WO2017126695A1 - Fil d'acier pour composant mécanique non traité thermiquement, et composant mécanique non traité thermiquement - Google Patents

Fil d'acier pour composant mécanique non traité thermiquement, et composant mécanique non traité thermiquement Download PDF

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Publication number
WO2017126695A1
WO2017126695A1 PCT/JP2017/002026 JP2017002026W WO2017126695A1 WO 2017126695 A1 WO2017126695 A1 WO 2017126695A1 JP 2017002026 W JP2017002026 W JP 2017002026W WO 2017126695 A1 WO2017126695 A1 WO 2017126695A1
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Prior art keywords
steel wire
less
section
pearlite
cross
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PCT/JP2017/002026
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English (en)
Japanese (ja)
Inventor
真 小此木
大輔 平上
達誠 多田
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新日鐵住金株式会社
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Priority to CN201780004566.3A priority Critical patent/CN108368583B/zh
Priority to JP2017562936A priority patent/JP6614245B2/ja
Priority to KR1020187016644A priority patent/KR102037089B1/ko
Publication of WO2017126695A1 publication Critical patent/WO2017126695A1/fr

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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
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/06—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of rods or wires
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/52—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for wires; for strips ; for rods of unlimited length
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • 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
    • 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
    • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
    • 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
    • C22C38/32—Ferrous alloys, e.g. steel alloys containing chromium with boron
    • 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

Definitions

  • This disclosure relates to steel wires for non-heat treated machine parts and non-heat treated machine parts.
  • Patent Document 11 discloses a high-strength bolt having a tensile strength of 1200 MPa or more, in which the structure is a pearlite structure and then subjected to wire drawing.
  • Patent Document 3 discloses a pearlite-structured wire rod for high-strength bolts having a tensile strength of 1200 MPa or more.
  • Patent Document 1 Japanese Patent Laid-Open No. 54-101743
  • Patent Document 2 Japanese Patent Laid-Open No. 11-315348
  • Patent Document 3 Japanese Patent Laid-Open No. 11-315349
  • Patent Document 4 Japanese Patent Laid-Open No. 2000-144306
  • Patent Document 5 Special JP 2000-337332
  • Patent Document 6 JP 2001-348618
  • Patent Document 7 JP 2002-069579
  • Patent Document 8 JP 2003-193183
  • Patent Document 9 JP 2004-307929
  • Patent Document 10 Japanese Patent Application Laid-Open No. 2005-281860
  • Patent Document 11 Japanese Patent Application Laid-Open No. 2008-261027
  • a high-strength mechanical part for example, high-strength bolt
  • a steel wire of alloy steel to which an alloy element such as Cr, Mo, V is added is formed into a predetermined shape.
  • machine parts for example, bolts
  • non-heat treated machine parts for example, non-heat treated bolts
  • Non-tempered mechanical parts having a tensile strength of 1100 MPa or more can be produced by cold working a steel wire having a tensile strength of 900 MPa or more.
  • a non-tempered mechanical part for example, a non-tempered bolt
  • the pearlite structure captures hydrogen at the interface between cementite and ferrite. It is considered that penetration is suppressed and the hydrogen embrittlement resistance is improved.
  • the hydrogen embrittlement resistance is improved to some extent by a technique for drawing a pearlite structure.
  • the subject of this indication is excellent in cold workability at the time of manufacturing a non-tempered machine part by cold work, although it is a steel wire of tensile strength 900MPa or more, and made it a non-tempered machine part.
  • An object of the present invention is to provide a steel wire for non-tempered mechanical parts having excellent hydrogen embrittlement resistance.
  • the subject of this indication is that it can manufacture using the steel wire excellent in cold workability, and is providing the non-tempered mechanical component excellent in tensile strength and hydrogen embrittlement resistance.
  • the chemical composition is mass%, C: 0.40 to 0.65%, Si: 0.05 to 0.50%, Mn: 0.20 to 1.00%, Al: 0.005 to 0.050%, P: 0 to 0.030%, S: 0 to 0.030%, N: 0 to 0.0050%, Cr: 0 to 1.00%, Ti: 0 to 0.050%, Nb: 0 to 0.050%, V: 0 to 0.10%, B: 0 to 0.0050%, O: 0 to 0.0030%, and The balance: Fe and impurities, When the metal structure has C mass% as [C%], the area ratio is (35 ⁇ [C%] + 65)% or more of pearlite, and the balance that is at least one of proeutectoid ferrite and bainite.
  • a cross section parallel to the axial direction of the steel wire and including the central axis is an L cross section
  • a cross section perpendicular to the axial direction of the steel wire is a C cross section
  • a diameter of the steel wire is D
  • a depth from the surface of the steel wire in the L cross section is
  • AR is 1.
  • (AR) / (average aspect ratio of pearlite block measured at a depth of 0.25D from the surface of the steel wire in the L section) is 1.1 or more
  • GD is (15 / AR) ⁇ m.
  • (GD) / (average block particle size of pearlite block measured at a position of depth 0.25D from the surface of the steel wire in the C cross section) is less than 1.0
  • ⁇ 2> By mass% Cr: more than 0 and 1.00% or less, Ti: more than 0 and 0.050% or less, Nb: more than 0 and 0.050% or less, The steel wire for non-heat treated machine parts according to ⁇ 1>, containing one or more of V: more than 0 and 0.10% or less and B: more than 0 and 0.0050% or less.
  • ⁇ 3> The steel wire for non-heat treated machine part according to ⁇ 1> or ⁇ 2>, wherein D is 3 to 30 mm.
  • ⁇ 4> Including a cylindrical shaft part, Chemical composition is mass%, C: 0.40 to 0.65%, Si: 0.05 to 0.50%, Mn: 0.20 to 1.00%, Al: 0.005 to 0.050%, P: 0 to 0.030%, S: 0 to 0.030%, N: 0 to 0.0050%, Cr: 0 to 1.00%, Ti: 0 to 0.050%, Nb: 0 to 0.050%, V: 0 to 0.10%, B: 0 to 0.0050%, O: 0 to 0.0030%, and The balance: Fe and impurities, When the metal structure has C mass% as [C%], the area ratio is (35 ⁇ [C%] + 65)% or more of pearlite, and the balance that is at least one of proeutectoid ferrite and bainite.
  • a cross section parallel to the axial direction of the cylindrical shaft portion and including the central axis is an L cross section
  • a cross section perpendicular to the axial direction of the cylindrical shaft portion is a C cross section
  • the diameter of the cylindrical shaft portion is Is D
  • the average aspect ratio of the pearlite block measured at a position 50 ⁇ m in depth from the surface of the cylindrical shaft portion in the L section is AR, and 50 ⁇ m in depth from the surface of the cylindrical shaft portion in the C section.
  • the average block particle size of the pearlite block measured at the position is GD
  • AR is 1.4 or more
  • (AR) / depth 0.25D from the surface of the cylindrical shaft portion in the L section
  • the average aspect ratio of the pearlite block measured at the position is 1.1 or more
  • GD is (15 / AR) ⁇ m or less
  • Average block grain diameter of pearlite blocks) is less than 1.0, A non-heat treated machine part, wherein the cylindrical shaft portion has a tensile strength of 1100 to 1500 MPa.
  • ⁇ 5> By mass% Cr: more than 0 and 1.00% or less, Ti: more than 0 and 0.050% or less, Nb: more than 0 and 0.050% or less, The non-heat treated machine part according to ⁇ 4>, containing one or more of V: more than 0 and 0.10% or less and B: more than 0 and 0.0050% or less.
  • ⁇ 6> A cold-worked product of a steel wire for non-tempered mechanical parts according to any one of ⁇ 1> to ⁇ 3>, including a cylindrical shaft portion, and tensioning the cylindrical shaft portion Non-tempered mechanical parts having a strength of 1100-1500 MPa.
  • ⁇ 7> The non-heat treated machine part according to any one of ⁇ 4> to ⁇ 6>, which is a non-heat treated bolt.
  • the present disclosure although it is a steel wire having a tensile strength of 900 MPa or more, it is excellent in cold workability when manufacturing a non-tempered mechanical part by cold working, and is a non-heat treated mechanical part.
  • a steel wire for non-tempered mechanical parts having excellent hydrogen embrittlement resistance is provided.
  • it can manufacture using the steel wire excellent in cold workability, and the non-tempered mechanical component excellent in tensile strength and hydrogen embrittlement resistance is provided.
  • a numerical range expressed using “to” means a range including numerical values described before and after “to” as a lower limit value and an upper limit value.
  • “%” indicating the content of a component (element) means “% by mass”.
  • the content of C (carbon) may be referred to as “C content”.
  • the content of other elements may be expressed in the same manner.
  • the term “process” is not limited to an independent process, and is included in this term if the intended purpose of the process is achieved even when it cannot be clearly distinguished from other processes. It is.
  • the steel wire for non-heat treated machine parts (hereinafter also simply referred to as “steel wire”) has a chemical composition of mass%, C: 0.40 to 0.65%, Si: 0.05 to 0. 50%, Mn: 0.20-1.00%, Al: 0.005-0.050%, P: 0-0.030%, S: 0-0.030%, N: 0-0.
  • a cross section parallel to the axial direction of the steel wire and including the central axis is an L cross section
  • a cross section perpendicular to the axial direction of the steel wire is a C cross section
  • a diameter of the steel wire is D
  • a depth from the surface of the steel wire in the L cross section is
  • AR is 1.
  • (AR) / (average aspect ratio of pearlite block measured at a depth of 0.25D from the surface of the steel wire in the L section) is 1.1 or more
  • GD is (15 / AR) ⁇ m.
  • (GD) / (average block particle size of pearlite block measured at a position of depth 0.25D from the surface of the steel wire in the C cross section) is less than 1.0
  • the tensile strength is 900-1500 MPa.
  • the steel wire of the present disclosure is a steel wire having a tensile strength of 900 MPa or more, cold workability when producing non-tempered mechanical parts by cold working (hereinafter, also simply referred to as “cold workability”) Excellent. Furthermore, the steel wire of the present disclosure is excellent in hydrogen embrittlement resistance (hereinafter also simply referred to as “hydrogen embrittlement resistance”) when used as a non-heat treated machine part. In other words, by cold working the steel wire of the present disclosure, it is possible to manufacture a non-tempered mechanical component having excellent hydrogen embrittlement resistance.
  • the above-described chemical composition contributes to both cold workability and hydrogen embrittlement resistance. Details of the chemical composition will be described later.
  • a steel wire having a low C content (specifically, a C content of 0.65% by mass or less) as in the above-described chemical composition is softened and improved in ductility, and has good cooling performance. Interworkability is obtained.
  • a two-phase structure of pro-eutectoid ferrite and pearlite is likely to be generated.
  • the C content is likely to further decrease due to decarburization, and proeutectoid ferrite is likely to be generated.
  • the cooling rate is high in the surface layer of the wire, a bainite structure is easily generated.
  • the two-phase structure of pro-eutectoid ferrite and pearlite, and bainite generally have lower hydrogen embrittlement resistance than pearlite.
  • the C content is reduced (specifically, the C content is 0.65% by mass or less), a structure such as pro-eutectoid ferrite and bainite is easily generated.
  • the hydrogen embrittlement resistance of the surface layer is lowered.
  • the metal structure of the steel wire of the present disclosure is a metal structure mainly composed of pearlite, and more specifically, the metal structure of the steel wire of the present disclosure has an area ratio of pearlite of (35 ⁇ [C% ] +65)% or more of the metal structure.
  • the pearlite structure is a lamination of a layer mainly composed of cementite phase (hereinafter sometimes simply referred to as “cementite layer”) and a layer primarily composed of ferrite phase (hereinafter sometimes simply referred to as “ferrite layer”). It has a structure.
  • This laminated structure is considered to provide resistance to crack propagation (hydrogen embrittlement resistance). Thereby, cold workability and hydrogen embrittlement resistance are improved.
  • the reason why the area ratio of pearlite depends on [C%] that is, C content
  • C content the reason why the area ratio of pearlite depends on [C%] (that is, C content) is that the lower the C content, the lower the C content within the range of 0.40 to 0.65%. This is because ferrite and bainite are easily generated, and pearlite tends to be hardly generated.
  • the steel wire of the present disclosure has an average aspect ratio of the pearlite block (ie, “AR” in the present specification) measured at a depth of 50 ⁇ m in the L cross section of 1.4 or more, and (AR) / ( The average aspect ratio of the pearlite block measured at a position at a depth of 0.25D from the surface of the steel wire in the L section is 1.1 or more.
  • a position having a depth of 50 ⁇ m from the surface of the steel wire may be referred to as a “depth 50 ⁇ m position” or a “surface layer”.
  • surface layer in the present specification means a position having a depth of 50 ⁇ m from the surface of the steel wire.
  • a position having a depth of 0.25D from the surface of the steel wire that is, a position where the depth from the surface of the steel wire is 0.25 times the diameter of the steel wire (ie, D) is referred to as “depth”.
  • depth Sometimes referred to as "0.25D position” or "0.25D”.
  • (AR) / average aspect ratio of pearlite block measured at a position of depth 0.25D from the surface of the steel wire in the L cross section
  • the aspect ratio [surface layer / 0.25D] is 1.1 or more. That is, in the L cross section of the steel wire of the present disclosure, the pearlite block in the surface layer of the steel wire (ie, at a depth of 50 ⁇ m) is stretched more than the pearlite block inside the steel wire (ie, at a depth of 0.25D). ing. Moreover, in the L cross section of the steel wire of this indication, the average aspect ratio (namely, AR) of the pearlite block in a surface layer is 1.4 or more. In the steel wire of the present disclosure, by satisfying these conditions, the hydrogen embrittlement resistance (that is, the hydrogen embrittlement resistance when a non-heat treated machine part is formed by cold working) is improved.
  • the pearlite block is elongated in the surface layer, the orientation of the layered structure of the pearlite structure in the surface layer becomes more uniform, and resistance to hydrogen intrusion from the surface of the steel wire, and / or cracking. This is considered to be resistance to progress. Therefore, in the steel wire of the present disclosure, the hydrogen embrittlement resistance is improved even if the metal structure includes proeutectoid ferrite and bainite.
  • the average block particle size (GD) of the pearlite block measured at a depth of 50 ⁇ m in the C cross section is (15 / AR) ⁇ m or less, and (GD) / (depth in the C cross section)
  • the average block particle size of the pearlite block measured at the 0.25D position is less than 1.0.
  • (GD) / (average block particle size of pearlite block measured at a depth of 0.25D position in the C cross section) is expressed as “block particle size ratio [surface layer / 0.25D]” of pearlite block. Sometimes called.
  • the block particle size ratio [surface layer / 0.25D] of the pearlite block is less than 1.0. That is, in the C cross section of the steel wire of the present disclosure, the pearlite block on the surface layer of the steel wire (ie, at a depth of 50 ⁇ m) is made finer than the pearlite block inside the steel wire (ie, at a depth of 0.25D). Has been. Moreover, in the C cross section of the steel wire of the present disclosure, the average block particle size (that is, GD) of the pearlite block in the surface layer is (15 / AR) ⁇ m or less.
  • the cold workability of the steel wire is improved, and the hydrogen embrittlement resistance (that is, the resistance to non-heat treated mechanical parts by cold working). Hydrogen embrittlement characteristics) are improved.
  • the reason why the cold workability of the steel wire is improved by satisfying the above conditions is that the ductility of the steel wire is improved because the pearlite block of the surface layer is fine (that is, (15 / AR) ⁇ m or less). Conceivable.
  • the reason why the hydrogen embrittlement resistance is improved by satisfying the above conditions is related to the fact that the surface pearlite block is fine and that hydrogen tends to segregate at the grain boundaries. it is conceivable that.
  • the fineness of the pearlite block on the surface layer increases the total area of the crystal grain boundaries in the surface layer, and as a result, the ability to capture hydrogen in the surface layer (that is, the ability to prevent hydrogen from penetrating into the steel wire). It is thought to improve.
  • the steel wire of the present disclosure has a tensile strength of 900 to 1500 MPa.
  • the steel wire of the present disclosure having a tensile strength of 900 to 1500 MPa (that is, a steel wire for non-tempered mechanical parts) produces a non-tempered mechanical part having a tensile strength of 1100 to 1500 MPa by cold working. Suitable for use.
  • the cold work in the present disclosure may be only one kind of work, or may be a plurality of kinds of work (for example, cold forging and rolling).
  • the non-tempered mechanical part having a tensile strength of 1100 to 1500 MPa may be manufactured by cold working the steel wire of the present disclosure and then holding it within a temperature range of 100 to 400 ° C.
  • the steel wire of the present disclosure is a steel wire having a tensile strength of 900 MPa or more in order to satisfy the above-described conditions. Excellent workability. Compared to the steel wire of the present disclosure, a steel wire having a tensile strength of 900 MPa or more and mainly having a pro-eutectoid ferrite-pearlite two-phase structure tends to have low cold workability.
  • ⁇ C 0.40 ⁇ 0.65% C is an element necessary for ensuring tensile strength.
  • the C content in the chemical composition in the present disclosure is 0.40% or more, preferably 0.45% or more.
  • the C content in the chemical composition in the present disclosure is 0.65% or less, preferably 0.60% or less.
  • Si 0.05-0.50%
  • Si is a deoxidizing element and is an element that increases the tensile strength by solid solution strengthening.
  • the Si content in the chemical composition in the present disclosure is 0.05% or more, preferably 0.15% or more.
  • the Si content in the chemical composition in the present disclosure is 0.50% or less, preferably 0.30% or less.
  • Mn is an element that increases the tensile strength of steel after pearlite transformation.
  • the Mn content in the chemical composition in the present disclosure is 0.20% or more, preferably 0.40% or more.
  • the Mn content in the chemical composition in the present disclosure is 1.00% or less, preferably 0.80% or less.
  • Al is a deoxidizing element and an element that forms AlN that functions as pinning particles. AlN refines crystal grains, thereby improving cold workability.
  • Al is an element having an action of reducing the solid solution N to suppress dynamic strain aging and an action of improving hydrogen embrittlement resistance.
  • the Al content in the chemical composition in the present disclosure is 0.005% or more, preferably 0.020% or more.
  • the Al content in the chemical composition in the present disclosure is 0.050% or less, preferably 0.040% or less.
  • P is an element that segregates at the grain boundaries to deteriorate the resistance to hydrogen embrittlement and to deteriorate the cold workability.
  • the P content in the chemical composition in the present disclosure is 0.030% or less, preferably 0.015% or less. Since the steel wire of this indication does not need to contain P, the lower limit of P content is 0%. However, from the viewpoint of reducing the manufacturing cost (dephosphorization cost), the P content may be more than 0%, 0.002% or more, or 0.005% or more. .
  • S is an element that segregates at the crystal grain boundaries to deteriorate the resistance to hydrogen embrittlement and the cold workability.
  • the S content is 0.030% or less, preferably 0.015% or less, and more preferably 0.010% or less. Since the steel wire of this indication does not need to contain S, the lower limit of S content is 0%. However, from the viewpoint of reducing manufacturing costs (desulfurization costs), the S content may be more than 0%, 0.002% or more, or 0.005% or more.
  • N is an element that degrades cold workability due to dynamic strain aging and may further degrade hydrogen embrittlement resistance.
  • the N content is set to 0.0050% or less in the chemical composition of the present disclosure.
  • the N content is preferably 0.0040% or less.
  • the lower limit of the N content is 0%.
  • the N content may be greater than 0%, may be 0.0010% or more, or may be 0.0020% or more. 0.0030% or more may be sufficient.
  • ⁇ Cr 0 to 1.00% Cr is an arbitrary element. That is, the lower limit of the Cr content in the chemical composition in the present disclosure is 0%. Cr is an element that increases the tensile strength of steel after pearlite transformation. From the viewpoint of obtaining such an effect, the Cr content is preferably more than 0%, more preferably 0.01% or more, still more preferably 0.03% or more, and further preferably 0.05% or more. And particularly preferably 0.10% or more. On the other hand, when the Cr content is more than 1.00%, martensite is liable to occur, thereby deteriorating cold workability. Therefore, the Cr content in the chemical composition in the present disclosure is 1.00% or less, preferably 0.70% or less, and more preferably 0.50% or less.
  • Ti is an arbitrary element. That is, the lower limit value of the Ti content in the chemical composition in the present disclosure is 0%.
  • Ti is a deoxidizing element, and is an element that forms TiN, reduces solid solution N to suppress dynamic strain aging, and enhances hydrogen embrittlement resistance. From the viewpoint of obtaining these effects, the Ti content is preferably more than 0%, more preferably 0.005% or more, and still more preferably 0.015% or more. On the other hand, when the Ti content is more than 0.050%, the above-described effects are saturated and wrinkles are likely to occur during hot rolling. Therefore, the Ti content in the chemical composition in the present disclosure is 0.050% or less, preferably 0.035% or less.
  • Nb is an arbitrary element. That is, the lower limit value of the Nb content in the chemical composition in the present disclosure is 0%.
  • Nb is an element that forms NbN, reduces solid solution N to suppress dynamic strain aging, and enhances hydrogen embrittlement resistance. From the viewpoint of obtaining these effects, the Nb content is preferably more than 0%, more preferably 0.005% or more, and still more preferably 0.015% or more. On the other hand, when the Nb content is more than 0.05%, the above effect is saturated and wrinkles are likely to occur during hot rolling. Therefore, the Nb content in the chemical composition in the present disclosure is 0.050% or less, preferably 0.035% or less.
  • V is an arbitrary element. That is, the lower limit value of the V content in the chemical composition in the present disclosure is 0%. V is an element that forms VN, reduces solid solution N to suppress dynamic strain aging, and enhances hydrogen embrittlement resistance. From the viewpoint of obtaining these effects, the V content is preferably more than 0%, more preferably 0.02% or more. On the other hand, when the V content is more than 0.10%, the above-described effects are saturated and wrinkles are easily generated during hot rolling. Therefore, the V content in the chemical composition in the present disclosure is 0.10% or less, preferably 0.05% or less.
  • B is an arbitrary element. That is, the lower limit of the B content in the chemical composition in the present disclosure is 0%. B has the effect of suppressing grain boundary ferrite and grain boundary bainite, improving the cold workability and hydrogen embrittlement resistance, and increasing the tensile strength after pearlite transformation. From the viewpoint of obtaining these effects, the B content is preferably more than 0%, more preferably 0.0003% or more. On the other hand, when the B content exceeds 0.0050%, the above-described effect is saturated. Therefore, the B content in the chemical composition in the present disclosure is 0.0050% or less.
  • the chemical composition in the present disclosure is, in terms of mass%, Cr: more than 0 and 1.00%, Ti: more than 0 and less than 0.050%, Nb: more than 0 and 0 from the viewpoint of obtaining the effects of each of the above-described arbitrary elements. It may contain one or more of 0.050% or less, V: more than 0 and 0.10% or less, and B: more than 0 and 0.0050% or less.
  • O exists in the steel wire as oxides such as Al and Ti.
  • the O content in the chemical composition in the present disclosure is 0.0030% or less, preferably 0.0020% or less. Since the steel wire of this indication does not need to contain O, the lower limit of O content is 0%. However, from the viewpoint of reducing the manufacturing cost (deoxidation cost), the O content may be more than 0%, may be 0.0002% or more, and may be 0.0005% or more. .
  • the remainder excluding the above-described elements is Fe and impurities.
  • the impurity refers to a component contained in the raw material or a component mixed in the manufacturing process and not intentionally contained in the steel. Examples of impurities include all elements other than the elements described above.
  • the element as the impurity may be only one type or two or more types.
  • the metal structure of the steel wire according to the present disclosure includes at least one of pearlite having an area ratio of (35 ⁇ [C%] + 65)% or more, pro-eutectoid ferrite, and bainite when the mass% of C is [C%]. And the rest. Thereby, cold workability and hydrogen embrittlement resistance are improved.
  • the area ratio of pearlite in the metal structure of the steel wire is less than (35 ⁇ [C%] + 65)%, the strength (tensile strength, hardness, etc.) of the steel wire becomes non-uniform. Cracks are likely to occur during cold working of parts (that is, cold workability is reduced).
  • the area ratio of pearlite in the metal structure of the steel wire is less than (35 ⁇ [C%] + 65)%, even in the non-heat treated machine part obtained by cold working the steel wire, the metal structure The area ratio of pearlite is less than (35 ⁇ [C%] + 65)%. As a result, the hydrogen embrittlement resistance of the non-tempered mechanical part deteriorates.
  • the area ratio of pearlite is preferably (35 ⁇ [C%] + 70)% or more, and (35 ⁇ [C%] + 75)%. More preferably. From the viewpoint of production suitability, the area ratio of pearlite is preferably 99% or less, more preferably 97% or less, and still more preferably 95% or less.
  • the specific preferable range of the pearlite area ratio is preferably 80 to 99%, more preferably 83 to 97%, and more preferably 85 to 95%, although it depends on [C%]. Is particularly preferred.
  • the balance in the metal structure of the steel wire of the present disclosure is at least one of proeutectoid ferrite and bainite.
  • the balance contains martensite, cold workability and hydrogen embrittlement resistance when used as a non-tempered mechanical part are deteriorated.
  • the area ratio (%) of pearlite refers to a value obtained by the following procedure.
  • the C cross section of the steel wire is etched using picral to reveal a metal structure.
  • four observation positions are selected every 90 ° in the circumferential direction from a position of 50 ⁇ m depth in the C cross-section after etching (that is, a circumferential position), and each observation position is subjected to FE-SEM ( Using a Field Emission-Scanning Electron Microscope), take an SEM photograph at a magnification of 1000 times.
  • observation positions are selected at 90 ° intervals in the circumferential direction from the depth 0.25D position (that is, the circumferential position) in the C cross-section after etching, and the FE ⁇ Using a SEM, take an SEM photograph at a magnification of 1000 times.
  • a structure other than pearlite proeutectoid ferrite, bainite, etc.
  • the area ratio (%) of pearlite is obtained by subtracting the area ratio (%) of the tissue other than the obtained pearlite from 100%.
  • the steel wire of the present disclosure has an AR (that is, an average aspect ratio of the pearlite block measured at a depth of 50 ⁇ m in the L cross section) of 1.4 or more. This improves the hydrogen embrittlement resistance.
  • AR that is, an average aspect ratio of the pearlite block measured at a depth of 50 ⁇ m in the L cross section
  • the reason is considered as follows.
  • the pearlite structure has a laminated structure of a cementite layer and a ferrite layer, and the elongated pearlite block on the surface layer (that is, the pearlite block having an AR of 1.4 or more) is the orientation of the layered structure of the pearlite structure. Becomes more uniform. This uniform layered structure is considered to be resistance to hydrogen intrusion from the surface of the steel wire and / or resistance to crack propagation.
  • the AR of the steel wire is less than 1.4
  • the AR of the non-heat treated machine part obtained by cold working the steel wire is also less than 1.4.
  • the hydrogen embrittlement resistance of non-tempered mechanical parts does not improve.
  • AR is preferably 1.5 or more, and more preferably 1.6 or more.
  • AR is preferably 2.5 or less, and more preferably 2.0 or less, from the viewpoint of suitability for manufacturing a steel wire.
  • the pearlite block means a pearlite structural unit in which the orientation of the ferrite is within 15 degrees from the ferrite crystal orientation map obtained by the EBSD (electron back scattering scattering) method. . That is, the boundary where the azimuth difference is 15 ° or more is a block grain boundary of the pearlite block.
  • AR means a value measured by the following procedure.
  • four observation positions are selected every 2.0 mm from the straight line indicating the position of the depth of 50 ⁇ m in the L cross section of the steel wire, and in the region of the depth direction of 50 ⁇ m and the axial direction of 250 ⁇ m centering on each observation position.
  • Each of the ferrite crystal orientation maps is obtained using an EBSD device.
  • ten pearlite blocks are selected in order from the group having the largest equivalent circle diameter from the group of pearlite blocks traversed by a straight line indicating a position having a depth of 50 ⁇ m.
  • the aspect ratio of each of the 10 selected pearlite blocks is obtained, and the average value of the aspect ratios (that is, 10 values) in the 10 pearlite blocks is determined as AR (that is, the depth in the L cross section is 50 ⁇ m). Average aspect ratio of pearlite block measured at the position).
  • the aspect ratio of the pearlite block means a value obtained by dividing the major axis of the pearlite block by the minor axis (that is, the major axis / minor axis).
  • the major axis of the pearlite block means the maximum length of the pearlite block
  • the minor axis of the pearlite block means the maximum value of the length in the direction orthogonal to the major axis direction.
  • FIG. 1 is a conceptual diagram illustrating an example of a pearlite block in an L cross section of a steel wire according to an example of the present disclosure.
  • the shape of the pearlite block may be a polygonal shape as shown in FIG. 1, an elliptical shape, or a shape other than the polygonal shape and the elliptical shape (for example, an indefinite shape).
  • the pearlite block only needs to have an AR of 1.4 or more, and the shape is not particularly limited.
  • the steel wire of the present disclosure has an aspect ratio ratio [surface layer / 0.25D] (that is, (AR) / (average aspect ratio of pearlite block measured at a depth of 0.25D position in the L cross section)) of 1. 1 or more.
  • the steel wire of the present disclosure has improved hydrogen embrittlement resistance as described above when the aspect ratio [surface layer / 0.25D] is 1.1 or more. This is because the orientation of the layered structure of the pearlite structure in the pearlite block elongated in the surface layer is made more uniform, and this layered structure becomes resistant to hydrogen intrusion from the surface of the steel wire and / or the progress of cracks. This is considered to be a resistance to the above. Further, since the steel wire of the present disclosure has an aspect ratio ratio [surface layer / 0.25D] of 1.1 or more, strain concentrates on the surface layer of the steel wire, so that the hydrogen embrittlement resistance can be effectively improved. Can be improved.
  • the ratio of the aspect ratio [surface layer / 0.25D] is less than 1.1, it is necessary to increase not only the surface layer of the steel wire but also the internal strain of the steel wire. In some cases, it cannot be improved, or the productivity of the steel wire may be reduced.
  • the aspect ratio [surface layer / 0.25D] is preferably 1.2 or more from the viewpoint of improving the hydrogen embrittlement resistance.
  • the aspect ratio ratio [surface layer / 0.25D] is preferably 2.0 or less, more preferably 1.8 or less, and 1.6 or less, from the viewpoint of the suitability for manufacturing the steel wire. Is particularly preferred.
  • the average aspect ratio of the pearlite block measured at the depth 0.25D position in the L cross section is to change the observation position from the 50 ⁇ m depth position in the L cross section to the depth 0.25D position in the L cross section. Except for the above, it is measured by the same method as the AR measurement method described above.
  • the steel wire of the present disclosure has a GD (that is, an average block particle size of a pearlite block measured at a depth of 50 ⁇ m in the C cross section) of (15 / AR) ⁇ m or less. Since the pearlite block is fine (that is, GD is (15 / AR) ⁇ m or less), as described above, cold workability and hydrogen embrittlement resistance are improved. The reason is considered as follows. When the pearlite block in the surface layer of the steel wire is coarse (that is, when the average block particle size of the pearlite block exceeds (15 / AR) ⁇ m), the ductility of the steel wire is lowered, thereby causing the coldness of the steel wire. Workability is reduced.
  • the block particle diameter of the pearlite block on the surface layer of the machine part obtained by cold working this steel wire becomes coarse. Hydrogen tends to segregate at the pearlite block grain boundaries.
  • the total area of the block grain boundaries of the pearlite block is reduced, so that the hydrogen capturing ability of the surface layer (that is, the ability to prevent hydrogen from penetrating into the wire) is reduced. .
  • the pearlite block of a surface layer becomes coarse, it is thought that a hydrogen embrittlement resistance characteristic falls.
  • GD is preferably 11.0 ⁇ m or less, and more preferably 10.0 ⁇ m or less. GD is preferably 7.0 ⁇ m or more, and more preferably 8.0 ⁇ m or more, from the viewpoint of manufacturing suitability of the steel wire.
  • GD means a value measured by the following procedure. First, on the circumference showing the position of 50 ⁇ m depth in the C cross section of the steel wire, eight observation positions are selected at intervals of 45 ° in the circumferential direction, and ferrite in a 50 ⁇ m ⁇ 50 ⁇ m region centering on each observation position. Each crystal orientation map is acquired using an EBSD device. The equivalent circle diameters of all pearlite blocks included in the entire eight crystal orientation maps obtained are measured. The average value of the measured values obtained is defined as GD (that is, the average block particle size of the pearlite block measured at a depth of 50 ⁇ m in the C cross section).
  • the steel wire of the present disclosure has a particle size ratio [surface layer / 0.25D] (that is, (GD) / (average block particle size of pearlite block measured at a depth of 0.25D position in the C cross section)) of 1 Less than 0.0.
  • the steel wire of the present disclosure has an improved particle size ratio [GD / 0.25D] of less than 1.0, thereby improving cold workability and hydrogen embrittlement resistance.
  • the particle size ratio [GD / 0.25D] is preferably 0.98 or less, and more preferably 0.96 or less, from the viewpoint of further improving cold workability and hydrogen embrittlement resistance. 0.94 or less is particularly preferable.
  • the particle size ratio [GD / 0.25D] is preferably 0.80 or more, more preferably 0.85 or more, and 0.90 or more, from the viewpoint of the suitability for manufacturing the steel wire. Is particularly preferred.
  • the average block particle size of the pearlite block measured at the depth 0.25D position in the C section changes the observation position from the 50 ⁇ m position in the C section to the 0.25D position in the C section. Except for this, the measurement is carried out by the same method as the above-mentioned GD measurement method.
  • the steel wire of the present disclosure has a tensile strength (TS) of 900 to 1500 MPa.
  • TS tensile strength
  • the steel wire of the present disclosure is 900 MPa or more, non-tempered mechanical parts having a TS of 1100 MPa or more can be easily manufactured by cold working the steel wire.
  • TS of a steel wire is 900 Mpa or more.
  • the steel wire of the present disclosure has the above-described chemical composition and metal structure, it is excellent in cold workability while being a steel wire having a TS of 900 MPa or more.
  • TS of the steel wire of this indication is 1500 Mpa or less, it is excellent in the manufacture aptitude and cold workability of a steel wire.
  • the tensile strength (TS) of the steel wire and the tensile strength (TS) of the non-heat treated machine part are both JIS Z 2201 (2011) using a 9A test piece, and JIS Z 2201 ( 2011) means a value measured in accordance with the test method described.
  • the TS of the steel wire of the present disclosure is preferably 900 to 1300 MPa, and more preferably 900 to 1200 MPa, from the viewpoint of further improving the steel wire production suitability and cold workability.
  • D that is, the diameter of the steel wire
  • D is preferably 3 to 30 mm, more preferably 5 to 25 mm, and particularly preferably 5 to 20 mm.
  • the steel wire of the present disclosure preferably has a critical compressibility of 75% or more from the viewpoint of cold workability.
  • the method for measuring the limit compression rate is as shown in the examples described later.
  • Production method A includes a step of obtaining a wire by heating a steel slab having a chemical composition according to the present disclosure to 1000 to 1150 ° C. and performing hot rolling at a finish rolling temperature of 800 to 950 ° C .; A step of isothermal transformation treatment by immersing the wire having a temperature of 800 to 950 ° C. in a molten salt bath at 400 to 550 ° C. for 50 seconds or more; A step of water-cooling the wire material subjected to the constant temperature transformation treatment to a temperature of 300 ° C. or less; A step of obtaining a steel wire by subjecting the water-cooled wire to a wire drawing process with a total area reduction of 15 to 25%; including.
  • the chemical composition of the steel wire (target product) obtained by the manufacturing method A can be regarded as the same as the chemical composition of the steel slab (raw material) in the manufacturing method A.
  • the reason is that the hot rolling, the isothermal transformation treatment, the water cooling, and the wire drawing do not affect the chemical composition of the steel.
  • Production method A includes the step of isothermal transformation treatment and the step of water cooling, thereby making it easy to produce the steel wire of the present disclosure in which the area ratio of pearlite and the balance satisfy the above-described conditions.
  • the immersion time for immersing the wire in the molten salt bath is 50 seconds or more, the area ratio of the pearlite and the remaining part easily satisfy the above-described conditions.
  • the upper limit of the immersion time is not particularly limited. From the viewpoint of steel wire productivity, the immersion time is preferably 100 seconds or shorter, and more preferably 80 seconds or shorter.
  • the total area reduction is 15% or more, so that the tensile strength is 900 MPa or more. It is easy to manufacture a certain steel material.
  • the wire drawing process may be a process that includes the wire drawing process only once, or may be a process that includes the wire drawing process a plurality of times. That is, the total area reduction rate of 15 to 25% in the wire drawing process may be achieved by a single wire drawing process or a plurality of wire drawing processes.
  • the wire drawing process includes wire drawing only once, it is preferable to use a die having an approach half angle exceeding 10 ° as a die used for wire drawing. Thereby, it is easy to manufacture a steel material having an aspect ratio ratio [surface layer / 0.25D] of 1.1 or more.
  • the wire drawing process includes wire drawing multiple times, it is preferable to perform wire drawing multiple times under the condition that the area reduction rate in the final pass is 10% or less.
  • the area reduction rate in the final pass is more preferably 5 to 10%, more preferably 5 to 9%, and more preferably 5 to 8%. It is particularly preferred.
  • the steel wire of the present disclosure is particularly suitable as a steel wire for manufacturing a non-tempered mechanical part including a cylindrical shaft portion having a tensile strength of 1100 to 1500 MPa. That is, the steel wire of the present disclosure is cold-worked (and preferably held at 100 to 400 ° C. after cold working), thereby including a non-cylindrical shaft portion having a tensile strength of 1100 to 1500 MPa. Easy to manufacture tempered machine parts.
  • the chemical composition of the non-tempered mechanical part obtained by cold working the steel wire of the present disclosure (and preferably holding at 100 to 400 ° C. after the cold working) It can be considered the same as the chemical composition of the wire.
  • the reason is that cold work and heat treatment do not affect the chemical composition of the steel.
  • the metal structure of the non-heat treated machine part obtained by cold working the steel wire of the present disclosure (and performing a heat treatment at 100 to 400 ° C. after the cold working as necessary) It can be considered the same as the metal structure of the steel wire.
  • the reason is that the amount of cold working for obtaining a non-tempered mechanical part having a cylindrical shaft portion is very small.
  • Non-tempered machine parts a first embodiment and a second embodiment of the non-heat treated mechanical component (hereinafter, also simply referred to as “mechanical component”) of the present disclosure will be described.
  • the mechanical component of the first embodiment of the present disclosure includes a cylindrical shaft portion
  • the chemical composition is the chemical composition in the present disclosure described above,
  • the pearlite having an area ratio of (35 ⁇ [C%] + 65)% or more and the balance that is at least one of pro-eutectoid ferrite and pearlite, Become A cross section parallel to the axial direction of the cylindrical shaft portion and including the central axis is an L cross section, a cross section perpendicular to the axial direction of the cylindrical shaft portion is a C cross section, and the diameter of the cylindrical shaft portion is D.
  • the average aspect ratio of the pearlite block measured at a position of 50 ⁇ m depth from the surface of the cylindrical shaft portion in the L section is AR, and the pearlite measured at a depth of 50 ⁇ m from the surface of the cylindrical shaft portion in the C section.
  • the average block particle size of the block is GD
  • AR is 1.4 or more
  • (AR) / perlite block measured at a depth of 0.25D from the surface of the cylindrical shaft portion in the L cross section (Average aspect ratio) is 1.1 or more
  • GD is (15 / AR) ⁇ m or less
  • (GD) / (measured at a depth of 0.25D from the surface of the cylindrical shaft portion in the C cross section)
  • Average of perlite blocks Lock particle size) is less than 1.0
  • the tensile strength (TS) of the cylindrical shaft portion is 1100 to 1500 MPa.
  • the chemical composition and the metal structure of the cylindrical shaft portion that is, the ratio of pearlite area ratio, AR, aspect ratio ratio [surface layer / 0.25D], GD, and average block particle size
  • the ratio [surface layer / 0.25D] (the same applies hereinafter) is the same as the chemical composition and metal structure of the steel wire of the present disclosure. Therefore, the mechanical component of the first embodiment is excellent in hydrogen embrittlement resistance.
  • the machine part of the first embodiment can be manufactured by a steel wire excellent in cold workability (for example, a steel wire of the present disclosure).
  • the preferable aspect of the chemical composition and the metal structure of the cylindrical shaft portion in the mechanical component of the first embodiment is the same as the preferable aspect of the chemical composition and the metal structure of the steel wire of the present disclosure, respectively.
  • the mechanical component of the second embodiment of the present disclosure is a cold-worked product of the steel wire of the present disclosure (that is, a mechanical component obtained by cold-working the steel wire of the present disclosure), and is cylindrical.
  • the tensile strength of the shaft portion is 1100 to 1500 MPa. Therefore, the mechanical component of the second embodiment is excellent in hydrogen embrittlement resistance.
  • the first embodiment and the second embodiment may have overlapping portions. That is, not only the machine parts corresponding to one of the first embodiment and the second embodiment but also the machine parts corresponding to both the first embodiment and the second embodiment are naturally included in the machine parts of the present disclosure. Included in the range.
  • the mechanical component of the present disclosure is not particularly limited as long as it is a non-tempered mechanical component including a cylindrical shaft portion, and among them, a non-tempered bolt is particularly preferable.
  • the following manufacturing method X is mentioned as an example of the method of manufacturing the mechanical component of this indication.
  • the manufacturing method X includes the process of obtaining a machine part by cold-working the steel wire of this indication.
  • the production method X preferably includes a step of holding a machine part obtained by cold working within a temperature range of 100 to 400 ° C. (hereinafter also referred to as “holding step”). By including the holding step, it is easier to manufacture a mechanical component having a tensile strength of 1100 to 1500 MPa.
  • the holding temperature in the holding step is 100 to 400 ° C., preferably 200 to 400 ° C., more preferably 300 to 400 ° C.
  • the holding time in the holding step (that is, the time for holding the machine part within the above temperature range) is preferably 10 to 120 minutes, and more preferably 10 to 60 minutes.
  • the steel wire for non-heat treated machine parts and the non-heat treated machine parts of the present disclosure described above can be used for various machines such as automobiles, buildings, and the like.
  • ⁇ Cold workability of steel wire (measurement of critical compressibility)> The cold workability was evaluated by measuring the following critical compressibility for each level of steel wire.
  • a steel wire was machined to prepare a sample having a diameter D (that is, the diameter of the steel wire) and a length of 1.5 ⁇ D. Both end faces of the obtained sample were constrained using a pair of molds. As the pair of molds, molds each having a concentric groove on the contact surface with the end surface of the sample were used. In this state, the sample was compressed in the longitudinal direction. By performing a test in which the compression ratio of the sample in this compression was variously changed, the maximum compression ratio at which the sample did not crack was determined.
  • the maximum compression ratio at which no cracking of the sample occurred was defined as the critical compression ratio (%).
  • G the critical compression ratio
  • NG the cold workability is poor
  • TS tensile strength
  • F and B mean pro-eutectoid ferrite and bainite, respectively.
  • Table 3 it has a chemical composition in the present disclosure, has a pearlite area ratio of (35 ⁇ [C%] + 65)% or more, and the remaining structure is at least pro-eutectoid ferrite (F) and bainite (B).
  • the AR is 1.4 or more
  • the aspect ratio [surface layer / 0.25D] is 1.1 or more
  • the GD is (15 / AR) ⁇ m or less
  • the particle size ratio [GD /0.25D] is less than 1.0
  • TS is 900 to 1500 MPa.
  • Each level of steel wire in the examples is a steel wire of TS 900 MPa or more, and is excellent in cold workability and machine parts. In this case, the hydrogen embrittlement resistance was also excellent.
  • a machine part having a TS of 1100 MPa or more could be produced by cold working the steel wires of each level in the examples.
  • the steel wire of levels 7 and 10 (both are comparative examples) having a pearlite area ratio of less than (35 ⁇ [C%] + 65)% is a hydrogen embrittlement resistance when used as a machine part. It was inferior to. Further, steel wires of levels 3, 5, 12, and 27 (all of which are comparative examples) having an AR of less than 1.4 were inferior in hydrogen embrittlement resistance when used as machine parts. Further, steel wires of levels 9, 21, 22, and 27 (all of which are comparative examples) having an aspect ratio ratio [surface layer / 0.25D] of less than 1.1 are resistant to hydrogen embrittlement when used as mechanical parts. It was inferior in chemical characteristics.
  • the steel wire of the level 14 and 25 (all are comparative examples) whose GD is more than (15 / AR) micrometer was inferior to the cold workability of a steel wire.
  • the steel wire of the level 14 and 26 (all are comparative examples) whose particle size ratio [GD / 0.25D] is 1.0 or more was inferior to the cold workability of the steel wire.
  • the steel wires of levels 23 and 24 both are comparative examples having a TS of less than 900 MPa, it was not possible to manufacture mechanical parts having a TS of 1100 MPa or more.
  • limit compression ratio is less than 70%
  • the frequency of occurrence of work cracks was high when manufacturing machine parts.
  • mechanical parts manufactured using steel wires with poor cold workability limit compressibility is less than 70% have poor dimensional accuracy.

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Abstract

L'invention concerne un fil d'acier pour composant mécanique non traité thermiquement qui contient, en % en masse, Ｃ：０,４０～０,６５％, Ｓｉ：０,０５～０,５０％, Ｍｎ：０,２０～１,００％ et Ａｌ：０,００５～０,０５０％, contenant pour le reste un Fe et des impuretés. Sa structure métallique contient （３５×［Ｃ％］＋６５）％ ou plus de perlite. Lorsque le diamètre est représenté par D, que le rapport longueur/diamètre moyen de blocs de perlite en une position de 50μｍ de profondeur dans un plan transversal L, est représenté par AR, et que le diamètre granulaire de bloc moyen des blocs de perlite en une position de 50μｍ de profondeur dans un plan transversal C, est représenté par GD, alors AR est supérieur ou égal à 1,4, （ＡＲ）／（rapport longueur/diamètre moyen de blocs de perlite en une position de 0,25D de profondeur dans le plan transversal L） est supérieur ou égal à 1,1, GD est inférieur ou égal à （１５／ＡＲ）μｍ, et （ＧＤ）／（diamètre granulaire de bloc moyen des blocs de perlite en une position de 0,25D de profondeur dans le plan transversal C）, est inférieur à 1,0.
PCT/JP2017/002026 2016-01-20 2017-01-20 Fil d'acier pour composant mécanique non traité thermiquement, et composant mécanique non traité thermiquement WO2017126695A1 (fr)

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JP6614245B2 (ja) 2019-12-04
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