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WO2024204819A1 - Fil machine, fil d'acier et composant de machine - Google Patents

Fil machine, fil d'acier et composant de machine Download PDF

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Publication number
WO2024204819A1
WO2024204819A1 PCT/JP2024/013327 JP2024013327W WO2024204819A1 WO 2024204819 A1 WO2024204819 A1 WO 2024204819A1 JP 2024013327 W JP2024013327 W JP 2024013327W WO 2024204819 A1 WO2024204819 A1 WO 2024204819A1
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Prior art keywords
less
wire
tensile strength
content
ratio
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PCT/JP2024/013327
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English (en)
Japanese (ja)
Inventor
真 小此木
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日本製鉄株式会社
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Publication of WO2024204819A1 publication Critical patent/WO2024204819A1/fr

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Classifications

    • 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

Definitions

  • This disclosure relates to wire rods, steel wires, and machine parts.
  • Patent Document 1 JP-A-2-166229
  • Patent Document 2 WO 2016/121820
  • Patent Document 3 WO 2017/122830
  • Patent Document 4 WO 2018/008698
  • Patent Document 5 JP-A-2021-183710
  • Patent Document 6 JP-A-3-6325
  • Non-tempered bolts are made by forming steel wire whose strength has been increased by wire drawing. As the strength of the steel wire increases, damage and wear to the mold during forming, or the product is more likely to crack during processing, making it difficult to apply this to high-strength bolts.
  • conventional non-tempered bolts have a high dislocation density, which means that the bolt's 0.2% yield strength is low, resulting in a problem of large permanent elongation of the bolt. To improve this, it is necessary to add a bluing process in which the bolt is held at 300 to 400°C after being formed into a mechanical part such as a bolt.
  • a mechanical part including a shaft portion In mass percent, C: 0.08-0.80%, Si: 0.03 to 1.50%, Mn: 0.50-2.00%, P: 0.050% or less, S: 0.050% or less, Al: 0.005-0.080%, N: 0.0010-0.0150%, O: 0.003% or less, Ti: 0 to 0.050%, B: 0 to 0.0050%, Cr: 0-1.50%, Mo: 0 to 0.50%, Nb: 0 to 0.050%, V: 0 to 0.20%, Cu: 0 to 0.50%, Ni: 0 to 0.70%, Sn: 0 to 0.30%, Sb: 0 to 0.005% and Ca: 0 to 0.0050%, and the balance being Fe and impurity elements, When the diameter of the shaft portion is dm, a metal structure at a 1/4 dm portion having a depth of 1/4 dm from a surface of the shaft portion in a cross section perpendicular to a longitudinal direction of the
  • a wire rod and steel wire for obtaining mechanical parts that have excellent strength and formability, and that have high 0.2% yield strength and reduced permanent elongation even when the bluing process after molding into the mechanical parts is omitted, as well as mechanical parts.
  • FIG. 2 is a diagram showing an example of an SEM photograph mainly of a bainite structure.
  • FIG. 13 is a diagram showing another example of an SEM photograph mainly of a bainite structure.
  • a numerical range expressed using “to” means a range that includes the numerical values before and after “to” as the lower and upper limits. However, when the numerical values before and after “to” are followed by “more than” or “less than,” the numerical range does not include these numerical values as the lower or upper limit.
  • the content of an element in a chemical composition may be expressed by adding “amount” to the element symbol (for example, C amount, Si amount, etc.). With regard to the contents of elements in chemical compositions, “%” means “mass %”. When the content of an element in a chemical composition is described as “0-”, this means that the element does not necessarily need to be contained.
  • process includes not only an independent process but also a process that cannot be clearly distinguished from other processes as long as the intended purpose of the process is achieved.
  • surface of a wire means the “outer peripheral surface.”
  • central axis of a wire means an imaginary line that passes through the center point of a cross section perpendicular to the longitudinal direction of the wire and extends in the longitudinal direction (axial direction).
  • “1/4D” is synonymous with "D/4".
  • the inventors of the present disclosure have studied the effects of the structure and mechanical properties of the wire on the properties of steel wire and machine parts after wire drawing, and have found that by setting the composition of the wire within a specific range, making the structure of the wire mainly bainite with the area ratios of ferrite, pearlite, and martensite suppressed, setting the ratio of the tensile strength and 0.05% yield strength of the wire, i.e., 0.05% yield strength/tensile strength (hereinafter referred to as the "0.05% yield strength ratio of the wire") within a specific range, and reducing the standard deviation of the hardness of the wire, it is possible to obtain a steel wire with excellent strength and formability after wire drawing, and a high 0.2% yield strength ratio (0.2% yield strength/tensile strength) and suppression of permanent elongation of the bolt after processing into a non-tempered bolt.
  • the ratio of the tensile strength and 0.05% yield strength of the wire i.e., 0.05% yield strength/tensile strength
  • Non-tempered bolts have a high dislocation density because their strength is imparted by wire drawing. If there are many mobile dislocations, they will undergo plastic deformation with small strains, lowering the elastic limit and, as a result, reducing the yield strength. In order to increase the yield strength of steel with high dislocation density, it is effective to fix the solute carbon and nitrogen contained in the steel to the dislocations and suppress their movement.
  • Non-tempered bolts use a heat treatment called bluing, in which the bolt is held at 300 to 400°C to fix carbon to the dislocations, suppressing their movement and increasing the bolt's 0.2% yield strength.
  • the inventors of the present disclosure have found that by making the structure of the wire rod mainly bainite and setting the 0.05% proof stress ratio of the wire rod within a specific range, the 0.2% proof stress ratio of the non-tempered bolt is increased even without bluing.
  • Wire rods with normal bainite structure have a high mobile dislocation density and therefore a low elastic limit. When solute carbon is fixed to mobile dislocations, the movement of dislocations is suppressed and the elastic limit is increased.
  • the martensite fraction of the wire is high, it may break during drawing, or cracks may occur during forming, and the 0.2% yield strength ratio of the bolt may decrease. Even if the wire has a bainite-based structure, if the 0.05% yield strength ratio of the wire is low, the 0.2% yield strength ratio of the bolt may decrease. The reason for this is that in order to increase the 0.2% yield strength ratio of the bolt, a sufficient amount of solute carbon is required to fix mobile dislocations after drawing, but when the 0.05% yield strength ratio of the wire is low, the 0.2% yield strength ratio of the bolt decreases due to a lack of solute carbon.
  • a bainite-based structure reduces work hardening, which is suppressed in high-strain processing such as bolt head processing, reducing the load on the die. Furthermore, the cementite in the bainite structure is fragmented and has high ductility, so work cracks can be suppressed.
  • the chemical composition of the wire according to the present disclosure is, as essential elements, in mass %, C: 0.08-0.80%, Si: 0.03 to 1.50%, Mn: 0.50-2.00%, P: 0.050% or less, S: 0.050% or less, Al: 0.005 to 0.080%, and N: 0.0010 to 0.0150%, O: Contains 0.003% or less, with the balance being Fe and impurity elements.
  • the wire according to the present disclosure may contain other optional elements as necessary.
  • C 0.08-0.80% C is contained to ensure the strength required for mechanical parts. If the C content is less than 0.08%, it is difficult to ensure the necessary strength for mechanical parts. If the C content exceeds 0.08%, the ductility, toughness, and cold forgeability are deteriorated. Therefore, the C content is set to 0.08 to 0.80%.
  • the lower limit of the C content is 0.08%, preferably 0.15%
  • the upper limit of the C content is 0.80%, preferably 0.75%, and more preferably 0.70%.
  • the C content is preferably 0.15 to 0.75%, and more preferably 0.20 to 0.70%.
  • Si 0.03 ⁇ 1.50% Silicon functions as a deoxidizing element and is an effective element for imparting the necessary strength to mechanical parts. If the amount of silicon is less than 0.03%, these effects are insufficient. If it exceeds 50%, the ductility and toughness of the machine parts will deteriorate, and the deformation resistance of the steel wire will increase, deteriorating the cold forgeability. Therefore, the Si content is set to 0.03 to 1.50%. The Si content is preferably 0.05 to 1.00%, and more preferably 0.10 to 0.60%.
  • Mn 0.50-2.00%
  • Mn is an element necessary for imparting the necessary strength to mechanical parts. If the Mn content is less than 0.50%, the effect is insufficient. If the Mn content exceeds 2.00%, the mechanical parts The toughness is deteriorated, and the deformation resistance of the steel wire is increased, deteriorating the cold forgeability. Therefore, the Mn content is set to 0.50 to 2.00%.
  • the preferable Mn content is 0.70 to 1. 50%, and more preferably 0.90 to 1.20%.
  • P 0.050% or less P is contained in the wire rod as an impurity. P segregates at the grain boundaries of mechanical parts and deteriorates toughness, so it is desirable to reduce the P content. For this reason, the upper limit of the P content is set to 0.050%. A preferable upper limit of the P content is 0.020%, and a more preferable upper limit is 0.015% or less. The lower limit of the P content is preferably 0% (i.e., no P is contained), but from the viewpoint of reducing the dephosphorization cost, it may be more than 0% (or 0.0001% or more).
  • S 0.050% or less S is contained in the wire rod as sulfides such as MnS. If the S content exceeds 0.050%, the cold heading property of the steel wire is deteriorated and the toughness of the mechanical parts is deteriorated. Therefore, the upper limit of the S content is set to 0.050%. A preferable upper limit of the S content is 0.030%. A more preferable upper limit is 0.015%. Note that the lower limit of the S content may be more than 0% (or 0.001% or more) from the viewpoint of reducing the desulfurization cost.
  • Al 0.005-0.080%
  • Al functions as a deoxidizing element, and also has the effect of forming AlN to refine crystal grains and improve the toughness of machine parts. It also fixes solute N to suppress dynamic strain aging, It has the effect of reducing deformation resistance. If the Al content is less than 0.005%, these effects are insufficient. If the Al content exceeds 0.080%, the effects are saturated and manufacturability may decrease. Therefore, the Al content is set to 0.005 to 0.080%, preferably 0.010 to 0.065%, and more preferably 0.020 to 0.055%.
  • N 0.0010-0.0150% N forms nitrides with Al, Ti, Nb, V, etc., refines crystal grains, and has the effect of improving the toughness of machine parts. If the N content is less than 0.0010%, the amount of nitrides precipitated is If the N content exceeds 0.0150%, the deformation resistance of the steel wire increases due to dynamic strain aging caused by the solute N, and the workability deteriorates.
  • the N content is preferably 0.0020 to 0.0100%, and more preferably 0.0025 to 0.0060%.
  • O 0.003% or less O is an impurity and is inevitably contained in steel. If the O content exceeds 0.003%, coarse oxides are formed, which may reduce fatigue strength, so the O content is limited to 0.003% or less. The preferred upper limit of the O content is 0.002%.
  • the balance Fe and impurity elements
  • the balance is Fe and impurity elements (which may be referred to as "impurities" as appropriate in the present disclosure).
  • impurities refers to components contained in raw materials or components mixed in during the manufacturing process and not intentionally added.
  • impurities also include components that are intentionally added but are contained in an amount that does not affect the performance of the steel wire obtained by drawing the wire rod according to the present disclosure.
  • the wire rod according to the present disclosure may contain, in mass %, one or more elements selected from the group consisting of the following groups A to D, in place of a portion of the Fe. Note that the elements in the following groups A to D are optional elements, and these elements may not be included, i.e., may be 0%.
  • Group A One or two selected from the group consisting of Ti: 0.050% or less and B: 0.0050% or less
  • Ti 0.050% or less Ti functions as a deoxidizing element and is effective in facilitating the formation of bainite. If the Ti content exceeds 0.050%, these effects become saturated and coarse oxides or nitrides are formed, which may deteriorate the fatigue strength of the mechanical parts. Therefore, if Ti is contained, the Ti content should be 0.002 to 0.050%. The preferred Ti content is 0.003 to 0.050%, and more preferably 0.007 to 0.040%.
  • B 0.0050% or less B has the effect of facilitating the formation of bainite. If the B content exceeds 0.0050%, carbides are formed at grain boundaries, which may deteriorate wiredrawability. Therefore, when B is contained, the B content should be 0.0002 to 0.0050%.
  • the preferred B content is 0.0003 to 0.0050%, and more preferably 0.0008 to 0.0030%.
  • Cr 1.50% or less Cr is an element necessary for imparting the necessary strength to mechanical parts. If the Cr content exceeds 1.50%, the martensite fraction of the wire increases, deteriorating wiredrawability, and the deformation resistance of the steel wire increases, deteriorating cold forgeability. Therefore, the Cr content is set to 1.50% or less.
  • the preferred Cr content is 0.02 to 0.80%, and more preferably 0.10 to 0.50%.
  • Mo 0.50% or less Mo has the effect of imparting the necessary strength to mechanical parts. If the Mo content exceeds 0.50%, the alloy cost increases, and the deformation resistance of the steel wire increases, deteriorating the cold forgeability. Therefore, when Mo is contained, the Mo content is preferably 0.02 to 0.50%. The preferred Mo content is 0.03 to 0.35%, and more preferably 0.05 to 0.25%. The Mo content may be 0.15% or less.
  • Nb 0.050% or less Nb has the effect of increasing the strength of machine parts by precipitating carbides and nitrides, the effect of improving toughness by refining crystal grains, the effect of reducing solute N and reducing deformation resistance, etc. If the Nb content exceeds 0.050%, the effect is saturated and the cold forgeability may deteriorate. Therefore, when Nb is contained, the Nb content is preferably 0.002 to 0.050%. The preferred Nb content is 0.001 to 0.040%. The more preferred Nb content is 0.005 to 0.030%.
  • V 0.20% or less V has the effect of precipitating carbides and nitrides to increase the strength of mechanical parts. If the V content exceeds 0.20%, the alloy cost increases. Therefore, if V is contained, the V content should be 0.02 to 0.20%. The preferred V content range is 0.01 to 0.15%.
  • Cu 0.50% or less Cu precipitates finely to impart the necessary strength to mechanical parts and improve corrosion resistance. If the Cu content exceeds 0.50%, hot ductility deteriorates and surface defects are likely to occur. Therefore, if Cu is contained, the Cu content should be 0.02 to 0.50%. The preferred Cu content is 0.02 to 0.30%.
  • Ni 0.70% or less Ni has the effect of improving corrosion resistance. If the Ni content exceeds 0.70%, the alloy cost increases. Therefore, if Ni is contained, the Ni content is preferably 0.02 to 0.70%. The Ni content is preferably 0.02 to 0.50%, and more preferably 0.05 to 0.30%.
  • Sn 0.30% or less Sn has the effect of improving corrosion resistance.
  • the Sn content is preferably 0.002% or more.
  • the Sn content is limited to 0.30% or less.
  • the preferred upper limit of the Sn content is 0.20%.
  • Sb 0.005% or less Sb has the effect of improving corrosion resistance.
  • the Sb content is preferably 0.001% or more. However, if the Sb content exceeds 0.005%, the ductility decreases and the cold workability deteriorates, so the Sb content is limited to 0.005% or less.
  • the preferred upper limit of the Sb content is 0.004%, and the more preferred upper limit is 0.003%.
  • Ca 0.0050% or less Ca is contained as a deoxidizing element. Ca has the effect of making oxides fine and improving fatigue strength. If the Ca content exceeds 0.0050%, ductility decreases and cold workability deteriorates, so it is limited to 0.0050% or less.
  • the preferred upper limit of the Ca content is 0.0040%, and the more preferred upper limit is 0.0030%.
  • the area ratio of bainite at a depth of 1/4D from the surface (outer peripheral surface) of the wire rod in a cross section (C cross section) perpendicular to the longitudinal direction of the wire rod is 70% or more. If the bainite area ratio is less than 70%, the 0.2% proof stress ratio of the mechanical component decreases and the workability deteriorates.
  • the bainite area ratio is preferably 80% or more, and more preferably 90% or more.
  • the microstructure observation was performed by taking two samples from positions 50 mm apart in the axial direction of the wire, mirror-polishing a cross section (C cross section) perpendicular to the central axis of each wire sample, etching it with picral, and observing the 1 ⁇ 4 D portion.
  • the C-section of the wire to be measured is mirror-polished and then etched with picral (a solution of 5% picric acid and 95% ethanol) to reveal the structure.
  • the metal structure may contain bainite, pearlite, martensite, and ferrite. Of these, martensite and ferrite do not contain carbides within the grains.
  • the pearlite structure is a structure in which cementite and ferrite are arranged alternately and almost parallel to one another. Therefore, structures other than bainite (structures that do not contain carbides within the grains, pearlite structures) in the photographed structure are visually marked, and the area of the regions of structures other than bainite is determined by image analysis (software name: Nireco's small general-purpose image processing analysis system LUZEX_AP). Note that this operation is performed by measuring and calculating two samples, averaging these values, and subtracting the area percentage of structures other than bainite from the total area (100%) to determine the area percentage of bainite in this disclosure.
  • the tensile test of the wire rod is carried out using JIS Z2241:2011 No. 14A test piece and following the test method of JIS Z2241:2011 to measure the tensile strength (TS), 0.05% yield strength, and reduction in area.
  • the 0.05% yield strength is the stress at which the plastic elongation becomes 0.05% of the extensometer gauge length according to the offset method defined in JIS Z2241:2011.
  • the tensile test piece is machined and taken from the wire rod immediately after straightening. The tensile test is carried out on three samples and the average value is used.
  • the wire rod according to the present disclosure has a value obtained by dividing the standard deviation of the Vickers hardness in a cross section (C cross section) perpendicular to the length direction of the wire rod by the average value of the Vickers hardness of 0.150 or less.
  • This value is 0.150 or less, the 0.2% proof stress ratio of a mechanical part manufactured from the steel wire through wire drawing is high.
  • the workability when forming into a mechanical part is improved.
  • the value is preferably 0.100 or less, more preferably 0.050 or less.
  • the hardness test was carried out by mirror-polishing the C-section of the wire and using a Vickers hardness tester to measure a total of nine points: four points at a depth of 1.0 mm from the surface of the wire, rotated at 90° intervals around the wire, four points at a depth of D/4 (where D is the diameter of the wire), rotated at 90° intervals around the wire, and one point at the center, and then calculating the average value and standard deviation.
  • the measured values are x1 , x2 , ..., xn
  • the average value Xave and standard deviation s were calculated from the following formula.
  • the wire diameter D of the wire according to the present disclosure is not particularly limited, but is preferably 3.0 to 25.0 mm, and more preferably 5.0 to 18.0 mm.
  • a steel slab made of predetermined components that satisfy the above-mentioned chemical composition is heated to 1100 to 1250°C and held in the furnace for 90 minutes or more. Thereafter, the slab is hot-rolled at an entry temperature of 750 to 800°C for finish rolling, and then coiled into a ring shape at 780 to 820°C. After coiling, the wire is primarily cooled to 750° C. at an average cooling rate of 2 to 15° C./s. Thereafter, secondary cooling is performed from 750° C. to 500° C. at an average cooling rate of 25° C./s or more. Next, the tertiary cooling is performed from 500° C.
  • the wire is then held at 420-440°C for 30-100 seconds (primary holding), heated from 490°C to 550°C at an average heating rate of 10°C/s or more, held at 580-620°C for 60-200 seconds (secondary holding), and then water-cooled to obtain the wire.
  • the heating temperature is less than 1100°C or the heating time is less than 90 minutes, the carbide is insufficiently dissolved, and the 0.05% yield strength ratio of the wire rod decreases. If the heating temperature exceeds 1250°C, the surface hardness of the wire rod decreases due to decarburization. If the entry temperature of the finish rolling exceeds 800° C., the gamma grains (austenite grains) become coarse, the ductility of the wire rod decreases, and the workability deteriorates. If the entry temperature is less than 750° C., the gamma grain size becomes non-uniform, and the standard deviation of the hardness of the wire rod increases.
  • the coiling temperature exceeds 820° C., the gamma grains become coarse, the ductility of the wire rod decreases, and the workability deteriorates. If the coiling temperature is less than 780° C., the area ratio of bainite decreases, and the 0.05% proof stress ratio of the wire rod decreases. If the primary average cooling rate to 750°C after coiling is less than 2°C/s, the gamma grains become coarse, the ductility of the wire rod decreases, and the workability deteriorates. If it exceeds 15°C/s, the recovery and recrystallization of the gamma grains are delayed, resulting in mixed grains.
  • the gamma grain size becomes non-uniform, the standard deviation of the hardness of the wire rod increases, and the 0.2% proof stress ratio and permanent elongation of the mechanical parts deteriorate.
  • the secondary average cooling rate from 750° C. to 500° C. is less than 25° C./s, the area ratio of ferrite and pearlite increases, and the 0.05% yield strength ratio of the wire rod decreases.
  • the tertiary average cooling rate from 500°C to 450°C exceeds 20°C/s, the standard deviation of the hardness of the wire becomes large, and the formability of the bolt after drawing deteriorates, as well as the 0.2% yield strength ratio and permanent elongation of the bolt deteriorate.
  • the hardness of the wire will vary widely, and the 0.2% yield strength ratio and permanent elongation of the mechanical parts will deteriorate. If the first holding time exceeds 100 seconds, the 0.05% yield strength ratio of the wire will decrease. If the average heating rate from 490°C to 550°C is less than 10°C/s, the 0.05% yield strength ratio of the wire rod will be low, and the 0.2% yield strength ratio and permanent elongation of the mechanical parts will be deteriorated. If the secondary holding temperature is less than 580°C, the 0.2% yield strength ratio and permanent elongation of the mechanical parts will be deteriorated, and if it exceeds 620°C, the strength will be reduced. If the secondary holding time is less than 60 seconds, the 0.05% yield strength ratio of the wire rod will be reduced. If the secondary holding time exceeds 200 seconds, the carbides will coarsen, and the reduction in area of the steel wire after drawing will be reduced.
  • the wire rod according to the present disclosure is drawn with an area reduction rate of 15 to 50% to produce steel wire, which is then cold heading and rolling processed into the shape of a mechanical part such as a bolt. If the area reduction rate of the wire drawing is less than 15%, the yield strength ratio of the mechanical part decreases and the permanent elongation increases. If the area reduction rate of the wire drawing is 50% or more, the workability of the mechanical part deteriorates. After the wire drawing, zinc plating and baking treatment are performed as necessary.
  • the steel wire manufactured using the wire rod of the present disclosure has high strength and drawing ability, and is excellent in strength and formability of the bolt.
  • a non-tempered bolt manufactured using such a steel wire has a high bolt 0.2% yield strength ratio and excellent permanent elongation even if the bluing treatment after forming is omitted.
  • the steel wire and the machine component according to the present disclosure will be described below. Note that the chemical composition of the steel wire and the machine component according to the present disclosure is the same as that of the wire rod described above, and therefore will not be described below.
  • the metal structure at a 1/4d portion which is 1/4d deep from the surface of the steel wire in a cross section perpendicular to the longitudinal direction of the steel wire, contains bainite with an area ratio of 70% or more. If the bainite area ratio is less than 70%, the 0.2% proof stress ratio of the mechanical component decreases and the workability deteriorates.
  • the bainite area ratio is preferably 80% or more, and more preferably 90% or more.
  • the metal structure of the steel wire can be measured in the same manner as the metal structure of the wire rod described above.
  • the tensile strength is 640 + 900 x (C%) MPa or more
  • the reduction in area is 66 - 32 x (C%)% or more
  • the tensile strength (MPa) x reduction in area (%) is 53,000 or more
  • the 0.2% yield strength ratio is 0.990 - 0.083 x (C%) or more.
  • the tensile strength, 0.2% yield strength ratio, and reduction in area of the steel wire disclosed herein can be measured in the same manner as in the tensile test of the wire rod described above, using a JIS Z2241:2011 No. 14A test piece and following the test method of JIS Z2241:2011.
  • the standard deviation of the Vickers hardness in a cross section (C cross section) perpendicular to the longitudinal direction of the steel wire is divided by the average Vickers hardness of 0.150 or less. If this value is 0.150 or less, the workability when forming into a mechanical part is improved, and the 0.2% proof stress ratio of the mechanical part is increased.
  • the value is preferably 0.100 or less, and more preferably 0.050 or less.
  • the hardness test of the steel wire can be carried out in the same manner as the hardness test of the wire rod described above, and the average value and standard deviation can be calculated in the same manner.
  • the wire diameter d of the steel wire according to the present disclosure is not particularly limited, but may be, for example, 2.0 to 23.0 mm, or 4.0 to 18.0 mm.
  • the mechanical part according to the present disclosure is obtained by performing cold heading and rolling on the above-mentioned steel wire and processing it into the shape of a mechanical part such as a bolt.
  • the mechanical part according to the present disclosure includes a shaft portion, and the shaft portion has the following metal structure and mechanical properties.
  • the metal structure at a 1/4 dm portion which is 1/4 dm deep from the surface of the shaft portion in a cross section (C cross section) perpendicular to the longitudinal direction of the shaft portion, contains bainite with an area ratio of 70% or more. If the bainite area ratio is less than 70%, the 0.2% proof stress ratio of the mechanical component decreases and workability deteriorates.
  • the bainite area ratio is preferably 80% or more, and more preferably 90% or more.
  • the metal structure of the shaft portion can be measured in the same manner as the metal structure of the wire rod described above.
  • the mechanical component according to the present disclosure has a ratio of 0.2% yield strength to the tensile strength of the shaft portion (0.2% yield strength/tensile strength) of 0.90 or more.
  • the mechanical component according to the present disclosure can obtain a high 0.2% yield strength ratio of 0.90 or more even without bluing treatment.
  • the 0.2% yield strength/tensile strength is preferably 0.92 or more.
  • the tensile test can be performed using a linear test piece with the shaft cut off, in the same manner as the tensile test of wire material described above, using a JIS Z2241:2011 No. 14A test piece, in accordance with the test method of JIS Z2241:2011.
  • the standard deviation of the Vickers hardness in a cross section (C cross section) perpendicular to the longitudinal direction of the shaft portion is divided by the average value of the Vickers hardness to be 0.150 or less.
  • the 0.2% proof stress ratio of the mechanical component manufactured from the steel wire through wire drawing is high.
  • the processability when forming into the mechanical component is improved. It is preferably 0.100 or less, more preferably 0.050 or less.
  • the hardness test of the shaft portion can be carried out in the same manner as the hardness test of the wire rod described above, and the average value and standard deviation can be calculated in the same manner.
  • the diameter dm of the shaft portion of the mechanical component according to the present disclosure is not particularly limited, but may be, for example, 2.0 to 23.0 mm, or 4.0 to 18.0 mm.
  • the mechanical component according to the present disclosure has a high 0.2% yield strength and is suppressed from permanent elongation.
  • the shaft of the machine part is machined or rolled to form a coarse thread shape.
  • the machine part is fitted with an adapter as described in JIS B1051:2014 so that the length of the play thread is equal to the outer diameter of the thread.
  • the tensile stress is 440 MPa, when the tensile strength is 700 MPa or more and less than 800 MPa, the tensile stress is 515 MPa, when the tensile strength is 800 MPa or more and less than 900 MPa, the tensile stress is 650 MPa, when the tensile strength is 1000 MPa or more and less than 1100 MPa, the tensile stress is 830 MPa, when the tensile strength is 1100 MPa or more and less than 1200 MPa, the tensile stress is 910 MPa, when the tensile strength is 1200 MPa or more and less than 1300 MPa, the tensile stress is 970 MPa, and when the tensile strength is 1300 MPa or more and less than 1400 MPa, the tensile stress is 1050 MPa.
  • the difference (L1-L0) between the total length L1 of the mechanical part after unloading and the total length L0 of the mechanical part before the test is defined as the permanent elongation.
  • the total length L1 of the mechanical part after unloading and the total length L0 of the mechanical part before the test were measured using a micrometer.
  • wire material according to this disclosure will be described in more detail with reference to examples. However, these examples do not limit the wire material according to this disclosure.
  • the obtained wire was used for structural observation, tensile testing, and hardness measurement using the methods described above.
  • Table 3 shows the structure and mechanical properties of the wire for each test number.
  • F in the remaining structure stands for ferrite, P for pearlite, and M for martensite.
  • Test numbers 1 and 13 had threads of M5 and shank lengths of 100 mm
  • test numbers 10 and 17 had threads of M6 and shank lengths of 100 mm
  • test numbers 2 to 9, 11, 12, 14 to 16, 18 to 20, and 22 to 25 had threads of M8 and shank lengths of 100 mm.
  • Test number 21 cracked during bolt processing and could not be processed into a bolt shape. From the shaft of the obtained bolt, a JIS Z2241:2011 No.
  • 14A test piece was obtained by machining, and was measured according to the test method of JIS Z2241:2011.
  • the diameter of the parallel part of the tensile test piece was 4 mm for the bolt with thread part M5, 5 mm for the bolt with thread part M6, and 7 mm for the bolt with thread part M8.
  • the tensile test piece was taken, and the structure observation, hardness measurement, and tensile test were performed by the above-mentioned method, and the tensile strength (TS) and 0.2% proof strength were measured.
  • the 0.2% proof strength ratio of the bolt was obtained by dividing the 0.2% proof strength by the tensile strength.
  • the obtained bolt was also used to measure the permanent elongation by the above-mentioned method.
  • Table 5 shows the TS of each bolt, the 0.2% proof strength ratio of the bolt, and the permanent elongation. It was judged as good when TS was 580 + 900 ⁇ (C%) MPa or more, 0.2% proof stress ratio (bolt proof stress ratio) was 0.90 or more, the value obtained by dividing the standard deviation of Vickers hardness by the average value of Vickers hardness was 0.150 or less, and permanent elongation was 1 ⁇ m or less.
  • a metal structure at a 1/4D portion having a depth of 1/4D from the surface of the wire in a cross section perpendicular to the longitudinal direction of the wire contains bainite at an area ratio of 70% or more,
  • the ratio of 0.05% proof stress to tensile strength (0.05% proof stress/tensile strength) is 0.72-0.40 ⁇ (C%) or more;
  • ⁇ 4> The wire according to ⁇ 2> or ⁇ 3>, having a chemical composition including, by mass%, the group B.
  • ⁇ 5> The wire according to any one of ⁇ 2> to ⁇ 4>, having a chemical composition including, by mass%, the group C.
  • ⁇ 6> The wire according to any one of ⁇ 2> to ⁇ 5>, having a chemical composition including, by mass%, the D group.
  • the chemical composition is, in mass%, C: 0.08-0.80%, Si: 0.03 to 1.50%, Mn: 0.50-2.00%, P: 0.050% or less, S: 0.050% or less, Al: 0.005-0.080%, N: 0.0010-0.0150%, O: 0.003% or less, with the balance being Fe and impurity elements;
  • a metal structure at a 1/4d part having a depth of 1/4d from the surface of the steel wire in a cross section perpendicular to the longitudinal direction of the steel wire contains bainite in an area ratio of 70% or more
  • the C content in mass% is (C%)
  • the tensile strength is 610+900 ⁇ (C%) MPa or more
  • the reduction in area is 62 ⁇ 32 ⁇ (C%)% or more
  • the tensile strength (MPa) ⁇ reduction in area (%) is 52,000 or more
  • the ratio of 0.2% proof stress to tensile strength (0.2% proof stress/tensile strength) is
  • a metal structure at a 1/4d part having a depth of 1/4d from the surface of the steel wire in a cross section perpendicular to the longitudinal direction of the steel wire contains bainite in an area ratio of 70% or more
  • the C content in mass% is (C%)
  • the tensile strength is 610+900 ⁇ (C%) MPa or more
  • the reduction in area is 62 ⁇ 32 ⁇ (C%)% or more
  • the tensile strength (MPa) ⁇ reduction in area (%) is 52,000 or more
  • the ratio of 0.2% proof stress to tensile strength (0.2% proof stress/tensile strength) is 0.985 ⁇ 0.083 ⁇ (C%) or more
  • a steel wire, wherein a value obtained by dividing the standard deviation of Vickers hardness in a cross section perpendicular to the longitudinal direction of the steel wire by the average value of the Vickers hardness is 0.150 or less.
  • a mechanical part including a shaft portion The chemical composition, in mass%, is C: 0.08-0.80%, Si: 0.03 to 1.50%, Mn: 0.50-2.00%, P: 0.050% or less, S: 0.050% or less, Al: 0.005-0.080%, N: 0.0010-0.0150%, O: 0.003% or less, with the balance being Fe and impurity elements;
  • a metal structure at a 1/4 dm portion having a depth of 1/4 dm from a surface of the shaft portion in a cross section perpendicular to a longitudinal direction of the shaft portion contains bainite in an area ratio of 70% or more
  • the tensile strength of the shaft portion is 580 + 900 ⁇ (C%) MPa or more
  • the ratio of 0.2% proof stress to the tensile strength (0.2% proof stress/tensile strength) is 0.90 or more,
  • a mechanical part including a shaft portion The chemical composition, in mass%, is C: 0.08-0.80%, Si: 0.03 to 1.50%, Mn: 0.50-2.00%, P: 0.050% or less, S: 0.050% or less, Al: 0.005-0.080%, N: 0.0010-0.0150%, O: Contains 0.003% or less, and further contains one or more selected from the group consisting of the following A group to D group, with the balance being Fe and impurity elements; [Group A] One or two selected from the group consisting of Ti: 0.050% or less and B: 0.0050% or less [Group B] Cr: 1.50% or less, Mo: 0.50% or less, One or more selected from the group consisting of Nb: 0.050% or less and V: 0.20% or less [Group C] Cu: 0.50% or less, Ni: 0.70% or less, One or more selected from the group consisting of Sn: 0.30% or less and Sb: 0.005% or less [Group D] Ca: 0.0050
  • a metal structure at a 1/4 dm portion that is 1/4 dm deep from the surface of the shaft portion in a cross section perpendicular to the longitudinal direction of the shaft portion contains bainite at an area ratio of 70% or more
  • the tensile strength of the shaft portion is 580 + 900 ⁇ (C%) MPa or more
  • the ratio of 0.2% proof stress to the tensile strength (0.2% proof stress/tensile strength) is 0.90 or more
  • a mechanical component, wherein a value obtained by dividing the standard deviation of Vickers hardness in a cross section perpendicular to the longitudinal direction of the shaft portion by the average value of the Vickers hardness is 0.150 or less.
  • ⁇ 15> The mechanical component according to ⁇ 14>, having a chemical composition including the A group in mass %.
  • ⁇ 16> The mechanical part according to ⁇ 14> or ⁇ 15>, having a chemical composition including the B group in mass%.
  • ⁇ 17> The mechanical component according to any one of ⁇ 14> to ⁇ 16>, having a chemical composition including, by mass%, the C group.
  • ⁇ 18> The mechanical component according to any one of ⁇ 14> to ⁇ 17>, having a chemical composition including, by mass%, the D group.

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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)

Abstract

L'invention concerne un fil machine qui a une composition chimique prédéterminée, dans lequel : lorsque le diamètre du fil machine est noté D, la structure métallique dans une partie 1/4 D, qui est une partie située dans une section transversale prise perpendiculairement à la direction de la longueur du fil machine, à la profondeur de 1/4 D à partir de la surface du fil machine, comprend de la bainite qui représente un rapport de surface supérieur ou égal à 70 % ; le rapport de la limite d'élasticité à 0,05 % à la résistance à la traction (limite d'élasticité à 0,05 %/résistance à la traction) est supérieur ou égal à 0,72 à 0,40 × (C%), où (C%) est la teneur en C en % en masse ; et une valeur obtenue par division de l'écart type de dureté Vickers dans une section transversale perpendiculaire à la direction de la longueur du fil machine par la valeur moyenne de dureté Vickers est inférieure ou égale à 0,150.
PCT/JP2024/013327 2023-03-31 2024-03-29 Fil machine, fil d'acier et composant de machine WO2024204819A1 (fr)

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Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2013031640A1 (fr) * 2011-08-26 2013-03-07 新日鐵住金株式会社 Matériau de fil pour un composant de machine non raffiné ; fil d'acier pour un composant de machine non raffiné ; composant de machine non raffiné ; et procédé permettant de fabriquer un matériau de fil pour un composant de machine non raffiné, un fil d'acier pour un composant de machine non raffiné et un composant de machine non raffiné
JP2015190002A (ja) * 2014-03-28 2015-11-02 Ｊｆｅ条鋼株式会社 非調質ウェルドボルト用鋼材およびその製造方法
WO2016121820A1 (fr) * 2015-01-27 2016-08-04 新日鐵住金株式会社 Matériau en barreau pour composant de machine non trempé, barreau d'acier pour composant de machine non trempé et composant de machine non trempé
WO2017122830A1 (fr) * 2016-01-15 2017-07-20 新日鐵住金株式会社 Fil d'acier pour élément de machine non affiné thermiquement et élément de machine non affiné thermiquement
WO2018008698A1 (fr) * 2016-07-05 2018-01-11 新日鐵住金株式会社 Fil machine, fil d'acier et pièce
JP2021183710A (ja) * 2020-05-21 2021-12-02 日本製鉄株式会社 鋼線、非調質機械部品用線材、及び非調質機械部品

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2013031640A1 (fr) * 2011-08-26 2013-03-07 新日鐵住金株式会社 Matériau de fil pour un composant de machine non raffiné ; fil d'acier pour un composant de machine non raffiné ; composant de machine non raffiné ; et procédé permettant de fabriquer un matériau de fil pour un composant de machine non raffiné, un fil d'acier pour un composant de machine non raffiné et un composant de machine non raffiné
JP2015190002A (ja) * 2014-03-28 2015-11-02 Ｊｆｅ条鋼株式会社 非調質ウェルドボルト用鋼材およびその製造方法
WO2016121820A1 (fr) * 2015-01-27 2016-08-04 新日鐵住金株式会社 Matériau en barreau pour composant de machine non trempé, barreau d'acier pour composant de machine non trempé et composant de machine non trempé
WO2017122830A1 (fr) * 2016-01-15 2017-07-20 新日鐵住金株式会社 Fil d'acier pour élément de machine non affiné thermiquement et élément de machine non affiné thermiquement
WO2018008698A1 (fr) * 2016-07-05 2018-01-11 新日鐵住金株式会社 Fil machine, fil d'acier et pièce
JP2021183710A (ja) * 2020-05-21 2021-12-02 日本製鉄株式会社 鋼線、非調質機械部品用線材、及び非調質機械部品

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