WO2022210125A1 - Fil d'acier pour composant structural mécanique et son procédé de fabrication - Google Patents

Fil d'acier pour composant structural mécanique et son procédé de fabrication Download PDF

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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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mass
less
temperature
steel wire
steel
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PCT/JP2022/013277
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English (en)
Japanese (ja)
Inventor
洋介 松本
憲史 池田
琢哉 高知
昌之 坂田
辰徳 内田
浩司 山下
悠太 井上
Original Assignee
株式会社神戸製鋼所
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Publication of WO2022210125A1 publication Critical patent/WO2022210125A1/fr

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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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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Thermal Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Physics & Mathematics (AREA)
  • Manufacturing & Machinery (AREA)
  • Heat Treatment Of Steel (AREA)
  • Wire Processing (AREA)
  • Treatment Of Steel In Its Molten State (AREA)

Abstract

L'invention concerne un fil d'acier pour composant structural mécanique, ledit fil d'acier contenant 0,05 % en masse à 0,60 % en masse de C, 0,005 % en masse à 0,50 % en masse de Si, 0,30 % en masse à 1,00 % en masse de Mn, plus de 0 % en masse, mais pas plus de 0,050 % en masse de P, plus de 0 % en masse, mais pas plus de 0,050 % en masse de S, 0,001 % en masse à 0,10 % en masse d'Al, plus de 0 % en masse, mais pas plus de 1,5 % en masse de Cr et plus de 0 % en masse, mais pas plus de 0,02 % en masse de N, le reste de celui-ci comprenant du fer et des impuretés inévitables, la demi-largeur de pic de diffraction par rayons X dans le plan (211) de grains de ferrite est de 0,500° ou moins, et le diamètre moyen en cercle équivalent à tous les carbures de fer, lorsque la quantité (% en masse) de C dans l'acier est représentée comme [C], est (1,863 à 2,13 [C]) µm ou moins.
PCT/JP2022/013277 2021-03-31 2022-03-22 Fil d'acier pour composant structural mécanique et son procédé de fabrication WO2022210125A1 (fr)

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
TWI854883B (zh) 2023-11-06 2024-09-01 中國鋼鐵股份有限公司 中碳鋼及其製備方法

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JP2000073137A (ja) * 1998-08-26 2000-03-07 Kobe Steel Ltd 冷間加工性に優れた鋼線材
JP2006225701A (ja) * 2005-02-16 2006-08-31 Nippon Steel Corp 球状化処理後の冷間鍛造性に優れた鋼線材及びその製造方法
JP2013147728A (ja) * 2011-12-19 2013-08-01 Kobe Steel Ltd 冷間加工用機械構造用鋼およびその製造方法
JP2015168882A (ja) * 2014-03-11 2015-09-28 株式会社神戸製鋼所 合金鋼の球状化熱処理方法
WO2016148037A1 (fr) * 2015-03-13 2016-09-22 株式会社神戸製鋼所 Tôle d'acier destinée à la cémentation possédant d'excellentes aptitudes au façonnage à froid et ténacité après traitement thermique de cémentation

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Publication number Priority date Publication date Assignee Title
JP6479538B2 (ja) * 2015-03-31 2019-03-06 株式会社神戸製鋼所 機械構造部品用鋼線

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2000073137A (ja) * 1998-08-26 2000-03-07 Kobe Steel Ltd 冷間加工性に優れた鋼線材
JP2006225701A (ja) * 2005-02-16 2006-08-31 Nippon Steel Corp 球状化処理後の冷間鍛造性に優れた鋼線材及びその製造方法
JP2013147728A (ja) * 2011-12-19 2013-08-01 Kobe Steel Ltd 冷間加工用機械構造用鋼およびその製造方法
JP2015168882A (ja) * 2014-03-11 2015-09-28 株式会社神戸製鋼所 合金鋼の球状化熱処理方法
WO2016148037A1 (fr) * 2015-03-13 2016-09-22 株式会社神戸製鋼所 Tôle d'acier destinée à la cémentation possédant d'excellentes aptitudes au façonnage à froid et ténacité après traitement thermique de cémentation

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
TWI854883B (zh) 2023-11-06 2024-09-01 中國鋼鐵股份有限公司 中碳鋼及其製備方法

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