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WO2017098964A1 - Fil d'acier pour éléments structuraux mécaniques - Google Patents

Fil d'acier pour éléments structuraux mécaniques Download PDF

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Publication number
WO2017098964A1
WO2017098964A1 PCT/JP2016/085371 JP2016085371W WO2017098964A1 WO 2017098964 A1 WO2017098964 A1 WO 2017098964A1 JP 2016085371 W JP2016085371 W JP 2016085371W WO 2017098964 A1 WO2017098964 A1 WO 2017098964A1
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WIPO (PCT)
Prior art keywords
mass
cementite
less
cooling
steel
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PCT/JP2016/085371
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English (en)
Japanese (ja)
Inventor
雄基 佐々木
琢哉 高知
政道 千葉
昌之 坂田
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Kobe Steel Ltd
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Kobe Steel Ltd
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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
    • 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
    • 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

Definitions

  • This disclosure relates to a steel wire used as a material for machine structural parts. More specifically, the present invention relates to a steel wire for machine structural parts having cold workability, particularly low cold deformation resistance and excellent crack resistance when cold working after spheroidizing annealing on a wire produced by rolling.
  • the following effects can be obtained by having cold workability, in particular, low deformation resistance and excellent crack resistance. If the deformation resistance of the steel wire is low, it is easy to process and it can be expected to improve the mold life. Moreover, the yield improvement of various components can be expected by improving the crack resistance of the steel wire.
  • Patent Document 1 includes a ferrite structure having an average particle diameter of 15 ⁇ m or less, spherical cementite having an average aspect ratio of 3 or less and an average particle diameter of 0.6 ⁇ m or less, and the number of the spherical cementite is 1 mm 2.
  • a technique of steel wire rods having a cold workability of 1.0 ⁇ 10 6 ⁇ C content (%) or more per one is disclosed.
  • Patent Document 1 as a method for obtaining the above metal structure, after hot rolling and winding a bloom or billet, the obtained rolled wire is placed in a molten salt bath at 400 ° C. or more and 600 ° C. or less for 10 seconds or more. It is disclosed that the substrate is immersed, further kept at a constant temperature in a molten salt bath at 450 ° C. or higher and 600 ° C. or lower for 20 seconds to 150 seconds, cooled, and then annealed at 600 ° C. or higher and 700 ° C. or lower.
  • Patent Document 2 discloses a steel wire having a structure in which a value obtained by dividing the standard deviation of the distance between cementites by the average value of the distance between cementites is 0.50 or less.
  • Patent Document 2 as a method for obtaining the above metal structure, in the cooling step after hot rolling, 750 to 1000 ° C. to 400 to 550 ° C. is cooled at a cooling rate of 20 ° C./s or more, and 400 to 550 ° C. Hold for 20 seconds or more to complete the isothermal transformation, cool to room temperature, and then perform rough wire drawing with a surface reduction of 40% or less and spheroidizing annealing, and then finish with a surface reduction of 20% or less Drawing is disclosed.
  • the steel wires proposed so far including the steel wires described in Patent Documents 1 and 2, have the effect of improving cold workability such as cold forging.
  • a steel wire that has further improved cold workability particularly a steel wire that reduces deformation resistance during cold work and has excellent crack resistance.
  • the embodiment of the present invention has been made under such circumstances, and the object thereof is a machine structure having low deformation resistance during cold working and excellent crack resistance, and thus excellent cold workability. It is to provide steel wires for parts.
  • the steel wire for machine structure according to the embodiment of the present invention has C: 0.3 mass% to 0.6 mass%, Si: 0.05 mass% to 0.5 mass%, Mn: 0.2 mass% to 1.7% by mass, P: more than 0% by mass, 0.03% by mass or less, S: 0.001% by mass to 0.05% by mass, Al: 0.005% by mass to 0.1% by mass, N: 0% by mass to 0.015% by mass and the balance: iron and inevitable impurities.
  • the metal structure is composed of ferrite and cementite, and the standard deviation ⁇ c of the cementite number included in the area of 5 ⁇ m ⁇ 5 ⁇ m is A steel wire for machine structural parts that satisfies the following formula (1) and has an average particle size of cementite of 0.5 ⁇ m or more. 1.5 ⁇ ⁇ c ⁇ 4.5 (1)
  • the steel wire for machine structural parts according to the embodiment of the present invention includes Cr: more than 0% by mass, 0.5% by mass or less, Cu: more than 0% by mass, 0.25% by mass or less, Ni: One or more selected from the group consisting of more than 0% by mass, 0.25% by mass or less, Mo: more than 0% by mass, 0.25% by mass or less, and B: more than 0% by mass, 0.01% by mass or less Further, the following formula (2) may be satisfied.
  • the steel wire for machine structural parts according to the embodiment of the present invention has low deformation resistance during cold working and excellent crack resistance, and thus has excellent cold workability.
  • FIG. 1 is a graph showing the relationship between the C concentration and the standard deviation of the cementite number in samples with good crack resistance and defective samples.
  • 2A shows test no. 15 is a result of observation of a metal structure by 15 FE-SEM.
  • FIG. It is a metal-structure observation result by 16 FE-SEM.
  • the present inventors have studied from various angles in order to realize a steel wire that has both deformation resistance reduction during cold working and improved crack resistance.
  • FE-SEM Field-Emission Scanning Electron Microscope, Field Emission Scanning Electron Microscope
  • EBSD Electro Back Scatter Diffraction Patterns
  • a "wire” is used for the meaning of a rolled wire, and points out the linear steel material cooled to room temperature after hot rolling.
  • the “steel wire” refers to a linear steel material obtained by subjecting a rolled wire material to a tempering treatment such as spheroidizing annealing.
  • the metal structure of a steel wire for machine structural parts according to an embodiment of the present invention (hereinafter sometimes simply referred to as “steel wire”) is a so-called spheroidized structure, which is more than ferrite and cementite. Composed.
  • the spheroidized structure is a metal structure that contributes to improving cold workability by reducing the deformation resistance of steel.
  • “consisting of ferrite and cementite” may contain a part of pearlite structure (including pseudo pearlite) in the metal structure, and if the adverse effect on cold workability is small, Precipitates such as AlN can be allowed to be less than 3% by area ratio.
  • the standard deviation ⁇ c of the cementite number contained in the unit area (area of 5 ⁇ m ⁇ 5 ⁇ m) needs to satisfy the following (1). 1.5 ⁇ ⁇ c ⁇ 4.5 (1)
  • the standard deviation ⁇ c of the cementite number contained in the unit area satisfies the equation (1), the crack resistance during cold working is improved, and the deformation resistance Increase can be suppressed.
  • the upper limit of the standard deviation ⁇ c of the cementite number contained in the unit area (5 ⁇ m ⁇ 5 ⁇ m area) is 4.5, but the upper limit of the standard deviation ⁇ c is preferably 4.3 or less, 4.0 or less is more preferable.
  • the lower limit of the standard deviation ⁇ c of the cementite number included in the unit area (5 ⁇ m ⁇ 5 ⁇ m area) is 1.5, but the lower limit of the standard deviation ⁇ c is 1.7 or more. It is preferable that it is 1.9 or more.
  • the average particle size of cementite needs to be 0.5 ⁇ m or more. By setting the average particle diameter of cementite to 0.5 ⁇ m or more, deformation resistance during cold working can be reduced.
  • the preferable lower limit of the average particle diameter of cementite is 0.6 ⁇ m, more preferably the lower limit is 0.7 ⁇ m.
  • the upper limit of the average particle diameter of cementite is not specifically limited, For example, it is 2.0 micrometers.
  • a preferable upper limit is 1.8 ⁇ m, and a more preferable upper limit is 1.6 ⁇ m.
  • the standard deviation ⁇ c of the cementite number is obtained by using a scanning electron microscope (SEM) at a position D / 4 with respect to the radius D of the steel wire in the cross section, as will be described in detail in the examples described later. Then, tissue observation photographs of 5 regions (5 fields of view) of 60 ⁇ m ⁇ 45 ⁇ m at a magnification of 2000 times were taken, and mesh lines of 5 ⁇ m were placed in the vertical and horizontal directions on each of the regions, and 108 5 ⁇ m The unit area may be divided into x5 ⁇ m units, the number of cementites contained in each unit area may be measured, and the standard deviation may be calculated using all the measured values of 5 fields ⁇ 108 unit areas.
  • SEM scanning electron microscope
  • the average particle diameter of cementite is determined by using SEM photographs of five visual fields taken to obtain the standard deviation ⁇ c of the cementite number, as will be described in detail in Examples described later.
  • Media Cybernetics, Inc. It may be obtained by an image analysis software such as Image-Pro Plus.
  • the area of all cementite in the photograph is measured, the average value of the areas with respect to the total number of cementites in five fields of view is obtained, and the equivalent circle diameter of the cementite is calculated using the area, and the average particle diameter of the cementite may be obtained.
  • the form of the total cementite is not particularly limited.
  • the shape of the cementite including rod-like cementite having a large ratio, layered cementite that forms a pearlite structure, and the like.
  • the standard of the size of the cementite to be measured is not limited, it is discriminated by the standard deviation ⁇ c of the cementite number contained in the unit area (5 ⁇ m ⁇ 5 ⁇ m area) to be described later and the measurement method of the average particle size of cementite.
  • the size of cementite that can be made is the minimum size. Specifically, a size of 0.1 ⁇ m or more is a measurement target.
  • Chemical composition Embodiment of this invention is intended for the steel wire used for the raw material of a machine structural part, and should just have a normal chemical component composition as a steel wire for machine structural parts, C, Si , Mn, P, S, Al and N are preferably adjusted to an appropriate range. From this point of view, the appropriate ranges of these chemical components and the reasons for their limitations are as follows. In the present specification, “%” used to indicate the chemical component composition means mass%.
  • C 0.3 mass% to 0.6 mass%
  • Si 0.05 mass% to 0.5 mass%
  • Mn 0.2 mass% % To 1.7% by mass
  • P more than 0% by mass, 0.03% by mass or less
  • S 0.001% by mass to 0.05% by mass
  • Chemical composition consisting essentially of Al: 0.005 mass% to 0.1 mass%, N: 0 mass% to 0.015 mass%, and the balance: iron and inevitable impurities (or C: 0.3 mass) % To 0.6% by mass, Si: 0.05% to 0.5% by mass, Mn: 0.2% to 1.7% by mass, P: more than 0% by mass, 0.03% by mass or less
  • Al 0.005% by mass to 0.1% by mass
  • N 0% by mass to 0.015% by mass with the balance being iron and inevitable impurities
  • the chemical composition is Cr: more than 0% by mass, 0.5% by mass or less, Cu: more than 0% by mass, 0.25% by mass.
  • % Ni: More than 0% by mass, 0.25% by mass or less, Mo: More than 0% by mass, 0.25% by mass or less, and B: More than 0% by mass, 0.01% by mass or less
  • a chemical composition that further contains one or more of the above and satisfies the following formula (2) can be given.
  • C 0.3 to 0.6%
  • the C content is preferably 0.32% or more, and more preferably 0.34% or more. However, if C is contained excessively, the strength becomes too high and the cold workability deteriorates, so it is necessary to make it 0.6% or less.
  • the C content is preferably 0.55% or less, more preferably 0.50% or less.
  • Si 0.05 to 0.5% Si is contained as a deoxidizing element and for the purpose of increasing the strength of the final product by solid solution strengthening. In order to effectively exhibit such an effect, the Si content was set to 0.05% or more.
  • the Si content is preferably 0.07% or more, and more preferably 0.10% or more.
  • the Si content is set to 0.5% or less.
  • the Si content is preferably 0.45% or less, more preferably 0.40% or less.
  • Mn 0.2 to 1.7%
  • Mn is an effective element for increasing the strength of the final product through improvement of hardenability.
  • the Mn content is set to 0.2% or more.
  • the Mn content is preferably 0.3% or more, and more preferably 0.4% or more.
  • the Mn content is set to 1.7% or less.
  • the Mn content is preferably 1.5% or less, and more preferably 1.3% or less.
  • P more than 0% and 0.03% or less
  • P is an element inevitably contained in steel, causes segregation of grain boundaries in steel, and causes ductility deterioration. Therefore, the P content is set to 0.03% or less.
  • the P content is preferably 0.02% or less, more preferably 0.017% or less, and particularly preferably 0.01% or less. The smaller the P content, the better. However, there may be a case where approximately 0.001% remains due to restrictions on the manufacturing process.
  • S 0.001 to 0.05%
  • S is an element inevitably contained in the steel and is present as MnS in the steel and deteriorates the ductility. Therefore, S is an element harmful to cold workability. Therefore, the S content is set to 0.05% or less.
  • the S content is preferably 0.04% or less, and more preferably 0.03% or less. However, since S has the effect
  • the S content is preferably 0.002% or more, and more preferably 0.003% or more.
  • Al 0.005 to 0.1%
  • Al is useful as a deoxidizing element and is useful for fixing solute N present in steel as AlN.
  • the Al content is set to 0.005% or more.
  • the Al content is preferably 0.008% or more, and more preferably 0.010% or more.
  • the Al content is determined to be 0.1% or less. Al content becomes like this. Preferably it is 0.090% or less, More preferably, it is 0.080% or less.
  • N 0 to 0.015%
  • N is an element inevitably contained in the steel. If excessively dissolved N is contained in the steel, hardness is increased and ductility is lowered due to strain aging, and cold workability is deteriorated. Therefore, the N content is set to 0.015% or less.
  • the N content is preferably 0.013% or less, and more preferably 0.010% or less.
  • the N content is preferably as low as possible, and is most preferably 0%, but it may remain about 0.001% due to restrictions on the manufacturing process.
  • the basic components of the steel wire according to the embodiment of the present invention are as described above, and the balance is substantially iron.
  • substantially iron can accept trace components (eg, Sb, Zn, etc.) that do not impair the characteristics of the present invention in addition to iron, and inevitable impurities other than P, S, N (eg, O). , H, etc.).
  • the following optional elements may be contained as necessary, and the properties of the steel wire are further improved according to the contained components.
  • P, S, and N are elements inevitably contained (unavoidable impurities), but their composition ranges are separately defined as described above.
  • “inevitable impurities” included as the balance mean elements inevitably included except for elements whose composition range is separately defined.
  • the Cr content is preferably 0.5% or less
  • the Cu, Ni and Mo contents are preferably 0.25% or less
  • the B content is preferably 0.01% or less.
  • a more preferable content of Cr is 0.45% or less, and further preferably 0.40% or less.
  • the more preferable contents of Cu, Ni and Mo are all 0.22% or less, more preferably 0.20% or less.
  • the more preferable content of B is 0.007% or less, and further preferably 0.005% or less.
  • [Cr%], [Cu%], [Ni%], [Mo%], and [B%] indicate the contents of Cr, Cu, Ni, Mo, and B expressed in mass%, respectively.
  • Cr, Cu, Ni, Mo, and B are elements that can be selectively added, and among these elements, the content of the element that is not added in the formula (2) is zero. It becomes.
  • the upper limit defined by the formula (2) (the value on the right side of the formula (2)) is more preferably 0.65% by mass or less, and further preferably 0.50% by mass or less.
  • the steel wire according to the embodiment of the present invention defines the structure form after spheroidizing annealing, and in order to obtain such a structure form, it is necessary to appropriately control the spheroidizing annealing conditions described later. It is.
  • the conditions at the stage of manufacturing the rolled wire are also controlled appropriately, and the cementite is uniformly distributed during the spheroidizing annealing in the structure of the rolled wire. It is preferable to have a structure that can be transformed.
  • the structure before spheroidizing annealing (or the structure after rolling) has pearlite and ferrite as the main phase (consisting of ferrite and cementite), and the bcc-Fe crystal grain size.
  • pearlite and ferrite as the main phase (consisting of ferrite and cementite)
  • the bcc-Fe crystal grain size can be controlled in an appropriate range, and the pro-eutectoid ferrite fraction can be controlled in an appropriate range, and the lamellar spacing of pearlite can be widened.
  • (A) Finishing rolling temperature The finish rolling temperature Tf satisfies the following expression (2A). 800 ° C. ⁇ T f ⁇ 1200 ⁇ 500 ⁇ [C%] (2A) (However, [C%] indicates the C content expressed in mass%.)
  • the bcc (body-centered cubic) (body-centered cubic lattice) -Fe crystal grain mean circle equivalent diameter (hereinafter, sometimes simply referred to as “bcc-Fe mean grain size”) of the rolled wire rod is small, that is, In order to make it difficult for regenerated pearlite to precipitate during spheroidizing annealing, it is preferable to appropriately control the finish rolling temperature.
  • Recycled pearlite makes the distribution of cementite uneven and causes cracking resistance to deteriorate, so it is important that it is not deposited as much as possible.
  • the finish rolling temperature exceeds (1200-500 ⁇ [C%]) ° C.
  • the finish rolling temperature is less than 800 ° C, the bcc-Fe crystal grain size becomes too small and softening becomes difficult.
  • the minimum with more preferable finish rolling temperature is 820 degreeC, More preferably, it is 840 degreeC.
  • a more preferable upper limit of the finish rolling temperature is (1180-500 ⁇ [C%]) ° C., and a more preferable upper limit is (1160-500 ⁇ [C%]) ° C. or less.
  • the first cooling starts from a finish rolling temperature of 800 ° C. or higher and (1200-500 ⁇ [C%]) ° C. or lower to an end temperature in the temperature range of 700 to 750 ° C.
  • the first cooling when the cooling rate is slow, the bcc-Fe crystal grains are coarsened, the bcc-Fe crystal grain size is increased, and regenerated pearlite is precipitated after spheroidizing annealing, resulting in a unit area (area of 5 ⁇ m ⁇ 5 ⁇ m). ) May have a standard deviation of the cementite number exceeding the appropriate range. Therefore, the average cooling rate in the first cooling is preferably set to 11 ° C./second or more.
  • the average cooling rate of the first cooling is more preferably 15 ° C./second or more, and further preferably 20 ° C./second or more.
  • the upper limit of the average cooling rate of the first cooling is not particularly limited, but is preferably 200 ° C./second or less as a realistic range.
  • the cooling rate may be changed as long as the average cooling rate is 11 ° C./second or more. Such a cooling rate of the first cooling can be achieved by appropriately cooling the rolled wire rod on the conveyor.
  • (C) Second cooling The second cooling starts from the end temperature of the first cooling in the temperature range of 700 to 750 ° C. and is performed to the end temperature in the temperature range of 600 to 650 ° C.
  • the second cooling is preferably performed at an average cooling rate of 4 ° C./second or more.
  • a more preferable average cooling rate of the second cooling is 5 ° C./second or more, and a more preferable cooling rate is 6 ° C./second or more.
  • the average cooling rate in the second cooling is preferably 10 ° C./second or less.
  • the average cooling rate of the second cooling is more preferably 9 ° C./second or less, and further preferably 8 ° C./second or less.
  • the cooling rate may be changed as long as the average cooling rate is 4 ° C./second or more and 10 ° C./second or less.
  • Such a cooling rate of the second cooling can be achieved by appropriately cooling the rolled wire rod on the conveyor.
  • the third cooling is performed from the end temperature of the second cooling in the temperature range of 600 to 650 ° C. to 500 ° C.
  • This third cooling it is possible to widen the average lamellar spacing of pearlite, leave more cementite, and leave many spherical cementite nuclei in the grains. For this reason, cementite exists also in a ferrite grain by performing a suitable spheroidizing annealing process later, and the distribution state of cementite can be controlled appropriately.
  • start cooling from a temperature range of 600 to 650 ° C.
  • the average cooling rate of the third cooling is more preferably 2.5 ° C./second or less, and further preferably 2 ° C./second or less. Such a cooling rate of the third cooling can be achieved by installing a cover on the conveyor for suppressing heat radiation from the rolled wire rod.
  • normal cooling such as cooling may be performed to cool to room temperature. Further, the cooling may be continued to a temperature lower than 500 ° C. (for example, 400 ° C.) at the same cooling rate as the third cooling.
  • wire drawing may be performed at room temperature as necessary, and the area reduction rate at that time may be, for example, 30% or less.
  • the carbides in the steel are destroyed (finely crushed), and agglomeration of the carbides can be promoted by the subsequent spheroidizing annealing, which is effective in shortening the soaking time of the spheroidizing annealing.
  • the area reduction rate of the wire drawing process exceeds 30%, the strength after annealing may increase and the cold workability may be deteriorated. Therefore, the area reduction rate of the wire drawing process is preferably 30% or less.
  • the lower limit of the area reduction rate is not particularly limited, but the effect of the wire drawing process can be obtained more reliably by preferably setting it to 2% or more.
  • the rolled wire is heated using an atmospheric furnace, for example, SA1 described later, and held at a holding temperature higher than 730 ° C., such as 740 ° C.
  • a holding temperature eg, 740 ° C
  • it is preferably cooled to 720 ° C. at an average cooling rate of 20 ° C./hour or more, cooled to 640 ° C. at an average cooling rate of 8-12 ° C./hour, and then allowed to cool.
  • the average heating rate from at least 500 ° C. to 730 ° C. is set to 50 ° C./hour or more, thereby suppressing the grain growth of the metal structure.
  • the average heating rate at this time is more preferably 60 ° C./hour or more.
  • the average heating rate is preferably 200 ° C./hour or less, more preferably 150 ° C./hour or less.
  • the average heating rate when heating from room temperature to 500 ° C. is usually 100 ° C./hour or more, but the average heating rate in this temperature range has little influence on the grain growth of the metal structure. Considering productivity, it is preferable that the heating rate at this time is fast, for example, 120 ° C./hour or more, and more preferably 140 ° C./hour or more.
  • the average heating rate at this time is preferably 200 ° C./hour or less, more preferably 150 ° C./hour or less, similarly to the average heating rate from 500 ° C. to 730 ° C.
  • the average cooling rate when heating from room temperature to 500 ° C. may be the same as or different from the average heating rate of at least 500 ° C. to 730 ° C.
  • the average heating rate is controlled from 730 ° C immediately above the A1 point to the holding temperature to 6-10 ° C / hour, the decomposition and solid solution of cementite in the pearlite structure is appropriately suppressed while suppressing the grain growth of the metal structure as much as possible. Can be done.
  • the average heating rate is faster than 10 ° C / hour, it is difficult to secure the time for decomposition and solid solution of cementite in the pearlite structure.
  • the average heating rate is slower than 6 ° C / hour, the holding temperature starts at 730 ° C. The heating time until is prolonged, and cementite is decomposed and dissolved excessively.
  • the average heating rate at this time is more preferably 7 ° C./hour or more and 9 ° C./hour or less.
  • the holding temperature it is preferable to hold at the holding temperature for 1 to 2 hours.
  • the holding temperature is shorter than 1 hour, cementite is not sufficiently decomposed and dissolved in the pearlite structure.
  • cementite is excessively decomposed and dissolved.
  • the holding time at this time is more preferably 1.2 hours or more and 1.8 hours or less.
  • the preferable average cooling rate up to 720 ° C. to 20 ° C./hour or more, the grain growth of the metal structure can be suppressed, and the precipitation of regenerated pearlite during cooling can be suppressed. it can.
  • the average cooling rate at this time is more preferably 30 ° C./hour or more. However, if the average cooling rate is too fast, it becomes difficult to follow the temperature of the rolled wire, and therefore it is preferably 100 ° C./hour or less.
  • the spheroidizing annealing as described above may be repeated a plurality of times. By repeating these steps, the individual particle sizes of cementite are increased, and the distribution state is made uniform to some extent. Test No. in Examples described later. Even when the rolling conditions are outside the range of the above-mentioned preferable conditions, such as 36 to 38 (steel types Q, R, S), by repeating the spheroidizing annealing of the above-described conditions a plurality of times,
  • the metal structure is composed of ferrite and cementite, and the standard deviation of the number of cementites contained in the unit area (5 ⁇ m ⁇ 5 ⁇ m area) and the average particle diameter of the cementite are within the appropriate ranges. As a result, deformation resistance and cracking rate It is possible to obtain a steel wire for machine structural parts that can reduce both of the above.
  • the number of repetitions of spheroidizing annealing is preferably at least 3 times or more, but the standard deviation of the number of cementites contained in the unit area (5 ⁇ m ⁇ 5 ⁇ m area) and the average particle diameter of cementite are not so much even if excessively repeated. Since it does not change, it is preferably 10 times or less.
  • spheroidizing annealing when spheroidizing annealing is repeated a plurality of times, it may be repeated under the same conditions or within different conditions within the range of the above preferable conditions. If it is those skilled in the art who contacted the steel wire for machine structure components which concerns on embodiment of this invention demonstrated above, and its manufacturing method, the machine structure component which concerns on this invention by a manufacturing method different from the manufacturing method mentioned above by trial and error. Steel wire may be obtained.
  • Steel types P, Q, R, S, T, U, V, and W produced rolled wire under conditions that deviated from the above-described preferable rolling conditions.
  • the steel type P has a condition that the average cooling rate in the second cooling is slower than the preferred range.
  • Steel grade Q has a finish rolling temperature higher than the preferred range.
  • Steel grade R is in a condition where the average cooling rate in the first cooling is slower than the preferred range.
  • Steel grade S is in a condition where the average cooling rate in the third cooling is faster than the preferred range.
  • Steel grade T is in a condition where the average cooling rate in the second cooling is faster than the preferred range.
  • steel type U after performing the first cooling to 435 ° C., that is, lower than the preferable range of the end temperature, a holding step of holding at the same temperature of 435 ° C. for 120 seconds is performed, and the mixture is allowed to cool to room temperature. Coarse wire drawing at a rate of 20% was performed.
  • steel type V after performing the first cooling to 500 ° C., that is, lower than the preferable range of the end temperature, a holding step of holding at the same temperature of 500 ° C. for 120 seconds is performed, and the mixture is left to cool to room temperature. Coarse wire drawing at a rate of 20% was performed.
  • Condition SA2 Repeat condition SA1 three times.
  • Condition SA3 When heating from room temperature to 730 ° C., heating from room temperature to 500 ° C. is performed at an average heating rate of 110 ° C./hour, and heating from 500 ° C. to 730 ° C. is performed at an average heating rate of 80 ° C./hour. Thereafter, the sample is heated to 740 ° C. at an average heating rate of 8 ° C./hour, held at 740 ° C. for 2 hours, cooled to 640 ° C. at an average cooling rate of 30 ° C./hour, and then allowed to cool.
  • the annealing conditions SA1 and SA2 are annealing conditions related to the spheroidizing annealing according to the embodiment of the present invention
  • the annealing condition SA3 is an annealing condition according to the embodiment of the present invention having an average cooling rate from 720 ° C to 640 ° C. It is faster than the range.
  • spheroidizing annealing was performed in an atmospheric furnace under annealing conditions SA4 shown below.
  • (D) Condition SA4 Heat from room temperature to 720 ° C. at an average heating rate of 150 ° C./hour, hold at 720 ° C. for 1 hour, and then allow to cool. Then, finish drawing with a surface reduction rate of 10% was performed.
  • the annealing condition SA4 is out of the range of the annealing condition according to the embodiment of the present invention.
  • the minimum equivalent circle diameter of the cementite to be measured was 0.1 ⁇ m.
  • Deformation resistance upper limit target value (MPa) 400 ⁇ Ceq + 420 (3)
  • Ceq [C%] + 0.2 ⁇ [Si%] + 0.2 ⁇ [Mn%]
  • [C%] and [Mn%] are C, Si and Mn, respectively. Content (mass%) is shown.
  • Table 3 shows the upper limit value and lower limit value of the standard deviation ⁇ c of the cementite number determined by the equation (1).
  • Table 3 shows the upper limit value and lower limit value of the standard deviation ⁇ c of the cementite number determined by the equation (1).
  • “OK” is indicated, and at least one of the deformation resistance and the crack resistance occurrence rate is indicated.
  • “NG” was described.
  • FIG. 1 is a graph showing the relationship between the C concentration and the standard deviation of the cementite number in samples with good crack resistance and defective samples obtained from the results shown in Table 3.
  • the lower dotted line corresponds to the lower limit value 1.5 shown on the left side of the formula (1)
  • the upper dotted line shows the upper limit value 4 shown on the right side of the formula (1).
  • all the samples satisfying the formula (1) and having a predetermined chemical composition and having an average particle size of cementite of 0.5 ⁇ m or more have an overall evaluation of OK, and samples not satisfying the formula (1) It turns out that comprehensive evaluation is NG.
  • the sample that does not satisfy either of the chemical composition and the average particle diameter of cementite has a comprehensive evaluation of NG.
  • test no. 15 is a result of observing the metal structure by FE-SEM
  • FIG. It is a metal-structure observation result by 16 FE-SEM.
  • Test No. 15 did not show much layered cementite. In 16, a relatively large amount of layered cementite was observed.
  • Test No. Reference numerals 1 to 3, 5 to 7, 9, 10, 12 to 15, 17 to 20, 22 to 24, and 36 to 38 are examples that satisfy all of the requirements defined in the embodiments of the present invention. It can be seen that both the reduction in the resistance and the improvement in the crack resistance are achieved.
  • test no. Examples 36 to 38 are examples using steel types Q, R, and S that are not manufactured under conditions where rolling is preferable. However, since repetitive spheroidizing annealing was performed under the SA2 annealing conditions, regenerated pearlite with a hard structure was decomposed. ⁇ As a result of the decrease, the distribution of cementite is uniform, and both the deformation resistance and crack generation rate have reached the target values.
  • Test No. 4, 8, 11, 16, 21, 25 to 35 are comparative examples lacking any of the requirements defined in the embodiment of the present invention, and either or both of the deformation resistance and the crack occurrence rate are set to the target values. You can see that it has not reached.
  • test No. Nos. 4, 8, 11, 16, 21, and 25 are subjected to spheroidizing annealing under an annealing condition SA3 where the conditions are not appropriate, and the standard deviation of the number of cementites contained in an area of 5 ⁇ m ⁇ 5 ⁇ m is defined by equation (1). It is larger than the upper limit value, and the crack occurrence rate, or both the deformation resistance and the crack occurrence rate do not reach the target values. A lot of regenerated pearlite was observed in the metal structure of the test in which both did not reach the target value. Therefore, it was considered that the deformation resistance was increased without satisfying the equation (1).
  • Test No. Nos. 26 and 27 use steel type N with excessive Mn content or steel type O with excessive Cr content, and the deformation resistance during cold working remains high.
  • Test No. Nos. 28 to 32 are examples using steel types P, Q, R, S, and T that were rolled under conditions other than the preferred conditions. Even if the subsequent spheroidizing annealing of SA1 was performed, an area of 5 ⁇ m ⁇ 5 ⁇ m was used. The standard deviation of the cementite number contained in is larger than the upper limit defined by the equation (1), and the crack occurrence rate, or both the deformation resistance and the crack occurrence rate have not reached the target values.
  • Test No. Nos. 33 to 35 are examples in which spheroidizing annealing was performed with SA4 in which the annealing conditions were not appropriate, using steel types U, V, and W in which the rolling conditions were not preferable.
  • Fine cementite was uniformly dispersed and 5 ⁇ m ⁇ 5 ⁇ m
  • the standard deviation of the number of cementites contained in the area is smaller than the lower limit defined by the equation (1), and the average particle size of the cementite is also smaller than the defined value.
  • No. Nos. 34 and 35 have a standard deviation of the cementite number contained in an area of 5 ⁇ m ⁇ 5 ⁇ m smaller than the lower limit value and high deformation resistance.
  • the average particle diameter of cementite is smaller than the lower limit, and the deformation resistance is high.
  • Steel wires for machine structural parts are various machine structural parts such as automobile parts and construction machine parts manufactured by cold working such as cold forging, cold forging, and cold rolling. It is suitably used for the material.
  • these mechanical structural parts include bolts, screws, nuts, sockets, ball joints, inner tubes, torsion bars, clutch cases, cages, housings, hubs, covers, cases, washers, tappets, saddles, bulgs, Inner case, clutch, sleeve, outer race, sprocket, core, stator, anvil, spider, rocker arm, body, flange, drum, fitting, connector, pulley, metal fitting, yoke, base, valve lifter, spark plug, pinion gear, steering Examples include mechanical parts such as shafts and common rails, and electrical parts.
  • a steel wire according to an embodiment of the present invention is industrially useful as a steel wire for a high-strength mechanical structural component that is preferably used as a material for the mechanical structural component.
  • Excellent cold workability can be exhibited by low deformation resistance at room temperature and by suppressing cracking of the material.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Heat Treatment Of Steel (AREA)
  • Heat Treatment Of Strip Materials And Filament Materials (AREA)

Abstract

L'invention concerne un fil d'acier pour des éléments structuraux mécaniques, comprenant sensiblement C : 0,3 à 0,6 % en masse, Si : 0,05 à 0,5 % en masse, Mn : 0,2 à 1,7 % en masse, P: plus de 0 % en masse à pas plus de 0,03 % en masse, S : 0,001 à 0,05 % en masse, Al : de 0,005 à 0,1 % en masse, et N : 0-0 015 % en masse, le reste étant du fer et des impuretés inévitables. La structure métallique est composée de ferrite et cémentite; l'écart type σc de la quantité de cémentite contenue dans une zone 5 × 5 μm satisfait l'expression (1) ci-dessous; et la taille moyenne de particule de la cémentite étant de 0.5 μm ou plus. 1,5 ≤ σc ≤ 4,5 (1), où [C %] indique la teneur en carbone exprimée en % en masse.
PCT/JP2016/085371 2015-12-07 2016-11-29 Fil d'acier pour éléments structuraux mécaniques Ceased WO2017098964A1 (fr)

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TWI637066B (zh) * 2017-12-05 2018-10-01 日商新日鐵住金股份有限公司 覆鋁鋼線及其製造方法
KR102085077B1 (ko) * 2017-12-26 2020-03-05 주식회사 포스코 중탄소강 선재, 이를 이용한 가공품, 이들의 제조방법
KR102224892B1 (ko) * 2019-06-24 2021-03-05 현대제철 주식회사 신선 가공성이 우수한 경강 선재 제조방법 및 이에 의해 제조된 경강 선재
FR3130848B1 (fr) * 2021-12-17 2023-12-15 Michelin & Cie Fil d’acier à fort taux de matériau recyclé pour le renforcement d’articles de caoutchouc

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH0426716A (ja) * 1990-05-23 1992-01-29 Nippon Steel Corp 棒鋼線材の短時間球状化焼鈍方法
JP2001011575A (ja) * 1999-06-30 2001-01-16 Nippon Steel Corp 冷間加工性に優れた機械構造用棒鋼・鋼線及びその製造方法
WO2013183648A1 (fr) * 2012-06-08 2013-12-12 新日鐵住金株式会社 Acier pour tige ou barre à fils d'acier
WO2016158428A1 (fr) * 2015-03-31 2016-10-06 株式会社神戸製鋼所 Fil d'acier pour pièces de construction mécanique
WO2016190396A1 (fr) * 2015-05-26 2016-12-01 新日鐵住金株式会社 Tôle d'acier et son procédé de production

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JP5486634B2 (ja) * 2012-04-24 2014-05-07 株式会社神戸製鋼所 冷間加工用機械構造用鋼及びその製造方法

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH0426716A (ja) * 1990-05-23 1992-01-29 Nippon Steel Corp 棒鋼線材の短時間球状化焼鈍方法
JP2001011575A (ja) * 1999-06-30 2001-01-16 Nippon Steel Corp 冷間加工性に優れた機械構造用棒鋼・鋼線及びその製造方法
WO2013183648A1 (fr) * 2012-06-08 2013-12-12 新日鐵住金株式会社 Acier pour tige ou barre à fils d'acier
WO2016158428A1 (fr) * 2015-03-31 2016-10-06 株式会社神戸製鋼所 Fil d'acier pour pièces de construction mécanique
WO2016190396A1 (fr) * 2015-05-26 2016-12-01 新日鐵住金株式会社 Tôle d'acier et son procédé de production

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