WO2004055226A1 - Steel wire for spring - Google Patents

Steel wire for spring Download PDF

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Publication number
WO2004055226A1
WO2004055226A1 PCT/JP2003/015689 JP0315689W WO2004055226A1 WO 2004055226 A1 WO2004055226 A1 WO 2004055226A1 JP 0315689 W JP0315689 W JP 0315689W WO 2004055226 A1 WO2004055226 A1 WO 2004055226A1
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WO
WIPO (PCT)
Prior art keywords
tempering
quenching
mass
spring
wire
Prior art date
Application number
PCT/JP2003/015689
Other languages
French (fr)
Japanese (ja)
Inventor
Yoshiro Fujino
Nozomu Kawabe
Norihito Yamao
Hiromu Izumida
Teruyuki Murai
Original Assignee
Sumitomo (Sei) Steel Wire Corp.
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Publication date
Application filed by Sumitomo (Sei) Steel Wire Corp. filed Critical Sumitomo (Sei) Steel Wire Corp.
Publication of WO2004055226A1 publication Critical patent/WO2004055226A1/en

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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
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/28—Ferrous alloys, e.g. steel alloys containing chromium with titanium or zirconium
    • 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
    • C22C38/22—Ferrous alloys, e.g. steel alloys containing chromium with molybdenum or tungsten
    • 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
    • C22C38/24—Ferrous alloys, e.g. steel alloys containing chromium with vanadium
    • 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
    • C22C38/26—Ferrous alloys, e.g. steel alloys containing chromium with niobium or tantalum
    • 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
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/34—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of silicon
    • 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
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/06—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of rods or wires
    • C21D8/065—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of rods or wires of ferrous alloys
    • 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

Definitions

  • the present invention relates to a spring steel wire having a quenched and tempered martensite structure and a spring manufactured from the steel wire.
  • the present invention relates to a high-strength, high-toughness spring steel wire and spring suitable for an engine valve spring of an automobile or a spring used in a transmission.
  • Patent Document 1 Japanese Patent Application Laid-Open No. 2-247354
  • Patent Patent Document 2 Japanese Patent Application Laid-Open No. 2000-313938 (Claims, see FIG. 1)
  • Patent Document 3 Japanese Patent Application Laid-Open No.
  • Patent Document 4 JP-A-2002-194496 (Claims, see Table 1)
  • Patent Document 5 JP-A-2002-180195, (Claims, Table 1)
  • Non-Patent Document 1 Spring Technical Meeting, Autumn Meeting, 1994, "8 Influence of Surface Defects on Fatigue Strength of High Fatigue Strength Spring," Jan. 1994, pp. 29-32 Gachi Has been.
  • Nitriding usually hardens the wire surface and increases the surface hardness, but reduces the hardness inside the wire. Also, by performing the nitriding treatment in addition to the strain relief annealing after the spring working, the hardness inside the wire is more likely to decrease. And, since the inside of the wire is low in hardness, there is a possibility that breakage starting from the inside of the wire may occur.
  • Patent Documents 1 and 4 do not describe the nitriding treatment, and do not consider the decrease in hardness inside the wire due to the nitriding treatment.
  • Patent Document 2 defines only the hardness of the wire surface.
  • the temperature of the nitriding treatment is increased. As can be seen from the test results described below, the higher the temperature of the nitriding treatment, the lower the toughness such as drawing tends to be.
  • a main object of the present invention is to provide a spring steel wire having good balance of strength and toughness, and a spring manufactured from this steel wire. Disclosure of the invention
  • the present invention achieves the above object by defining the internal hardness after heat treatment performed after spring working and the reduction value in addition to the chemical composition, austenite crystal grain size, and residual austenite amount.
  • the spring steel wire of the present invention has the following features.
  • C 0.55 to 0.75%
  • Si 1.80 to 2.70%
  • Mn 0.1 to 0.7%
  • Cr 0.70 to 1.50%
  • V 0.05 to 0.50%
  • Mo 0.05 to 0.50%
  • W 0.05 to 0.15%
  • Nb 0.05 to 0.15%
  • Ti at least one selected from the group consisting of 0.01 to 0.20%, with the balance being Fe and unavoidable impurities
  • Tempered martensite structure obtained by quenching and tempering
  • Austenite grain size after quenching and tempering is 1.0 to 18.0 m
  • the austenite crystal grain size is the former austenite crystal grain size.
  • Residual austenite after quenching and tempering is 10% by volume or less
  • an aperture value is used as an index of toughness.
  • heat resistance is improved by solid solution strengthening by Si in the above component range and precipitation strengthening of carbides of V, Mo, W, Nb, Ti.
  • heat treatment such as strain relief annealing (tempering treatment) and nitriding treatment is performed after quenching and tempering, the hardness inside the wire is hardly reduced and high hardness can be obtained.
  • the toughness can be improved not only after quenching and tempering but also after the subsequent heat treatment. Based on this knowledge, the above chemical components are specified.
  • the hardness at a position 1/4 of the diameter from the center of the line is defined as the hardness inside the line, not as the hardness of the surface layer such as the surface of the line or near the surface of the line.
  • the position 1/4 of the diameter from the center of the line is least susceptible to the increase in hardness near the surface due to surface decarburization / nitrogen treatment, segregation of the center, etc., so it is easy to properly evaluate the internal hardness after heat treatment. .
  • the chemical components are specified as described above in order to prevent a decrease in the hardness inside the wire, but the internal hardness may also be reduced by heat treatment. Specifically, the higher the heat treatment temperature and the longer the holding time, the lower the temperature. Therefore, in order to prevent the decrease in internal hardness due to heat treatment and to obtain the effect of improving heat resistance and improving surface hardness by heat treatment such as nitriding treatment, a relatively higher temperature range than that conventionally used: Heating at 420 "C or more and 480 ° C or less is required for 2 hours or more. Therefore, in the present invention, the heat treatment conditions after quenching and tempering are specified as 420 to 480 and 2 hours or more.
  • the improvement in toughness is affected by the crystal grain size of old austenite and the amount of residual austenite. Based on this knowledge, the present invention Defines these parameters.
  • the steel wire for springs of the present invention configured based on the above findings improves toughness, reduces a decrease in internal hardness after heat treatment performed after quenching and tempering, and suppresses breakage of a spring starting from inside the wire. Can be.
  • C is an important element that determines the strength of steel. If it is less than 0.55% by mass, sufficient strength cannot be obtained, and if it exceeds 0.75% by mass, the toughness is impaired. 75 mass% or less.
  • Si is used as a deoxidizing agent during refining. Further, the solid solution in the ferrite improves heat resistance, and prevents a decrease in hardness inside the wire due to heat treatment such as strain relief annealing and nitriding after spring processing. In order to maintain heat resistance, 1.8 mass% or more is required, and if it exceeds 2.7 mass%, toughness is reduced. Therefore, the content is 1.8 mass% or more and 2.7 mass% or less. Mn: 0.1 to 0.7 mass%
  • Mn like Si
  • the lower limit of the required amount of the deoxidizing agent is set to 0.1% by mass.
  • Mn is an element that easily causes center segregation.If added excessively, Mn forms martensite in the center segregated part during the patenting process after hot rolling, which causes wire breakage during subsequent wire drawing.
  • the toughness after quenching and tempering In order to improve toughness, the amount of addition is made relatively small compared to conventional ones. Specifically, the upper limit is set to 0.7% by mass as the amount of addition to prevent a decrease in toughness. Cr: 0.7 to 1.5 mass%
  • Cr improves the hardenability of steel and increases the softening resistance after quenching and tempering, so it is effective in preventing softening during heat treatment such as tempering and nitriding after spring processing. If the addition amount is less than 0.7% by mass, the effect of preventing softening during the heat treatment is small, so the lower limit is set to 0.7% by mass as an addition amount that can provide a sufficient effect. On the other hand, if it is added in excess of 1.5% by mass, martensite is liable to be generated during patenting, causing wire breakage during wire drawing and reducing toughness after oil tempering. Therefore, the amount of Cr added is set to 1.5% by mass or less.
  • Si and Cr have an effect of improving heat resistance by forming carbides. Therefore, in the present invention, the content of Si and Cr is set relatively high to improve the heat resistance. However, the amount to be included depends on the balance with toughness. In order to obtain sufficient heat resistance, it is preferable that the atomic% of Si + the atomic% of Cr be 0.09 or more.
  • C 0.60% to 0.70% by mass
  • Si 2.20% to 2.5% by mass
  • Mn 0.2% by mass or more and 0.5% by mass or less
  • Cr 0.9% by mass or more and 1.3% by mass or less.
  • Co 0.02 to 1.00 mass%
  • Co is an element that raises the Ms point (martensite transformation start temperature). Reduces the amount of residual austenite after quenching and improves toughness after quenching and tempering. Therefore, in the present invention, it is added to further improve the toughness. In order to obtain the effect of improving toughness, it is preferable to add 0.02% by mass or more. On the other hand, even if a certain amount or more is added, the above effect cannot be improved, and Co is relatively expensive, so the upper limit is made 1.00% by mass or less. A more preferable addition amount in consideration of both improvement in toughness and cost is 0.05% by mass or more and 0.20% by mass or less.
  • T i forms carbides during tempering and has the effect of increasing softening resistance. To obtain this effect, it is preferable to add 0.01% by mass or more. However, if added in excess, high melting point non-metallic inclusions TIO may be formed and the toughness may be reduced. In consideration of the decrease in toughness due to the formation of inclusions, the content is set to 0.20% by mass or less.
  • the hardness inside the wire may be reduced, or breakage may occur from the inside of the wire.
  • the internal hardness and toughness tend to decrease as the heating temperature of the nitriding treatment increases. Therefore, in the present invention, heat resistance and toughness are improved by defining chemical components. Specifically, the hardness inside the wire is 550HV or more.
  • the grain size of the former onestenite affects the fatigue resistance.
  • the grain size is 18.0 ⁇ m or less, the fatigue characteristics are improved due to the effect of refining the crystal grains.
  • the crystal grain size of the former austenite is set to be more than 1.0 m and 18.0 m or less.
  • the crystal grain size of old austenite can be controlled by changing the heating temperature during quenching when the holding time is constant. Specifically, the particle size can be reduced by lowering the heating temperature, and can be increased by increasing the heating temperature.
  • the content of residual austenite is set to 10% by volume or less.
  • the amount of residual austenite can be controlled by specifying the chemical components as described above. ⁇ Toughness>
  • the drawn value after heat treatment performed after quenching and tempering is set to 35% or more.
  • the aperture value can be controlled by specifying the chemical composition, austenite crystal grain size, and residual austenite amount as described above.
  • the spring steel wire of the present invention is preferably used for manufacturing a spring by performing spring working after quenching and tempering, nitriding, and performing one or more shot peening.
  • the manufactured spring may be used for an engine valve spring of an automobile, an interior of a transmission, and the like.
  • wires with a diameter of 6.3 ⁇ were prepared by hot rolling. After patenting this wire, stripping, annealing, and wire drawing were performed sequentially to obtain a wire with a diameter of 3.2 mm. The wire was quenched and tempered.
  • the tensile strength was controlled by changing the tempering temperature.
  • the grain size was controlled by changing the quenching temperature.
  • the particle size is 10 Sample Nos. 4 to 6, 14, and 15 with a particle size of less than 900 m are 900, heating rate is 500 ° C / s, holding time is 2 s, and sample Nos. 2, 3, and 7-13 have a particle size of 10 to 15 zm or less.
  • the sample No. 1 having a temperature of 1000, a heating rate of 500 / s, a holding time of 2 s and an r particle size of more than 20 m was set to 1100 ° C, a heating rate of 500 / s, and a holding time of 2 s.
  • the amount of residual a and the hardness inside the wire were varied depending on the chemical composition.
  • samples ⁇ 8 to 15 that satisfy the specified chemical composition, ⁇ particle size, and residual r content have high internal hardness and excellent toughness even after heat treatment after quenching and tempering. You can see it. Also, it can be seen that the relatively low heat treatment temperature has excellent internal hardness and toughness.
  • Sample No. 1 which has a low C content and a high quenching temperature, has a low internal hardness after heat treatment.
  • Samples Nos. 3 and 7 have low heat resistance due to their low Cr and Si contents, low internal hardness after heat treatment, and small aperture values.
  • Sample No. 2 has a high residual C content due to a high C content, and has low toughness.
  • Samples Nos. 4 to 6 each had a high Si, Mn, and Cr content, resulting in poor toughness and a low drawing value.
  • the spring steel wire of the present invention by providing both the strength and the toughness in a well-balanced manner, it is possible to achieve an excellent effect that the fatigue characteristics can be improved. Therefore, the spring having excellent fatigue characteristics can be obtained by using the spring steel wire of the present invention.

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

Abstract

A steel wire for a spring, characterized in that it has a chemical composition, in mass %: C: 0.55 to 0.75 %, Si: 1.80 to 2.70 %, Mn: 0.1 to 0.7 %, Cr: 0.70 to 1.50 %; one or more selected from the group consisting of V: 0.05 to 0.50 %, Mo: 0.05 to 0.50 %, W: 0.05 to 0.15 %, Nb: 0.05 to 0.15 % and Ti: 0.01 to 0.20 %; and the balance: Fe and inevitable impurities, it has a tempered martensite structure formed by quenching followed by tempering, and it exhibits, after quenching and tempering, an austenite grain diameter of 1.0 to 18.0 μm and an amount of retained austenite of 10 volume % or less and, after the heat treatment at 420 to 480°C for 2 hr or more subsequent to the quenching and tempering, a hardness at a position 1/4 of the diameter of the wire off the center of the wire of 550 Hv or more and a reduction of area of 35 % or more. The steel wire offers excellent balance of strength and toughness, and thus is improved in fatigue characteristics.

Description

明 細 書 ばね用鋼線 技術分野  Description Steel wire for spring Technical field
本発明は、 焼入れ焼戻しを行って焼戻しマルテンサイ ト組織を有す るばね用鋼線及びこの鋼線により製造されたばねに関するものである。 特に、 自動車のエンジン弁ばねやトランスミッション内部に用いられ るばねなどに適した高強度高靭性のばね用鋼線及びばねに関するもの である。 背景技術  The present invention relates to a spring steel wire having a quenched and tempered martensite structure and a spring manufactured from the steel wire. In particular, the present invention relates to a high-strength, high-toughness spring steel wire and spring suitable for an engine valve spring of an automobile or a spring used in a transmission. Background art
自動車の低燃費化に対応して、 近年、 自動車のエンジンやトランス ミッションの小型軽量化が進められている。 それに伴って、 エンジン の弁ばねやトランスミツション用のばねに負荷される応力は年々厳し くなつており、 用いられるばね材料にも一層の疲労強度の向上が求め られている。 これらエンジンの弁ばねやトランスミツションのばねに は、 従来、 シリコンクロム系のオイルテンパー線が用いられており、 例えば、 特許文献 1 ： 特開平 2-247354号公報（特許請求の範囲、 第 1 図参照）、 特許文献 2： 特開 2000- 31 3938号公報（特許請求の範囲、 図 1 参照）、 特許文献 3： 特開平 10-251760 号公報（特許請求の範囲、 実 施例、 表 1、 表 2参照）、 特許文献 4： 特開 2002-194496号公報（特許 請求の範囲、 表 1 参照）、 特許文献 5： 特開 2002- 180195号公報（特許 請求の範囲、 表 1 参照）、 非特許文献 1 ： ばね技術研究会 1994 年度 秋季講演会講演論文集 「8 高疲労強度ばねの疲労強度に及ぼす表 面欠陥の影響」 1 994 年 1 1 月、 29- 32 ページに記載されるものが知 られている。 In response to the reduction in fuel consumption of automobiles, the size and weight of automobile engines and transmissions have been reduced in recent years. Accordingly, the stress applied to engine valve springs and transmission springs is becoming severer year by year, and the spring materials used are required to further improve fatigue strength. Conventionally, silicon-chromium oil-tempered wires have been used for valve springs and transmission springs of these engines. For example, Patent Document 1: Japanese Patent Application Laid-Open No. 2-247354 (Patent Patent Document 2: Japanese Patent Application Laid-Open No. 2000-313938 (Claims, see FIG. 1) Patent Document 3: Japanese Patent Application Laid-Open No. 10-251760 (Claims, Examples, Table 1) , Table 2), Patent Document 4: JP-A-2002-194496 (Claims, see Table 1), Patent Document 5: JP-A-2002-180195, (Claims, Table 1), Non-Patent Document 1: Spring Technical Meeting, Autumn Meeting, 1994, "8 Influence of Surface Defects on Fatigue Strength of High Fatigue Strength Spring," Jan. 1994, pp. 29-32 Gachi Has been.
上記のようにばねに要求される特性は、 近年厳しくなつており、 ば ね用鋼線及びばねに対して更なる改善が求められており、 特に、 強度 と靭性とをよりバランスよく具えることが望まれている。  As described above, the characteristics required for springs have become stricter in recent years, and further improvements are required for spring steel wires and springs.In particular, a balance between strength and toughness must be provided. Is desired.
ここで、 近年、 オイルテンパー線を用いてばねを製造する際、 ばね 加工後に歪み取り焼鈍を施した後、 表面処理として窒化処理ゃショッ トピーニングを行うことが知られている（特許文献 2参照）。 窒化処理 は、 通常、 線表面を硬化させ、 表面硬度を高くすることができるが、 線内部の硬度を低下させる。 また、 ばね加工後の歪み取り焼鈍に加え て、 窒化処理を施すことで、 線内部の硬度がより低下し易くなる。 そ して、 線内部が低硬度であることで、 線内部を起点とする折損が生じ る可能性がある。  Here, in recent years, it has been known that when manufacturing a spring using an oil-tempered wire, after performing the strain relief annealing after the spring working, a nitriding short shot peening is performed as a surface treatment (see Patent Document 2). ). Nitriding usually hardens the wire surface and increases the surface hardness, but reduces the hardness inside the wire. Also, by performing the nitriding treatment in addition to the strain relief annealing after the spring working, the hardness inside the wire is more likely to decrease. And, since the inside of the wire is low in hardness, there is a possibility that breakage starting from the inside of the wire may occur.
特許文献 1及び 4では、 窒化処理について記載されておらず、 窒化 処理による線内部の硬度の低下が考慮されていない。 特許文献 2では、 線表面の硬度のみを規定している。 また、 特許文献 2及び非特許文献 1 では、 窒化処理の温度を高くしている。 後述する試験結果からわか るように、 窒化処理の温度が高いほど、 絞りなどの靭性が低下する傾 向にある。  Patent Documents 1 and 4 do not describe the nitriding treatment, and do not consider the decrease in hardness inside the wire due to the nitriding treatment. Patent Document 2 defines only the hardness of the wire surface. In Patent Document 2 and Non-Patent Document 1, the temperature of the nitriding treatment is increased. As can be seen from the test results described below, the higher the temperature of the nitriding treatment, the lower the toughness such as drawing tends to be.
更に、 硬度のみでは十分な疲労特性が得られにくいため、 靭性につ いても管理する必要があるが、 いずれの文献も、 高硬度であると共に、 靭性をよりよくするための構成について言及されていない。 特に、 い ずれの文献も、 靭性の指標の一つである絞り値を規定していない。  In addition, it is difficult to obtain sufficient fatigue properties only with hardness, so it is necessary to control toughness.Both documents refer to configurations that are high in hardness and have better toughness. Absent. In particular, none of the documents specify an aperture value, which is one of the indicators of toughness.
そこで、 本発明の主目的は、 強度と靱性とをパランスよく具えるば ね用鋼線、 及びこの鋼線から製造されたばねを提供することにある。 発明の開示 Therefore, a main object of the present invention is to provide a spring steel wire having good balance of strength and toughness, and a spring manufactured from this steel wire. Disclosure of the invention
本発明は、 化学成分、 オーステナイ ト結晶粒径、 残留オーステナイ ト量に加えて、 ばね加工後に施す熱処理後の内部硬度及び絞り値を規 定することで上記目的を達成する。  The present invention achieves the above object by defining the internal hardness after heat treatment performed after spring working and the reduction value in addition to the chemical composition, austenite crystal grain size, and residual austenite amount.
即ち、 本発明ばね用鋼線は、 以下を特徴とする。  That is, the spring steel wire of the present invention has the following features.
<化学成分 > <Chemical composition>
質量％で、 C： 0.55〜0.75%、 Si ： 1.80〜2.70%、 Mn： 0.1〜0.7%、 Cr ： 0.70〜1.50%と、 V： 0.05〜 0.50 %、 Mo： 0· 05〜 0.50 %、 W： 0.05 〜0.15%、 Nb： 0.05〜0.15%及び Ti ： 0.01〜0.20%よりなる群から 選択される 1種以上とを含有し、 残部が Fe及び不可避不純物  In mass%, C: 0.55 to 0.75%, Si: 1.80 to 2.70%, Mn: 0.1 to 0.7%, Cr: 0.70 to 1.50%, V: 0.05 to 0.50%, Mo: 0.05 to 0.50%, W : 0.05 to 0.15%, Nb: 0.05 to 0.15%, and Ti: at least one selected from the group consisting of 0.01 to 0.20%, with the balance being Fe and unavoidable impurities
<組織 > <Organization>
焼入れ焼戻しによって得られる焼戻しマルテンサイ ト組織  Tempered martensite structure obtained by quenching and tempering
<オーステナイ ト結晶粒径 > <Austenite grain size>
焼入れ焼戻し後のオーステナイ ト結晶粒径が 1.0〜18.0 m  Austenite grain size after quenching and tempering is 1.0 to 18.0 m
本発明においてオーステナイ ト結晶粒径とは、 旧オーステナイ ト結 晶粒径とする。  In the present invention, the austenite crystal grain size is the former austenite crystal grain size.
<残留オーステナイ ト量 > <Residual austenite amount>
焼入れ焼戻し後の残留オーステナイ ト量が 10体積％以下  Residual austenite after quenching and tempering is 10% by volume or less
<線内部の硬度 > <Hardness inside wire>
焼入れ焼戻し後に施す 420〜480°Cで 2hr 以上の熱処理後において、 線中心から直径の 1/4の位置における硬度： 550Hv以上  After heat treatment at 420 to 480 ° C for 2 hours or more after quenching and tempering, hardness at 1/4 of the diameter from the line center: 550Hv or more
<靭性 > <Toughness>
焼入れ焼戻し後に施す 420〜480"Cで 2hr 以上の熱処理後において、 絞り値 ： 35%以上  After quenching and tempering, after heat treatment at 420 to 480 "C for 2 hours or more, Aperture: 35% or more
本発明では、 靱性の指標として絞り値を用いる。 本発明者らが種々の検討試験を行った結果、 上記成分範囲の S i に よる固溶強化と、 V、 Mo、 W、 Nb , T i の炭化物の析出強化とにより耐 熱性を向上させることで、 焼入れ焼戻し後に歪み取り焼鈍（テンパー 処理）ゃ窒化処理などの熱処理を施しても、 線内部の硬度の低下が少 なく、 高い硬度が得られるとの知見を得た。 また、 Mn の含有量を比 較的少なくすることで、 焼入れ焼戻し後だけでなく、 その後に施す熱 処理後においても、 靭性を向上することができるとの知見を得た。 こ の知見に基づき、 上記化学成分を規定する。 In the present invention, an aperture value is used as an index of toughness. As a result of various studies conducted by the present inventors, it has been found that heat resistance is improved by solid solution strengthening by Si in the above component range and precipitation strengthening of carbides of V, Mo, W, Nb, Ti. Thus, it has been found that even if heat treatment such as strain relief annealing (tempering treatment) and nitriding treatment is performed after quenching and tempering, the hardness inside the wire is hardly reduced and high hardness can be obtained. It was also found that by making the Mn content relatively low, the toughness can be improved not only after quenching and tempering but also after the subsequent heat treatment. Based on this knowledge, the above chemical components are specified.
また、 従来のように線表面や線表面よりもわずかに内側の線内部の 硬度を規定するだけでは、 熱処理後の内部硬度の評価を正当に行いに くい。 そこで、 本発明では、 線表面や線表面付近といった表層部の硬 度ではなく、 線内部の硬度として、 線中心から直径の 1/4の位置にお ける硬度を規定する。 線中心から直径の 1/4の位置は、 表面脱炭ゃ窒 化処理などによる表面付近の硬度の上昇や中心偏析などの影響を最も 受けにくいため、 熱処理後の内部硬度を正当に評価し易い。  Further, it is difficult to properly evaluate the internal hardness after heat treatment by simply defining the hardness of the wire surface or the wire inside the wire slightly inside as in the conventional case. Therefore, in the present invention, the hardness at a position 1/4 of the diameter from the center of the line is defined as the hardness inside the line, not as the hardness of the surface layer such as the surface of the line or near the surface of the line. The position 1/4 of the diameter from the center of the line is least susceptible to the increase in hardness near the surface due to surface decarburization / nitrogen treatment, segregation of the center, etc., so it is easy to properly evaluate the internal hardness after heat treatment. .
線内部の硬度の低下を防止するべく、 本発明では、 上記のように化 学成分を規定しているが、 内部硬度は、 熱処理によっても低下するこ とがある。 具体的には、 熱処理温度が高く、 かつ保持時間が長いほど 低下し易い。 そのため、 熱処理による内部硬度の低下を抑制防止し、 かつ耐熱性の向上と共に窒化処理などの熱処理による表面硬度の向上 という効果を得るには、 従来行われている温度よりも比較的高い温度 域 ： 420"C以上 480°C以下で 2 時間以上の加熱が必要である。 そこで、 本発明では、 焼入れ焼戻し後に施す熱処理条件を 420〜480 で 2hr 以上と規定する。  In the present invention, the chemical components are specified as described above in order to prevent a decrease in the hardness inside the wire, but the internal hardness may also be reduced by heat treatment. Specifically, the higher the heat treatment temperature and the longer the holding time, the lower the temperature. Therefore, in order to prevent the decrease in internal hardness due to heat treatment and to obtain the effect of improving heat resistance and improving surface hardness by heat treatment such as nitriding treatment, a relatively higher temperature range than that conventionally used: Heating at 420 "C or more and 480 ° C or less is required for 2 hours or more. Therefore, in the present invention, the heat treatment conditions after quenching and tempering are specified as 420 to 480 and 2 hours or more.
更に、 靭性の向上には、 旧オーステナイ トの結晶粒径、 残留オース テナイ ト量が影響するとの知見を得た。 この知見に基づき、 本発明で は、 これらのパラメータを規定するものである。 In addition, it was found that the improvement in toughness is affected by the crystal grain size of old austenite and the amount of residual austenite. Based on this knowledge, the present invention Defines these parameters.
上記知見に基づき構成された本発明ばね用鋼線は、 靭性を向上する と共に、 焼入れ焼戻し後に施す熱処理後の内部硬度の低下を低減して、 線内部を起点とするばねの折損を抑制することができる。  The steel wire for springs of the present invention configured based on the above findings improves toughness, reduces a decrease in internal hardness after heat treatment performed after quenching and tempering, and suppresses breakage of a spring starting from inside the wire. Can be.
以下、 本発明ばね用鋼線の規定事項の限定理由をより詳しく説明す る。  Hereinafter, the reasons for limiting the specified items of the steel wire for spring of the present invention will be described in more detail.
<化学成分 >  <Chemical composition>
C： 0. 55 - 0. 75質量％  C: 0.55-0.75 mass%
Cは鋼の強度を決定する重要な元素であり、 0. 55質量％未満では十 分な強度が得られず、 0. 75 質量％を超えると靭性を損なうため、 0. 55質量％以上 0. 75質量％以下とする。  C is an important element that determines the strength of steel. If it is less than 0.55% by mass, sufficient strength cannot be obtained, and if it exceeds 0.75% by mass, the toughness is impaired. 75 mass% or less.
S i ： 1. 80〜2. 70質量％ S i: 1.80 to 2.70 mass%
S i は溶解精鍊時の脱酸剤として使用される。 また、 フェライ ト中 に固溶して耐熱性を向上させ、 ばね加工後の歪み取り焼鈍ゃ窒化処理 などの熱処理による線内部の硬度の低下を防ぐことができる。 耐熱性 を保持するためには 1. 8質量％以上が必要であり、 2. 7質量％を超え ると靭性が低下するため、 1. 8質量％以上 2. 7質量％以下とする。 Mn： 0. 1〜0. 7質量％  Si is used as a deoxidizing agent during refining. Further, the solid solution in the ferrite improves heat resistance, and prevents a decrease in hardness inside the wire due to heat treatment such as strain relief annealing and nitriding after spring processing. In order to maintain heat resistance, 1.8 mass% or more is required, and if it exceeds 2.7 mass%, toughness is reduced. Therefore, the content is 1.8 mass% or more and 2.7 mass% or less. Mn: 0.1 to 0.7 mass%
Mn は S i と同様に溶解精鍊時の脱酸剤として使用され、 鋼の焼入れ 性を向上させる。 そのため、 脱酸剤に必要な添加量として下限を 0. 1 質量％とする。 一方、 Mn は中心偏析を生じ易くする元素であり、 過 剰に添加すると、 熱間圧延後のパテンチング処理時において中心偏析 部分にマルテンサイ トを生じ、 その後の伸線加工の際、 断線の原因と なると共に、 焼入れ焼戻し後の靭性を低下させる。 本発明では、 特に、 靭性の向上を目指すため、 添加量を従来と比べて比較的少なくする。 具体的には、 靭性の低下を防止する添加量として上限を 0. 7質量％と する。 Cr： 0. 7〜1. 5質量％ Mn, like Si, is used as a deoxidizer during melting and refining, and improves the hardenability of steel. For this reason, the lower limit of the required amount of the deoxidizing agent is set to 0.1% by mass. On the other hand, Mn is an element that easily causes center segregation.If added excessively, Mn forms martensite in the center segregated part during the patenting process after hot rolling, which causes wire breakage during subsequent wire drawing. As well as reducing the toughness after quenching and tempering. In the present invention, In order to improve toughness, the amount of addition is made relatively small compared to conventional ones. Specifically, the upper limit is set to 0.7% by mass as the amount of addition to prevent a decrease in toughness. Cr: 0.7 to 1.5 mass%
Cr は鋼の焼入れ性を向上させ、 焼入れ焼戻し後の軟化抵抗を増加 させるため、 ばね加工後のテンパー処理ゃ窒化処理などの熱処理時の， 軟化防止に有効である。 添加量が 0. 7質量％未満であると、 上記熱処 理時の軟化防止効果が少ないため、 十分な効果が得られる添加量とし て下限を 0. 7質量％とする。 一方、 1 . 5 質量％を超えて添加すると、 パテンチング時にマルテンサイ トを発生し易く、 伸線時に断線の原因 となると共に、 オイルテンパー後の靭性を低下させる。 そのため、' Cr の添加量は、 1. 5質量％以下とする。  Cr improves the hardenability of steel and increases the softening resistance after quenching and tempering, so it is effective in preventing softening during heat treatment such as tempering and nitriding after spring processing. If the addition amount is less than 0.7% by mass, the effect of preventing softening during the heat treatment is small, so the lower limit is set to 0.7% by mass as an addition amount that can provide a sufficient effect. On the other hand, if it is added in excess of 1.5% by mass, martensite is liable to be generated during patenting, causing wire breakage during wire drawing and reducing toughness after oil tempering. Therefore, the amount of Cr added is set to 1.5% by mass or less.
上記化学成分のうち、 特に、 S i 及び Cr は、 炭化物を形成すること で耐熱性を向上させる効果がある。 そこで、 本発明では、 S i 及び Cr の含有量を比較的高めに設定して、 耐熱性の向上を図る。 但し、 どの 程度含有させるかは、 靭性との兼ね合いによる。 十分な耐熱性を得る ためには、 S i の原子％ + Crの原子％を 0. 09以上とすることが好まし い。  Among the above chemical components, in particular, Si and Cr have an effect of improving heat resistance by forming carbides. Therefore, in the present invention, the content of Si and Cr is set relatively high to improve the heat resistance. However, the amount to be included depends on the balance with toughness. In order to obtain sufficient heat resistance, it is preferable that the atomic% of Si + the atomic% of Cr be 0.09 or more.
また、 上記化学成分において硬度と靭性とのバランスをよりよくす るためには、 C： 0. 60 質量％以上 0. 70 質量％以下、 S i : 2. 20 質量％ 以上 2. 50質量％以下、 Mn： 0. 2質量％以上 0. 5質量％以下、 Cr： 0. 9 質量％以上 1. 3質量％以下とすることが好ましい。 Co： 0. 02〜1. 00質量％  In order to improve the balance between hardness and toughness in the above chemical components, C: 0.60% to 0.70% by mass, Si: 2.20% to 2.5% by mass Hereinafter, it is preferable that Mn: 0.2% by mass or more and 0.5% by mass or less, and Cr: 0.9% by mass or more and 1.3% by mass or less. Co: 0.02 to 1.00 mass%
Co は Ms 点（マルテンサイ ト変態開始温度）を上昇させる元素であり、 焼入れ後の残留オーステナイ ト量を減少させて、 焼入れ焼戻し後の靭 性を向上させる。 従って、 本発明では、 靭性をより向上させるために 添加する。 靭性向上の効果を得るためには、 0. 02 質量％以上添加す ることが好ましい。 一方、 一定量以上添加しても上記効果の向上が得 られず、 また Coは比較的高価であるため、 上限を 1. 00質量％以下と する。 靱性向上とコス卜の両面から考慮してより好ましい添加量は、 0. 05質量％以上 0. 20質量％以下である。 Co is an element that raises the Ms point (martensite transformation start temperature). Reduces the amount of residual austenite after quenching and improves toughness after quenching and tempering. Therefore, in the present invention, it is added to further improve the toughness. In order to obtain the effect of improving toughness, it is preferable to add 0.02% by mass or more. On the other hand, even if a certain amount or more is added, the above effect cannot be improved, and Co is relatively expensive, so the upper limit is made 1.00% by mass or less. A more preferable addition amount in consideration of both improvement in toughness and cost is 0.05% by mass or more and 0.20% by mass or less.
Mo、 V： 0. 05〜0. 50質量％ Mo, V: 0.05 to 0.50 mass%
W、 Nb： 0. 05〜0. 15質量％ W, Nb: 0.05 to 0.15 mass%
これらの元素は、 焼戻し時に炭化物を形成し、 軟化抵抗を増加させ る傾向がある。 0. 05 質量％未満では軟化抵抗の増加効果が得られに くく、 硬度を向上させにくい。 一方、 Mo、 V は 0. 50 質量％を超える と、 W、 Nb は 0. 1 5 質量％を超えると、 靭性を低下させ易い。 - そのた め、 Mo、 Vは、 0. 05質量％以上 0. 50質量％以下とする。 また、 W、 Nb は、 0. 05質量％以上 0. 15質量％以下とする。  These elements tend to form carbides during tempering and increase softening resistance. If it is less than 0.05% by mass, the effect of increasing the softening resistance is not easily obtained, and it is difficult to improve the hardness. On the other hand, if Mo and V exceed 0.50% by mass, W and Nb exceed 0.15% by mass, the toughness tends to decrease. -Therefore, Mo and V should be between 0.05 mass% and 0.50 mass%. Also, W and Nb should be 0.05% by mass or more and 0.15% by mass or less.
T i： 0. 01〜 20質量％ Ti: 0.01 to 20% by mass
T i は焼戻し時に炭化物を形成し、 軟化抵抗を増加させる効果があ る。 この効果を得るには、 0. 01 質量％以上添加することが好ましい。 しかし、 過剰に添加すると高融点非金属介在物 T i Oが形成されて、 靭 性を低下させる恐れがある。 この介在物の生成による靭性の低下を考 慮して、 0. 20質量％以下とする。 <線内部の硬度 >  T i forms carbides during tempering and has the effect of increasing softening resistance. To obtain this effect, it is preferable to add 0.01% by mass or more. However, if added in excess, high melting point non-metallic inclusions TIO may be formed and the toughness may be reduced. In consideration of the decrease in toughness due to the formation of inclusions, the content is set to 0.20% by mass or less. <Hardness inside wire>
焼入れ焼戻し後、 窒化処理により十分な表面硬度を得るためには、 上記のように 420〜480 で 2hr 以上の加熱が必要であるが、 一方で、 線内部の硬度が低下したり、 線内部を起点とした折損が生じる恐れが ある。 また、 後述する実験結果から明らかなように、 窒化処理の加熱 温度が高くなるほど、 内部硬度及び靱性が低下する傾向にある。 そこ で、 本発明では、 化学成分を規定することにより、 耐熱性と靭性とを 高める。 具体的には、 線内部の硬度 550HV以上を実現する。 After quenching and tempering, in order to obtain sufficient surface hardness by nitriding, As described above, heating at 420 to 480 for 2 hours or more is necessary, but on the other hand, the hardness inside the wire may be reduced, or breakage may occur from the inside of the wire. Also, as is clear from the experimental results described later, the internal hardness and toughness tend to decrease as the heating temperature of the nitriding treatment increases. Therefore, in the present invention, heat resistance and toughness are improved by defining chemical components. Specifically, the hardness inside the wire is 550HV or more.
<オーステナイ ト結晶粒径 > <Austenite grain size>
旧ォ一ステナイ トの結晶粒径は耐疲労性に影響を与える.。 粒径が 18.0^ m 以下の場合、 結晶粒の微細化効果により、 疲労特性が向上し、 18. Ο ΠΙ超ではこの効果が得られにくい。 また、 l. O i m以下の場合、 焼入れ焼戻し後の熱処理の際に十分に炭化物を固溶させることができ ず、 かえって靭性の低下を招く。 そこで、 本発明では、 旧オーステナ ィ トの結晶粒径を 1. 0 m超 18. 0 m以下とする。 旧オーステナイ ト の結晶粒径は、 保持時間を一定とする場合、 焼入れ時の加熱温度を変 化させることで制御することができる。 具体的には、 加熱温度を低め にすると粒径を小さく、 高めにすると粒径を大きくすることができる。  The grain size of the former onestenite affects the fatigue resistance. When the grain size is 18.0 ^ m or less, the fatigue characteristics are improved due to the effect of refining the crystal grains. In addition, if it is less than l.Oim, the carbide cannot be sufficiently dissolved in the heat treatment after quenching and tempering, and the toughness is rather lowered. Therefore, in the present invention, the crystal grain size of the former austenite is set to be more than 1.0 m and 18.0 m or less. The crystal grain size of old austenite can be controlled by changing the heating temperature during quenching when the holding time is constant. Specifically, the particle size can be reduced by lowering the heating temperature, and can be increased by increasing the heating temperature.
<残留オーステナイ ト量 > <Residual austenite amount>
残留オーステナイ トは、 含有量が多いと、 焼入れ焼戻し後の靭性を 低下させると共に、 その後のばね加工時に加工誘起マルテンサイ 卜に 変態してばね成形特性を低下させる。 そのため、 本発明では、 10 体 積％以下とする。 残留オーステナイ ト量は、 上記のように化学成分を 特定することで制御可能である。 <靭性 > If the content of residual austenite is large, the toughness after quenching and tempering is reduced, and at the time of subsequent spring working, it is transformed into a work-induced martensite and the spring forming properties are deteriorated. Therefore, in the present invention, the content is set to 10% by volume or less. The amount of residual austenite can be controlled by specifying the chemical components as described above. <Toughness>
本発明では、 疲労強度の向上とばね加工に必要な靭性を具えるため に、 焼入れ焼戻し後に行う熱処理後の絞り値を 35 %以上とする。 絞 り値は、 上記のように化学成分、 オーステナイ ト結晶粒径、 残留ォー ステナイ ト量を特定することで制御可能である。  In the present invention, in order to improve the fatigue strength and to provide the toughness required for spring working, the drawn value after heat treatment performed after quenching and tempering is set to 35% or more. The aperture value can be controlled by specifying the chemical composition, austenite crystal grain size, and residual austenite amount as described above.
本発明ばね用鋼線は、 焼入れ焼戻しを行った後、 ばね加工を施し、 窒化処理、 更に 1 回以上のショッ トピーニングを実施してばねを製造 するのに用いることが好適である。 また、 製造されたばねは、 自動車 のエンジン弁ばねやトランスミツション内部などに用いることが挙げ られる。 発明を実施するための最良の形態  The spring steel wire of the present invention is preferably used for manufacturing a spring by performing spring working after quenching and tempering, nitriding, and performing one or more shot peening. In addition, the manufactured spring may be used for an engine valve spring of an automobile, an interior of a transmission, and the like. BEST MODE FOR CARRYING OUT THE INVENTION
以下、 本発明の実施の形態を説明する。 Hereinafter, embodiments of the present invention will be described.
表 1 に示す化学成分を有する鋼材を溶解した後、 熱間圧延により直 径 6. 3 φ ππηの線材を作製した。 この線材をパテンチングした後、 皮剥 ぎ、 焼鈍、 伸線加工を順次行い直径 3. 2 φ mmのワイヤを得た。 このヮ ィャに焼入れ焼戻しを行った。 After melting steel materials having the chemical components shown in Table 1, wires with a diameter of 6.3 φππη were prepared by hot rolling. After patenting this wire, stripping, annealing, and wire drawing were performed sequentially to obtain a wire with a diameter of 3.2 mm. The wire was quenched and tempered.
表 1 table 1
Figure imgf000011_0001
Figure imgf000011_0001
単位： 質量％ Si原子量： 28.1 Cr原子量： 51.9 焼入れ焼戻しを行ったサンプル A 0 について焼入れ焼戻し後の引 張強度（TS)、 旧オーステナイ トの結晶粒径（ァ粒径）、 残留オーステナ イ ト量（残留ァ量）を表 2に示す。 また、 各サンプルのワイヤを二つず つ用意し、 焼入れ焼戻し後（0T 後）、 窒化処理を想定して 420°CX2hr の熱処理、 480 X 2hr の熱処理を各サンプルのそれぞれのワイヤに 施した。 これらワイヤの熱処理後の内部硬度及び絞り値を表 2に示す。 本例において内部硬度は、 線中心より直径の 1/4 の位置（本例では、 線表面から 0. 8mmの位置）において任意の 4点の硬度をとり、 その平 均硬度とした。 Unit: mass% Si atomic weight: 28.1 Cr atomic weight: 51.9 Tensile strength (TS) after quenching and tempering, crystal grain size of old austenite (grain size), amount of residual austenite for quenched and tempered sample A0 (Residual amount) is shown in Table 2. Also, prepare two wires for each sample, and after quenching and tempering (after 0T), assume a nitriding treatment at 420 ° C for 2 hours. Heat treatment and 480 X 2 hr heat treatment were applied to each wire of each sample. Table 2 shows the internal hardness and the reduction value of these wires after heat treatment. In this example, the internal hardness was taken as the average hardness of four arbitrary points at a position 1/4 of the diameter from the center of the line (in this example, 0.8 mm from the line surface).
表 2  Table 2
Figure imgf000012_0001
引張強度は、 焼戻し温度を変化させることで制御した。 ァ粒径は、 焼入れ温度を変化させることで制御した。 具体的には、 ァ粒径が 10 m未満の試料 No.4〜6、 14、 15は、 900 、 昇温速度 500°C/s、 保持 時間 2s、 ァ粒径が 10〜15 zm 以下の試料 No.2、 3、 7-13 は、 1000 、 昇温速度 500 / s、 保持時間 2s、 r粒径が 20 m超の試料 No.1 は、 1100°C、 昇温速度 500 /s、 保持時間 2s とした。 残留ァ量及び線内 部の硬度は、 化学成分により変化させた。
Figure imgf000012_0001
The tensile strength was controlled by changing the tempering temperature. The grain size was controlled by changing the quenching temperature. Specifically, the particle size is 10 Sample Nos. 4 to 6, 14, and 15 with a particle size of less than 900 m are 900, heating rate is 500 ° C / s, holding time is 2 s, and sample Nos. 2, 3, and 7-13 have a particle size of 10 to 15 zm or less. The sample No. 1 having a temperature of 1000, a heating rate of 500 / s, a holding time of 2 s and an r particle size of more than 20 m was set to 1100 ° C, a heating rate of 500 / s, and a holding time of 2 s. The amount of residual a and the hardness inside the wire were varied depending on the chemical composition.
その結果、 表 2に示すように特定の化学成分、 ァ粒径、 残留 r量を 満たす試料 Νο·8〜15 は、 焼入れ焼戻し後に熱処理を行っても、 内部 硬度が高く、 優れた靭性を具えることがわかる。 また、 熱処理温度は 比較的低い方が優れた内部硬度及び靭性を有することが分かる。  As a result, as shown in Table 2, samples ΝοΝ8 to 15 that satisfy the specified chemical composition, α particle size, and residual r content have high internal hardness and excellent toughness even after heat treatment after quenching and tempering. You can see it. Also, it can be seen that the relatively low heat treatment temperature has excellent internal hardness and toughness.
一方、 C の含有量が低く、 焼入れ温度が高い試料 No. l は、 熱処理 後の内部硬度が低い。 試料 No.3、 7 は、 それぞれ Cr、 Si の含有量が 低いことで耐熱性に乏しくなり、 熱処理後の内部硬度が低く、 絞り値 も小さい。 試料 No.2 は、 C の含有量が高いことで残留ァ量が多くな り、 靭性が低い。 試料 No.4〜6 は、 それぞれ Si、 Mn、 Cr の含有量が 高いため、 靭性に乏しくなり、 絞り値が低くなつている。  On the other hand, Sample No. 1, which has a low C content and a high quenching temperature, has a low internal hardness after heat treatment. Samples Nos. 3 and 7 have low heat resistance due to their low Cr and Si contents, low internal hardness after heat treatment, and small aperture values. Sample No. 2 has a high residual C content due to a high C content, and has low toughness. Samples Nos. 4 to 6 each had a high Si, Mn, and Cr content, resulting in poor toughness and a low drawing value.
上記 480°CX2hr の熱処理を行った各試料に対し、 それぞれ中村式 回転曲げ疲労試験機にかけて、 疲れ強さを調べてみた。 試験は、 ひず み速度を一定にして各試料に応力を加え、 評価は、 繰り返し回数 ： 1 X107回で折損がなかった振幅応力にて行った（n 数 = 8)。 結果を表 3 に示す。 表 3 Each of the samples subjected to the heat treatment at 480 ° C for 2 hours was subjected to a Nakamura-type rotary bending fatigue tester to examine the fatigue strength. In the test, stress was applied to each sample at a constant strain rate, and the evaluation was performed at an amplitude stress at which the number of repetitions was 1 × 10 7 times and there was no breakage (n number = 8). Table 3 shows the results. Table 3
Figure imgf000014_0001
Figure imgf000014_0001
表 3に示すように試料 No. 8〜1 5は、 試料 No. 1〜7と比較して高い 疲労限を有することがわかる。 このことから、 本発明は、 硬度と靭性 との両立により疲労強度の向上が図られていることが分かる。 産業上の利用可能性  As shown in Table 3, it can be seen that Sample Nos. 8 to 15 have a higher fatigue limit than Sample Nos. 1 to 7. From this, it can be seen that in the present invention, fatigue strength is improved by achieving both hardness and toughness. Industrial applicability
以上説明したように本発明ばね用鋼線によれば、 強度と靭性との双 方をバランスよく具えることで、 疲労特性を向上することができると いう優れた効果を奏し得る。 従って、 本発明ばね用鋼線を用いれば、 疲労特性に優れたばねを得ることができる。  As described above, according to the spring steel wire of the present invention, by providing both the strength and the toughness in a well-balanced manner, it is possible to achieve an excellent effect that the fatigue characteristics can be improved. Therefore, the spring having excellent fatigue characteristics can be obtained by using the spring steel wire of the present invention.

Claims

4 請求の範囲 4 Claims
1. 質量％で、  1. In mass%,
C： 0.55- 0.75 % , Si ： 1.80〜2.70%、 Mn： 0.1〜0.7%、 Cr： 0.70 -1.50%と、  C: 0.55-0.75%, Si: 1.80-2.70%, Mn: 0.1-0.7%, Cr: 0.70-1.50%
V:0.05〜0.50%、 Mo： 0.05〜0.50%、 W： 0.05〜 0.15 %、 Nb： 0.05 〜0.15%及び Ti ： 0.01〜0.20%よりなる群から選択される 1 種以上 とを含有し、  V: 0.05 to 0.50%, Mo: 0.05 to 0.50%, W: 0.05 to 0.15%, Nb: 0.05 to 0.15%, and Ti: one or more selected from the group consisting of 0.01 to 0.20%,
残部が Fe及び不可避不純物からなり、  The balance consists of Fe and inevitable impurities,
焼入れ焼戻しによって得られる焼戻しマルテンサイ ト組織を有し、 焼入れ焼戻し後において、  It has a tempered martensite structure obtained by quenching and tempering, and after quenching and tempering,
オーステナィ ト結晶粒径が 1.0~18.0 mであり、  Austenite grain size is 1.0-18.0 m,
残留オーステナイ ト量が 10体積％以下であり、  The residual austenite amount is 10% by volume or less,
焼入れ焼戻し後に施す 420〜480t で 2hr 以上の熱処理後において、 線中心から直径の 1/4の位置における硬度が 550Hv以上であり、 絞り値が 35%以上であることを特徴とするばね用鋼線。  After heat treatment at 420 to 480 t for 2 hours or more after quenching and tempering, the hardness at a position 1/4 of the diameter from the wire center is 550 Hv or more, and the drawing value is 35% or more. .
2. 質量％で、  2. In mass%,
C： 0.55〜0.75%、 Si ： 1.80〜2.70%、 Mn： 0.1〜0.7%、 Cr ： 0.70 〜1.50%、 Co： 0.02〜 00%と、  C: 0.55-0.75%, Si: 1.80-2.70%, Mn: 0.1-0.7%, Cr: 0.70-1.50%, Co: 0.02-00%,
V:0.05〜0.50%、 Mo： 0.05〜0.50%、 W： 0.05〜 0.15 %、 Nb： 0.05 〜0.15%及び Ti ： 0.01〜0.20%よりなる群から選択される 1 種以上 とを含有し、  V: 0.05 to 0.50%, Mo: 0.05 to 0.50%, W: 0.05 to 0.15%, Nb: 0.05 to 0.15%, and Ti: one or more selected from the group consisting of 0.01 to 0.20%,
残部が Fe及び不可避不純物からなり、  The balance consists of Fe and inevitable impurities,
焼入れ焼戻しによって得られる焼戻しマルテンサイ ト組織を有し、 焼入れ焼戻し後において、  It has a tempered martensite structure obtained by quenching and tempering, and after quenching and tempering,
オーステナイ ト結晶粒径が 1.0〜 18.0 /inであり、  Austenite grain size is 1.0-18.0 / in,
残留オーステナイ ト量が 10体積％以下であり、 焼入れ焼戻し後に施す 420〜480Τ で 2hr 以上の熱処理後において、 線中心から直径の 1/4の位置における硬度が 550HV以上であるこ とを特徴とするばね用鋼線。 ' The residual austenite amount is 10% by volume or less, A spring steel wire having a hardness of 550 HV or more at a position 1/4 of the diameter from the wire center after heat treatment at 420 to 480 mm for 2 hours or more after quenching and tempering. '
3. 更に、 焼入れ焼戻し後に施す 420〜480 で 2hr 以上の熱処理 後において、 絞り値が 35%以上であることを特徴とする請求項 2 記 載のばね用鋼線。  3. The steel wire for a spring according to claim 2, further comprising, after heat treatment at 420 to 480 applied after quenching and tempering for 2 hours or more, an aperture value of 35% or more.
4. 質量％で C ： 0.60〜0.70%、 Si ： 2.20〜 2· 50%、 Mn : 0.2〜 0.5%、 Cr： 0.9〜1.3%を含有することを特徴とする請求項 1 に記載 のばね用鋼線。  4. The spring according to claim 1, characterized in that C: 0.60 to 0.70%, Si: 2.20 to 250%, Mn: 0.2 to 0.5%, and Cr: 0.9 to 1.3% by mass%. Steel wire.
5. 質量％で Co： 0.05〜0.20%を含有することを特徴とする請求 項 2に記載のばね用鋼線。  5. The spring steel wire according to claim 2, wherein the steel wire contains 0.05 to 0.20% by mass of Co.
6. 請求項 1〜5のいずれかに記載のばね用鋼線を用いて製造され たことを特徴とするばね。  6. A spring manufactured using the spring steel wire according to any one of claims 1 to 5.
PCT/JP2003/015689 2002-12-13 2003-12-08 Steel wire for spring WO2004055226A1 (en)

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JP2003213372A (en) * 2002-01-25 2003-07-30 Sumitomo Denko Steel Wire Kk Steel wire for spring and spring
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JPH108203A (en) * 1996-06-24 1998-01-13 Nippon Steel Corp Wire rod excellent in descaling property and wire drawability
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EP1731625A1 (en) * 2004-02-04 2006-12-13 Sumitomo (Sei) Steel Wire Corp. Steel wire for spring
EP1731625A4 (en) * 2004-02-04 2012-03-28 Sumitomo Sei Steel Wire Corp Steel wire for spring
EP1930458A1 (en) * 2005-08-05 2008-06-11 Sumitomo Electric Industries, Ltd. Oil-tempered wire and process for producing the same
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