Classifications

• • 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
  • C21D9/02—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for springs
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
  • C21D1/18—Hardening; Quenching with or without subsequent tempering
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
  • C21D1/18—Hardening; Quenching with or without subsequent tempering
  • C21D1/19—Hardening; Quenching with or without subsequent tempering by interrupted quenching
  • C21D1/20—Isothermal quenching, e.g. bainitic hardening
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
  • C21D1/18—Hardening; Quenching with or without subsequent tempering
  • C21D1/25—Hardening, combined with annealing between 300 degrees Celsius and 600 degrees Celsius, i.e. heat refining ("Vergüten")
• • 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 of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment
  • C21D8/06—Modifying the physical properties of ferrous metals or ferrous alloys 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
  • C21D9/525—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for wires; for strips ; for rods of unlimited length for wire, for rods
• • 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
  • C22C38/30—Ferrous alloys, e.g. steel alloys containing chromium with cobalt
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D2211/00—Microstructure comprising significant phases
  • C21D2211/008—Martensite

Definitions

• the present invention relates to a spring steel wire having a martensite structure tempered by quenching and tempering, a method of manufacturing a spring steel wire suitable for manufacturing the spring steel wire, and a spring manufactured by the steel wire. is there.
• it relates to a high-strength steel wire for a spring having high strength and excellent fatigue characteristics, which is suitable for a spring used in an engine valve spring of a car or inside a transmission.
• Patent Document 1 Japanese Patent No. 2842579
• Patent Document 2 Japanese Patent Application Laid-Open No. 2002-194496
• Patent Document 3 Japanese Patent No. 3045795
• the C (carbon) content of a steel wire is set to 0.3 to 0.5% by weight. To improve toughness. However, since the heat resistance is reduced by reducing the carbon content to less than 0.50% by weight, if the steel wire is subjected to the above-mentioned high-temperature nitriding treatment, the fatigue may be reduced. The strength is reduced, and it may cause internal breakage when used as a spring.
• the surface of the steel wire is intentionally decarburized at the time of oil tempering to reduce the surface hardness and improve the spring workability. It is difficult to obtain a suitable decarburized layer, which is unsuitable for mass production of steel wires and springs. In addition, it is necessary to control the oxygen concentration when heating the steel wire (during oil tempering), which increases costs.
• a main object of the present invention is to provide a high-strength spring steel wire excellent in both fatigue strength and toughness.
• Another object of the present invention is to provide a spring made of the above-mentioned spring steel wire, and a manufacturing method suitable for manufacturing the above-mentioned spring steel wire.
• the drawing value of the steel wire after quenching and tempering and the shear yield stress of the steel wire subjected to heat treatment equivalent to nitriding after the quenching and tempering are specified to specific values. Achieves the above objectives.
• the present invention is a spring steel wire having a martensite structure tempered by quenching and tempering.
• This spring steel wire has a drawing value of 40% or more, and the shear yield stress of the steel wire after heat treatment at 420 ° C or more and 480 ° C or less for 2 hours or more is 100000Pa or more.
• the spring steel wire also has any one of the following chemical component forces.
• the method for producing a steel wire for a spring comprises the steps of patenting a steel material having a chemical component described in any one of the following (A) to (C), and drawing the patented steel material by a wire drawing force. And quenching and tempering the drawn steel wire.
• the patenting comprises an austenitizing step of heating at 900-1050 ° C for 60-180 seconds, and a constant temperature transformation step of heating at 600-750 ° C for 20-100 seconds after the austenite step. I'll be exempt.
• steel materials further contain mass% V: 0.05-0.50%, Mo: 0.05-0.50%, W: 0.05-0.15%, Nb: 0.05-0.15%, And Ti: containing one or more elements selected from the five element groups consisting of 0.01-0.20%! /.
• the spring In order to improve the fatigue characteristics of the spring, it is desired to suppress the fatigue fracture of the spring.
• the spring When a spring is used repeatedly, the spring is repeatedly stressed in the shear direction as well as in the tension and compression directions. Due to the externally applied repetitive stress, the spring repeatedly or locally undergoes slip deformation (plastic deformation), and irregularities are generated near the surface of the spring, causing cracks and fracture. Or fatigue failure. Therefore, in order to suppress the fatigue fracture of the spring, it is effective to suppress the local or intensive plastic deformation.
• a steel wire is subjected to a heat treatment such as a nitriding treatment after a spring is applied to the spring to increase the surface hardness of the spring and improve the fatigue limit.
• the present inventors have conducted various studies, and found that after heat treatment such as the above-described nitriding treatment, It was found that the inside of the material (spring) should have the appropriate torsional strength. Specifically, it was found that the fatigue properties of the spring can be improved if the spring yield stress is equal to or more than 100 MPa after the heat treatment such as the nitriding treatment. Based on this finding, the steel wire for springs of the present invention specifies the shear yield stress of the steel wire after a specific heat treatment after quenching and tempering to lOOOMPa or more.
• the present inventors have conducted various studies and found that setting the drawing value of the steel wire after quenching and tempering to 40% or more is effective in preventing breakage of the steel wire during spring working, and mass production of springs. The knowledge that it was excellent was obtained. Based on this finding, the present invention sets the drawing value of the steel wire to 40% or more. If the aperture value is less than 40%, breakage of the steel wire is likely to occur during spring processing, which may hinder mass production of the spring.
• the iris value may be reduced slightly by subjecting the steel wire to a specific heat treatment at 420 ° C or more and 480 ° C or less and corresponding to the above-mentioned nitriding treatment for 2 hours or more after quenching and tempering.
• a specific heat treatment at 420 ° C or more and 480 ° C or less and corresponding to the above-mentioned nitriding treatment for 2 hours or more after quenching and tempering.
• the drawing value is 40% or more, the steel wire can maintain the drawing value at 35% or more even after the above heat treatment, and the spring obtained from this steel wire has high fatigue strength. Characteristics are obtained.
• the steel wire for spring of the present invention defines the drawing value and the shear yield stress after subjecting the steel wire to a heat treatment equivalent to nitriding treatment, whereby the steel wire of the present invention and the steel wire of the present invention are defined.
• the aim is to achieve both high fatigue strength and high toughness of the spring obtained by the method.
• the heat treatment such as nitriding, applied to the spring after the steel wire is processed into a spring, improves the surface hardness of the spring, which can improve the fatigue limit of the spring, but decreases the internal hardness of the spring. Therefore, internal breakage may occur during use. Therefore, in the present invention, C and Si for improving the heat resistance of the parent phase of the steel wire processed into the spring are set within a predetermined range ( % By mass). Further, when the steel wire is tempered, a predetermined amount of Cr is contained in order to form carbides in the structure of the steel wire and increase the softening resistance of the steel wire.
• the steel wire for spring of the present invention can be obtained by subjecting a steel material having the above-mentioned chemical components to melting, hot forging, hot rolling, patenting, wire drawing, and quenching and tempering.
• the steel structure is sufficiently austenitized to dissolve undissolved carbides, and to have a uniform pearlite structure by appropriate isothermal transformation.
• Get. Insufficient austenite dangling causes a reduction in the toughness and shear yield stress of the steel wire. Therefore, it is appropriate to heat at a temperature of 900 to 1050 ° C for 60 to 180 seconds in order to sufficiently austenite. If the heating temperature is less than 900 ° C, or if the heating temperature is 900-1050 ° C and the heating time is less than 60 seconds, sufficient austenite shaping cannot be performed, and undissolved carbide remains. If the heating temperature is higher than 1050 ° C, or if the heating temperature is 900-1050 ° C and the heating time is longer than 180 seconds, the austenite grains become coarse and martensite is easily formed during transformation. In drawing, the drawability is impaired.
• the quenching temperature should be more than 850 ° C and less than 1050 ° C! /.
• the steel wire for spring of the present invention has a tempered martensite structure.
• austenite crystal grains (former austenite crystal grains) of the steel wire after quenching and tempering are refined, the steel wire and the spring obtained from this steel wire will be locally and intensively even if repeated stress is applied. Slip deformation occurs. That is, since the shear yield stress of a steel wire or a spring can be improved, the refinement of austenite crystal grains (former austenite crystal grains) as a result can contribute to the improvement of fatigue properties.
• the average crystal grain size of austenite crystal grains is 3.0 to 7.0 / zm.
• the average crystal grain size can be changed by changing the temperature of the patenting applied to the steel material. More specifically, when the temperature at which the austenite is reduced in patenting is lowered, the crystal grain size tends to decrease, and when the temperature is increased, the crystal grain size tends to increase. When the average crystal grain size is less than 3.0 m, the austenite temperature is low, so that undissolved carbides remain and the toughness of the steel wire is likely to decrease. On the other hand, if the average crystal grain size exceeds 7.0 m, the fatigue limit of the steel wire or the spring obtained from the steel wire is not easily improved.
• the average crystal grain size is a value measured after quenching and tempering a drawn steel wire.
• C is an important element that determines the strength of steel. If the carbon content is less than 0.50% by mass of the entire steel, a steel wire with sufficient strength cannot be obtained, and if it exceeds 0.75% by mass, toughness is impaired. And the carbon content is 0.50% by mass or more and 0.75% by mass or less.
• Si 1.80-2.70 Si is used as a deoxidizer at the time of melting and refining steel materials.
• Si forms a solid solution in ferrite to improve heat resistance, and prevents the hardness inside the steel wire (spring) from decreasing due to heat treatment such as strain relief annealing / nitriding that is applied to the spring after spring kneading. There is. To maintain heat resistance, it must be 1.80% by mass or more, and if it exceeds 2.70% by mass, toughness is reduced. Therefore, the content of Si should be 1.80% by mass or more and 2.70% by mass or less.
• Mn is used as a deoxidizing agent at the time of dissolving and refining, like Si. Therefore, the lower limit of the content of Mn required for the deoxidizing agent is set to 0.1% by mass. In addition, Mn has the effect of improving the hardenability of the steel wire, increasing the strength of the steel wire, and improving the shear yield stress of the steel wire and the spring obtained from the steel wire. However, if the content of Mn is more than 1.5% by mass with respect to the entire steel, martensite is likely to be generated in the steel material during patenting, which may cause wire breakage during wire drawing. To 1.5% by mass. In particular, if the steel contains Co, as described below, the Mn content can be as low as 0.1-0.7% by mass. If no Co is contained, the Mn content should be higher than 0.7-1.5% by mass. Is preferred. It may contain a large amount of Mn and also contain Co.
• Cr is effective in preventing the softening of the spring when the spring is subjected to a heat treatment such as a tempering treatment and a nitriding treatment after the spring working in order to improve the hardenability of the steel and increase the calorie resistance. If the Cr content is less than 0.70% by mass with respect to the entire steel, a sufficient effect for preventing softening cannot be obtained. Therefore, the Cr content is set to 0.70% by mass or more, and if it exceeds 1.50% by mass, the Cr content during patenting is reduced. Martensite is liable to be generated, causing wire breakage during wire drawing, and reducing the toughness of the steel material after patenting (oil tempering). Therefore, the content of Cr is specified as 0.70-1.50%.
• Co has an effect of improving heat resistance, and is effective in preventing tempering treatment or nitriding treatment of a spring after spring processing. Further, when the content of Co is small, the toughness of the steel wire is not reduced. If the Co content is less than 0.02% by mass, the steel wire or spring It is difficult to obtain effects such as improvement of yield stress and heat resistance of steel wire. Even if Co content exceeds 1.00% by mass, Co is added compared to the case where 1.00% by mass or less is added.
• the Co content should be 0.02% by mass or more and 1.00% by mass or less. If Co is contained in steel, the Mn content may be as low as 0.1-0.7% by mass as described above!
• Ni in steel has the effect of improving the corrosion resistance and toughness of the steel wire. If the Ni content is less than 0.1% by mass, it is difficult to obtain the above-mentioned steel wire effect. Even if the Ni content exceeds 1.0% by mass, the cost of steel wire production only increases, and the toughness of the steel wire is further increased. No improvement effect is obtained. Therefore, the content of Ni is set to 0.1% by mass or more and 1.0% by mass or less.
• Ti has the effect of forming carbides during tempering and increasing the softening resistance of the steel wire. If the content of ⁇ ⁇ is less than 0.01% by mass, the above effect cannot be obtained. If the content of ⁇ exceeds 0.20% by mass, the high melting point nonmetallic inclusions TiO are formed in the steel wire structure, and the It is easy to reduce toughness. Therefore, the content of Ti is set to 0.01% by mass or more and 0.20% by mass or less.
• the cross-sectional shape of the spring steel wire of the present invention perpendicular to the longitudinal direction (drawing direction) of the steel wire may be not only a circle but also an elliptical shape, a trapezoid, a square, a rectangular shape, or the like.
• the spring of the present invention can be obtained by applying a spring force such as coiling to the spring steel wire.
• a spring force such as coiling
• the spring steel wire of the present invention is subjected to heat treatment such as nitriding after the spring steel wire is subjected to heat treatment, the surface hardness of the spring is improved and the spring has an excellent fatigue limit. it can.
• a steel material consisting of the chemical components shown in Table 1 and the balance consisting of Fe and impurities was smelted in a vacuum melting furnace, and a ⁇ 6.5 mm wire was manufactured by hot forging and hot rolling. After that, the wire was subjected to patenting (austenite shading ⁇ constant temperature transformation), peeling, annealing, and wire drawing to obtain a ⁇ 3.0 mm wire.
• Table 2 shows the patenting conditions.
• the patenting performed on the wire with a diameter of 6.5 mm was performed by preparing a plurality of conditions with different heating times and holding times for the wire as the conditions for austenitizing the wire as shown in Table 2.
• As conditions for constant temperature transformation of the wire after austenitization a plurality of conditions having different heating times and holding times of the wire were prepared.
• the obtained wire (3.0 mm in diameter) was quenched and tempered.
• the quenching was performed under the conditions shown in Table 3, and the tempering was performed at a heating temperature of 450 to 530 ° C. for all the wires.
• the aperture value (RA) and the average grain size (average ⁇ grain size) of austenite grains (former austenite grains) were measured. The results are shown in Table 3.
• the average grain size of austenite grains (former austenite grains) was changed by changing the quenching temperature of the wire.
• the average grain size of the austenite grains was calculated by a cutting method defined in JIS G0522.
• the steel wire subjected to a heat treatment (420 ° C for 2 hours or 480 ° C for 2 hours) equivalent to nitriding treatment was applied to the steel wire to obtain the shear yield stress and fatigue characteristics (fatigue property). Limit) was measured. Table 3 shows the results.
• the shear yield stress of the heat-treated steel wire was determined from a torque-0 curve by conducting a twist test with a sample length of 100 d (d: sample diameter). The fatigue limit was evaluated by Nakamura's rotary bending fatigue test.
• Sample Nos. 1-4, 6, and 8 resulted in low shear yield stress and low fatigue limit after heat treatment corresponding to nitriding.
• Sample Nos. 2 and 4 had low drawing values and poor toughness.
• the experiment was stopped because martensite was generated in the wire structure during patenting, and the wire was frequently broken by peeling in the next step.
• sample No. ll the shear yield stress after heat treatment was low, and the V content in the entire steel was large, so the drawing of the steel wire was reduced and the fatigue limit was reduced.
• Sample No. 12 had low shear yield stress after heat treatment and high Ti content, so the fatigue limit was low due to breakage by Ti-based inclusions. I gave it.
• the steel wire for springs of the present invention is excellent in fatigue characteristics and toughness, and thus is most suitable for a material of a spring used in a part where fatigue strength is required.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Organic Chemistry (AREA)
• Mechanical Engineering (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Thermal Sciences (AREA)
• Physics & Mathematics (AREA)
• Crystallography & Structural Chemistry (AREA)
• Manufacturing & Machinery (AREA)
• Heat Treatment Of Strip Materials And Filament Materials (AREA)
• Heat Treatment Of Steel (AREA)
• Springs (AREA)

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• 2004
  • 2004-02-04 JP JP2004027891A patent/JP4357977B2/ja not_active Expired - Fee Related
• 2005
  • 2005-02-04 EP EP05709768.5A patent/EP1731625B1/en not_active Expired - Lifetime
  • 2005-02-04 US US10/588,287 patent/US20080271824A1/en not_active Abandoned
  • 2005-02-04 CN CNB2005800039621A patent/CN100449026C/zh not_active Expired - Fee Related
  • 2005-02-04 WO PCT/JP2005/001703 patent/WO2005075695A1/ja not_active Ceased
• 2006
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