JP5826383B2 - Wire rod excellent in hydrogen delayed fracture resistance, method for producing the same, high strength bolt using the same, and method for producing the same - Google Patents

Wire rod excellent in hydrogen delayed fracture resistance, method for producing the same, high strength bolt using the same, and method for producing the same Download PDF

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JP5826383B2
JP5826383B2 JP2014520107A JP2014520107A JP5826383B2 JP 5826383 B2 JP5826383 B2 JP 5826383B2 JP 2014520107 A JP2014520107 A JP 2014520107A JP 2014520107 A JP2014520107 A JP 2014520107A JP 5826383 B2 JP5826383 B2 JP 5826383B2
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delayed fracture
fracture resistance
wire
hydrogen
bolt
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JP2014525987A (en
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ユー−ファン イ、
ユー−ファン イ、
ドン−ヒュン キム、
ドン−ヒュン キム、
グン−ス リュ、
グン−ス リュ、
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Posco Holdings Inc
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    • 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
    • C21D9/0093—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for screws; for bolts
    • 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
    • C21D9/52—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
    • C22C38/005—Ferrous alloys, e.g. steel alloys containing rare earths, i.e. Sc, Y, Lanthanides
    • 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
    • C22C38/08—Ferrous alloys, e.g. steel alloys containing nickel
    • 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
    • C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium

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

Description

本発明は、自動車エンジン用ボルト等に用いられる線材に関し、より詳細には、水素による遅れ破壊特性（Ｈｙｄｒｏｇｅｎ Ｄｅｌａｙｅｄ Ｆｒａｃｔｕｒｅ Ｒｅｓｉｓｔａｎｃｅ）を向上させた線材とその製造方法及び上記線材を用いた高強度ボルトとその製造方法に関する。   The present invention relates to a wire used for a bolt for an automobile engine, and more specifically, a wire having improved delayed fracture characteristics by hydrogen, a manufacturing method thereof, a high-strength bolt using the wire, and It relates to the manufacturing method.

最近、自動車の軽量化及び高性能化に伴い、エネルギー低減のために、駆動体、特に、ボルト等のエンジン用部品への高強度化の要求が高まっている。現在用いられている高強度ボルトとしては、ＳＣＭ４３５、ＳＣＭ４４０等の合金鋼を用いて焼き入れ及び焼き戻しにより製造された１２００ＭＰａ級のボルトがある。しかしながら、引張強度１２００ＭＰａ以上のボルトを用いる場合は水素による遅れ破壊が発生しやすいため、このような線材を超高強度ボルトの製造に用いるのは未だに容易ではない。   Recently, with the reduction in weight and performance of automobiles, there is an increasing demand for higher strength in driving parts, particularly engine parts such as bolts, in order to reduce energy. As high-strength bolts currently used, there are 1200 MPa class bolts manufactured by quenching and tempering using alloy steels such as SCM435 and SCM440. However, when a bolt having a tensile strength of 1200 MPa or more is used, delayed fracture due to hydrogen is likely to occur, and it is still not easy to use such a wire for manufacturing an ultrahigh strength bolt.

ボルトの製造工程を調べると、低温アニーリングを経てサイジング目的の伸線を行った後、球状化熱処理、ボルト成形、焼き入れ、焼き戻し工程を経て、最終的に焼き戻しマルテンサイトの単相組織を有する。したがって、ボルトの強度は、組成及び焼き入れ、焼き戻し熱処理工程によって決められる。しかしながら、素材である線材の状態では、ボルトの成形を容易にするために、できる限り低い強度を有するほうがよい。   When examining the bolt manufacturing process, after low-temperature annealing, the wire was drawn for sizing purposes, followed by spheroidizing heat treatment, bolt forming, quenching, and tempering processes, and finally the tempered martensite single-phase structure Have. Therefore, the strength of the bolt is determined by the composition, quenching and tempering heat treatment process. However, in the state of the wire material, it is better to have as low a strength as possible in order to facilitate the forming of the bolt.

焼き戻しマルテンサイトの単相組織を有する鋼の高強度化には、合金元素、特に、炭素の添加が最も効果的であると知られているが、炭素の添加は、線材の強度を増加させる上、延性−脆性遷移温度を急激に上昇させて、水素遅れ破壊抵抗性を大きく低下させることがある。また、加工硬化が増加するため、ボルトの成形に不利になり、別途の軟化熱処理が必要になることがある。   Addition of alloying elements, especially carbon, is known to be the most effective for increasing the strength of steels with a single-phase structure of tempered martensite, but the addition of carbon increases the strength of the wire. In addition, the ductile-brittle transition temperature may be rapidly increased to greatly reduce hydrogen delayed fracture resistance. Moreover, since work hardening increases, it becomes disadvantageous for bolt shaping | molding and a separate softening heat processing may be needed.

上記のように製造されたボルトの一般的な特徴は、焼き戻しマルテンサイト組織を有し、粒界又は粒内に炭化物析出相が分布し、母材はラスマルテンサイトに析出物が分布する点である。なお、母材の高強度化の達成の主な阻害要因としては、水素の侵入による遅れ破壊抵抗性の低下が挙げられる。これは、侵入した水素が粒界の強度を劣化させるためであると知られている。したがって、既存の焼き戻しマルテンサイトを高強度ボルト用鋼に用いるためには、遅れ破壊抵抗性を向上させるための作業が必要である。   The general characteristics of bolts manufactured as described above are that they have a tempered martensite structure, carbide precipitate phases are distributed at grain boundaries or grains, and precipitates are distributed at lath martensite in the base material. It is. In addition, as a main impediment to achieving high strength of the base material, there is a decrease in delayed fracture resistance due to the penetration of hydrogen. This is known to be due to the invading hydrogen deteriorating the grain boundary strength. Therefore, in order to use existing tempered martensite for steel for high-strength bolts, work for improving delayed fracture resistance is required.

したがって、ボルトの高強度化を達成するためには、臨界遅れ破壊強度を高くするための遅れ破壊抵抗性の改善が必要である。これを達成するための手段としては、オーステナイト粒界を脆化させるＰ、Ｓを最大限抑制させながら特定の元素を添加して拡散性水素をトラップすることができる析出物を生成させたり、微細組織を制御したりする方法等がある。   Therefore, in order to achieve higher strength of the bolt, it is necessary to improve delayed fracture resistance in order to increase the critical delayed fracture strength. As means for achieving this, precipitates that can trap diffusible hydrogen by adding a specific element while suppressing P and S that make the austenite grain boundary brittle are generated, There are ways to control the organization.

水素遅れ破壊抵抗性を改善するための従来の技術としては、１）鋼材の腐食抑制、２）水素侵入量の最小化、３）遅れ破壊に寄与する拡散性水素の抑制、４）限界拡散性水素濃度の大きい鋼材の使用、５）引張応力の最小化、６）応力の集中緩和、７）オーステナイト粒界のサイズの微細化等の技術が挙げられる。これを達成するための手段として、高合金化を目指すか、外部からの水素の侵入を防止するための表面コーティング又はメッキを施す方法が主に用いられている。   Conventional technologies for improving hydrogen delayed fracture resistance include 1) corrosion inhibition of steel materials, 2) minimization of hydrogen penetration, 3) suppression of diffusible hydrogen contributing to delayed fracture, and 4) limit diffusivity. Techniques such as the use of a steel material having a high hydrogen concentration, 5) minimization of tensile stress, 6) relaxation of stress concentration, and 7) miniaturization of the size of austenite grain boundaries. As means for achieving this, a method of applying a surface coating or plating for aiming at high alloying or preventing hydrogen from entering from the outside is mainly used.

しかしながら、上記国内外で考案された発明のほとんどには、製造費用が非常に高くて工程が複雑であり、鋼材の生産時に非常に精密な圧延及び冷却条件が求められるという問題がある。一例として、１６００ＭＰａ級の高強度線材の遅れ破壊特性を改善するために結晶粒微細化元素であるＴｉ、Ｎｂ、Ｖを０．５重量％以上添加し、Ｍｏ、Ｎｉ、Ｃｕ、Ｃｏ等の耐食性元素及び炭化物元素を添加する技術があるが、この技術には、生産単価が非常に高いという短所がある。また、粒界に析出されたフェライト組織を用いて水素の脆性を改善する技術があるが、この技術にも、化学的結合ではなく、相当量のＭｏを添加することにより製品の製造費用が高くなるという短所がある。   However, most of the inventions devised at home and abroad have a problem that the manufacturing cost is very high and the process is complicated, and very precise rolling and cooling conditions are required during the production of the steel material. As an example, in order to improve delayed fracture characteristics of a high strength wire of 1600 MPa class, Ti, Nb, V, which is a grain refinement element, is added by 0.5% by weight or more, and corrosion resistance of Mo, Ni, Cu, Co, etc. There is a technique of adding elements and carbide elements, but this technique has a disadvantage that the unit production cost is very high. In addition, there is a technology that improves the brittleness of hydrogen using the ferrite structure precipitated at the grain boundaries, but this technology also increases the manufacturing cost of the product by adding a considerable amount of Mo instead of chemical bonding. There are disadvantages.

また、完全パーライトを用いて１６００ＭＰａ級以上の高強度線材の遅れ破壊特性を改善する技術があるが、この技術には、線材を生産した後にサイジングのための伸線を行うとき、伸線による引張強度の向上及び伸線性の確保のためにクロムを０．２重量％以上添加しなければならず、恒温変態のためのリードパテンティング（ｌｅａｄ ｐａｔｅｎｔｉｎｇ）を必要とする等、製造費用が非常に高くて工程が複雑であり、線材の生産時に非常に精密な圧延及び冷却条件が求められるという問題がある。   In addition, there is a technology that improves the delayed fracture characteristics of high-strength wire of 1600 MPa class or more using perfect pearlite. This technology, when drawing wire for sizing after producing the wire, In order to improve strength and secure drawability, chromium must be added in an amount of 0.2% by weight or more, and lead patenting for constant temperature transformation is required. The process is complicated, and there is a problem that very precise rolling and cooling conditions are required during production of the wire.

また、フェライトとパーライトの二相微細組織を用いて最終的に１２００〜１５００ＭＰａを確保する技術は、他の技術とは異なり、最終熱処理がなくても引張強度の確保が可能な方法であるが、基本的にはＭｏを多量添加して水素遅れ破壊抵抗性の向上を図るものであるため、製造費用が増加するという困難がある。   In addition, the technique of finally securing 1200 to 1500 MPa using the two-phase microstructure of ferrite and pearlite is a method that can ensure the tensile strength without the final heat treatment, unlike other techniques. Basically, a large amount of Mo is added to improve the resistance to delayed hydrogen fracture, so that there is a difficulty that the manufacturing cost increases.

上述したように、引張強度１２００ＭＰａ級以上の熱処理及び非熱処理炭素鋼の有する引張強度の向上に対する水素遅れ破壊抵抗性の減少の限界性を未だに克服できていない上、高価の合金元素の添加による価格競争力の確保を達成しておらず、特に、水素による遅れ破壊特性に関する安定したデータの確保に問題がある。   As described above, the limit of the decrease in hydrogen delayed fracture resistance with respect to the improvement of the tensile strength of heat-treated and non-heat-treated carbon steel having a tensile strength of 1200 MPa class or more has not yet been overcome, and the price due to the addition of expensive alloy elements There is a problem in securing stable data on delayed fracture characteristics caused by hydrogen, in particular, without ensuring competitiveness.

本発明の目的は、熱処理により超高強度を確保すると共に優れた水素遅れ破壊抵抗性を有する線材とこれを製造する方法を提供することである。   An object of the present invention is to provide a wire rod that has ultrahigh strength by heat treatment and has excellent hydrogen delayed fracture resistance, and a method for producing the wire rod.

また、上記線材を用いて水素遅れ破壊抵抗性に優れ且つ高強度を有するボルトとその製造方法を提供することである。   Another object of the present invention is to provide a bolt having excellent hydrogen delayed fracture resistance and high strength using the wire and a method for producing the same.

本発明によれば、重量％で、Ｃ：０．３〜０．７％、Ｓｉ：０．０５〜２．０％、Ｍｎ：０．７〜１．５％、Ｌａ：３０〜７０ｐｐｍ、Ｎｉ：０．０１〜０．１％、並びに残部Ｆｅ及び不可避不純物を含む水素遅れ破壊抵抗性に優れた高強度線材が提供される。   According to the present invention, by weight, C: 0.3-0.7%, Si: 0.05-2.0%, Mn: 0.7-1.5%, La: 30-70 ppm, Ni : 0.01 to 0.1%, and a high-strength wire excellent in hydrogen delayed fracture resistance containing the remaining Fe and inevitable impurities.

また、本発明によれば、上記組成を満たす鋼材をＡｅ３＋１５０〜Ａｅ３＋２５０℃に加熱する段階と、上記加熱された鋼材を５〜１５℃／ｓで冷却し、Ａｅ３＋５０〜Ａｅ３＋１５０℃で圧延して線材を製造する段階と、上記圧延された線材を０．５〜３℃／ｓで６００℃以下まで冷却する段階と、を含む水素遅れ破壊抵抗性に優れた高強度線材の製造方法が提供される。   Moreover, according to this invention, the steel material which satisfy | fills the said composition is heated to Ae3 + 150-Ae3 + 250 degreeC, the said heated steel material is cooled at 5-15 degreeC / s, it rolls at Ae3 + 50-Ae3 + 150 degreeC, and a wire is carried out. There is provided a method for producing a high-strength wire excellent in hydrogen delayed fracture resistance, comprising a step of producing, and a step of cooling the rolled wire at a rate of 0.5 to 3 ° C / s to 600 ° C or lower.

また、本発明によれば、重量％で、Ｃ：０．３〜０．７％、Ｓｉ：０．０５〜２．０％、Ｍｎ：０．７〜１．５％、Ｌａ：３０〜７０ｐｐｍ、Ｎｉ：０．０１〜０．１％、並びに残部Ｆｅ及び不可避不純物を含み、引張強度１２００ＭＰａ以上の強度を有する水素遅れ破壊抵抗性に優れたボルトが提供される。   Moreover, according to the present invention, by weight, C: 0.3 to 0.7%, Si: 0.05 to 2.0%, Mn: 0.7 to 1.5%, La: 30 to 70 ppm , Ni: 0.01 to 0.1%, the balance Fe and inevitable impurities are included, and a bolt excellent in hydrogen delayed fracture resistance having a tensile strength of 1200 MPa or more is provided.

また、本発明によれば、上記線材をボルト成形する段階と、上記成形されたボルトを８５０〜９５０℃で熱処理する段階と、上記加熱の後に急冷し３００〜５００℃の温度で焼き戻しする段階と、を含む水素遅れ破壊抵抗性に優れたボルトの製造方法が提供される。   Further, according to the present invention, the step of bolt-forming the wire, the step of heat-treating the formed bolt at 850 to 950 ° C., the step of quenching after the heating and tempering at a temperature of 300 to 500 ° C. And a method for producing a bolt excellent in hydrogen delayed fracture resistance.

本発明の線材は、自動車部品締結用又は自動車部品用等に用いられる高強度線材であり、ランタンとニッケルを極微量添加して、最終熱処理後にマルテンサイト微細組織が生成されても優れた強度（１２００〜２０００ＭＰａ級）及び水素遅れ破壊抵抗性を有することができる線材を、低い製造費用で製造することができるという長所を有する。   The wire rod of the present invention is a high-strength wire rod used for fastening an automobile part or for an automobile part, etc., and adding a very small amount of lanthanum and nickel, and excellent strength (even if a martensite microstructure is generated after the final heat treatment ( It has an advantage that a wire rod that can have a resistance to hydrogen delayed fracture at a low production cost can be produced.

水素遅れ破壊抵抗性に優れ且つ高強度化が可能なボルト用線材の開発に伴い、ボルト締結時の締結力の強化と締結部の空孔の減少による鋼構造物の安全性を高め、ボルトの締結個数の減少によって鋼材の使用量を減らすことができる。また、自動車部品としての面においては、部品の軽量化に寄与し、部品の軽量化による自動車組立装置の設計多様化及びコンパクト化が可能であるという長所を有する。   With the development of bolt wires with excellent hydrogen delayed fracture resistance and high strength, the safety of steel structures can be improved by strengthening the fastening force at the time of bolt fastening and reducing the number of holes in the fastening part. The amount of steel used can be reduced by reducing the number of fastenings. Further, in terms of automobile parts, it contributes to weight reduction of parts, and has the advantage that it is possible to diversify the design of the automobile assembly apparatus and make it compact by reducing the weight of the parts.

本発明の線材の微細組織を図式化した模式図である。It is the schematic diagram which schematized the fine structure of the wire of this invention. 従来のＭｏを添加した場合のＭｏ析出物の水素トラップを示す模式図である。It is a schematic diagram which shows the hydrogen trap of the Mo deposit at the time of adding the conventional Mo. 本発明の線材に含まれた析出物の水素トラップを示す模式図である。It is a schematic diagram which shows the hydrogen trap of the precipitate contained in the wire of this invention. 図３の析出物の結晶構造を示す図である。It is a figure which shows the crystal structure of the deposit of FIG.

以下では、本発明について詳細に説明する。   Hereinafter, the present invention will be described in detail.

まず、本発明の線材について詳細に説明する。以下では、本発明の線材の組成範囲について説明する（以下、重量％）。   First, the wire rod of the present invention will be described in detail. Below, the composition range of the wire of this invention is demonstrated (henceforth, weight%).

炭素（Ｃ）の含量は０．３〜０．７％であることが好ましい。上記Ｃの含量が０．７％を超える場合は、通常の冷間伸線を用いた高炭素伸線材の形で主に用いられるものの、本発明で提案する熱処理を行うときにオーステナイト粒界にフィルム状の炭化物が頻繁に析出されて水素遅れ破壊抵抗性を低下させるため、好ましくない。これに対し、上記含量が０．３％未満の場合は、焼き入れ、焼き戻し熱処理によるボルトの引張強度が十分に確保されない。したがって、十分な強度を確保するために、Ｃは０．３％以上添加されることが好ましい。   The carbon (C) content is preferably 0.3 to 0.7%. When the content of C is more than 0.7%, it is mainly used in the form of a high carbon wire using ordinary cold drawing, but at the austenite grain boundaries when the heat treatment proposed in the present invention is performed. Since film-like carbides are frequently deposited to reduce hydrogen delayed fracture resistance, it is not preferable. On the other hand, when the content is less than 0.3%, the tensile strength of the bolt by quenching and tempering heat treatment is not sufficiently ensured. Therefore, in order to ensure sufficient strength, C is preferably added in an amount of 0.3% or more.

シリコン（Ｓｉ）の含量は０．０５〜２．０％であることが好ましい。上記Ｓｉの含量が２．０％を超える場合は、ボルトを製造するための冷間鍛造工程中に加工硬化現象が急激に起こるため、加工性に多くの問題があり、０．０５％未満の場合は、十分な強度を確保することができず、セメンタイトの球状化にも悪影響を及ぼす。   The content of silicon (Si) is preferably 0.05 to 2.0%. When the Si content exceeds 2.0%, work hardening phenomenon occurs abruptly during the cold forging process for manufacturing the bolt, so there are many problems in workability, and less than 0.05% In such a case, sufficient strength cannot be ensured, and the spheroidization of cementite is also adversely affected.

マンガン（Ｍｎ）の含量は０．７〜１．５％であることが好ましい。上記Ｍｎは、マトリックス組織内に置換型固溶体を形成して固溶強化する元素であって、高張力ボルト特性に非常に有用な元素である。上記Ｍｎの含量が１．５％を超える場合は、固溶強化効果を有するよりは、マンガン偏析による組織不均質がボルト特性に有害な影響を及ぼす。即ち、鋼の凝固時に偏析機構によって巨視偏析と微視偏析が生じやすいが、マンガン偏析は他の元素に比べて相対的に低い拡散係数により偏析帯を形成し、これによる硬化能の向上は中心部低温組織（例えば、ｃｏｒｅ ｍａｒｔｅｎｓｉｔｅ）を生成する主原因となる。即ち、鋳造時のマンガン偏析による局部焼き入れ性の増大及び偏析帯の形成によって組織の二相性が深化するという問題がある。   The content of manganese (Mn) is preferably 0.7 to 1.5%. The Mn is an element that forms a substitutional solid solution in the matrix structure and strengthens the solid solution, and is an extremely useful element for high tension bolt characteristics. When the Mn content exceeds 1.5%, the structure heterogeneity due to manganese segregation has a detrimental effect on the bolt characteristics rather than having a solid solution strengthening effect. In other words, macrosegregation and microsegregation are likely to occur due to the segregation mechanism during solidification of steel, but manganese segregation forms a segregation zone with a relatively low diffusion coefficient compared to other elements, and this mainly improves the hardenability. This is the main cause of generating a partial cryogenic tissue (for example, core martensite). That is, there is a problem that the dual phase of the structure deepens due to the increase in local hardenability due to manganese segregation during casting and the formation of segregation zones.

これに対し、上記Ｍｎが０．７％未満の場合は、マンガン偏析による偏析帯の影響はほぼないが、固溶強化による最終製品の引張強度の確保が容易ではないという問題がある。即ち、０．７％未満の場合は、固溶強化効果が弱いため、焼き入れ性及び永久変形抵抗性を改善するのが容易ではない。   On the other hand, when the Mn is less than 0.7%, there is almost no influence of the segregation zone due to manganese segregation, but there is a problem that it is not easy to secure the tensile strength of the final product by solid solution strengthening. That is, if it is less than 0.7%, the solid solution strengthening effect is weak, so it is not easy to improve the hardenability and the permanent deformation resistance.

ニッケル（Ｎｉ）の含量は０．０１〜０．１％であることが好ましい。上記Ｎｉは、ランタンと共に粒内に化合物を形成する元素であって、非常に重要な元素である。上記Ｎｉの含量が０．０１％未満の場合は、効果的な化合物、特に、析出物を完全に生成することができないため、水素遅れ破壊抵抗性の改善効果を期待するのが困難であり、０．１％を超える場合は、残留オーステナイト量が増加して衝撃靭性が低下する恐れがあり、過剰の添加により製造費用が増加するという問題がある。   The content of nickel (Ni) is preferably 0.01 to 0.1%. Ni is an element that forms a compound in the grains together with lanthanum, and is a very important element. When the content of Ni is less than 0.01%, it is difficult to expect an effect of improving hydrogen delayed fracture resistance because an effective compound, particularly, a precipitate cannot be generated completely. If it exceeds 0.1%, the amount of retained austenite may increase and impact toughness may decrease, and there is a problem that the production cost increases due to excessive addition.

ランタン（Ｌａ）の含量は０．００３〜０．００７％（３０〜７０ｐｐｍ）であることが好ましい。上記Ｌａは、Ｎｉと共に結晶粒内に化合物を形成する元素であって、粒界に偏析された燐と硫黄を低減させる非常に重要な元素である。上記Ｌａの含量が３０ｐｐｍ未満の場合は、化合物が効果的に形成されず、粒界の燐及び硫黄の除去が容易ではないため、引張強度の確保は可能であるが、優れた水素遅れ破壊抵抗性は期待することができないという短所がある。これに対し、７０ｐｐｍを超える場合は、製造費用が増加するという問題があり、過剰の添加により水素遅れ破壊抵抗性の向上を期待することが困難である。したがって、その上限を７０ｐｐｍとすることが好ましい。   The content of lanthanum (La) is preferably 0.003 to 0.007% (30 to 70 ppm). La is an element that forms a compound in crystal grains together with Ni, and is a very important element that reduces phosphorus and sulfur segregated at grain boundaries. When the content of La is less than 30 ppm, the compound is not formed effectively, and it is not easy to remove phosphorus and sulfur at the grain boundaries. Therefore, it is possible to ensure the tensile strength, but excellent hydrogen delayed fracture resistance. There is a disadvantage that sex cannot be expected. On the other hand, when it exceeds 70 ppm, there exists a problem that manufacturing cost increases and it is difficult to expect improvement in hydrogen delayed fracture resistance by excessive addition. Therefore, the upper limit is preferably 70 ppm.

残部は、Ｆｅ及び不可避不純物を含む。しかしながら、上記組成以外に有効な成分が添加されることを排除するものではない。   The balance contains Fe and inevitable impurities. However, the addition of effective components other than the above composition is not excluded.

本発明の線材は、微細組織内にＬａ系、Ｎｉ系又はＬａＮｉ系析出物を含むことが好ましい。上記析出物の種類は特に限定されず、その例としてはＬａＮｉ５、ＬａＰＯ４、Ｌａ２Ｏ２Ｓ等がある。上記析出物は、微細組織の結晶粒内又は結晶粒界に形成され、侵入した水素をトラップし、侵入した水素が粒界の強度を劣化させることを防止して水素遅れ破壊抵抗性を向上させる役割を行う。 The wire of the present invention preferably contains La-based, Ni-based or LaNi-based precipitates in the microstructure. The kind of the precipitate is not particularly limited, and examples thereof include LaNi 5 , LaPO 4 , La 2 O 2 S and the like. The precipitate is formed in a crystal grain of a fine structure or in a crystal grain boundary, traps invading hydrogen, prevents the invading hydrogen from degrading the strength of the grain boundary, and improves hydrogen delayed fracture resistance. Perform a role.

図１は、本発明の線材の微細組織を観察して析出物が分布されていることを模式的に示す図である。図１を参照すると、ＬａＮｉ５、ＬａＰＯ４、Ｌａ２Ｏ２Ｓの析出物が結晶粒内又は結晶粒界に分布されており、水素がトラップされてＬａＮｉ５Ｈ６の化合物が存在することが分かる。 FIG. 1 is a diagram schematically showing that precipitates are distributed by observing the microstructure of the wire of the present invention. Referring to FIG. 1, precipitates of LaNi 5 , LaPO 4 , and La 2 O 2 S are distributed in the crystal grains or in the crystal grain boundaries, and hydrogen is trapped and there is a compound of LaNi 5 H 6. I understand.

なお、本発明において、上記析出物による水素トラップ効果は、Ｍｏにより水素遅れ破壊抵抗性を改善しようとした従来技術に比べて格段に優れている。図２は、従来のＭｏ析出物を用いた水素トラップの効果を模式的に示す図であり、侵入した水素をＭｏ析出物を用いて析出物と結晶粒の界面にトラップさせて水素遅れ破壊抵抗性を改善しようとしたものである。しかしながら、本発明の析出物による水素トラップ効果を模式的に示す図３を参照すると、本発明の析出物は、侵入した水素が当該析出物の表面に拘束されず、水素を含む化合物（例：ＬａＮｉ５Ｈ６）を形成することにより、鋼中水素が完全に拘束されて水素遅れ破壊に対する抵抗性が向上する。したがって、図２のような場合には水素が析出物の表面から脱離するという問題があるが、本発明の場合には上記のような問題が発生しないため優れた水素遅れ破壊抵抗性を有する。図４は、図３のＬａＮｉ５Ｈ６の結晶構造を示す図であり、内部に相当量の水素が貯蔵できる構造を有する。 In the present invention, the hydrogen trap effect due to the precipitate is much superior to the prior art that attempts to improve hydrogen delayed fracture resistance by Mo. FIG. 2 is a diagram schematically showing the effect of a conventional hydrogen trap using Mo precipitates, in which hydrogen that has penetrated is trapped at the interface between the precipitates and crystal grains using Mo precipitates to prevent hydrogen delayed fracture resistance. I tried to improve the sex. However, referring to FIG. 3 schematically showing the hydrogen trap effect by the precipitate of the present invention, the precipitate of the present invention is a compound containing hydrogen (for example: By forming LaNi 5 H 6 ), hydrogen in the steel is completely restrained and resistance to delayed hydrogen fracture is improved. Therefore, in the case of FIG. 2, there is a problem that hydrogen is desorbed from the surface of the precipitate, but in the case of the present invention, since the above problem does not occur, it has an excellent hydrogen delayed fracture resistance. . FIG. 4 is a diagram showing the crystal structure of LaNi 5 H 6 in FIG. 3, and has a structure capable of storing a considerable amount of hydrogen inside.

上記析出物の縦横比（ａｓｐｅｃｔ ｒａｔｉｏ）は１．２〜２．０であることが好ましい。結晶構造上、縦横比が１．２未満の析出物を確保することは困難である。一方、上記析出物の縦横比が２．０を超える場合は、析出物が割れやすいという問題がある。素材の内部で析出物が割れると、マトリックスとの連続性が欠如して微細空洞が生成されて欠陥となるため、線材が破損する恐れがあり、所望の水素遅れ破壊抵抗性を確保することができない。   The aspect ratio of the precipitate is preferably 1.2 to 2.0. Due to the crystal structure, it is difficult to ensure a precipitate having an aspect ratio of less than 1.2. On the other hand, when the aspect ratio of the precipitate exceeds 2.0, there is a problem that the precipitate is easily cracked. If the precipitate breaks inside the material, the continuity with the matrix is lacking and fine cavities are generated, resulting in defects, which may damage the wire and ensure the desired hydrogen delayed fracture resistance. Can not.

一方、上記析出物のサイズは、円相当径が１００〜４００ｎｍであることが好ましい。上記円相当径が１００ｎｍ未満の場合は、析出物のサイズが小さすぎて析出物にトラップされる水素の量が少なくなるため、効果的な水素トラップ効果を確保するのが困難であり、４００ｎｍを超える場合は、単位面積当たりの分布する析出物の個数が少なくなって鋼全体の析出物の表面積が減少するため、水素トラップの効果が減少する。したがって、その上限を４００ｎｍとすることが好ましい。   On the other hand, the size of the precipitate is preferably 100 to 400 nm in equivalent circle diameter. When the equivalent circle diameter is less than 100 nm, the size of the precipitate is too small and the amount of hydrogen trapped in the precipitate is small, so that it is difficult to ensure an effective hydrogen trapping effect. In the case of exceeding, the number of precipitates distributed per unit area is reduced and the surface area of the precipitates in the whole steel is reduced, so that the effect of the hydrogen trap is reduced. Therefore, the upper limit is preferably 400 nm.

以下では、本発明の線材の製造方法について詳細に説明する。   Below, the manufacturing method of the wire of this invention is demonstrated in detail.

本発明の線材を製造するためには、まず、上記組成を満たす鋼材をＡｅ３＋１５０℃〜Ａｅ３＋２５０℃の温度に加熱する。上記温度範囲は、オーステナイト単相を維持するためのものであり、オーステナイト結晶粒が粗大化しない温度範囲であって、残存する偏析、炭化物及び介在物の効果的な溶解が可能な温度範囲である。上記温度がＡｅ３＋２５０℃を超える場合は、オーステナイト結晶粒が非常に粗大化することから、冷却後に形成される最終微細組織が粗大化する可能性があるため、高強度高靭性線材を確保することができず、Ａｅ３＋１５０℃未満の場合は、加熱による効果が得られない。したがって、加熱温度はＡｅ３＋１５０℃〜Ａｅ３＋２５０℃であることが好ましい。   In order to produce the wire of the present invention, first, a steel material satisfying the above composition is heated to a temperature of Ae3 + 150 ° C. to Ae3 + 250 ° C. The above temperature range is for maintaining the austenite single phase, and is a temperature range in which the austenite crystal grains do not coarsen, and is a temperature range in which the remaining segregation, carbides and inclusions can be effectively dissolved. . When the temperature exceeds Ae3 + 250 ° C., since the austenite crystal grains become very coarse, the final microstructure formed after cooling may be coarsened, so that a high-strength and high-toughness wire can be secured. If it is not possible and the temperature is lower than Ae3 + 150 ° C., the effect of heating cannot be obtained. Therefore, it is preferable that heating temperature is Ae3 + 150 degreeC-Ae3 + 250 degreeC.

上記加熱は、３０分〜１時間３０分間行われることが好ましい。上記加熱時間が３０分未満の場合は、温度が全体的に均一にならないという問題があり、１時間３０分を超える場合は、オーステナイト結晶粒の粗大化可能性が高くなる上、生産性が顕著に減少する。   The heating is preferably performed for 30 minutes to 1 hour and 30 minutes. When the heating time is less than 30 minutes, there is a problem that the temperature is not uniform as a whole. When it exceeds 1 hour and 30 minutes, the austenite crystal grains are likely to be coarsened and the productivity is remarkable. To decrease.

その後、上記加熱された鋼材を冷却し、熱間圧延を行う。５〜１５℃／ｓの冷却速度で冷却し、Ａｅ３＋５０℃〜Ａｅ３＋１５０℃で圧延して線材を製造する。   Thereafter, the heated steel material is cooled and hot rolled. It cools with the cooling rate of 5-15 degreeC / s, and it rolls at Ae3 + 50 degreeC-Ae3 + 150 degreeC, and manufactures a wire.

上記冷却は、微細組織の変態を最小化する目的で制御するものである。熱間圧延前の冷却速度が５℃／ｓ未満の場合は、生産性が減少し、徐冷を維持するために更なる装置が必要であり、長時間加熱した場合のように熱間圧延後の線材の強度と靭性が低下する。これに対し、冷却速度が１５℃／ｓを超える場合は、圧延前の鋼材の有する変態の駆動力が増加するため、圧延中に新たな微細組織が現れる可能性が大きくなり、圧延温度を低く再設定しなければならないという問題がある。   The cooling is controlled for the purpose of minimizing the transformation of the microstructure. When the cooling rate before hot rolling is less than 5 ° C./s, productivity is reduced and further equipment is required to maintain slow cooling, after hot rolling as in the case of heating for a long time. The strength and toughness of the wire rod are reduced. On the other hand, when the cooling rate exceeds 15 ° C./s, the driving force of transformation of the steel material before rolling increases, so the possibility that a new microstructure will appear during rolling increases, and the rolling temperature is lowered. There is a problem that it must be reset.

また、上記圧延温度は、圧延中に変形による微細組織の出現が抑制され、再結晶が発生せず、サイジング圧延のみが可能な温度である。上記圧延温度がＡｅ３＋５０℃未満の場合は、動的再結晶温度に近いため、本発明の微細組織を確保することができず、一般的な軟質のフェライトが得られる可能性が非常に大きく、Ａｅ３＋１５０℃を超える場合は、冷却後に再度加熱しなければならないという問題がある。したがって、その上限を上記のように設定する。   The rolling temperature is a temperature at which the appearance of a fine structure due to deformation is suppressed during rolling, recrystallization does not occur, and only sizing rolling is possible. When the rolling temperature is less than Ae3 + 50 ° C., it is close to the dynamic recrystallization temperature, so the microstructure of the present invention cannot be ensured, and it is very likely that a general soft ferrite is obtained. Ae3 + 150 If it exceeds ° C., there is a problem that it must be heated again after cooling. Therefore, the upper limit is set as described above.

次に、上記のように圧延により製造された線材を０．５〜３℃／ｓで６００℃以下まで冷却する。上記冷却速度とは、マンガンの添加によって炭素の拡散が阻止され、不完全パーライトが生成され、十分な面積分率を有し、且つ効果的な生成が可能な冷却速度のことである。上記冷却速度が０．５℃／ｓ未満の場合は、冷却速度が遅すぎるため、実際に操業が困難な程度に生産性が低下し、３℃／ｓを超える場合は、添加した元素の重なり効果による硬化能の向上によってフェライト／パーライト変態が遅れてマルテンサイト／ベイナイトのような低温組織が発生する。   Next, the wire produced by rolling as described above is cooled to 600 ° C. or lower at 0.5 to 3 ° C./s. The cooling rate is a cooling rate at which carbon is prevented from diffusing by adding manganese, incomplete pearlite is generated, has a sufficient area fraction, and can be effectively generated. When the cooling rate is less than 0.5 ° C./s, the cooling rate is too slow, and thus the productivity is lowered to the extent that it is actually difficult to operate, and when it exceeds 3 ° C./s, the added elements overlap. Due to the improvement of the hardening ability due to the effect, the ferrite / pearlite transformation is delayed and a low temperature structure such as martensite / bainite is generated.

以下では、本発明のボルトとその製造方法について詳細に説明する。   Below, the bolt of this invention and its manufacturing method are demonstrated in detail.

本発明の線材を用いて製造されたボルトは、超高強度を確保すると共に析出物によって優れた水素遅れ破壊抵抗性を確保することができる。本発明のボルトは、１２００ＭＰａ以上の超高強度を確保すると共に優れた水素遅れ破壊抵抗性を有する。   The bolt manufactured using the wire rod of the present invention can ensure ultrahigh strength and excellent hydrogen delayed fracture resistance due to precipitates. The bolt of the present invention ensures an ultrahigh strength of 1200 MPa or more and has excellent hydrogen delayed fracture resistance.

本発明において、１２００ＭＰａ以上の引張強度を確保するための製造方法としては、下記の方法を用いることが好ましい。まず、上記本発明の線材を用いてボルト成形を行い、８５０〜９５０℃で熱処理することが好ましい。上記熱処理は、オーステナイト化（ａｕｓｔｅｎｉｚｉｎｇ）により組織を均質化するためのものである。上記熱処理の温度が８５０℃未満の場合は、十分な均質化がなされるのが困難であり、９５０℃を超える場合は、更なる温度上昇の効果を得るのが困難であり、結晶粒の粗大化により延性が低下する可能性がある。したがって、その上限を９５０℃とすることが好ましい。   In the present invention, the following method is preferably used as a production method for ensuring a tensile strength of 1200 MPa or more. First, it is preferable to perform bolt formation using the wire of the present invention and to perform heat treatment at 850 to 950 ° C. The heat treatment is for homogenizing the structure by austenizing. When the temperature of the heat treatment is less than 850 ° C., it is difficult to achieve sufficient homogenization, and when it exceeds 950 ° C., it is difficult to obtain a further temperature increase effect, and the crystal grains are coarse. There is a possibility that ductility is lowered by the conversion. Therefore, the upper limit is preferably 950 ° C.

上記熱処理の後に急冷（ｑｕｅｎｃｈｉｎｇ）し、３００〜５００℃の温度で焼き戻しすることが好ましい。上記急冷により均質化した組織がマルテンサイト組織のような低温変態組織を形成し、ボルトの強度を向上させる。   It is preferable to quench after the heat treatment and to temper at a temperature of 300 to 500 ° C. The structure homogenized by the rapid cooling forms a low-temperature transformation structure such as a martensite structure and improves the strength of the bolt.

上記焼き戻しは、上記急冷により発生した残留応力を除去し、強度の調整と脆性を改善するためのものである。上記温度が３００℃未満の場合は、十分な残留応力の除去が困難な上、焼き戻し脆性現象により却って脆性が発生し、５００℃を超える場合は、過度な熱処理により強度が低下するため、所望の強度を確保することが困難である。したがって、上記焼き戻しは、３００〜５００℃の温度で行われることが好ましい。   The tempering is for removing the residual stress generated by the rapid cooling and improving the strength and brittleness. When the temperature is less than 300 ° C., it is difficult to remove sufficient residual stress, and brittleness is generated due to the temper embrittlement phenomenon. When the temperature exceeds 500 ° C., the strength decreases due to excessive heat treatment. It is difficult to ensure the strength. Therefore, the tempering is preferably performed at a temperature of 300 to 500 ° C.

上記ボルトを製造する方法は、通常の熱処理を適用して所望の強度を確保するものである。これは、通常の知識を有する者が所望の強度を確保するために温度と時間を制御して適用することができるものであり、特に限定されない。   The method for producing the bolt is to secure a desired strength by applying a normal heat treatment. This can be applied by a person having ordinary knowledge by controlling the temperature and time in order to secure a desired strength, and is not particularly limited.

以下では、本発明の実施例について詳細に説明する。下記実施例は、本発明の理解のためのものに過ぎず、本発明を限定するものではない。   Below, the Example of this invention is described in detail. The following examples are only for the understanding of the present invention and are not intended to limit the present invention.

（実施例１）
表１の組成とＡｅ３温度を有する鋼材を製造し、この鋼材に表２の条件を適用して線材を製造し、この線材を用いてボルトを製造した。なお、ボルトの製造工程中の熱処理条件を表２に共に併記した。 Example 1
A steel material having the composition shown in Table 1 and an Ae3 temperature was manufactured, a wire rod was manufactured by applying the conditions shown in Table 2 to the steel material, and a bolt was manufactured using the wire rod. The heat treatment conditions during the bolt manufacturing process are also shown in Table 2.

上記で製造されたボルトの引張強度と水素遅れ破壊抵抗性を測定し、その結果を表３に示した。上記水素遅れ破壊抵抗性に関連しては、酸度（ｐＨ）が約２程度のＨ２Ｏ：２０００ｃｃ、ＣＨ３ＣＯＯＨ：８０ｍｌ、ＮａＣｌ：１００ｇからなる試験溶液を用い、各ボルトを上記試験溶液に浸漬した状態で、上記測定された引張強度の約０．９倍の引張強度を付加し、試片が破損する時間を測定して示した。上記試験では、１００時間以上維持される場合に水素遅れ破壊に対する抵抗性に優れると評価した。 The tensile strength and hydrogen delayed fracture resistance of the bolts produced above were measured, and the results are shown in Table 3. In relation to the hydrogen delayed fracture resistance, a test solution consisting of H 2 O: 2000 cc, CH 3 COOH: 80 ml, NaCl: 100 g with an acidity (pH) of about 2 is used, and each bolt is used as the test solution. In the dipped state, a tensile strength of about 0.9 times the measured tensile strength was added, and the time for the specimen to break was measured and shown. In the said test, when it maintained for 100 hours or more, it evaluated that it was excellent in the resistance with respect to hydrogen delayed fracture.

上記本発明の条件を満たす場合には、ボルトの製造時に１２００ＭＰａ以上の高強度を有すると共に優れた水素遅れ破壊抵抗性を有することが確認できた。但し、比較例９と１０の場合には、十分な強度と水素遅れ破壊抵抗性を有するが、過量のＬａとＮｉが添加されることから経済性の面で好ましくないため、比較例に分類した。   When the conditions of the present invention were satisfied, it was confirmed that the bolt had a high strength of 1200 MPa or more and excellent hydrogen delayed fracture resistance during the production of the bolt. However, in the case of Comparative Examples 9 and 10, it has sufficient strength and hydrogen delayed fracture resistance, but since excessive amounts of La and Ni are added, it is not preferable in terms of economy, and therefore classified as Comparative Examples. .

一方、Ｃの含量が少なすぎる比較例１の場合には、十分な強度を確保することができず、過量のＣが添加された比較例２の場合には、水素遅れ破壊抵抗性が非常に低いことが確認できた。また、モリブデン（Ｍｏ）を添加した比較例３〜５の場合には、１００時間前に破損が発生して十分な水素遅れ破壊抵抗性を確保することができず、ＬａやＮｉのいずれか一つのみを添加した比較例６及び７の場合には、十分な水素遅れ破壊抵抗性を確保することができないことが確認できた。   On the other hand, in the case of Comparative Example 1 in which the content of C is too small, sufficient strength cannot be ensured, and in the case of Comparative Example 2 in which an excessive amount of C is added, the hydrogen delayed fracture resistance is very high. It was confirmed that it was low. In the case of Comparative Examples 3 to 5 to which molybdenum (Mo) was added, breakage occurred 100 hours ago and sufficient hydrogen delayed fracture resistance could not be ensured, and either La or Ni In Comparative Examples 6 and 7 in which only one was added, it was confirmed that sufficient hydrogen delayed fracture resistance could not be ensured.

また、ＬａやＮｉの添加が本発明で設定した範囲に及ばない比較例８及び１０の場合にも、十分な水素遅れ破壊抵抗性を確保することができないことが確認できた。   It was also confirmed that sufficient hydrogen delayed fracture resistance could not be ensured in Comparative Examples 8 and 10 where the addition of La or Ni did not reach the range set in the present invention.

（実施例２）
一方、Ｌａ系、Ｎｉ系又はＬａＮｉ系析出物のサイズと縦横比による水素遅れ破壊抵抗性を調べるために、上記発明例１〜３に対して更なる熱処理を行い、上記析出物のサイズと縦横比を変化させた。 (Example 2)
On the other hand, in order to investigate the hydrogen delayed fracture resistance due to the size and aspect ratio of La-based, Ni-based, or LaNi-based precipitates, further heat treatment was performed on the inventive examples 1 to 3, and the size and vertical and horizontal dimensions of the precipitates were measured. The ratio was changed.

上記のように析出物のサイズと縦横比を変化させた後、上記実施例１と同じ方法により水素遅れ破壊抵抗性を測定し、その結果を表４に示した。   After changing the size and aspect ratio of the precipitate as described above, hydrogen delayed fracture resistance was measured by the same method as in Example 1, and the results are shown in Table 4.

上記表４の結果から、析出物の縦横比が本発明の範囲を外れる場合には、水素遅れ破壊抵抗性が低いことが確認できた。   From the results in Table 4 above, it was confirmed that the hydrogen delayed fracture resistance was low when the aspect ratio of the precipitates was outside the range of the present invention.

Claims (10)

質量％で、Ｃ：０．３〜０．７％、Ｓｉ：０．０５〜２．０％、Ｍｎ：０．７〜１．５％、Ｌａ：３０〜７０ｐｐｍ、Ｎｉ：０．０１〜０．１％、並びに残部Ｆｅ及び不可避不純物からなり、縦横比が１．２〜２．０であるＬａ系、Ｎｉ系又はＬａＮｉ系析出物を含む、水素遅れ破壊抵抗性に優れた線材。   In mass%, C: 0.3 to 0.7%, Si: 0.05 to 2.0%, Mn: 0.7 to 1.5%, La: 30 to 70 ppm, Ni: 0.01 to 0 A wire rod excellent in hydrogen delayed fracture resistance, comprising La, Ni-based or LaNi-based precipitates having an aspect ratio of 1.2 to 2.0, consisting of 0.1% and the balance Fe and inevitable impurities. 前記析出物の平均円相当径は１００〜４００ｎｍである、請求項１に記載の水素遅れ破壊抵抗性に優れた線材。   The wire having excellent hydrogen delayed fracture resistance according to claim 1, wherein an average equivalent circular diameter of the precipitate is 100 to 400 nm. 前記析出物はＬａＮｉ５、ＬａＰＯ４及びＬａ２Ｏ２Ｓのうち一種以上である、請求項１または２に記載の水素遅れ破壊抵抗性に優れた線材。 The precipitates LaNi 5, LaPO 4 and La is 2 O 2 one or more of S, according to claim 1 or 2 hydrogen delayed fracture resistance excellent in wire according to. 質量％で、Ｃ：０．３〜０．７％、Ｓｉ：０．０５〜２．０％、Ｍｎ：０．７〜１．５％、Ｌａ：３０〜７０ｐｐｍ、Ｎｉ：０．０１〜０．１％、並びに残部Ｆｅ及び不可避不純物からなる鋼材をＡｅ３＋１５０〜Ａｅ３＋２５０℃に加熱する段階と、
前記加熱された鋼材を５〜１５℃／ｓで冷却し、Ａｅ３＋５０〜Ａｅ３＋１５０℃で圧延して線材を製造する段階と、
前記圧延された線材を０．５〜３℃／ｓで６００℃以下まで冷却する段階と、
を含む、水素遅れ破壊抵抗性に優れた線材の製造方法。 In mass%, C: 0.3 to 0.7%, Si: 0.05 to 2.0%, Mn: 0.7 to 1.5%, La: 30 to 70 ppm, Ni: 0.01 to 0 Heating the steel material composed of 1% and the balance Fe and inevitable impurities to Ae3 + 150 to Ae3 + 250 ° C .;
Cooling the heated steel at 5-15 ° C./s, rolling at Ae 3 + 50 to Ae 3 + 150 ° C. to produce a wire;
Cooling the rolled wire rod to 600 ° C. or lower at 0.5 to 3 ° C./s;
A method for producing a wire material having excellent hydrogen delayed fracture resistance. 前記加熱は３０分〜１時間３０分間行われる、請求項４に記載の水素遅れ破壊抵抗性に優れた線材の製造方法。   The said heating is performed for 30 minutes-1 hour and 30 minutes, The manufacturing method of the wire excellent in hydrogen delayed fracture resistance of Claim 4. 質量％で、Ｃ：０．３〜０．７％、Ｓｉ：０．０５〜２．０％、Ｍｎ：０．７〜１．５％、Ｌａ：３０〜７０ｐｐｍ、Ｎｉ：０．０１〜０．１％、並びに残部Ｆｅ及び不可避不純物からなり、縦横比が１．２〜２．０であるＬａ系、Ｎｉ系又はＬａＮｉ系析出物を含み、引張強度１２００ＭＰａ以上の強度を有する、水素遅れ破壊抵抗性に優れたボルト。 In mass%, C: 0.3 to 0.7%, Si: 0.05 to 2.0%, Mn: 0.7 to 1.5%, La: 30 to 70 ppm, Ni: 0.01 to 0 Hydrogen delayed fracture, including La-based, Ni-based or LaNi-based precipitates having an aspect ratio of 1.2 to 2.0, and having a tensile strength of 1200 MPa or more. Bolt with excellent resistance . 前記析出物の平均円相当径は１００〜４００ｎｍである、請求項６に記載の水素遅れ破壊抵抗性に優れたボルト。   The bolt with excellent hydrogen delayed fracture resistance according to claim 6, wherein the average equivalent circle diameter of the precipitate is 100 to 400 nm. 前記析出物はＬａＮｉ５、ＬａＰＯ４及びＬａ２Ｏ２Ｓのうち一種以上である、請求項６または７に記載の水素遅れ破壊抵抗性に優れたボルト。 The precipitate is one or more of LaNi 5, LaPO 4 and La 2 O 2 S, bolt having excellent hydrogen delayed fracture resistance as set forth in claim 6 or 7. 質量％で、Ｃ：０．３〜０．７％、Ｓｉ：０．０５〜２．０％、Ｍｎ：０．７〜１．５％、Ｌａ：３０〜７０ｐｐｍ、Ｎｉ：０．０１〜０．１％、並びに残部Ｆｅ及び不可避不純物からなる鋼材をＡｅ３＋１５０〜Ａｅ３＋２５０℃に加熱する段階と、
前記加熱された鋼材を５〜１５℃／ｓで冷却し、Ａｅ３＋５０〜Ａｅ３＋１５０℃で圧延して線材を製造する段階と、
前記圧延された線材を０．５〜３℃／ｓで６００℃以下まで冷却する段階と、
前記冷却された線材をボルト成形する段階と、
前記成形されたボルトを８５０〜９５０℃で熱処理する段階と、
前記加熱の後に、急冷し、３００〜５００℃の温度で焼き戻しする段階と、
を含む、水素遅れ破壊抵抗性に優れたボルトの製造方法。 In mass%, C: 0.3 to 0.7%, Si: 0.05 to 2.0%, Mn: 0.7 to 1.5%, La: 30 to 70 ppm, Ni: 0.01 to 0 Heating the steel material composed of 1% and the balance Fe and inevitable impurities to Ae3 + 150 to Ae3 + 250 ° C .;
Cooling the heated steel at 5-15 ° C./s, rolling at Ae 3 + 50 to Ae 3 + 150 ° C. to produce a wire;
Cooling the rolled wire rod to 600 ° C. or lower at 0.5 to 3 ° C./s;
Bolting the cooled wire;
Heat treating the molded bolt at 850-950 ° C .;
After the heating, quenching and tempering at a temperature of 300 to 500 ° C .;
A method for producing a bolt having excellent hydrogen delayed fracture resistance. 前記加熱する段階は３０分〜１時間３０分間行われる、請求項９に記載の水素遅れ破壊抵抗性に優れたボルトの製造方法。   The method for manufacturing a bolt excellent in hydrogen delayed fracture resistance according to claim 9, wherein the heating is performed for 30 minutes to 1 hour and 30 minutes.
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