annealing, a step of wire drawing with a reduction in area of preferably 15% or less may be included for the purpose of adjusting dimensions. By setting the area reduction rate to 15% or less, an increase in hardness before cold working can be suppressed. The area reduction rate is more preferably 10% or less, still more preferably 8% or less, and even more preferably 5% or less.
本発明の組織形態の生成を促進するため、球状化焼鈍前に、線材に対して、5%超の減面率で伸線加工を施す工程を設けることが好ましい。上記減面率で伸線加工を施すことで、鋼中のセメンタイトが破壊され、その後の球状化焼鈍でセメンタイトの凝集を促進できるため、セメンタイトが過剰すぎない程度に粗大化しやすく、軟質化に有効である。減面率は、より好ましくは10%以上、更に好ましくは15%以上、より更に好ましくは20%以上である。一方、減面率を過度に大きくすると、断線リスクを招く可能性がある。そのため、減面率は好ましくは50%以下とする。伸線加工を複数回行う場合、伸線加工の回数は、特に限定されず、例えば2回とすることができる。なお、複数回の伸線加工が行われる場合、上記「伸線加工時の減面率」とは、伸線加工前の鋼材から複数回の伸線加工が行われた後の鋼材への減面率を意味する。
In order to promote the formation of the structure morphology of the present invention, it is preferable to provide a step of drawing the wire with a reduction in area of more than 5% before the spheroidizing annealing. By performing wire drawing with the above area reduction rate, the cementite in the steel is destroyed, and the subsequent spheroidizing annealing can promote the aggregation of cementite. is. The area reduction rate is more preferably 10% or more, still more preferably 15% or more, and even more preferably 20% or more. On the other hand, excessively increasing the area reduction rate may invite disconnection risk. Therefore, the area reduction rate is preferably 50% or less. When wire drawing is performed multiple times, the number of times of wire drawing is not particularly limited, and can be, for example, two times. In addition, when wire drawing is performed multiple times, the above "area reduction rate during wire drawing" is the reduction from the steel material before wire drawing to the steel material after wire drawing is performed multiple times. means area ratio.
以下、実施例を挙げて本開示をより具体的に説明する。本開示は以下の実施例によって制限を受けるものではなく、前記、後記の趣旨に適合し得る範囲で適当に変更を加えて実施することも勿論可能であり、それらはいずれも本開示の技術的範囲に包含される。
Hereinafter, the present disclosure will be described more specifically with examples. The present disclosure is not limited by the following examples, and it is of course possible to make appropriate modifications within the scope that can be adapted to the spirit of the above and below, and any of them are technical aspects of the present disclosure. Included in scope.
表1に示す化学成分組成の供試材を転炉溶製した後、鋳造して得られた鋼片に熱間圧延を施し、直径12~16mmの線材を製造した。尚、後述する表2において、球状化焼鈍前の伸線加工「有」の場合、すなわち表3のサンプルNo.2および12では、上記線材に対して、25%の減面率で伸線加工を行って得た鋼線を、球状化焼鈍に供した。
After the test material with the chemical composition shown in Table 1 was smelted in a converter, the steel slab obtained by casting was subjected to hot rolling to produce a wire rod with a diameter of 12 to 16 mm. In Table 2, which will be described later, in the case of wire drawing "yes" before spheroidizing annealing, that is, sample No. In Nos. 2 and 12, the steel wires obtained by drawing the above wire rods at a rate of area reduction of 25% were subjected to spheroidizing annealing.
上記線材または鋼線を用い、ラボ炉を用いて焼鈍を実施した。焼鈍では、線材または鋼線を、表2に示すT1まで昇温してt1時間保持した。次いで、5℃/時間~100℃/時間の平均冷却速度で、表2の温度T2まで冷却してから、表2の温度T2よりも高く(A1+60℃)以下の加熱温度まで5℃/時間~100℃/時間の平均昇温速度で加熱した。この冷却と加熱の工程を、表2に示す冷却-加熱繰返回数分実施した。次いで、冷却-加熱工程の最終回での加熱温度から、表2の平均冷却速度R3で温度T4まで冷却した。次いで、空冷してサンプルを得た。なお、表2に示す通り、製造条件G1、G2、TおよびUは、冷却-加熱工程を繰り返していない。具体的に、例えば製造条件G1は、740℃まで昇温後に5時間保持し、その後、10℃/時間の平均冷却速度で640℃まで冷却し、その後空冷した。
Annealing was performed using the above wire or steel wire using a laboratory furnace. In annealing, the wire or steel wire was heated to T1 shown in Table 2 and held for t1. Then, at an average cooling rate of 5 ° C. / hour to 100 ° C. / hour, after cooling to the temperature T2 in Table 2, 5 ° C. / hour to a heating temperature higher than the temperature T2 in Table 2 (A1 + 60 ° C.) or less Heating was performed at an average heating rate of 100°C/hour. This cooling and heating process was repeated for the number of cooling-heating cycles shown in Table 2. Next, from the heating temperature in the final cooling-heating process, the material was cooled to temperature T4 at an average cooling rate R3 in Table 2. Then, it was air-cooled to obtain a sample. As shown in Table 2, manufacturing conditions G1, G2, T and U do not repeat the cooling-heating process. Specifically, for example, under the manufacturing conditions G1, the temperature was raised to 740° C., held for 5 hours, cooled to 640° C. at an average cooling rate of 10° C./hour, and then air-cooled.
また、比較例として、表3に示すサンプルNo.13では、製造条件Hとして、特許文献3の製造条件を満たす熱処理条件、詳細には、特許文献3の実施例においてSA2と示された条件を実施、すなわち図2に示す熱処理工程を5回繰り返した。表3に示すサンプルNo.17では、製造条件Lとして、特許文献1の製造条件を満たす熱処理条件、詳細には特許文献1の表2のNo.1における5番目の球状化焼きなまし条件を実施、すなわち図3に示す熱処理工程を3回繰り返した。また、表3に示すサンプルNo.18では、製造条件Mとして、特許文献2の製造条件を満たす熱処理条件、詳細には特許文献2の表2の条件c、すなわち図4に示すパターンの熱処理を行った。表2に記載の焼鈍パラメータ-は熱処理炉の設定温度である。鋼材に熱電対をつけて、実際の鋼材の温度と設定温度の乖離について試験したところ、鋼材の温度と設定温度は同程度であることを確認した。
Also, as a comparative example, the sample No. shown in Table 3. In 13, the heat treatment conditions that satisfy the manufacturing conditions of Patent Document 3, specifically, the conditions indicated as SA2 in the example of Patent Document 3 are performed as the manufacturing conditions H, that is, the heat treatment process shown in FIG. 2 is repeated five times. rice field. Sample No. shown in Table 3. 17, as the manufacturing condition L, the heat treatment conditions satisfying the manufacturing conditions of Patent Document 1; The fifth spheroidizing annealing condition in 1 was performed, ie the heat treatment step shown in FIG. 3 was repeated three times. In addition, sample No. shown in Table 3. In No. 18, as manufacturing conditions M, heat treatment conditions satisfying the manufacturing conditions of Patent Document 2, specifically condition c in Table 2 of Patent Document 2, that is, heat treatment in the pattern shown in FIG. 4 was performed. The annealing parameters listed in Table 2 are the set temperatures of the heat treatment furnace. A thermocouple was attached to the steel material to test the difference between the actual temperature of the steel material and the set temperature.
上記焼鈍により得られたサンプルを用い、金属組織の評価として、フェライト結晶粒径の平均値、全セメンタイトの平均円相当直径およびフェライト粒の(211)面におけるX線回折ピークの半価幅を、以下の通り求めた。また、特性として、球状化焼鈍後の硬さと、焼入れ処理後の硬さを下記の方法によって測定し、評価した。
Using the sample obtained by the above annealing, as evaluation of the metal structure, the average value of the ferrite crystal grain size, the average equivalent circle diameter of all cementite, and the half-value width of the X-ray diffraction peak on the (211) plane of the ferrite grains. sought as follows. As characteristics, the hardness after spheroidizing annealing and the hardness after quenching treatment were measured and evaluated by the following methods.
〔金属組織の評価〕
[フェライト結晶粒径の平均値]
まず、フェライト結晶粒度の測定を次の通り行った。球状化焼鈍後の鋼線の横断面、すなわち鋼線の軸方向と直交する断面のD/4位置(D:鋼線の直径)を観察できるように試験片を樹脂埋めし、腐食液として、ナイタール(硝酸2体積%、エタノール98体積%)を用いて上記試験片のエッチングを行い、組織を現出させた。そして、光学顕微鏡にて、上記組織を現出させた試験片の組織観察を倍率400倍で行い、評価面内で、鋼線全体の組織を代表する平均的なサイズのフェライト結晶粒を観察できる1視野を選定して、顕微鏡写真を得た。次いで、フェライト結晶粒度(G)の値を、撮影した写真からJIS G0551(2020)の比較法に基づいて算出した。そして、算出したフェライト結晶粒度(G)の値を用い、「入門講座 専門用語-鉄鋼材料編-3 結晶粒度番号と結晶粒径」,梅本 実, ふぇらむ Vol.2(1997)No.10,p29~34の、p32の表1に記載の結晶粒度と粒径に関する諸量間の関係において、フェライト結晶粒度G(orN)とフェライト結晶粒径の平均値dnの関係として示された、下記式(4)から、フェライト結晶粒径の平均値dnを求めた。その結果を表3に示す。なお、本実施例において、表3のサンプルNo.1~10はいずれも、フェライトの面積率が90%以上であった。
dn=0.254/(2(G-1)/2) ・・・(4) [Evaluation of metal structure]
[Average value of ferrite grain size]
First, the ferrite grain size was measured as follows. The cross section of the steel wire after spheroidizing annealing, that is, the test piece was embedded in resin so that the D/4 position (D: diameter of the steel wire) of the cross section perpendicular to the axial direction of the steel wire could be observed. The test piece was etched using nital (2% by volume of nitric acid, 98% by volume of ethanol) to expose the structure. Then, with an optical microscope, the structure of the test piece in which the above structure is exposed is observed at a magnification of 400 times, and ferrite grains of an average size representing the structure of the entire steel wire can be observed within the evaluation surface. One field was selected to obtain a photomicrograph. Then, the value of the ferrite grain size (G) was calculated from the photographed based on the comparison method of JIS G0551 (2020). Then, using the calculated value of the ferrite grain size (G), "Introductory Lecture Technical Terms-Iron and Steel Materials Edition-3 Grain Size Number and Grain Size", Minoru Umemoto, Ferrum Vol. 2 (1997) No. 10, p29 to 34, in the relationship between various amounts related to the grain size and grain size described in Table 1 on p32, the relationship between the ferrite grain size G (orN) and the average value dn of the ferrite grain size, The average value dn of the ferrite crystal grain size was obtained from the following formula (4). Table 3 shows the results. Note that sample No. in Table 3 was used in this example. All of Nos. 1 to 10 had a ferrite area ratio of 90% or more.
dn=0.254/(2 (G−1)/2 ) (4)
[フェライト結晶粒径の平均値]
まず、フェライト結晶粒度の測定を次の通り行った。球状化焼鈍後の鋼線の横断面、すなわち鋼線の軸方向と直交する断面のD/4位置(D:鋼線の直径)を観察できるように試験片を樹脂埋めし、腐食液として、ナイタール(硝酸2体積%、エタノール98体積%)を用いて上記試験片のエッチングを行い、組織を現出させた。そして、光学顕微鏡にて、上記組織を現出させた試験片の組織観察を倍率400倍で行い、評価面内で、鋼線全体の組織を代表する平均的なサイズのフェライト結晶粒を観察できる1視野を選定して、顕微鏡写真を得た。次いで、フェライト結晶粒度(G)の値を、撮影した写真からJIS G0551(2020)の比較法に基づいて算出した。そして、算出したフェライト結晶粒度(G)の値を用い、「入門講座 専門用語-鉄鋼材料編-3 結晶粒度番号と結晶粒径」,梅本 実, ふぇらむ Vol.2(1997)No.10,p29~34の、p32の表1に記載の結晶粒度と粒径に関する諸量間の関係において、フェライト結晶粒度G(orN)とフェライト結晶粒径の平均値dnの関係として示された、下記式(4)から、フェライト結晶粒径の平均値dnを求めた。その結果を表3に示す。なお、本実施例において、表3のサンプルNo.1~10はいずれも、フェライトの面積率が90%以上であった。
dn=0.254/(2(G-1)/2) ・・・(4) [Evaluation of metal structure]
[Average value of ferrite grain size]
First, the ferrite grain size was measured as follows. The cross section of the steel wire after spheroidizing annealing, that is, the test piece was embedded in resin so that the D/4 position (D: diameter of the steel wire) of the cross section perpendicular to the axial direction of the steel wire could be observed. The test piece was etched using nital (2% by volume of nitric acid, 98% by volume of ethanol) to expose the structure. Then, with an optical microscope, the structure of the test piece in which the above structure is exposed is observed at a magnification of 400 times, and ferrite grains of an average size representing the structure of the entire steel wire can be observed within the evaluation surface. One field was selected to obtain a photomicrograph. Then, the value of the ferrite grain size (G) was calculated from the photographed based on the comparison method of JIS G0551 (2020). Then, using the calculated value of the ferrite grain size (G), "Introductory Lecture Technical Terms-Iron and Steel Materials Edition-3 Grain Size Number and Grain Size", Minoru Umemoto, Ferrum Vol. 2 (1997) No. 10, p29 to 34, in the relationship between various amounts related to the grain size and grain size described in Table 1 on p32, the relationship between the ferrite grain size G (orN) and the average value dn of the ferrite grain size, The average value dn of the ferrite crystal grain size was obtained from the following formula (4). Table 3 shows the results. Note that sample No. in Table 3 was used in this example. All of Nos. 1 to 10 had a ferrite area ratio of 90% or more.
dn=0.254/(2 (G−1)/2 ) (4)
[フェライト粒の(211)面におけるX線回折ピークの半価幅]
フェライト粒におけるX線回折ピークの半価幅は、球状化焼鈍後の鋼線のD/4位置(D:直径)において、フェライトの(211)面におけるX線回折ピークの半価幅を測定した。具体的には、球状化焼鈍後の鋼線の横断面が観察できるよう試験片を樹脂埋めし、エミリー研磨、ダイヤモンドバフおよび、試料調製時に導入される評価表面のひずみ除去のため、電解研磨を施した。そして、(株)リガク製PSPC(PosItion-SensItIve PropotIonal Counter)微小部X線応力測定装置を用い、フェライト鉄148°~165°付近のピーク半価幅を求めた。測定値は2回測定した値の平均値とした。なお、X線回折における他の条件は下記の通りである。
・ターゲット:Cr
・加速電圧:40kV
・加速電流:40mA
・コリメータ:φ0.5mm [Half width of X-ray diffraction peak in (211) plane of ferrite grain]
The half-value width of the X-ray diffraction peak in ferrite grains was obtained by measuring the half-value width of the X-ray diffraction peak in the (211) plane of ferrite at the D/4 position (D: diameter) of the steel wire after spheroidizing annealing. . Specifically, the test piece was embedded in resin so that the cross section of the steel wire after spheroidizing annealing could be observed, and was subjected to Emily polishing, diamond buffing, and electropolishing to remove strain on the evaluation surface introduced during sample preparation. provided. Then, a PSPC (Position-Sensitive Propotional Counter) manufactured by Rigaku Corporation was used to determine the peak half-value width around 148° to 165° of ferrite iron. The measured value was the average value of the values measured twice. Other conditions for X-ray diffraction are as follows.
・Target: Cr
・Acceleration voltage: 40 kV
・Acceleration current: 40mA
・Collimator: φ0.5mm
フェライト粒におけるX線回折ピークの半価幅は、球状化焼鈍後の鋼線のD/4位置(D:直径)において、フェライトの(211)面におけるX線回折ピークの半価幅を測定した。具体的には、球状化焼鈍後の鋼線の横断面が観察できるよう試験片を樹脂埋めし、エミリー研磨、ダイヤモンドバフおよび、試料調製時に導入される評価表面のひずみ除去のため、電解研磨を施した。そして、(株)リガク製PSPC(PosItion-SensItIve PropotIonal Counter)微小部X線応力測定装置を用い、フェライト鉄148°~165°付近のピーク半価幅を求めた。測定値は2回測定した値の平均値とした。なお、X線回折における他の条件は下記の通りである。
・ターゲット:Cr
・加速電圧:40kV
・加速電流:40mA
・コリメータ:φ0.5mm [Half width of X-ray diffraction peak in (211) plane of ferrite grain]
The half-value width of the X-ray diffraction peak in ferrite grains was obtained by measuring the half-value width of the X-ray diffraction peak in the (211) plane of ferrite at the D/4 position (D: diameter) of the steel wire after spheroidizing annealing. . Specifically, the test piece was embedded in resin so that the cross section of the steel wire after spheroidizing annealing could be observed, and was subjected to Emily polishing, diamond buffing, and electropolishing to remove strain on the evaluation surface introduced during sample preparation. provided. Then, a PSPC (Position-Sensitive Propotional Counter) manufactured by Rigaku Corporation was used to determine the peak half-value width around 148° to 165° of ferrite iron. The measured value was the average value of the values measured twice. Other conditions for X-ray diffraction are as follows.
・Target: Cr
・Acceleration voltage: 40 kV
・Acceleration current: 40mA
・Collimator: φ0.5mm
[全セメンタイトの平均円相当直径]
球状化焼鈍後の鋼線の全セメンタイトの平均円相当直径の測定は、横断面が観察できるように試験片を樹脂埋めし、エメリー紙、ダイヤモンドバフによって切断面を鏡面研磨した。次いで、切断面に対し、腐食液として、ナイタール(硝酸2体積%、エタノール98体積%)を用いて30秒間~1分間のエッチングを行い、D/4位置(D:鋼線の直径)のフェライト結晶粒界およびセメンタイトを現出させた。そして、FE-SEM(Field-Emission Scanning Electron Microscope、電解放出型走査電子顕微鏡)を用いて、上記セメンタイト等を現出させた試験片の組織観察を行い、倍率2500倍にて、3視野を撮影した。 [Average circle equivalent diameter of all cementite]
For the measurement of the average equivalent circle diameter of all cementite in the steel wire after spheroidizing annealing, the test piece was embedded in resin so that the cross section could be observed, and the cut surface was mirror-polished with emery paper and a diamond buff. Next, the cut surface is etched for 30 seconds to 1 minute using nital (2% by volume of nitric acid, 98% by volume of ethanol) as an etchant to obtain ferrite at the D/4 position (D: diameter of steel wire). Grain boundaries and cementite were revealed. Then, using FE-SEM (Field-Emission Scanning Electron Microscope, field emission scanning electron microscope), the structure of the test piece in which the above cementite etc. is exposed is observed, and 3 fields of view are photographed at a magnification of 2500 times. did.
球状化焼鈍後の鋼線の全セメンタイトの平均円相当直径の測定は、横断面が観察できるように試験片を樹脂埋めし、エメリー紙、ダイヤモンドバフによって切断面を鏡面研磨した。次いで、切断面に対し、腐食液として、ナイタール(硝酸2体積%、エタノール98体積%)を用いて30秒間~1分間のエッチングを行い、D/4位置(D:鋼線の直径)のフェライト結晶粒界およびセメンタイトを現出させた。そして、FE-SEM(Field-Emission Scanning Electron Microscope、電解放出型走査電子顕微鏡)を用いて、上記セメンタイト等を現出させた試験片の組織観察を行い、倍率2500倍にて、3視野を撮影した。 [Average circle equivalent diameter of all cementite]
For the measurement of the average equivalent circle diameter of all cementite in the steel wire after spheroidizing annealing, the test piece was embedded in resin so that the cross section could be observed, and the cut surface was mirror-polished with emery paper and a diamond buff. Next, the cut surface is etched for 30 seconds to 1 minute using nital (2% by volume of nitric acid, 98% by volume of ethanol) as an etchant to obtain ferrite at the D/4 position (D: diameter of steel wire). Grain boundaries and cementite were revealed. Then, using FE-SEM (Field-Emission Scanning Electron Microscope, field emission scanning electron microscope), the structure of the test piece in which the above cementite etc. is exposed is observed, and 3 fields of view are photographed at a magnification of 2500 times. did.
上記撮影した顕微鏡写真にOHPフィルムを重ね、OHPフィルムの上から顕微鏡写真の全セメンタイトを塗りつぶし、全セメンタイトを解析する投影画像を得た。投影画像を2値化して白黒写真とし、画像解析ソフト「粒子解析ver3.5」(日鉄テクノロジー株式会社)を用いて、全セメンタイトの円相当直径を算出した。なお、表3に記載の全セメンタイトの平均円相当直径は、3視野から算出した値の平均値である。測定するセメンタイトの最小サイズ(円相当直径)は0.3μmとした。
An OHP film was superimposed on the micrograph taken above, and all the cementite in the micrograph was painted over from above the OHP film to obtain a projection image for analyzing all cementite. The projected image was binarized into a black-and-white photograph, and the equivalent circle diameter of all cementite was calculated using image analysis software "particle analysis ver 3.5" (Nippon Steel Technology Co., Ltd.). The average circle equivalent diameter of all cementites shown in Table 3 is the average of values calculated from three fields of view. The minimum size (equivalent circle diameter) of cementite to be measured was 0.3 μm.
〔特性の評価〕
[球状化焼鈍後の硬さの測定]
冷間加工性を評価するため、球状化焼鈍後の各サンプルの硬さを、次の通り測定した。試験片の横断面のD/4位置(D:鋼線の直径)で、JISZ2244(2009)に準拠してビッカース硬さ試験を実施した。3点以上の平均を算出して得られるビッカース硬さを、球状化焼鈍後の硬さとした。その測定結果を表3に示す。表3では球状化焼鈍後の硬さを「球状化硬さ」と示す。本実施例では、球状化焼鈍後の硬さが、鋼中のC量(質量%)、Cr量(質量%)、Mo量(質量%)を各々[C]、[Cr]、[Mo]で表したときに(含まれない元素はゼロ質量%とする)、下記式(2)を満たす場合を、冷間加工性に優れるとして「OK」と評価し、下記式(2)を満たさない場合を、冷間加工性に劣るとして「NG」と評価した。
球状化焼鈍後の硬さ(HV)<91([C]+[Cr]/9+[Mo]/2)+91 ・・・(2) [Evaluation of characteristics]
[Measurement of hardness after spheroidizing annealing]
In order to evaluate cold workability, the hardness of each sample after spheroidizing annealing was measured as follows. A Vickers hardness test was performed in accordance with JISZ2244 (2009) at the D/4 position (D: diameter of steel wire) of the cross section of the test piece. The Vickers hardness obtained by calculating the average of 3 or more points was defined as the hardness after spheroidizing annealing. Table 3 shows the measurement results. In Table 3, the hardness after spheroidizing annealing is indicated as "spheroidizing hardness". In this example, the hardness after spheroidizing annealing is determined by the amount of C (% by mass), the amount of Cr (% by mass), and the amount of Mo (% by mass) in the steel [C], [Cr], and [Mo], respectively. (elements not included are zero mass%), the case where the following formula (2) is satisfied is evaluated as "OK" as being excellent in cold workability, and the following formula (2) is not satisfied The case was evaluated as "NG" as being inferior in cold workability.
Hardness after spheroidizing annealing (HV)<91([C]+[Cr]/9+[Mo]/2)+91 (2)
[球状化焼鈍後の硬さの測定]
冷間加工性を評価するため、球状化焼鈍後の各サンプルの硬さを、次の通り測定した。試験片の横断面のD/4位置(D:鋼線の直径)で、JISZ2244(2009)に準拠してビッカース硬さ試験を実施した。3点以上の平均を算出して得られるビッカース硬さを、球状化焼鈍後の硬さとした。その測定結果を表3に示す。表3では球状化焼鈍後の硬さを「球状化硬さ」と示す。本実施例では、球状化焼鈍後の硬さが、鋼中のC量(質量%)、Cr量(質量%)、Mo量(質量%)を各々[C]、[Cr]、[Mo]で表したときに(含まれない元素はゼロ質量%とする)、下記式(2)を満たす場合を、冷間加工性に優れるとして「OK」と評価し、下記式(2)を満たさない場合を、冷間加工性に劣るとして「NG」と評価した。
球状化焼鈍後の硬さ(HV)<91([C]+[Cr]/9+[Mo]/2)+91 ・・・(2) [Evaluation of characteristics]
[Measurement of hardness after spheroidizing annealing]
In order to evaluate cold workability, the hardness of each sample after spheroidizing annealing was measured as follows. A Vickers hardness test was performed in accordance with JISZ2244 (2009) at the D/4 position (D: diameter of steel wire) of the cross section of the test piece. The Vickers hardness obtained by calculating the average of 3 or more points was defined as the hardness after spheroidizing annealing. Table 3 shows the measurement results. In Table 3, the hardness after spheroidizing annealing is indicated as "spheroidizing hardness". In this example, the hardness after spheroidizing annealing is determined by the amount of C (% by mass), the amount of Cr (% by mass), and the amount of Mo (% by mass) in the steel [C], [Cr], and [Mo], respectively. (elements not included are zero mass%), the case where the following formula (2) is satisfied is evaluated as "OK" as being excellent in cold workability, and the following formula (2) is not satisfied The case was evaluated as "NG" as being inferior in cold workability.
Hardness after spheroidizing annealing (HV)<91([C]+[Cr]/9+[Mo]/2)+91 (2)
[焼入れ処理後の硬さの測定]
焼入性を評価するため、焼入れ処理後の各サンプルの硬さを、次の通り測定した。まず、焼入れ処理用試料として、球状化焼鈍後の各サンプルを、焼入れ処理で焼きが十分に入るように、圧延方向の長さである厚み(t)が5mmとなるように加工した試料を用意した。該試料に対し、焼入れ処理として、A3+(30~50℃)で5分間の高温保持を行い、該高温保持後に水冷した。前記A3は、下記式(5)から導出される値である。また、ここでの高温保持の時間は、炉温が設定温度に達してからの時間とした。
A3(℃)=910-203×√([C])-14.2×[Ni]+44.7×[Si]+104×[V]+31.5×[Mo]+13.1×[W]-30×[Mn]-11×[Cr]-20×[Cu]+700×[P]+400×[Al]+120×[As]+400×[Ti]・・・(5)
ただし、[元素]は、各元素の含有量(質量%)を表し、含まれない元素は、0%として計算する。 [Measurement of hardness after quenching]
In order to evaluate hardenability, the hardness of each sample after hardening treatment was measured as follows. First, as a sample for quenching treatment, each sample after spheroidizing annealing is processed so that the thickness (t), which is the length in the rolling direction, is 5 mm so that quenching can be sufficiently performed in the quenching treatment. did. As a quenching treatment, the sample was held at a high temperature of A3+ (30 to 50° C.) for 5 minutes, and then water-cooled after the high temperature holding. A3 is a value derived from the following formula (5). Also, the high temperature holding time here was the time after the furnace temperature reached the set temperature.
A3 (°C) = 910 - 203 x √ ([C]) - 14.2 x [Ni] + 44.7 x [Si] + 104 x [V] + 31.5 x [Mo] + 13.1 x [W] - 30×[Mn]−11×[Cr]−20×[Cu]+700×[P]+400×[Al]+120×[As]+400×[Ti] (5)
However, [element] represents the content (% by mass) of each element, and an element not contained is calculated as 0%.
焼入性を評価するため、焼入れ処理後の各サンプルの硬さを、次の通り測定した。まず、焼入れ処理用試料として、球状化焼鈍後の各サンプルを、焼入れ処理で焼きが十分に入るように、圧延方向の長さである厚み(t)が5mmとなるように加工した試料を用意した。該試料に対し、焼入れ処理として、A3+(30~50℃)で5分間の高温保持を行い、該高温保持後に水冷した。前記A3は、下記式(5)から導出される値である。また、ここでの高温保持の時間は、炉温が設定温度に達してからの時間とした。
A3(℃)=910-203×√([C])-14.2×[Ni]+44.7×[Si]+104×[V]+31.5×[Mo]+13.1×[W]-30×[Mn]-11×[Cr]-20×[Cu]+700×[P]+400×[Al]+120×[As]+400×[Ti]・・・(5)
ただし、[元素]は、各元素の含有量(質量%)を表し、含まれない元素は、0%として計算する。 [Measurement of hardness after quenching]
In order to evaluate hardenability, the hardness of each sample after hardening treatment was measured as follows. First, as a sample for quenching treatment, each sample after spheroidizing annealing is processed so that the thickness (t), which is the length in the rolling direction, is 5 mm so that quenching can be sufficiently performed in the quenching treatment. did. As a quenching treatment, the sample was held at a high temperature of A3+ (30 to 50° C.) for 5 minutes, and then water-cooled after the high temperature holding. A3 is a value derived from the following formula (5). Also, the high temperature holding time here was the time after the furnace temperature reached the set temperature.
A3 (°C) = 910 - 203 x √ ([C]) - 14.2 x [Ni] + 44.7 x [Si] + 104 x [V] + 31.5 x [Mo] + 13.1 x [W] - 30×[Mn]−11×[Cr]−20×[Cu]+700×[P]+400×[Al]+120×[As]+400×[Ti] (5)
However, [element] represents the content (% by mass) of each element, and an element not contained is calculated as 0%.
そして、上記焼入れ処理後の試料の、t/2位置かつD/4位置(D:鋼線の直径、t:サンプルの厚み)において、ビッカース硬さ試験を実施した。3点以上の平均を算出して得られるビッカース硬さを、焼入れ処理後の硬さとした。その測定結果を表3に示す。表3では焼入れ処理後の硬さを「焼入れ硬さ」と示す。本実施例では、焼入れ処理後の硬さが、鋼中のC量(質量%)を[C]で表したときに、下記式(3)を満たす場合を、焼入れ性に優れるとして「OK」と評価し、下記式(3)を満たさない場合を、焼入れ性に劣るとして「NG」と評価した。
焼入れ処理後の硬さ(HV)>380ln([C])+1010・・・(3) Then, a Vickers hardness test was performed on the quenched sample at the t/2 position and the D/4 position (D: diameter of steel wire, t: thickness of sample). The Vickers hardness obtained by calculating the average of 3 or more points was defined as the hardness after the quenching treatment. Table 3 shows the measurement results. In Table 3, the hardness after quenching treatment is shown as "quenching hardness". In this example, when the hardness after quenching satisfies the following formula (3) when the amount of C (% by mass) in the steel is represented by [C], it is considered to be excellent in hardenability. When the following formula (3) was not satisfied, the hardenability was evaluated as "NG".
Hardness after quenching treatment (HV) > 380 ln ([C]) + 1010 (3)
焼入れ処理後の硬さ(HV)>380ln([C])+1010・・・(3) Then, a Vickers hardness test was performed on the quenched sample at the t/2 position and the D/4 position (D: diameter of steel wire, t: thickness of sample). The Vickers hardness obtained by calculating the average of 3 or more points was defined as the hardness after the quenching treatment. Table 3 shows the measurement results. In Table 3, the hardness after quenching treatment is shown as "quenching hardness". In this example, when the hardness after quenching satisfies the following formula (3) when the amount of C (% by mass) in the steel is represented by [C], it is considered to be excellent in hardenability. When the following formula (3) was not satisfied, the hardenability was evaluated as "NG".
Hardness after quenching treatment (HV) > 380 ln ([C]) + 1010 (3)
表3において、上記球状化焼鈍後の硬さと焼入れ処理後の硬さがいずれもOKの場合を、優れた冷間加工性と優れた焼入れ性を兼備するとして総合判定「OK」とし、上記球状化焼鈍後の硬さと焼入れ処理後の硬さの少なくともいずれかがNGの場合を、優れた冷間加工性と優れた焼入れ性を兼備できないとして総合判定「NG」とした。表2および表3において、下線を付した数値は、本開示の規定範囲から外れるか、所望の特性を満たしていないことを示す。
In Table 3, when both the hardness after the spheroidizing annealing and the hardness after the quenching treatment are OK, the overall judgment is "OK" as having both excellent cold workability and excellent hardenability. When at least one of the hardness after annealing and the hardness after quenching treatment was NG, it was judged that both excellent cold workability and excellent hardenability could not be achieved, and was judged as "NG". In Tables 2 and 3, the underlined values indicate values outside the specified range of the present disclosure or failing to meet the desired properties.
表の結果について考察する。以下のNo.は表3のサンプルNo.を示す。No.1~10は、本発明の実施形態で規定する成分組成、金属組織および球状化焼鈍条件をすべて満足する発明例である。
Consider the results in the table. The following No. is sample No. in Table 3. indicates No. Nos. 1 to 10 are invention examples that satisfy all of the chemical composition, metallographic structure and spheroidizing annealing conditions specified in the embodiments of the present invention.
No.11、12、19、21~26は、冷却-加熱工程を行わなかった、または、1回しか行っていないため、図1の[3]の工程で生成する界面ひずみの多い棒状セメンタイトにより、フェライト中のひずみ量が増大し、X線回折ピークの半価幅が0.500°を超えていた。そのため、球状化焼鈍後の硬さが基準値よりも高く、冷間加工性に劣る結果となった。
No. 11, 12, 19, 21 to 26 were not subjected to the cooling-heating process, or were performed only once. The amount of strain inside increased, and the half width of the X-ray diffraction peak exceeded 0.500°. Therefore, the hardness after spheroidizing annealing was higher than the reference value, resulting in poor cold workability.
No.13は、特許文献3に示された製造条件を満たす製造条件Hとして、特許文献3の焼鈍条件SA2で焼鈍を行った例である。この製造条件では、焼鈍によってセメンタイトが過剰に粗大化し、焼入れ処理後の硬さが基準値より低く、焼入れ性に劣る結果となった。
No. No. 13 is an example in which annealing is performed under the annealing conditions SA2 of Patent Document 3 as the manufacturing condition H that satisfies the manufacturing conditions shown in Patent Document 3. Under these manufacturing conditions, the cementite was excessively coarsened by annealing, and the hardness after quenching treatment was lower than the reference value, resulting in poor hardenability.
No.14、20は、T1が730℃であり、A1+8℃を下回っているため、焼鈍前から残存する界面ひずみの多い棒状セメンタイトにより、フェライト中のひずみ量が増大し、X線回折ピークの半価幅が0.500°を超えていた。そのため、球状化焼鈍後の硬さが基準値より高く、冷間加工性に劣る結果となった。
No. 14 and 20, T1 is 730 ° C., which is lower than A1 + 8 ° C., so the amount of strain in ferrite increases due to rod-shaped cementite with a large amount of interfacial strain remaining from before annealing, and the half-value width of the X-ray diffraction peak was over 0.500°. Therefore, the hardness after spheroidizing annealing was higher than the reference value, resulting in poor cold workability.
No.15は、平均冷却速度R3が21℃/時間と高いため、図1の[8]の工程で生成する界面ひずみの多い棒状セメンタイトにより、フェライト中のひずみ量が増大し、X線回折ピークの半価幅が0.500°を超えていた。そのため、球状化焼鈍後の硬さが基準値より高く、冷間加工性に劣る結果となった。
No. In No. 15, the average cooling rate R3 is as high as 21 ° C./hour, so the rod-shaped cementite with a large interface strain generated in the step [8] in FIG. The price range exceeded 0.500°. Therefore, the hardness after spheroidizing annealing was higher than the reference value, resulting in poor cold workability.
No.16は、T2が710℃と高いため、図1の[3]の工程で生成する界面ひずみの多い棒状セメンタイトにより、フェライト中のひずみ量が増大し、X線回折ピークの半価幅が0.500°を超えていた。そのため、球状化焼鈍後の硬さが基準値より高く、冷間加工性に劣る結果となった。
No. In No. 16, T2 is as high as 710° C., so the amount of strain in the ferrite increases due to rod-shaped cementite with a large interface strain generated in the step [3] of FIG. over 500°. Therefore, the hardness after spheroidizing annealing was higher than the reference value, resulting in poor cold workability.
No.17は、特許文献1に示された製造条件を満たす、製造条件Lで焼鈍を行った例である。この製造条件ではt1の保持がない等により、焼鈍前から残存する界面ひずみの多い棒状セメンタイトにより、フェライト中のひずみ量が増大し、X線回折ピークの半価幅が0.500°を超えていた。そのため、球状化焼鈍後の硬さが基準値より高く、冷間加工性に劣る結果となった。
No. No. 17 is an example in which annealing is performed under manufacturing condition L, which satisfies the manufacturing conditions shown in Patent Document 1. Under these manufacturing conditions, t1 is not maintained, etc., and due to rod-shaped cementite with a large amount of interfacial strain remaining from before annealing, the amount of strain in the ferrite increases, and the half-value width of the X-ray diffraction peak exceeds 0.500°. rice field. Therefore, the hardness after spheroidizing annealing was higher than the reference value, resulting in poor cold workability.
No.18は、特許文献2に示された製造条件を満たす製造条件Mとして、特許文献2の条件cで焼鈍した例である。焼鈍前から残存する界面ひずみの多い棒状セメンタイトにより、フェライト中のひずみ量が増大し、X線回折ピークの半価幅が0.500°を超えていた。そのため、球状化焼鈍後の硬さが基準値より高く、冷間加工性に劣る結果となった。
No. No. 18 is an example in which annealing is performed under the condition c of Patent Document 2 as the manufacturing condition M that satisfies the manufacturing conditions shown in Patent Document 2. The amount of strain in the ferrite increased due to rod-shaped cementite with a large amount of interfacial strain remaining from before annealing, and the half width of the X-ray diffraction peak exceeded 0.500°. Therefore, the hardness after spheroidizing annealing was higher than the reference value, resulting in poor cold workability.
本出願は、日本国特許出願である特願2021-061473号と特願2021-211500号を基礎出願とする優先権主張を伴う。特願2021-061473号と特願2021-211500号は参照することにより本明細書に取り込まれる。
This application is accompanied by a priority claim based on Japanese Patent Application Nos. 2021-061473 and 2021-211500. Japanese Patent Application No. 2021-061473 and Japanese Patent Application No. 2021-211500 are incorporated herein by reference.
本実施形態に係る機械構造部品用鋼線は、各種機械構造用部品を製造するときの室温における変形抵抗が低く、金型などの塑性加工用冶工具の磨耗や破壊を抑制でき、また、例えば圧造加工時の割れ発生も抑制できるといった優れた冷間加工性を発揮する。更には、焼入性に優れているため、冷間加工後の焼入れ処理で高硬度を確保することもできる。これらのことから、本実施形態に係る機械構造部品用鋼線は、冷間加工用機械構造部品用鋼線として有用である。例えば、本実施形態に係る機械構造部品用鋼線は、冷間鍛造、冷間圧造、冷間転造等の冷間加工に供することで、自動車用部品、建設機械用部品等の各種機械構造部品の製造に用いられる。こうした機械構造部品として、具体的には、ボルト、ねじ、ナット、ソケット、ボールジョイント、インナーチューブ、トーションバー、クラッチケース、ケージ、ハウジング、ハブ、カバー、ケース、受座金、タペット、サドル、バルグ、インナーケース、クラッチ、スリーブ、アウターレース、スプロケット、コア、ステータ、アンビル、スパイダー、ロッカーアーム、ボディー、フランジ、ドラム、継手、コネクタ、プーリ、金具、ヨーク、口金、バルブリフター、スパークプラグ、ピニオンギヤ、ステアリングシャフト、コモンレール等の機械部品、電装部品等が挙げられる。
The steel wire for machine structural parts according to the present embodiment has low deformation resistance at room temperature when manufacturing various machine structural parts, and can suppress abrasion and breakage of jigs and tools for plastic working such as molds. It exhibits excellent cold workability, such as suppressing the occurrence of cracks during forging. Furthermore, since it is excellent in hardenability, high hardness can be secured by hardening treatment after cold working. For these reasons, the steel wire for machine structural parts according to the present embodiment is useful as a steel wire for cold working machine structural parts. For example, the steel wire for machine structural parts according to the present embodiment can be subjected to cold working such as cold forging, cold heading, and cold rolling to obtain various machine structures such as parts for automobiles and parts for construction machinery. Used to manufacture parts. Specific examples of such mechanical structural parts include bolts, screws, nuts, sockets, ball joints, inner tubes, torsion bars, clutch cases, cages, housings, hubs, covers, cases, receiving washers, tappets, saddles, bulks, Inner cases, clutches, sleeves, outer races, sprockets, cores, stators, anvils, spiders, rocker arms, bodies, flanges, drums, joints, connectors, pulleys, metal fittings, yokes, mouthpieces, valve lifters, spark plugs, pinion gears, steering Examples include mechanical parts such as shafts and common rails, electrical parts, and the like.
Claims (5)
- C :0.05質量%~0.60質量%、
Si:0.005質量%~0.50質量%、
Mn:0.30質量%~1.20質量%、
P :0質量%超、0.050質量%以下、
S :0質量%超、0.050質量%以下、
Al:0.001質量%~0.10質量%、
Cr:0質量%超、1.5質量%以下、および
N :0質量%超、0.02質量%以下、
を含有し、残部が鉄および不可避不純物からなり、
フェライト粒の(211)面におけるX線回折ピークの半価幅が0.500°以下であり、
全セメンタイトの平均円相当直径が、鋼中のC量(質量%)を[C]で表したときに、(1.863-2.13[C])μm以下である、機械構造部品用鋼線。 C: 0.05% by mass to 0.60% by mass,
Si: 0.005% by mass to 0.50% by mass,
Mn: 0.30% by mass to 1.20% by mass,
P: more than 0% by mass, 0.050% by mass or less,
S: more than 0% by mass, 0.050% by mass or less,
Al: 0.001% by mass to 0.10% by mass,
Cr: more than 0% by mass, 1.5% by mass or less, and N: more than 0% by mass, 0.02% by mass or less,
containing, the balance consisting of iron and inevitable impurities,
The half width of the X-ray diffraction peak on the (211) plane of the ferrite grain is 0.500° or less,
Steel for machine structural parts, wherein the average equivalent circle diameter of all cementite is (1.863-2.13 [C]) μm or less when the amount of C (% by mass) in the steel is represented by [C] line. - 下記(a)~(c)のうちの1以上を満足する、請求項1に記載の機械構造部品用鋼線。
(a)更に、
Cu:0質量%超、0.25質量%以下、
Ni:0質量%超、0.25質量%以下、
Mo:0質量%超、0.50質量%以下、および
B :0質量%超、0.01質量%以下よりなる群から選択される1種以上を含有する
(b)更に、
Ti:0質量%超、0.2質量%以下、
Nb:0質量%超、0.2質量%以下、および
V :0質量%超、0.5質量%以下よりなる群から選択される1種以上を含有する
(c)更に、
Mg:0質量%超、0.02質量%以下、
Ca:0質量%超、0.05質量%以下、
Li:0質量%超、0.02質量%以下、および
REM:0質量%超、0.05質量%以下よりなる群から選択される1種以上を含有する The steel wire for machine structural parts according to claim 1, which satisfies one or more of the following (a) to (c).
(a) further
Cu: more than 0% by mass, 0.25% by mass or less,
Ni: more than 0% by mass, 0.25% by mass or less,
Mo: more than 0% by mass, 0.50% by mass or less, and B: more than 0% by mass, 0.01% by mass or less (b) Further,
Ti: more than 0% by mass, 0.2% by mass or less,
Nb: more than 0% by mass, 0.2% by mass or less, and V: more than 0% by mass, 0.5% by mass or less (c) Further,
Mg: more than 0% by mass, 0.02% by mass or less,
Ca: more than 0% by mass, 0.05% by mass or less,
Contains one or more selected from the group consisting of Li: more than 0% by mass and 0.02% by mass or less, and REM: more than 0% by mass and 0.05% by mass or less - フェライト結晶粒径の平均値が30μm以下である、請求項1または2に記載の機械構造部品用鋼線。 The steel wire for machine structural parts according to claim 1 or 2, wherein the average ferrite grain size is 30 µm or less.
- 請求項1または2に記載の機械構造部品用鋼線の製造方法であって、
請求項1または2に記載の化学成分組成を満たす条鋼に、
下記(1)~(3)の工程を含む球状化焼鈍を施す工程を含む、機械構造部品用鋼線の製造方法。
(1)(A1+8℃)~(A1+31℃)の温度T1に加熱した後に、該温度T1で1時間超、6時間以下で加熱保持し、
(2)650℃超、(A1-17℃)以下の温度T2まで冷却し、次いで、温度T2よりも高く(A1+60℃)以下の加熱温度まで加熱する、冷却-加熱工程を、合計2回~6回実施し、
(3)5℃/時間~20℃/時間の平均冷却速度で(A1-30℃)未満の温度まで冷却する。
ここで、A1は、下記式(1)で算出される。
A1(℃)=723+29.1×[Si]-10.7×[Mn]+16.9×[Cr]-16.9×[Ni]・・・(1)
ただし、[元素]は、各元素の含有量(質量%)を表し、含まれない元素の含有量はゼロとする。 A method for manufacturing a steel wire for machine structural parts according to claim 1 or 2,
In a long steel satisfying the chemical composition according to claim 1 or 2,
A method for manufacturing a steel wire for machine structural parts, comprising a step of performing spheroidizing annealing including the following steps (1) to (3).
(1) After heating to a temperature T1 of (A1 + 8 ° C.) to (A1 + 31 ° C.), heating and holding at the temperature T1 for more than 1 hour and 6 hours or less,
(2) Cooling to a temperature T2 exceeding 650 ° C. and not exceeding (A1-17 ° C.), and then heating to a heating temperature higher than the temperature T2 and not exceeding (A1 + 60 ° C.), a total of 2 or more cooling-heating steps 6 times,
(3) Cool to a temperature below (A1-30°C) at an average cooling rate of 5°C/hr to 20°C/hr.
Here, A1 is calculated by the following formula (1).
A1 (° C.)=723+29.1×[Si]−10.7×[Mn]+16.9×[Cr]−16.9×[Ni] (1)
However, [element] represents the content (% by mass) of each element, and the content of elements not included is zero. - 前記条鋼は、線材に、5%超の減面率で伸線加工を施して得られた鋼線である、請求項4に記載の機械構造部品用鋼線の製造方法。 The method of manufacturing a steel wire for machine structural parts according to claim 4, wherein the steel bar is a steel wire obtained by drawing a wire with a reduction in area of more than 5%.
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JP2000073137A (en) * | 1998-08-26 | 2000-03-07 | Kobe Steel Ltd | Steel wire rod excellent in cold workability |
JP2006225701A (en) * | 2005-02-16 | 2006-08-31 | Nippon Steel Corp | Steel wire rod excellent in cold-forgeability after spheroidizing-treatment and producing method therefor |
JP2013147728A (en) * | 2011-12-19 | 2013-08-01 | Kobe Steel Ltd | Steel for mechanical structure for cold working, and method for manufacturing the same |
JP2015168882A (en) * | 2014-03-11 | 2015-09-28 | 株式会社神戸製鋼所 | Spheroidizing heat treatment method for alloy steel |
WO2016148037A1 (en) * | 2015-03-13 | 2016-09-22 | 株式会社神戸製鋼所 | Steel sheet for carburization having excellent cold workability and toughness after carburizing heat treatment |
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JP2000073137A (en) * | 1998-08-26 | 2000-03-07 | Kobe Steel Ltd | Steel wire rod excellent in cold workability |
JP2006225701A (en) * | 2005-02-16 | 2006-08-31 | Nippon Steel Corp | Steel wire rod excellent in cold-forgeability after spheroidizing-treatment and producing method therefor |
JP2013147728A (en) * | 2011-12-19 | 2013-08-01 | Kobe Steel Ltd | Steel for mechanical structure for cold working, and method for manufacturing the same |
JP2015168882A (en) * | 2014-03-11 | 2015-09-28 | 株式会社神戸製鋼所 | Spheroidizing heat treatment method for alloy steel |
WO2016148037A1 (en) * | 2015-03-13 | 2016-09-22 | 株式会社神戸製鋼所 | Steel sheet for carburization having excellent cold workability and toughness after carburizing heat treatment |
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