WO2014157142A1 - 伸線加工性、および伸線加工後の曲げ加工性に優れた高強度ばね用鋼線材、およびその製造方法、並びに高強度ばね、およびその製造方法 - Google Patents
伸線加工性、および伸線加工後の曲げ加工性に優れた高強度ばね用鋼線材、およびその製造方法、並びに高強度ばね、およびその製造方法 Download PDFInfo
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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
- 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
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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
- 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
- C21D8/065—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of rods or wires of ferrous alloys
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- 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
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- 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
- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
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- 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
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/34—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of silicon
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- 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
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/42—Ferrous alloys, e.g. steel alloys containing chromium with nickel with copper
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- 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
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
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- 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
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/46—Ferrous alloys, e.g. steel alloys containing chromium with nickel with vanadium
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- 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
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/48—Ferrous alloys, e.g. steel alloys containing chromium with nickel with niobium or tantalum
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- 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
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/54—Ferrous alloys, e.g. steel alloys containing chromium with nickel with boron
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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
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/009—Pearlite
Definitions
- the present invention is used for automobile valve springs and the like, and has high workability, specifically, wire drawing workability, bending workability after wire drawing work, and further high-strength spring steel having skinning workability described later.
- the present invention relates to a wire, a manufacturing method thereof, and a high-strength spring obtained from the steel wire for a high-strength spring, such as a hard spring and an oil temper spring.
- a manufacturing method of a valve spring mainly used for an engine is shown below.
- a steel ingot that has been refined and divided into predetermined components is processed into a round wire having a diameter of about 5.0 to 8.0 mm by hot rolling, wound into a coil, and cooled.
- a skin removal process (hereinafter sometimes referred to as “SV treatment”) is performed to remove the decarburized portion of the surface layer without subjecting the steel wire (hereinafter sometimes referred to as “hot rolled wire”) to heat treatment.
- SV treatment skin removal process
- hot rolled wire to heat treatment.
- soft annealing is performed at a high frequency or the like, and the wire is drawn to a desired wire diameter, for example, about 3 to 4 mm in the case of a valve spring.
- quenching-tempering treatment for improving the spring characteristics, it is processed into a spring shape.
- the wire drawing workability resulting from the structure of the hot-rolled wire material affects the pre-process of the heat treatment process accompanied with austenitization.
- internal defects and the like generated during wire drawing remain as defects in the structure even after heat treatment accompanied by austenitization, and affect the properties of the wire after heat treatment. Therefore, at the present time when the production process is being reduced, it is very important to secure the wire drawing workability and the bending workability after the wire drawing work that are secured by improving the ductility of the hot rolled wire rod. ing.
- Patent Document 1 adjusts the chemical composition of steel, sets the rolling wire rod mounting temperature to 900 ° C. or higher, sets the pearlite transformation start temperature to 650 to 750 ° C., and makes the structure mainly composed of pearlite.
- a steel wire for a high-strength spring excellent in wire drawing workability has been proposed by reducing variations in pearlite nodules.
- an object of the present invention is to provide a steel wire material excellent in wire drawing workability and bending workability after wire drawing work.
- the present invention is applied only to high softening annealing without austenitization or intermediate heat treatment of high frequency heating, and a final wire diameter of about 85% of wire drawing area reduction used as a spring, for example, ⁇ 2.0 to 4.0 mm
- An object of the present invention is to provide a steel wire for a high-strength spring that can be drawn and has excellent bending workability after the drawing, and a method useful for producing such a steel wire for a high-strength spring.
- the steel wire for a high-strength spring of the present invention that has solved the above problems is C: 0.5 to 0.8% (% means “mass%”, the same applies to the chemical composition), Si: 1 0.5-2.5%, Mn: 0.5-1.5%, Ni: 0.05-0.5%, Cr: 0.05-2.5%, V: 0.05-0.5 %,
- the balance is made of iron and inevitable impurities, the area ratio of the pearlite structure occupying the whole structure is 95% or more, and the tensile strength (TS) and the drawing (RA) are expressed by the following formula (1).
- the standard deviation of tensile strength (TS ⁇ ) and the standard deviation of drawing (RA ⁇ ) satisfy the following formula (2), and a lamella with a diameter of 0.9 ⁇ m or more at the diameter d ⁇ 1/4 position of the steel wire rod
- the gist is that the area ratio of the pearlite structure having an interval is 20% or less.
- Nb more than 0% to 0.10%
- Mo more than 0% to 0.50%
- Cu more than 0% to 0.50%
- B 0.0010 to You may contain at least 1 type selected from the group which consists of 0.0100%.
- the present invention also includes a high-strength spring obtained from the above steel wire for high-strength spring.
- the present invention also includes a method for producing the steel wire for high strength springs. Specifically, a steel wire after hot rolling that satisfies the above chemical composition is wound into a coil at a mounting temperature of 750 to 890 ° C., and then 2.0 to 10.0 ° C. / The dense portion of the coil and the sparse portion of the coil are cooled to the start temperature of slow cooling at an average cooling rate of 2 seconds, and then gradually cooled at an average cooling rate of 1.0 ° C./second or less for 120 seconds or more. The temperature of the dense part of the coil and the sparse part of the coil are in the range of 600 to 650 ° C., and the temperature difference between the dense part of the coil and the sparse part of the coil is 30 ° C. or less. It has a gist to do.
- the steel wire rod for high-strength spring is subjected to a skin treatment without heat treatment, and then subjected to a softening annealing or high-frequency heating followed by a wire drawing process, followed by a quenching and tempering treatment. It includes forming the spring.
- the present invention appropriately controls the chemical composition and the metal structure, makes the tensile strength and drawing of the steel wire within a predetermined range, and further appropriately controls the area ratio of the predetermined pearlite structure inside the steel wire. I tried to do it. As a result, it is possible to provide a high-strength steel wire for springs that has good wire drawing workability and bending workability after wire drawing work. Moreover, such a steel wire for high strength springs is extremely useful as a material for producing a high strength spring.
- FIG. 1 is a schematic explanatory diagram of the sampling position of the coil.
- FIG. 2 is a schematic explanatory view showing the state of the coil on the cooling conveyor. It is a schematic explanatory drawing of the sampling method of the coil which is a sample for evaluation. It is sectional drawing of the wire which is a sample for evaluation, Comprising: It is a schematic explanatory drawing of the measurement position of a pearlite structure
- the hot-rolled steel wire rods are wound in a coil shape, placed on a cooling conveyor, and cooled by air cooling or the like.
- the state of the coil on the cooling conveyor is shown in FIG.
- a portion of the steel wire that is relatively densely overlapped hereinafter sometimes referred to as “dense portion”
- sparse portion a portion that is relatively sparse
- the present inventors examined the relationship between the rolling structure and workability of high-strength spring steel, specifically, wire drawing workability and bending workability after wire drawing work.
- mechanical properties collectively of tensile strength and drawing
- the longitudinal variation in mechanical properties it is important to reduce the variation in structure caused by the cooling rate in the longitudinal direction, that is, the coil dense portion and the sparse portion.
- the present inventors perform the SV treatment by omitting the heat treatment after rolling, and furthermore, sufficient wire drawing workability and bending after wire drawing only by soft annealing such as high-frequency heat treatment.
- the conditions for ensuring workability were further examined.
- an area ratio of 95% or more of the steel wire structure becomes a pearlite structure, and tensile strength (TS) and drawing (RA), which are mechanical properties, and tensile strength, which is an index of longitudinal dispersion of mechanical properties, are obtained.
- the spring steel wire rod of the present invention has a pearlite structure as a main phase.
- supercooled structures such as bainite and martensite, and ferrite may be included.
- the supercooled structure such as bainite and martensite is increased, ductility and toughness are lowered, and breakage is likely to occur during the skin cutting process or the wire drawing process.
- the structure becomes non-uniform and wire drawing workability may deteriorate, or internal defects such as voids may occur after wire drawing work, and bending workability after wire drawing work may deteriorate.
- the area ratio of the pearlite structure in the entire structure needs to be 95% or more, preferably 97% or more, more preferably 98% or more.
- Tensile strength (TS) and drawing (RA) are both important indexes for suppressing disconnection during wire drawing of a steel wire.
- a steel wire obtained by hot rolling is subjected to a skin treatment (SV treatment) without being subjected to a heat treatment, and then subjected to a softening annealing treatment or a high-frequency heating, followed by wire drawing. In such a manufacturing process, if ductility is poor, disconnection is likely to occur during SV treatment or wire drawing.
- the present invention appropriately controls the mechanical properties.
- the tensile strength (TS) of the steel wire is 1250 MPa or less, preferably 1200 MPa or less.
- the drawing (RA) of the steel wire rod is 35% or more, preferably 40% or more.
- the variation in mechanical properties is appropriately controlled. Since the rolling wire has a different cooling rate between the dense part and the sparse part of the coil during cooling, there may be a large difference in mechanical properties. Therefore, tensile strength (TS) and drawing are reduced from the viewpoint of improving wire breakability after wire drawing by suppressing breakage in the SV treatment and wire drawing, and defects in the structure after wire drawing. It is desirable to reduce (RA) variation. Therefore, in the present invention, the standard deviation (TS ⁇ ) of tensile strength is 55.0 or less, preferably 50.0 or less, more preferably 48 or less.
- the standard deviation (RA ⁇ ) of the aperture is 6.0 or less, preferably 5.0 or less, more preferably 4.8 or less.
- Control of the area ratio of a specific pearlite structure at a predetermined position of the steel wire is effective in suppressing wire breakage in wire drawing and bending workability after wire drawing.
- it is a metal structure having pearlite as a main phase.
- the pearlite structure is poor in deformability, and therefore in the structure that causes disconnection. Prone to defects.
- the defects often remain in the structure after heat treatment, it is desirable to suppress them.
- the total area ratio of the pearlite structure having a lamellar interval of 0.9 ⁇ m or more at the 1/4 position of the diameter d of the steel wire rod is 20% or less, preferably 15% or less. Preferably it is 10% or less. Further, from the viewpoint of suppressing the above defects, it is desirable to control the total area ratio of the pearlite structure having a lamellar interval of 0.8 ⁇ m or more, more preferably 0.7 ⁇ m or more within the above range. Moreover, SV property also becomes favorable for the wire which satisfies the above requirements.
- a steel billet having a predetermined chemical component is hot-rolled and processed into a desired wire diameter.
- the heating temperature at the time of rolling is not particularly limited, but processing at as low a temperature as possible is preferable from the viewpoint of refining the structure. However, when the temperature is lowered, the deformation resistance of the steel material increases and the equipment load increases. Therefore, the temperature is appropriately set according to the equipment owned.
- the heating temperature at the time of hot rolling for example, the steel billet heating temperature is about 900 to 1000 ° C.
- the steel wire after hot rolling is coiled and placed on the cooling conveyor, but when the placement temperature at this time exceeds 890 ° C., the structure becomes coarse and the drawing (RA) becomes low, Ductility may decrease and wire drawing workability and bending workability after wire drawing may deteriorate.
- the temperature is lower than 750 ° C., the deformation resistance increases and the equipment load increases, so the mounting temperature is set to 750 ° C. or higher and 890 ° C. or lower. This mounting temperature is preferably 770 ° C. or higher and 830 ° C. or lower.
- the annealing start temperature 600 to 650 ° C
- the annealing start temperature 600 to 650 ° C
- the dense and sparse portions of the coil are cooled at an average cooling rate of 2.0 ° C./second or more and 10.0 ° C./second or less, and then gradually slowed for 120 seconds or more at an average cooling rate of 1.0 ° C./second or less.
- the wire temperature at the start of gradual cooling is controlled so that both the sparse part and the dense part are in the range of 600 ° C.
- the region for starting slow cooling is usually performed by installing a slow cooling cover in that region, hereinafter, the slow cooling region is “in the slow cooling cover” and the slow cooling start position is “slow cooling”. Sometimes called “cold cover inlet”.
- the average cooling rate to the annealing start temperature is less than 2.0 ° C / second, the structure cannot be sufficiently controlled, the area ratio of the rough pearlite structure increases, and the wire drawing workability and bending after wire drawing work are increased. Workability deteriorates.
- the average cooling rate exceeds 10.0 ° C./second, a local supercooled structure such as bainite is generated, the area ratio of the pearlite structure is lowered, and the ductility is lowered. Bending workability after wire drawing deteriorates.
- a preferable average cooling rate is 3.0 ° C./second or more and 7.0 ° C./second or less.
- the dense and sparse parts of the coil are cooled at a cooling rate in the above temperature range, and the steel wire temperature when starting slow cooling is 600 ° C. or more and 650 ° C. or less for both the dense and sparse parts of the coil.
- the temperature is controlled so that the temperature difference between the dense part and the sparse part of the coil is 30 ° C. or less.
- the annealing start temperature of the dense part and the sparse part of the coil exceeds 650 ° C.
- a rough pearlite structure is generated, the area ratio is increased, and internal defects are increased.
- the bending workability after wire drawing deteriorates.
- the annealing start temperature is below 600 ° C.
- the pearlite transformation in the annealing cover becomes insufficient.
- a supercooled structure such as bainite is generated, the pearlite area ratio is lowered, the ductility is lowered, and the wire drawing workability and the bending workability after the wire drawing work are deteriorated.
- a preferable annealing cover inlet temperature is 620 ° C. or more and 640 ° C. or less.
- the temperature difference at the inlet of the slow cooling cover between the dense coil portion and the loose coil portion is controlled to 30 ° C. or less, preferably 20 ° C. or less.
- the variation in mechanical properties (TS ⁇ , RA ⁇ ) in the longitudinal direction of the rolled wire can be reduced to the predetermined range.
- the cooling speed of the coil dense part / sparse part at the inlet of the slow cooling cover after the rolled wire rod is placed on the conveyor is adjusted by adjusting the air volume of the cooling blower to the coil dense part / sparse part. It is possible to reduce the temperature difference between the coil dense part and the sparse part on the region entering side. Since the cooling rate of the coil dense part and the sparse part varies depending on the rolling line speed, the conveyor speed, etc., it is necessary to set the air volume according to each rolling condition.
- the cooling rate in the slow cooling cover is too fast, or the staying time, specifically the slow cooling region staying time, or the slow cooling time is too short, the slow cooling ends before the transformation is completed, and the subsequent cooling.
- water cooling may cause a supercooled structure such as bainite or martensite. Therefore, it is preferable that the cooling rate in the slow cooling region is 1.0 ° C./second or less, preferably 0.4 ° C./second or less, and the residence time is 120 seconds or more.
- the steel wire rod for high-strength springs of the present invention needs to adjust its chemical composition appropriately in order to exhibit properties as a final product, for example, a high-strength spring.
- the reason for the range limitation by each component (element) in the chemical component composition is as follows.
- C is an element that ensures the basic strength of the steel material and is effective in increasing the strength and sag resistance of the spring. In order to acquire such an effect, it is necessary to contain C 0.5% or more. As the C content increases, the spring strength and sag resistance improve. However, when the amount of C added is excessive, a large amount of coarse cementite is precipitated, ductility is lowered, and wire drawing workability, bending workability after wire drawing work, and spring characteristics may be adversely affected. Therefore, the C content needs to be 0.8% or less.
- the preferable lower limit of the C content is 0.55% or more, more preferably 0.6% or more, and the preferable upper limit is 0.75% or less, more preferably 0.7% or less.
- Si is an element necessary for deoxidizing steel and ensuring the strength, hardness, and sag resistance of the spring. In order to acquire such an effect, it is necessary to contain Si 1.5% or more. However, when the Si content is excessive, not only the material is hardened, but also the drawing workability and the bending workability after the drawing work are lowered due to the reduction in ductility, and the surface decarburization is increased and the SV is increased. The processability and spring fatigue characteristics may be reduced. Therefore, the Si content needs to be 2.5% or less.
- the preferable lower limit of the Si content is 1.7% or more, more preferably 1.8% or more, and the preferable upper limit is 2.3% or less, more preferably 2.2% or less.
- Mn 0.5 to 1.5%
- Mn is an element necessary for deoxidation of steel like Si. Moreover, in addition to fixing S in steel as MnS, it enhances hardenability and contributes to improvement of spring strength. In order to acquire such an effect, it is necessary to contain Mn 0.5% or more. However, when the Mn content is excessive, the hardenability becomes excessively high, and a supercooled structure such as martensite and bainite is easily generated. As a result, wire drawing workability and bending workability after wire drawing are reduced. Therefore, the Mn content needs to be 1.5% or less. The minimum with preferable Mn content is 0.7% or more, More preferably, it is 0.8% or more, and a preferable upper limit is 1.3% or less, More preferably, it is 1.2% or less.
- Ni contributes to the improvement of ductility, toughness, and corrosion resistance after quenching and tempering as well as suppressing decarburization during hot rolling. In order to acquire such an effect, it is necessary to contain Ni 0.05% or more. However, when the Ni content is excessive, the hardenability becomes excessively high, so that a supercooled structure such as martensite and bainite is easily generated. As a result, wire drawing workability and bending workability after wire drawing are reduced. In addition, since retained austenite is excessively generated by quenching and tempering, which is a manufacturing process of an oil tempered wire (OT wire), the sag resistance of the spring is significantly reduced. Therefore, the Ni content needs to be 0.5% or less.
- the preferable lower limit of the Ni content is 0.10% or more, more preferably 0.15% or more, and the preferable upper limit is 0.30% or less, more preferably 0.25% or less.
- Cr 0.05-2.5%
- Cr has the effect of reducing the activity of C and preventing decarburization during rolling and heat treatment. In order to acquire such an effect, it is necessary to contain Cr 0.05% or more. However, if the Cr content is excessive, the precipitation of Cr-based alloy carbides, nitrides, and carbonitrides becomes excessive, and the ductility is lowered, thereby reducing the wire drawing workability and the bending workability after wire drawing. Therefore, the Cr content needs to be 2.5% or less.
- the preferable lower limit of the Cr content is 0.10% or more, more preferably 0.20% or more, and the preferable upper limit is 2.2% or less, more preferably 2.0% or less.
- V has the effect
- secondary precipitation hardening occurs at the time of strain relief annealing after spring formation, which contributes to improvement of the strength of the spring.
- the V content needs to be 0.5% or less.
- the minimum with preferable V content is 0.10% or more, More preferably, it is 0.15% or more, and a preferable upper limit is 0.3% or less, More preferably, it is 0.2% or less.
- the basic components in the steel wire for high-strength spring according to the present invention are as described above, and the balance is iron and inevitable impurities (for example, P, S, etc.).
- Nb more than 0% and 0.10% or less
- Mo more than 0% and 0.50% or less
- Cu more than 0% and 0.50% or less
- B At least one selected from the group consisting of 0.0010 to 0.0100% may be included, and these are elements having the same effect, and depending on the type of element to be included, the characteristics of the steel wire Is further improved.
- the reason for setting a preferable range of these elements is as follows.
- Nb more than 0% and 0.10% or less
- Nb has the effect of refining crystal grains in hot rolling and quenching / tempering treatments, and has the effect of improving ductility.
- the Nb addition amount is set to 0.10% or less.
- the minimum with preferable Nb content is 0.01% or more, More preferably, it is 0.02% or more, and a preferable upper limit is 0.07% or less, More preferably, it is 0.05% or less.
- Mo more than 0% and 0.50% or less
- Mo contributes to improving the strength of the spring by causing secondary precipitation hardening at the time of stress relief annealing after spring forming.
- the addition amount of Mo is 0.50% or less.
- the minimum with preferable Mo content is 0.05% or more, More preferably, it is 0.10% or more, and a preferable upper limit is 0.40% or less, More preferably, it is 0.30% or less.
- Cu more than 0% and 0.50% or less
- Cu has the effect of suppressing decarburization during hot rolling. It also contributes to improved corrosion resistance. However, if Cu is contained excessively, the hot ductility is lowered and there is a risk of causing cracks during hot rolling. Therefore, the Cu content is 0.50% or less.
- the minimum with preferable Cu content is 0.05% or more, More preferably, it is 0.10% or more, and a preferable upper limit is 0.40% or less, More preferably, it is 0.30% or less.
- B has an effect of improving ductility and toughness by improving hardenability and cleaning austenite grain boundaries. In order to acquire such an effect, it is desirable to contain B 0.0010% or more. However, if B is contained excessively, a composite compound of Fe and B precipitates, and there is a risk of causing cracks during hot rolling. Moreover, since hardenability improves excessively, a supercooled structure
- the preferable lower limit of the B content is 0.0015% or more, more preferably 0.0020% or more, and the preferable upper limit is 0.0050% or less, more preferably 0.0040% or less.
- the steel wire for high-strength spring of the present invention is assumed to be after hot rolling, but this steel wire for high-strength spring is then formed into a high-strength spring by being processed into a spring. Therefore, a spring exhibiting good characteristics can be obtained.
- a steel ingot having a chemical composition shown in Table 1 below was melted in a converter, and the steel ingot was subjected to split rolling to produce a steel billet having a cross section of 155 mm ⁇ 155 mm.
- the steel billet was heated to 950 ° C., hot-rolled, placed at the conveyor placement temperature shown in Table 2 below (“placement temperature” in the table), and then subjected to the wire diameter under the temperature conditions shown in Table 2.
- a coil having a diameter of ⁇ 5.5 to 8.0 mm and a single weight of 2 ton was manufactured (Test Nos. 1 to 29). The following tests were performed on each of the obtained coils.
- the transparent film After printing out the image of the optical micrograph and painting the white part from the top of the transparent film with black magic, the transparent film is taken into a personal computer with a scanner, and image analysis software (“Image Pro Plus by Media Cybernetics) is used. )), The pearlite area ratio was determined after binarizing the image.
- the part with a white image of an optical microscope photograph was made into the ferrite and the lower bainite.
- the average value was obtained from the pearlite area ratio of 4 fields per sample. In the present invention, the average value was calculated from the pearlite areas of all 6 samples (4 locations each).
- regulated by JISG0058 was excluded from the measurement site
- the area ratio is shown in Table 3 on the basis of the following criteria (in the table, “rolled wire structure” column).
- P Area ratio of pearlite structure is 95% or more
- P + B Area ratio of pearlite structure is less than 95% and bainite structure is generated
- P + B + M Area ratio of pearlite structure is less than 95%, and bainite structure and martensite structure are generated
- the area ratio of pearlite colonies (FIG. 5) having a lamellar interval of 0.9 ⁇ m or more was obtained even at one place in the pearlite structure of each photograph.
- Print out the SEM image paint the perlite colony part with a lamellar spacing of 0.9 ⁇ m or more at one place from the top of the transparent film with black magic, then import the transparent film into the personal computer with the scanner and analyze the image
- a pearlite area ratio having a lamellar interval of 0.9 ⁇ m or more was obtained.
- the average value was computed from the pearlite area rate which has the lamella space
- the rough pearlite area ratio having a lamellar interval of 0.9 ⁇ m or more was determined after excluding it in advance. Note that a line segment was drawn so that the lamella spacing was perpendicular to the lamella, and the distance between the centers of cementite sandwiching the ferrite was measured.
- Test No. Nos. 1 to 10 and 25 to 29 are test pieces that satisfy the requirements of the present invention, and were excellent in the shaving processability (SV property), the wire drawing workability, and the bending workability after wire drawing (coiling property). .
- Test No. No. 12 had a higher temperature at the inlet of the slow cooling cover of the coil dense part, and thus the coarse pearlite area ratio was higher. With this test piece, the shaving processability (SV property) and the wire drawing workability were good. However, since there are many internal defects in the wire drawing structure, bending workability (coiling property) after wire drawing was poor.
- Test No. 13 is an example in which the temperature of the slow cooling cover inlet of the coil sparse part was low. For this reason, the pearlite area ratio of the coil sparse portion was lowered, and an overcooled structure such as bainite was generated. As a result, since the ductility was lowered, the wire was broken at a drawing area reduction rate of about 75%, and the drawing workability was poor.
- Test No. No. 14 is an example in which the difference in the temperature of the slow cooling cover inlet between the coil dense part and the coil sparse part is large.
- the standard deviation (TS ⁇ ) of the tensile strength and the standard deviation (RA ⁇ ) of the drawing became large.
- TS ⁇ standard deviation
- RA ⁇ standard deviation
- the shaving processability (SV property) and the wire drawing workability were good.
- bending workability (coiling property) after wire drawing was poor.
- Test No. 15 is an example in which the average cooling rate from placement to the slow cooling cover inlet was slow. Therefore, the growth of austenite crystal grains progressed, and the coarse pearlite area ratio increased. As a result, the drawing (RA) was lowered, the ductility was lowered, the wire was cut at a drawing area reduction rate of about 70%, and the drawing workability was poor.
- Test No. 16 is an example in which the average cooling rate from the placement of the coil sparse part to the slow cooling cover inlet was high. For this reason, the pearlite area ratio of the coil sparse part was lowered, and an overcooled structure such as bainite was generated. As a result, the ductility was lowered, the wire was broken at a drawing area reduction rate of about 75%, and the drawing workability was poor.
- Test No. No. 17 is an example in which the cooling rate in the slow cooling cover of the coil sparse part and the coil dense part is too high. For this reason, cooling progressed before the completion of the pearlite transformation, the pearlite area ratio of the coil sparse portion was lowered, and an overcooled structure such as bainite was generated. As a result, the ductility was lowered and disconnection occurred in the shaving process.
- Test No. No. 18 is an example in which the holding time in the slow cooling cover is short. Therefore, the slow cooling was completed before the pearlite transformation was completed, the cooling rate was increased, the pearlite area ratio of the coil sparse part was lowered, and a supercooled structure such as bainite was generated. As a result, the ductility was lowered and disconnection occurred in the shaving process.
- Test No. 19 is an example with a high C content. Therefore, the tensile strength (TS) was high and the drawing (RA) was low. As a result, the ductility was lowered, the wire was broken at a drawing area reduction rate of about 70%, and the drawing workability was poor.
- Test No. 20 is an example in which the Si content is high. Therefore, the tensile strength (TS) is high, the aperture (RA) is decreased, and the standard deviation (RA ⁇ ) of the aperture is varied. As a result, the ductility was lowered and disconnection occurred in the shaving process.
- Test No. 21 is an example with high Si and Mn content.
- Test No. 22 is an example with high Ni content.
- the hardenability was excessively high, the pearlite transformation was not completed in the slow cooling cover, and a supercooled structure such as a bainite structure was generated, resulting in a decrease in the pearlite area ratio.
- TS tensile strength
- RA drawing
- RA ⁇ standard deviation of tensile strength
- RA ⁇ standard deviation of drawing
- Test No. 23 is an example with a large Cr content. Therefore, the precipitation of Cr-based carbides became excessive and the ductility decreased. As a result, the ductility was lowered, the wire was broken at a drawing area reduction rate of about 75%, and the drawing workability was poor.
- Test No. 24 is an example with a large V content. For this reason, precipitation of V-based carbides became excessive, and ductility decreased. As a result, the ductility was lowered, the wire was disconnected at a drawing area reduction rate of about 80%, and the drawing workability was poor.
Abstract
Description
TS≦1250MPa、RA≧35% ・・・(1)
TSσ≦55.0、RAσ≦6.0 ・・・(2)
TS≦1250MPa、RA≧35% ・・・(1)
TSσ≦55.0、RAσ≦6.0 ・・・(2)
本発明のばね用鋼線材は、パーライト組織を主相とするものである。パーライト組織以外の組織としては、ベイナイト、マルテンサイト等の過冷組織や、フェライトが含まれることがある。ベイナイトやマルテンサイト等の過冷組織が増加すると、延性や靭性が低下して、皮削り処理時や伸線加工処理時に断線が生じやすくなる。またフェライトが増加すると、組織が不均一となって伸線加工性が低下したり、伸線加工後にボイド等の内部欠陥が生じて伸線加工後の曲げ加工性が低下することがある。本発明ではパーライト組織の面積率を高めて、相対的にベイナイト等の上記望ましくない組織を抑制し、均一なパーライト主体の組織とすることによって、断線や内部欠陥などを減少させ、伸線加工性や伸線加工後の曲げ加工性を向上させている。こうした効果を得るために、全組織に占めるパーライト組織の面積率を95%以上とする必要があり、好ましくは97%以上、より好ましくは98%以上である。
引張り強さ(TS)と絞り(RA)はいずれも鋼線材の伸線加工時の断線を抑制するために重要な指標である。本発明では、熱間圧延して得られた鋼線材に、熱処理を施さずに皮削り処理(SV処理)を施し、その後、軟化焼鈍処理若しくは高周波加熱を施してから伸線加工を行う。このような製造工程において、延性が乏しいとSV処理や伸線加工時に断線が生じやすくなる。特に引張り強さ(TS)が高すぎたり、絞り(RA)が低すぎる場合は、SV処理や伸線加工時に断線が生じやすくなる。このような断線を抑制する観点から、本発明では機械的性質を適切に制御することとした。具体的には、鋼線材の引張り強さ(TS)を1250MPa以下、好ましくは1200MPa以下とする。また鋼線材の絞り(RA)を35%以上、好ましくは40%以上とする。
更に本発明では機械的性質のばらつきを適切に制御することとした。圧延線材は、冷却時のコイルの密部と疎部で冷却速度が異なるため、機械的性質に大きな差異が生じる場合がある。そのため、SV処理や伸線加工処理での断線、および伸線加工後の組織中の欠陥発生を抑制して伸線加工後の曲げ加工性を向上させる観点から、引張り強さ(TS)と絞り(RA)ばらつきを低減することが望ましい。そこで本発明では引張り強さの標準偏差(TSσ)を55.0以下、好ましくは50.0以下、より好ましくは48以下とする。また絞りの標準偏差(RAσ)を6.0以下、好ましくは5.0以下、より好ましくは4.8以下とする。
鋼線材の所定位置における特定のパーライト組織の面積率の制御は、伸線加工、および伸線加工後の曲げ加工性などにおける断線の抑制に有効である。本発明では上記したようにパーライトを主相とする金属組織であるが、線材内部においてラメラ間隔の粗いパーライト組織が存在すると、該パーライト組織は変形能に乏しいため、断線の原因となる組織中の欠陥となりやすい。また該欠陥は熱処理後も組織中に残存することが多いため、抑制することが望ましい。こうした欠陥を抑制する観点から、本発明では鋼線材の直径dの1/4位置における0.9μm以上のラメラ間隔を有するパーライト組織の面積率の合計を20%以下、好ましくは15%以下、より好ましくは10%以下とする。また上記欠陥を抑制する観点から好ましくは0.8μm以上、より好ましくは0.7μm以上のラメラ間隔を有するパーライト組織の面積率の合計を上記範囲に制御することが望ましい。また上記のような要件を満足する線材は、SV性も良好となる。
Cは、鋼材の基本的な強度を確保し、ばねの強度・耐へたり性の上昇に有効な元素である。このような効果を得るために、Cは0.5%以上含有させる必要がある。C含有量の増加に伴ってばねの強度・耐へたり性は向上する。しかしながらC添加量が過剰になると粗大セメンタイトを多量に析出し、延性が低下し、伸線加工性や伸線加工後の曲げ加工性、およびばね特性に悪影響を及ぼすことがある。そのためC含有量は、0.8%以下とする必要がある。C含有量の好ましい下限は0.55%以上、より好ましくは0.6%以上であり、好ましい上限は0.75%以下、より好ましくは0.7%以下である。
Siは、鋼の脱酸、及びばねの強度、硬度、および耐へたり性を確保するために必要な元素である。このような効果を得るために、Siは1.5%以上含有させる必要がある。しかしながら、Si含有量が過剰になると、材料を硬化させるだけでなく、延性の低下により伸線加工性、および伸線加工後の曲げ加工性を低下させる他、表面の脱炭が増加してSV処理性、およびばね疲労特性を低下させることがある。そのためSi含有量は2.5%以下とする必要がある。Si含有量の好ましい下限は1.7%以上、より好ましくは1.8%以上であり、好ましい上限は2.3%以下、より好ましくは2.2%以下である。
MnはSiと同様に、鋼の脱酸に必要な元素である。また鋼中SをMnSとして固定することに加えて、焼入れ性を高めてばね強度の向上に貢献する。このような効果を得るために、Mnは0.5%以上含有させる必要がある。しかしながら、Mn含有量が過剰になると、焼入れ性が過度に高くなって、マルテンサイト、ベイナイト等の過冷組織が生成しやすくなる。その結果、伸線加工性、伸線加工後の曲げ加工性が低下する。そのためMn含有量は1.5%以下とする必要がある。Mn含有量の好ましい下限は0.7%以上、より好ましくは0.8%以上であり、好ましい上限は1.3%以下、より好ましくは1.2%以下である。
Niは、熱間圧延時の脱炭を抑制する他、焼入れ焼戻し後の延性、靭性、および耐腐食性の向上に寄与する。このような効果を得るために、Niは0.05%以上含有させる必要がある。しかしながら、Ni含有量が過剰になると焼入れ性が過度に高くなるため、マルテンサイト、ベイナイト等の過冷組織が生成しやすくなる。その結果、伸線加工性、伸線加工後の曲げ加工性が低下する。また、オイルテンパー線(OT線)の製造工程である焼入れ焼戻しで残留オーステナイトが過度に生成するので、ばねの耐へたり性を著しく低下させる。そのため、Ni含有量は0.5%以下とする必要がある。Ni含有量の好ましい下限は0.10%以上、より好ましくは0.15%以上であり、好ましい上限は0.30%以下、より好ましくは0.25%以下である。
Crは、焼入れ性を高めてばね強度を向上させることに加え、Cの活量を低下させて圧延時や熱処理時の脱炭を防止する効果がある。このような効果を得るために、Crは0.05%以上含有させる必要がある。しかしながらCr含有量が過剰になると、Cr系合金炭化物、窒化物、炭窒化物の析出が過剰となり、延性が低下して伸線加工性、伸線加工後の曲げ加工性を低下させる。そのため、Cr含有量は2.5%以下とする必要がある。Cr含有量の好ましい下限は0.10%以上、より好ましくは0.20%以上であり、好ましい上限は2.2%以下、より好ましくは2.0%以下である。
Vは、熱間圧延および焼入れ焼戻し処理において結晶粒を微細化する作用があり、延性、靭性を向上させる。また、ばね成形後の歪取焼鈍時に2次析出硬化を起こしてばねの強度の向上に寄与する。このような効果を得るために、Vは0.05%以上含有させる必要がある。しかしながらV含有量が過剰になると、CrとVの複合合金炭化物の析出が過剰となり、延性が低下して伸線加工性、伸線加工後の曲げ加工性が悪化する。そのため、V含有量は0.5%以下とする必要がある。V含有量の好ましい下限は0.10%以上、より好ましくは0.15%以上であり、好ましい上限は0.3%以下、より好ましくは0.2%以下である。
Nbは熱間圧延、および焼入れ・焼戻し処理において結晶粒を微細化する作用があり、延性を向上させる効果がある。しかしながらNbを過剰に含有させると、CrとNbの複合合金炭化物の析出が過剰となり、延性が低下し伸線加工性、曲げ加工性を低下させる。そのため、Nb添加量は0.10%以下とする。Nb含有量の好ましい下限は0.01%以上、より好ましくは0.02%以上であり、好ましい上限は0.07%以下、より好ましくは0.05%以下である。
Moは、ばね成形後の歪取焼鈍時に2次析出硬化を起こしてばねの強度の向上に寄与する。しかしながら、Mo含有量が過剰になると、CrとMoの複合合金炭化物の析出が過剰となり、延性が低下し伸線加工性、伸線加工後の曲げ加工性を低下させる。そのため、Mo添加量は0.50%以下とする。Mo含有量の好ましい下限は0.05%以上、より好ましくは0.10%以上であり、好ましい上限は0.40%以下、より好ましくは0.30%以下である。
Cuは、熱間圧延時の脱炭を抑制する効果がある。また耐腐食性の向上にも寄与する。しかしながら、Cuを過剰に含有させると熱間延性を低下させ、熱間圧延時に割れを生じる危険がある。そのため、Cu含有量は0.50%以下とする。Cu含有量の好ましい下限は0.05%以上、より好ましくは0.10%以上であり、好ましい上限は0.40%以下、より好ましくは0.30%以下である。
Bは、焼入れ性の向上とオーステナイト結晶粒界の清浄化による延性・靱性の向上効果がある。このような効果を得るために、Bは0.0010%以上含有させることが望ましい。しかしながら、Bを過剰に含有させるとFeとBの複合化合物が析出し、熱間圧延時の割れを引き起こす危険がある。また、焼入れ性が過度に向上するため、ベイナイト等の過冷組織が生成し、圧延線材の延性を低下させることがある。そのため、B含有量は0.0100%以下とする。B含有量の好ましい下限は0.0015%以上、より好ましくは0.0020%以上であり、好ましい上限は0.0050%以下、より好ましくは0.0040%以下である。
図1に示すように2トンコイルの各位置、すなわち、コイル全体の1/3までのTOP、コイル全体の1/3までのBOT、前記TOP、およびBOTを除いた残りの1/3のMIDから夫々3巻ずつ、合計9巻をサンプリングした。図3に示すように各リングを円周方向に8分割、すなわち、コイル長手方向に8分割して採取したサンプル、すなわち、サンプル数(n)=72で引張り試験(TS)、および絞り(RA)を実施した。また引張り強さの標準偏差(TSσ)、及び絞りの標準偏差(RAσ)は全サンプル(n=72)から求めた。
上記2トンコイルのTOP、MID、およびBOTの各位置で引張強度(TS)が最大のもの、および最小のものを夫々2本ずつ、合計6本をサンプリングした。まず、各サンプルの横断面を埋め込み研磨し、ピクリン酸を用いた化学腐食を実施した。次に図4に示すように横断面の直径d×1/4位置を光学顕微鏡を用いて倍率400倍で200μm×200μmの領域にて写真を撮影した。該撮影は図示するように互いに90度をなす4箇所において行った。光学顕微鏡写真の画像をプリントアウトして、透明フィルムを重ねた上から白い部分を黒マジックで塗りつぶした後、透明フィルムをスキャナーでパーソナルコンピューターに取り込み、画像解析ソフト(Media Cybernetics社製「Image Pro Plus」)を用いて、画像を2値化した後、パーライト面積率を求めた。なお、光学顕微鏡写真の画像が白い部分をフェライトおよび下部ベイナイトとした。1サンプル当たり4視野のパーライト面積率から平均値を求めた。本発明では全6サンプル(各4箇所)のパーライト面積から平均値を算出した。なお、表層に脱炭層が存在する場合には、JIS G 0058で規定される全脱炭部は測定部位から除外した。面積率について、表3には以下の基準で表記した(表中、「圧延線材組織」欄)。
P:パーライト組織の面積率が95%以上
P+B:パーライト組織の面積率が95%未満、且つベイナイト組織が生成
P+B+M:パーライト組織の面積率が95%未満、且つベイナイト組織とマルテンサイト組織が生成
上記2トンコイルの各位置(TOP、MID、BOT)で引張強度(TS)が最小のものを夫々1本づつ、合計3本をサンプリングした。上記パーライトの面積率と同様、研磨、化学腐食を実施した。次に図4に示すように横断面の直径d×1/4位置を走査型電子顕微鏡(SEM、倍率:2000倍、50μm×40μmの領域)にて撮影した。該撮影は図示するように4箇所において行った。
皮削り処理性は、コイルのTOP側1トン全量(コイル全体×1/2)に熱処理を加えることなく皮削り処理を実施し、該皮削り処理での断線の有無で評価した(表中、「SV性」)。
A(合格 皮削り処理性が良い) :断線が生じなかったコイル
F(不合格 皮削り処理性が悪い):断線が生じたコイル
伸線加工性は、皮削り処理後のコイルを600℃で3時間の焼鈍処理を施した後、酸洗処理、ボンデ処理を施し、連続伸線機で1パス当たりの減面率を15~20%として総減面率85%まで伸線し、伸線時の断線の有無で評価した(表中、「伸線加工性」)。なお、表中の「-」は、上記皮削り処理によって断線が生じたため(表中、「SV性」が「F」)、伸線加工を行わなかったことを示す。
A(合格 伸線加工性が良い) :断線の生じなかったコイル
F(不合格 伸線加工性が悪い):断線が生じたコイル
伸線後に自径巻きを1000巻き行った際の折損回数(自径巻き折損回数)で評価した(表中、「コイリング性」)。なお、表中の「-」は、上記皮削り処理で断線が生じたか(表中、「F」)、或いは伸線加工によって断線が生じたため(表中、「F」)、伸線後の曲げ加工を行わなかったことを示す。
折損回数0回(コイリング性が良い) :自径巻きで折損が生じなかったコイル
折損回数1回以上(コイリング性が悪い):自径巻きで折損が生じたコイル
Claims (5)
- C :0.5~0.8%(%は「質量%」の意味、化学成分組成について以下同じ)、
Si:1.5~2.5%、
Mn:0.5~1.5%、
Ni:0.05~0.5%、
Cr:0.05~2.5%、
V:0.05~0.5%
を夫々含有し、残部が鉄および不可避不純物からなり、
全組織に占めるパーライト組織の面積率が95%以上であり、
引張り強さ(TS)、および絞り(RA)が下記式(1)を満足すると共に、引張り強さの標準偏差(TSσ)、および絞りの標準偏差(RAσ)が下記式(2)を満足し、
且つ鋼線材の直径d×1/4位置における0.9μm以上のラメラ間隔を有するパーライト組織の面積率が20%以下であることを特徴とする伸線加工性、および伸線加工後の曲げ加工性に優れた高強度ばね用鋼線材。
TS≦1250MPa、RA≧35% ・・・(1)
TSσ≦55.0、RAσ≦6.0 ・・・(2) - 更に、
Nb:0%超~0.10%、
Mo:0%超~0.50%、
Cu:0%超~0.50%、および
B:0.0010~0.0100%よりなる群から選択される少なくとも一種を含有する請求項1に記載の高強度ばね用鋼線材。 - 請求項1または2に記載の高強度ばね用鋼線材から得られた高強度ばね。
- 請求項1または2に記載の高強度ばね用鋼線材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足する熱間圧延後の鋼線材を載置温度:750~890℃としてコイル状に巻き取った後、冷却コンベア上にて2.0~10.0℃/秒の平均冷却速度でコイルの密部とコイルの疎部を徐冷の開始温度まで冷却し、引続き1.0℃/秒以下の平均冷却速度で120秒以上徐冷することとし、前記徐冷の開始温度を、コイルの密部とコイルの疎部の温度が、600~650℃の範囲内で、且つ前記コイルの密部と前記コイルの疎部の温度差が30℃以下となるようにすることを特徴とする高強度ばね用鋼線材の製造方法。
- 請求項1または2に記載の高強度ばね用鋼線材に、熱処理することなく皮削り処理を施し、その後、軟化焼鈍若しくは高周波加熱を施してから伸線加工を行った後、焼入れ焼戻し処理を施してばねに成形加工することを特徴とする高強度ばねの製造方法。
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CN201480017018.0A CN105051230B (zh) | 2013-03-25 | 2014-03-25 | 拉丝加工性和拉丝加工后的弯曲加工性优异的高强度弹簧用钢线材及其制造方法、和高强度弹簧及其制造方法 |
KR1020157026246A KR101770490B1 (ko) | 2013-03-25 | 2014-03-25 | 신선 가공성 및 신선 가공 후의 굽힘 가공성이 우수한 고강도 스프링용 강 선재, 및 그 제조 방법과, 고강도 스프링, 및 그 제조 방법 |
DE112014001616.0T DE112014001616T5 (de) | 2013-03-25 | 2014-03-25 | Stahlwalzdraht für eine hochfeste Feder mit hervorragendem Ziehvermögen zu einem Draht und hervorragendem Biegevermögen nach dem Ziehen, Verfahren zu dessen Herstellung, hochfeste Feder und Verfahren zu deren Herstellung |
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CN112853068A (zh) * | 2020-12-31 | 2021-05-28 | 河南富瑞德金属制品有限公司 | 一种超细规格油淬火-回火弹簧钢丝制备工艺 |
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CN105112774B (zh) * | 2015-08-28 | 2017-12-01 | 浙江美力科技股份有限公司 | 高强韧性低中碳微合金风冷硬化弹簧钢及其成形和热处理工艺 |
KR101797381B1 (ko) | 2016-08-02 | 2017-11-14 | 주식회사 포스코 | 내식성이 우수한 스프링용 강선 및 이의 제조방법 |
CN106544494B (zh) * | 2017-01-18 | 2017-12-15 | 中钢集团郑州金属制品研究院有限公司 | 一种适用于1Cr17Ni2不锈钢冷拉线材的在线软化退火方法 |
KR102020385B1 (ko) * | 2017-09-29 | 2019-11-04 | 주식회사 포스코 | 내부식 피로특성이 우수한 스프링용 선재, 강선 및 이들의 제조방법 |
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