JP5251633B2 - High strength steel material with excellent delayed fracture resistance, high strength bolt and manufacturing method thereof - Google Patents
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Description
本発明は、耐遅れ破壊特性の優れた鋼材、ボルト、特に１３００ＭＰａ以上の引張強度を有する、耐遅れ破壊特性の優れた高強度鋼材（線材、ＰＣ鋼棒）、高強度ボルト、及びその製造方法に関するものである。 The present invention relates to a steel material and a bolt excellent in delayed fracture resistance, particularly a high strength steel material (wire rod, PC steel rod) having a tensile strength of 1300 MPa or more and excellent in delayed fracture resistance, a high strength bolt, and a method for producing the same. It is about.
機械、自動車、橋梁、建築物に多数使用されている高強度鋼は、Ｃ量が０．２０〜０．３５％の中炭素鋼、例えばＪＩＳ Ｇ ４１０４、ＪＩＳ Ｇ ４１０５に規定されている、ＳＣｒ、ＳＣＭ等を用いて、調質処理を施すことによって製造されている。しかし、どの鋼種についても、引張強度が１３００ＭＰａを超えると、遅れ破壊の危険性が高まることがよく知られている。 High strength steels used in many machines, automobiles, bridges, and buildings are medium carbon steels with a C content of 0.20 to 0.35%, such as JIS G 4104 and JIS G 4105, SCr. , SCM or the like is used to perform a tempering process. However, it is well known that for any steel type, the risk of delayed fracture increases when the tensile strength exceeds 1300 MPa.
高強度鋼の耐遅れ破壊特性を向上させる技術として、組織をベイナイト化させる方法が有効であり、更に旧オーステナイト粒を微細化させた鋼が特許文献１に、鋼成分の偏析を抑制した鋼が特許文献２、３に開示されている。しかし、ベイナイト組織は耐遅れ破壊特性向上に寄与する一方、ベイナイト組織を作りこむためには、合金コストや熱処理コストが高くなる問題がある。また、旧オーステナイト粒の微細化、成分偏析の抑制により、大幅な耐遅れ破壊特性の改善には至っていない。
As a technique for improving the delayed fracture resistance of high-strength steel, a method of making the structure bainite is effective, and steel in which the prior austenite grains are further refined is disclosed in Patent Document 1, and steel in which segregation of steel components is suppressed. It is disclosed in
また、特許文献４〜６には、強伸線加工パーライトによる耐遅れ破壊特性の改善が開示されているが、伸線加工によりコストが高くなることや、線径の大きなものを製造することが困難である。
Further,
以上のように、従来の技術では、安価に耐遅れ破壊特性を大幅に向上させた高強度鋼材を製造することには限界があった。 As described above, according to the conventional technique, there is a limit to manufacturing a high-strength steel material with greatly improved delayed fracture resistance at low cost.
また、微細な析出物を分散させ、水素トラップしても、外部から進入する水素が多い腐食環境下では、耐遅れ破壊を抑制することは困難であった。 In addition, even if fine precipitates are dispersed and hydrogen trapped, it is difficult to suppress delayed fracture resistance in a corrosive environment where there is a large amount of hydrogen entering from the outside.
本発明は、上記の課題に鑑みてなされたものであって、優れた耐遅れ破壊特性を有する高強度鋼材（線材、ＰＣ鋼棒）、高強度ボルト及びその製造方法の提供を目的とするものである。 This invention is made in view of said subject, Comprising: It aims at provision of the high strength steel materials (wire rod, PC steel bar), the high strength bolt which have the outstanding delayed fracture resistance, and its manufacturing method. It is.
本発明の要旨とするところは、以下のとおりである。
（１） 質量％で、Ｃ：０．１０〜０．５５％、Ｓｉ：０．０１〜３％、Ｍｎ：０．１〜２％を含有し、さらに、Ｃｒ：０．０５〜１．５％、Ｖ：０．０５〜０．２％、Ｍｏ：０．０５〜０．４％、Ｎｂ：０．００１〜０．０５％、Ｃｕ：０．０１〜４％、Ｎｉ：０．０１〜４％、Ｂ：０．０００１〜０．００５％の１種又は２種以上を含有し、残部がＦｅ及び不可避的不純物からなり、焼戻しマルテンサイトの面積率が８５％以上である組織で、表面から少なくとも２００μｍ深さまでの窒素濃度が平均窒素濃度より０．０２％以上高いことを特徴とする耐遅れ破壊特性に優れた高強度鋼材。
（２） さらに、Ａｌ：０．００３〜０．１％、Ｔｉ：０．００３〜０．０５％、Ｍｇ：０．０００３〜０．０１％、Ｃａ：０．０００３〜０．０１％、Ｚｒ：０．０００３〜０．０１％の１種又は２種以上を含有することを特徴とする（１）記載の耐遅れ破壊特性に優れた高強度鋼材。
（３） 表面に、窒素濃度が平均窒素濃度より０．０２％以上高い窒化層を有し、該窒化層の深さが表面から２００μｍ以上、１０００μｍ以下であることを特徴とする（１）又は（２）に記載の耐遅れ破壊特性に優れた高強度鋼材。
（４） 鋼材表面の圧縮残留応力が２００ＭＰａ以上であることを特徴とする（１）〜（３）の何れか１項に記載の耐遅れ破壊特性に優れた高強度鋼材。
（５） 質量％で、Ｃ：０．１０〜０．５５％、Ｓｉ：０．０１〜３％、Ｍｎ：０．１〜２％を含有し、さらに、Ｃｒ：０．０５〜１．５％、Ｖ：０．０５〜０．２％、Ｍｏ：０．０５〜０．４％、Ｎｂ：０．００１〜０．０５％、Ｃｕ：０．０１〜４％、Ｎｉ：０．０１〜４％、Ｂ：０．０００１〜０．００５％の１種又は２種以上を含有し、残部がＦｅ及び不可避的不純物からなり、焼戻しマルテンサイトの面積率が８５％以上である組織で、表面から少なくとも２００μｍ深さまでの窒素濃度が平均窒素濃度より０．０２％以上高いことを特徴とする耐遅れ破壊特性に優れた高強度ボルト。
（６） さらに、Ａｌ：０．００３〜０．１％、Ｔｉ：０．００３〜０．０５％、Ｍｇ：０．０００３〜０．０１％、Ｃａ：０．０００３〜０．０１％、Ｚｒ：０．０００３〜０．０１％の１種又は２種以上を含有することを特徴とする（５）記載の耐遅れ破壊特性に優れた高強度ボルト。
（７） 表面に、窒素濃度が平均窒素濃度より０．０２％以上高い窒化層を有し、該窒化層の深さが表面から２００μｍ以上、１０００μｍ以下であることを特徴とする（５）又は（６）に記載の耐遅れ破壊特性に優れた高強度ボルト。
（８） 鋼材表面の圧縮残留応力が２００ＭＰａ以上であることを特徴とする（５）〜（７）の何れか１項に記載の耐遅れ破壊特性に優れた高強度ボルト。
（９） （１）〜（４）の何れか１項に記載の高強度鋼材の製造方法であって、（１）又は（２）に記載の成分を有する鋼材を所望の形状に加工した後、窒化処理温度を５００℃以下で窒化処理することを特徴とする耐遅れ破壊特性に優れた高強度鋼材の製造方法。
（１０） （５）〜（８）の何れか１項に記載のボルトの製造方法であって、（５）又は（６）に記載の成分を有する鋼材をボルトに加工した後、窒化処理温度を５００℃以下で窒化処理することを特徴とする耐遅れ破壊特性に優れた高強度ボルトの製造方法。
The gist of the present invention is as follows.
(1) By mass%, C: 0.10 to 0.55%, Si: 0.01 to 3%, Mn: 0.1 to 2%, Cr: 0.05 to 1.5 %, V: 0.05 to 0.2%, Mo: 0.05 to 0.4%, Nb: 0.001 to 0.05%, Cu: 0.01 to 4%, Ni: 0.01 to 4%, B: 0.0001 to 0.005% of one type or two or more types, the balance is Fe and inevitable impurities, and the area ratio of tempered martensite is 85% or more , surface To a depth of at least 200 μm is a high strength steel material having excellent delayed fracture resistance, characterized by being 0.02% or more higher than the average nitrogen concentration.
(2) Furthermore, Al: 0.003-0.1%, Ti: 0.003-0.05%, Mg: 0.0003-0.01%, Ca: 0.0003-0.01%, Zr : 0.0003-0.01% of 1 type or 2 types or more, The high strength steel material excellent in delayed fracture resistance according to (1).
(3) The surface has a nitride layer having a nitrogen concentration of 0.02% or more higher than the average nitrogen concentration, and the depth of the nitride layer is 200 μm or more and 1000 μm or less from the surface (1) or A high-strength steel material having excellent delayed fracture resistance as described in (2) .
(4 ) The high-strength steel material having excellent delayed fracture resistance according to any one of (1) to ( 3 ), wherein the compressive residual stress on the surface of the steel material is 200 MPa or more.
( 5 ) By mass%, C: 0.10 to 0.55%, Si: 0.01 to 3%, Mn: 0.1 to 2%, Cr: 0.05 to 1.5 %, V: 0.05 to 0.2%, Mo: 0.05 to 0.4%, Nb: 0.001 to 0.05%, Cu: 0.01 to 4%, Ni: 0.01 to 4%, B: 0.0001 to 0.005% of one type or two or more types, the balance is Fe and inevitable impurities, and the area ratio of tempered martensite is 85% or more , surface A high-strength bolt excellent in delayed fracture resistance, characterized in that the nitrogen concentration at a depth of at least 200 μm is 0.02% or more higher than the average nitrogen concentration.
( 6 ) Furthermore, Al: 0.003-0.1%, Ti: 0.003-0.05%, Mg: 0.0003-0.01%, Ca: 0.0003-0.01%, Zr : 0.0003-0.01% of 1 type or 2 types or more, The high strength bolt excellent in delayed fracture resistance according to ( 5 ).
( 7 ) The surface has a nitride layer having a nitrogen concentration 0.02% or more higher than the average nitrogen concentration, and the depth of the nitride layer is 200 μm or more and 1000 μm or less from the surface ( 5 ) or A high-strength bolt excellent in delayed fracture resistance as described in ( 6 ) .
(8 ) The high strength bolt excellent in delayed fracture resistance according to any one of ( 5 ) to ( 7 ), wherein the compressive residual stress on the surface of the steel material is 200 MPa or more.
( 9 ) A method for producing a high-strength steel material according to any one of (1) to ( 4 ), wherein the steel material having the component according to (1) or (2) is processed into a desired shape. A method for producing a high-strength steel material excellent in delayed fracture resistance, characterized by nitriding at a nitriding temperature of 500 ° C. or lower.
( 10 ) The method for producing a bolt according to any one of ( 5 ) to ( 8 ), wherein the steel material having the component according to (5) or (6) is processed into a bolt, and then a nitriding temperature Is produced by nitriding at 500 ° C. or less, and a method for producing a high-strength bolt excellent in delayed fracture resistance.
本発明により、腐食の厳しい環境においても耐遅れ破壊特性を維持する高強度鋼材（線材、ＰＣ鋼棒）、高強度ボルト及びその安価な製造方法の提供が可能になり、産業上の貢献が極めて顕著である。 The present invention makes it possible to provide high-strength steel materials (wire rods, PC steel bars), high-strength bolts and their inexpensive manufacturing methods that maintain delayed fracture resistance even in corrosive environments, making a significant industrial contribution. It is remarkable.
鋼の遅れ破壊は、鋼中の水素が関与していることが知られている。また、鋼への水素の侵入過程は、実環境使用時における腐食に伴って起こることが知られている。侵入した拡散性水素が、引張の応力集中部に拡散して、遅れ破壊を発生させる。 It is known that delayed fracture of steel involves hydrogen in steel. In addition, it is known that the process of hydrogen intrusion into steel is accompanied by corrosion during actual environment use. The invading diffusible hydrogen diffuses into the tensile stress concentration part and causes delayed fracture.
図１は、鋼材を１００℃／ｈの昇温速度で加熱した際に得られる温度−水素放出速度曲線を模式的に示したものであるが、拡散性水素は図１の１００℃付近にピークを持つものである。本発明では、試料を昇温し、室温から４００℃までに測定された水素量を拡散性水素量と定義した。 FIG. 1 schematically shows a temperature-hydrogen release rate curve obtained when a steel material is heated at a rate of temperature increase of 100 ° C./h. Diffusible hydrogen peaks in the vicinity of 100 ° C. in FIG. It has something. In the present invention, the amount of hydrogen measured from room temperature to 400 ° C. is defined as the amount of diffusible hydrogen when the sample is heated.
拡散性水素量が少ないと遅れ破壊は発生せず、拡散性水素量が多くなると遅れ破壊が発生する。遅れ破壊が発生する最少の拡散性水素量をここでは限界拡散性水素量と呼ぶ。限界拡散性水素量は、鋼の種類によって異なる。限界拡散性水素量が高いほど、遅れ破壊が起きづらくなるので好ましい。しかし、腐食環境からの侵入水素量が多くなると、限界拡散性水素量と比較して侵入水素量の方が多くなるため、遅れ破壊が発生するという問題があった。 When the amount of diffusible hydrogen is small, delayed fracture does not occur, and when the amount of diffusible hydrogen is large, delayed fracture occurs. The minimum amount of diffusible hydrogen at which delayed fracture occurs is referred to herein as the limit diffusible hydrogen amount. The amount of critical diffusible hydrogen varies depending on the type of steel. A higher limit diffusible hydrogen amount is preferable because delayed fracture is less likely to occur. However, when the amount of intrusion hydrogen from the corrosive environment increases, the amount of intrusion hydrogen increases as compared with the limit diffusible hydrogen amount, and there is a problem that delayed fracture occurs.
本発明者は、種々の高強度の鋼材に様々な窒化処理を行い、腐食促進試験及び暴露試験により、水素侵入特性及び耐遅れ破壊特性を検討した。その結果、鋼材の表面に窒化処理を施して窒化層を形成すること、具体的には、鋼材の表面から少なくとも２００μｍ以上の深さまで平均窒素濃度より０．０２％以上窒素濃度を高めることにより、拡散性水素の侵入が大幅に抑制されることが判った。また、窒化処理後に急冷することにより表面に圧縮残留応力が発生し、耐遅れ破壊特性が向上することを見出した。特に、鋼材を加工し、表層に歪みが導入される高強度ボルトでは、窒化層の生成が促進され、また、窒素濃度が高くなるため、耐遅れ破壊特性の向上が顕著である。 The present inventor performed various nitriding treatments on various high-strength steel materials, and examined hydrogen penetration characteristics and delayed fracture resistance characteristics by a corrosion acceleration test and an exposure test. As a result, nitriding the surface of the steel material to form a nitrided layer, specifically, by increasing the nitrogen concentration by 0.02% or more from the average nitrogen concentration from the surface of the steel material to a depth of at least 200 μm, It was found that invasion of diffusible hydrogen was greatly suppressed. Further, it has been found that rapid cooling after nitriding treatment generates compressive residual stress on the surface and improves delayed fracture resistance. In particular, in a high-strength bolt in which a steel material is processed and strain is introduced into the surface layer, the formation of a nitrided layer is promoted and the nitrogen concentration is increased, so that the delayed fracture resistance is significantly improved.
以下、本発明について詳細に説明する。 Hereinafter, the present invention will be described in detail.
本発明の高強度鋼材及び高強度ボルトは、所定成分の鋼からなり、その表面に窒化層を形成したものである。 The high-strength steel material and high-strength bolt of the present invention are made of steel having a predetermined component, and a nitride layer is formed on the surface thereof.
まず、表面の窒化層について説明する。窒素濃度が平均窒素濃度より０．０２％以上高い領域が表面から２００μｍ以上になると水素侵入量が大幅に減少することが判明した。そのため、窒素が高い領域として、窒素濃度が平均窒素濃度より０．０２％以上高い領域と定めた。そして、窒素濃度の高い領域を表面から２００μｍ以上に限定した。窒化層の厚みの上限は、特に規定しないが、１０００μｍ超とすることは生産性の低下につながり、コストが高くなるという問題が生じるため、１０００μｍ以下とすることが好ましい。 First, the nitride layer on the surface will be described. It has been found that the amount of hydrogen intrusion is greatly reduced when the region where the nitrogen concentration is 0.02% or more higher than the average nitrogen concentration is 200 μm or more from the surface. Therefore, the region where nitrogen is high is determined as a region where the nitrogen concentration is 0.02% or more higher than the average nitrogen concentration. And the area | region with high nitrogen concentration was limited to 200 micrometers or more from the surface. The upper limit of the thickness of the nitrided layer is not particularly specified, but if it exceeds 1000 μm, it leads to a decrease in productivity and increases costs, so it is preferably set to 1000 μm or less.
このような鋼からなり、その表面に窒化層を有する鋼材（線材又はＰＣ鋼棒）、ボルトの断面を研磨して、エネルギー分散型蛍光Ｘ線分析装置（ＥＤＸと言う）もしくは波長分散型蛍光Ｘ線分析装置（ＷＤＳと言う）にて線分析すると、図２に示すように表層部から中心部に向かい窒素濃度が減少し、表面からある深さまでの窒素濃度が、平均窒素濃度より０．０２％以上高くなるプロファイルを示すため、表面の窒素濃度が平均窒素濃度より０．０２％以上高くなっている範囲が判別可能である。図２の窒素濃度が平均窒素濃度より０．０２％以上高くなっている領域の表面からの距離を窒化層深さと定義する。 A steel material (wire or PC steel rod) made of such steel and having a nitride layer on its surface, a cross section of a bolt is polished, and an energy dispersive X-ray fluorescence analyzer (referred to as EDX) or wavelength dispersive X-ray fluorescence X When line analysis is performed with a line analyzer (referred to as WDS), the nitrogen concentration decreases from the surface layer portion toward the center portion as shown in FIG. 2, and the nitrogen concentration from the surface to a certain depth is 0.02 from the average nitrogen concentration. Since the profile becomes higher by at least%, it is possible to discriminate a range where the surface nitrogen concentration is 0.02% higher than the average nitrogen concentration. The distance from the surface of the region where the nitrogen concentration in FIG. 2 is 0.02% or more higher than the average nitrogen concentration is defined as the nitrided layer depth.
窒化層深さの測定は、任意の５ヶ所の単純平均として求めることができる。 The measurement of the nitride layer depth can be obtained as a simple average of any five locations.
なお、平均窒素濃度とは、窒化前の鋼材又はボルトに含まれる窒素量である。したがって、窒化後の鋼材又はボルトの平均窒素濃度は、ＥＤＸや、ＷＤＳによって、表面から窒素濃度を測定し、数値が一定になった深さでの窒素濃度として求めることができる。表面から２０００μｍ以上の深さで、窒素濃度を測定してもよい。また、表面から２０００μｍ以上を研削して、分析試料を採取し、化学分析によって平均窒素濃度を測定することも可能である。 The average nitrogen concentration is the amount of nitrogen contained in the steel material or bolt before nitriding. Therefore, the average nitrogen concentration of the steel material or bolt after nitriding can be obtained as the nitrogen concentration at a depth where the numerical value is constant by measuring the nitrogen concentration from the surface by EDX or WDS. The nitrogen concentration may be measured at a depth of 2000 μm or more from the surface. It is also possible to grind 2000 μm or more from the surface, collect an analytical sample, and measure the average nitrogen concentration by chemical analysis.
次に、鋼材の成分を限定した理由について説明する。 Next, the reason which limited the component of steel materials is demonstrated.
Ｃ：Ｃは、鋼材の強度を確保する上で必須の元素であるが、０．１０％未満であると所要の強度が得られず、０．５５％を超えると延性、靭性を低下させると共に、耐遅れ破壊特性も低下する。そのため、Ｃの含有量を０．１０〜０．５５％の範囲に限定した。 C: C is an essential element for securing the strength of the steel material, but if it is less than 0.10%, the required strength cannot be obtained, and if it exceeds 0.55%, ductility and toughness are reduced. Also, delayed fracture resistance is reduced. Therefore, the C content is limited to a range of 0.10 to 0.55%.
Ｓｉ：Ｓｉは、固溶体硬化作用によって強度を高める元素であるが、Ｓｉの含有量が０．０１％未満では効果が不十分であり、３％超では効果が飽和する。そのため、Ｓｉの含有量を０．０１〜３％に限定した。 Si: Si is an element that increases the strength by the solid solution hardening action, but if the Si content is less than 0.01%, the effect is insufficient, and if it exceeds 3%, the effect is saturated. Therefore, the Si content is limited to 0.01 to 3%.
Ｍｎ：Ｍｎは、脱酸、脱硫のために必要であるばかりではなく、マルテンサイト組織を得るための焼入れ性を高めることや、パーライト組織、ベイナイト組織の変態温度を下げて、高強度を得るために有効な元素である。しかし、Ｍｎの含有量が０．１％未満であると効果が不十分であり、２％を超えるとオーステナイト加熱時に粒界に偏析し、粒界を脆化させると共に、耐遅れ破壊特性を劣化させる。そのため、Ｍｎの含有量を０．１〜２％の範囲に限定した。 Mn: Mn is not only necessary for deoxidation and desulfurization, but also increases the hardenability for obtaining a martensite structure, and lowers the transformation temperature of a pearlite structure and a bainite structure to obtain high strength. Is an effective element. However, if the Mn content is less than 0.1%, the effect is insufficient, and if it exceeds 2%, segregation occurs at the grain boundary during austenite heating, embrittles the grain boundary, and degrades delayed fracture resistance. Let Therefore, the Mn content is limited to a range of 0.1 to 2%.
更に、高強度にすることを目的に、Ｃｒ、Ｎｂ、Ｖ、Ｍｏ、Ｃｕ、Ｎｉ、Ｂの１種又は２種以上を含有する。 Further, for the purpose of increasing the strength, one or more of Cr, Nb, V, Mo, Cu, Ni, and B are contained.
Ｃｒ：Ｃｒは、マルテンサイト組織を得るための焼入れ性を高めること及び焼戻し処理時の軟化抵抗増加させることや、パーライト組織、ベイナイト組織の変態温度を下げて、高強度を得るために有効な元素である。Ｃｒの含有量が、０．０５％未満ではその効果が十分には得られ難く、１．５％を超えると靭性の劣化を招くことがある。そのため、Ｃｒの含有量を０．０５〜１．５％の範囲とする。 Cr: Cr is an element effective for increasing the hardenability for obtaining the martensite structure and increasing the softening resistance during the tempering process, and lowering the transformation temperature of the pearlite structure and the bainite structure to obtain high strength. It is. If the Cr content is less than 0.05%, it is difficult to obtain the effect sufficiently, and if it exceeds 1.5%, the toughness may be deteriorated. Therefore, the Cr content is in the range of 0.05 to 1.5%.
Ｖ：Ｖは、マルテンサイト組織を得るための焼入れ性を高めること及び焼戻し処理時の軟化抵抗増加させることや、パーライト組織、ベイナイト組織の変態温度を下げて、高強度を得るために有効な元素である。Ｖの含有量が、０．０５％未満ではその効果が十分には得られ難く、０．２％を超えるとその効果が飽和してくる。そのため、Ｖの含有量を０．０５〜０．２％の範囲とする。 V: V is an element effective for increasing the hardenability for obtaining a martensite structure, increasing softening resistance during tempering treatment, and lowering the transformation temperature of pearlite structure and bainite structure to obtain high strength. It is. If the V content is less than 0.05%, it is difficult to obtain the effect sufficiently, and if it exceeds 0.2%, the effect is saturated. Therefore, the V content is in the range of 0.05 to 0.2%.
Ｍｏ：Ｍｏは、マルテンサイト組織を得るための焼入れ性を高めること及び焼戻し処理時の軟化抵抗増加させることや、パーライト組織、ベイナイト組織の変態温度を下げて、高強度を得るために有効な元素である。Ｍｏの含有量が、０．０５％未満ではその効果が十分には得られ難く、０．４％を超えるとその効果が飽和してくる。そのため、Ｍｏの含有量を０．０５〜０．４％の範囲とする。 Mo: Mo is an element effective for increasing the hardenability for obtaining the martensite structure and increasing the softening resistance during the tempering process, and lowering the transformation temperature of the pearlite structure and the bainite structure to obtain high strength. It is. If the Mo content is less than 0.05%, it is difficult to obtain the effect sufficiently, and if it exceeds 0.4%, the effect becomes saturated. Therefore, the Mo content is in the range of 0.05 to 0.4%.
Ｎｂ：Ｎｂは、Ｃｒ、Ｖ、Ｍｏと同様に、マルテンサイト組織を得るための焼入れ性を高めること及び焼戻し処理時の軟化抵抗増加させることや、パーライト組織、ベイナイト組織の変態温度を下げて、高強度を得るために有効な元素である。Ｎｂの含有量が、０．００１％未満ではその効果が十分には得られ難く、０．０５％を超えるとその効果が飽和してくる。そのため、Ｎｂの含有量を０．００１〜０．０５％とする。 Nb: Nb, like Cr, V, and Mo, increases the hardenability to obtain a martensite structure and increases the softening resistance during tempering, and lowers the transformation temperature of the pearlite structure and bainite structure, It is an effective element for obtaining high strength. If the Nb content is less than 0.001%, it is difficult to obtain the effect sufficiently, and if it exceeds 0.05%, the effect is saturated. Therefore, the Nb content is set to 0.001 to 0.05%.
Ｃｕ：Ｃｕの添加により、焼入れ性の向上、焼戻し軟化抵抗の増大、及び析出効果による高強度化を図ることができる。しかし、Ｃｕの含有量が０．０１未満では効果が十分には得られ難く、４％を超えると粒界脆化を起こして耐遅れ破壊特性を劣化させることがある。そのため、Ｃｕの含有量を０．０１〜４％の範囲とする。 By adding Cu: Cu, it is possible to improve the hardenability, increase the temper softening resistance, and increase the strength by the precipitation effect. However, if the Cu content is less than 0.01, it is difficult to obtain the effect sufficiently, and if it exceeds 4%, grain boundary embrittlement may occur and the delayed fracture resistance may be deteriorated. Therefore, the Cu content is in the range of 0.01 to 4%.
Ｎｉ：Ｎｉは、焼入れ性を向上させ、高強度化に伴って低下する延靭性を改善する効果がある。しかし、Ｎｉの含有量が０．０１％未満であると効果が十分には得られ難く、４％を超えて含有させても効果が飽和する。そのため、Ｎｉの含有量を０．０１〜４％の範囲とする。 Ni: Ni has the effect of improving hardenability and improving ductility that decreases with increasing strength. However, if the Ni content is less than 0.01%, it is difficult to obtain the effect sufficiently, and even if the content exceeds 4%, the effect is saturated. Therefore, the Ni content is in the range of 0.01 to 4%.
Ｂ：Ｂは、粒界破壊を抑制し、耐遅れ破壊特性を向上させる効果がある。さらに、Ｂは、オーステナイト粒界に偏析し、焼入れ性を著しく高める。しかし、Ｂの含有量が０．０００１％未満であると効果が十分には得られ難く、０．００５％を超えると粒界にＢ炭化物やＦｅ炭硼化物が生成し、粒界脆化を起こして耐遅れ破壊特性が低下する。そのため、Ｂの含有量を０．０００１〜０．００５％の範囲とする。 B: B has an effect of suppressing grain boundary fracture and improving delayed fracture resistance. Further, B segregates at the austenite grain boundaries and remarkably increases the hardenability. However, if the content of B is less than 0.0001%, it is difficult to obtain the effect sufficiently. If it exceeds 0.005%, B carbide or Fe carbon boride is generated at the grain boundary, and grain boundary embrittlement occurs. Cause delayed fracture resistance. Therefore, the B content is in the range of 0.0001 to 0.005%.
更に、組織を微細化することを目的に、Ａｌ、Ｔｉ、Ｍｇ、Ｃａ、Ｚｒの１種又は２種以上を含有することができる。 Furthermore, one or more of Al, Ti, Mg, Ca, and Zr can be contained for the purpose of refining the structure.
Ａｌ：Ａｌは、脱酸及び熱処理によりＡｌ酸化物やＡｌ窒化物を形成して、オーステナイト粒の粗大化を防止する。これにより、耐遅れ破壊特性の劣化を抑制する効果を奏するが、この効果は、Ａｌの含有量が、０．００３％未満ではやや不十分であり、０．１％超では飽和する。そのため、Ａｌの含有量を０．００３〜０．１％の範囲とすることが好ましい。 Al: Al forms Al oxide and Al nitride by deoxidation and heat treatment, and prevents austenite grains from becoming coarse. As a result, the effect of suppressing the deterioration of the delayed fracture resistance is exhibited. This effect is slightly insufficient when the Al content is less than 0.003%, and is saturated when the content exceeds 0.1%. Therefore, it is preferable to make Al content into the range of 0.003-0.1%.
Ｔｉ：Ｔｉも、Ａｌと同様に、酸化物や窒化物を形成してオーステナイト粒の粗大化を防止し、耐遅れ破壊特性の劣化を抑制する元素である。この効果は、Ｔｉの含有量が０．００３％未満ではやや不十分であり、０．０５％を超えると粗大なＴｉ炭窒化物が圧延や加工あるいは熱処理のための加熱時に粗大化し、靭性が低下する。そのため、Ｔｉの含有量を０．００３〜０．０５％の範囲とすることが好ましい。 Ti: Ti, like Al, is an element that forms oxides and nitrides to prevent coarsening of austenite grains and suppresses deterioration of delayed fracture resistance. This effect is somewhat insufficient if the Ti content is less than 0.003%, and if it exceeds 0.05%, coarse Ti carbonitrides become coarse during heating for rolling, processing or heat treatment, and toughness is increased. descend. Therefore, the Ti content is preferably in the range of 0.003 to 0.05%.
Ｍｇ：Ｍｇは、脱酸や脱硫効果を有し、また、Ｍｇ酸化物やＭｇ硫化物、Ｍｇ−Ａｌ、Ｍｇ−Ｔｉ、Ｍｇ−Ａｌ−Ｔｉの複合酸化物や複合硫化物等を形成し、オーステナイト粒の粗大化を防止する。これにより、耐遅れ破壊特性の劣化を抑制する効果を奏するが、この効果は、Ｍｇの含有量が０．０００３％未満であるとやや不十分であり、０．０１％超では飽和する。そのため、Ｍｇの含有量を０．０００３〜０．０１％の範囲とすることが好ましい。 Mg: Mg has deoxidation and desulfurization effects, and forms Mg oxide, Mg sulfide, Mg-Al, Mg-Ti, Mg-Al-Ti composite oxide and composite sulfide, etc. Prevent coarsening of austenite grains. Thereby, although there exists an effect which suppresses deterioration of a delayed fracture resistance, this effect is a little inadequate when content of Mg is less than 0.0003%, and will be saturated when it exceeds 0.01%. Therefore, the Mg content is preferably in the range of 0.0003 to 0.01%.
Ｃａ：Ｃａは、脱酸や脱硫効果を有し、また、Ｃａ酸化物やＣａ硫化物、Ａｌ、Ｔｉ、Ｍｇの複合酸化物や複合硫化物等を形成して、オーステナイト粒の粗大化を防止し、耐遅れ破壊特性の劣化を抑制する。この効果は、Ｃａの含有量が０．０００３％未満ではやや不十分であり、０．０１％超では飽和する。そのため、Ｃａの含有量を０．０００３〜０．０１％の範囲とすることが好ましい。 Ca: Ca has a deoxidizing and desulfurizing effect, and also forms Ca oxide, Ca sulfide, Al, Ti, Mg composite oxide and composite sulfide to prevent austenite grain coarsening. And suppresses the deterioration of delayed fracture resistance. This effect is slightly insufficient when the Ca content is less than 0.0003%, and is saturated when it exceeds 0.01%. Therefore, the Ca content is preferably in the range of 0.0003 to 0.01%.
Ｚｒ：Ｚｒは、Ｚｒ酸化物やＺｒ硫化物、Ａｌ、Ｔｉ、Ｍｇ、Ｚｒの複合酸化物や複合硫化物等を形成し、オーステナイト粒の粗大化を防止して、耐遅れ破壊特性の劣化を抑制する。この効果は、Ｚｒの含有量が、０．０００３％未満ではやや不十分である。一方、Ｚｒを０．０１％を超えて含有させても効果が飽和する。そのため、Ｚｒの含有量を０．０００３〜０．０１％の範囲とすることが好ましい。 Zr: Zr forms Zr oxide, Zr sulfide, composite oxide or composite sulfide of Al, Ti, Mg, Zr, etc., prevents austenite grains from coarsening, and deteriorates delayed fracture resistance. Suppress. This effect is somewhat insufficient when the Zr content is less than 0.0003%. On the other hand, the effect is saturated even if Zr is contained in excess of 0.01%. Therefore, the Zr content is preferably in the range of 0.0003 to 0.01%.
次に、本発明の組織形態について説明する。 Next, the organization form of the present invention will be described.
本発明の高強度鋼材の組織形態は、焼き戻しマルテンサイト主体の組織である。８５％以上焼戻しマルテンサイト組織で、残部が、残留オーステナイト、ベイナイト、パーライト、フェライトの１種又は２種以上からなる組織を焼戻しマルテンサイト主体の組織と規定する。Ａｃ1変態温度〜Ａｃ3変態温度＋２５０℃まで再加熱、もしくは熱間圧延後に焼入れ、５００℃以下の温度で焼戻しすることにより、もしくは窒化処理することによりこのような組織を得ることができる。マルテンサイト組織率の測定は、Ｃ断面を研磨したものをナイタールエッチングし、光学顕微鏡で０．０４ｍｍ2の範囲の５視野測定した平均値を用いることができる。本発明は焼戻しマルテンサイト主体の組織としているので、１３００ＭＰａ以上の引張強度で延性、靭性が良好である。 The structure form of the high-strength steel material of the present invention is a structure mainly composed of tempered martensite. An tempered martensite structure having a balance of one or more of retained austenite, bainite, pearlite, and ferrite in the tempered martensite structure is defined as a tempered martensite-based structure. Such a structure can be obtained by reheating from Ac 1 transformation temperature to Ac 3 transformation temperature + 250 ° C., quenching after hot rolling, tempering at a temperature of 500 ° C. or less, or nitriding. For the measurement of the martensite structure ratio, an average value obtained by performing nital etching on a polished C cross section and measuring five visual fields in a range of 0.04 mm 2 with an optical microscope can be used. Since the structure of the present invention is mainly tempered martensite, the ductility and toughness are good at a tensile strength of 1300 MPa or more.
表面の圧縮残留応力は、窒化後に急冷することにより発生し、耐遅れ破壊特性を改善する。特に、２００ＭＰａ以上の圧縮残留応力が発生すると、耐遅れ破壊特性が向上するため、表面の圧縮残留応力を２００ＭＰａ以上とすることが好ましい。残留応力は、Ｘ線残留応力測定装置を用いて測定することができる。測定では、表面の残留応力測定後、電解研磨にて２５μｍずつエッチングを行い、深さ方向の残留応力を測定する。残留応力測定は、任意の３箇所を測定し、その平均値を用いる。 The compressive residual stress on the surface is generated by rapid cooling after nitriding and improves delayed fracture resistance. In particular, when a compressive residual stress of 200 MPa or more is generated, the delayed fracture resistance is improved, so the surface compressive residual stress is preferably 200 MPa or more. The residual stress can be measured using an X-ray residual stress measuring device. In the measurement, after measuring the residual stress on the surface, etching is performed by 25 μm at a time by electrolytic polishing, and the residual stress in the depth direction is measured. Residual stress measurement measures arbitrary three places and uses the average value.
引張強度は、１３００ＭＰａ以上になると、遅れ破壊の発生頻度が著しく増加するため、表面に窒化層を形成させて耐遅れ破壊特性を向上させる効果が顕著になる。引張強度の上限は、２２００ＭＰａを超えることは、技術的に困難である。引張強度の測定は、ＪＩＳ Ｚ ２２４１に準拠して行えば良い。 When the tensile strength is 1300 MPa or more, the frequency of occurrence of delayed fracture is remarkably increased. Therefore, the effect of improving the delayed fracture resistance by forming a nitride layer on the surface becomes remarkable. It is technically difficult for the upper limit of the tensile strength to exceed 2200 MPa. The tensile strength may be measured according to JIS Z 2241.
遅れ破壊の限界拡散性水素量は、図３に示した遅れ破壊試験片に水素を侵入させた後、図４に示した試験機で引張強度の９０％の荷重を負荷し、１００時間以上破断しなかった時の上限の拡散性水素量である。図４に示す試験機では、試験片１に引張加重を付加するに際し、支点３を支点とするテコの一方の端にバランスウェイト２を設置し、他方の端に試験片１を設置して行う。遅れ破壊試験片に水素を侵入させる水素チャージは、電解チャージ法で行う。また、水素チャージ後に、拡散性水素の逃散を防止するため、試験片の表面にＣｄめっきを施し、試験片内部の水素濃度を均質化するために室温で３時間放置した。拡散性水素量は、試料を１００℃／ｈで昇温し、室温から４００℃までに放出された水素量の積算値を、ガスクロマトグラフにより測定したものである。
The critical diffusible hydrogen content of delayed fracture was determined by injecting hydrogen into the delayed fracture specimen shown in FIG. 3 and then applying a load of 90% of the tensile strength with the tester shown in FIG. The upper limit is the amount of diffusible hydrogen when not. In the testing machine shown in FIG. 4, when applying a tensile load to the test piece 1, the
次に、本発明の高強度鋼材、高強度ボルトの製造方法について説明する。 Next, the manufacturing method of the high strength steel materials and high strength bolts of the present invention will be described.
本発明の高強度鋼材（線材、ＰＣ鋼棒）の製造方法は、所定の成分からなる鋼を常法にしたがって溶製、鋳造により鋼片とし、加熱して熱間加工又はこれに加えて冷間加工により鋼材とし、表面に窒化層を形成するものである。熱間加工後、冷間加工、熱処理を適宜行っても良い。また、本発明の高強度ボルトの製造方法は、所定の成分からなる鋼を常法にしたがって線材とし、冷間又は温間加工によりボルトとし、表面に窒化層を形成するものである。 The manufacturing method of the high-strength steel material (wire material, PC steel bar) of the present invention is a method in which steel comprising a predetermined component is melted and cast into a steel slab according to a conventional method, and heated to hot work or cold in addition to this. A steel material is formed by inter-working, and a nitride layer is formed on the surface. After hot working, cold working and heat treatment may be appropriately performed. Moreover, the manufacturing method of the high intensity | strength bolt of this invention uses the steel which consists of a predetermined component as a wire according to a conventional method, makes it a bolt by cold or warm processing, and forms a nitrided layer on the surface.
鋼の表面の窒化層は、「ガス窒化法」、「ガス軟窒化法」、「プラズマ窒化法」、「塩浴窒化法」等の一般的な窒化法を用いて形成することができる。 The nitride layer on the surface of the steel can be formed using a general nitriding method such as “gas nitriding method”, “gas soft nitriding method”, “plasma nitriding method”, “salt bath nitriding method” and the like.
窒化処理時の温度は、５００℃を超えると鋼材の強度を得ることが困難になるため、５００℃以下とする。また、処理温度の下限は、特に限定しないが、４００℃未満であると、表面からの窒素拡散に時間がかかり、コスト的に不利である。 If the temperature during the nitriding process exceeds 500 ° C, it becomes difficult to obtain the strength of the steel material. Further, the lower limit of the treatment temperature is not particularly limited, but if it is less than 400 ° C., it takes time to diffuse nitrogen from the surface, which is disadvantageous in terms of cost.
窒化処理時の時間は、１時間未満であると窒素濃度の高い領域が表面から２００μｍ深さまで得られないため、１時間以上とする。また、処理時間の上限は規定しないが、１２時間を越えるとコスト的にメリットが得られないため、１２時間以下とすることが好ましい。 When the nitriding time is less than 1 hour, a region with a high nitrogen concentration cannot be obtained from the surface to a depth of 200 μm, so that it is 1 hour or longer. Moreover, although the upper limit of processing time is not prescribed | regulated, since a merit is not acquired if it exceeds 12 hours, it is preferable to set it as 12 hours or less.
表１に示す化学組成を有する鋼を、常法にしたがって、溶製、熱間加工し、線材とした。その鋼材に、Ａｃ1変態温度〜Ａｃ3変態温度＋２５０℃範囲内の温度である８５０℃〜１０００℃で加熱して焼入れを行い、その後にガス軟窒化法で窒化層を形成した。ガス軟窒化では、４００〜５００℃の温度範囲、処理ガス雰囲気中のアンモニア体積比を３０〜５０％、処理時間を１〜１２時間の条件での処理を行った。窒化処理温度は表２に示す温度とした。また、熱間加工後の線材をボルトに加工し、同様の条件で、焼入れを行い、ガス軟窒化法で窒化層を形成した。 Steel having the chemical composition shown in Table 1 was melted and hot worked according to a conventional method to obtain a wire. The steel material was quenched by heating at 850 ° C. to 1000 ° C., which is a temperature within the range of Ac 1 transformation temperature to Ac 3 transformation temperature + 250 ° C., and then a nitride layer was formed by gas soft nitriding. In gas soft nitriding, the treatment was performed under the conditions of a temperature range of 400 to 500 ° C., an ammonia volume ratio in the treatment gas atmosphere of 30 to 50%, and a treatment time of 1 to 12 hours. The nitriding temperature was the temperature shown in Table 2. Further, the hot-worked wire was processed into a bolt, quenched under the same conditions, and a nitrided layer was formed by gas soft nitriding.
焼戻しマルテンサイト比率の測定は、Ｃ断面を研磨したものをナイタールエッチングし、光学顕微鏡で０．０４ｍｍ2の範囲の５視野測定した平均値を用いた。なお、焼戻しマルテンサイトの残部の組織は、残留オーステナイト、ベイナイト、パーライト、フェライトの１種又は２種以上であった。 The average tempered martensite ratio was obtained by performing nital etching on the polished C cross section and measuring five visual fields in the range of 0.04 mm 2 with an optical microscope. The remaining structure of the tempered martensite was one or more of retained austenite, bainite, pearlite, and ferrite.
引張強度を、ＪＩＳ Ｚ ２２４１に準拠して測定した。 The tensile strength was measured according to JIS Z 2241.
試料の断面を研磨し、任意の５箇所をＥＤＸで分析し、表面からの窒素濃度分布を測定し、窒素濃度が平均窒素濃度より０．０２％以上高い領域の深さを「窒化層深さ」とした。併せて平均窒素濃度と表層から２００μｍ深さの窒素濃度との差を測定した。いずれも５箇所の平均値を測定値とした。 Polish the cross section of the sample, analyze any five locations with EDX, measure the nitrogen concentration distribution from the surface, and determine the depth of the region where the nitrogen concentration is 0.02% or more higher than the average nitrogen concentration as “nitride layer depth” " In addition, the difference between the average nitrogen concentration and the nitrogen concentration at a depth of 200 μm from the surface layer was measured. In all cases, the average value at five locations was taken as the measured value.
残留応力は、Ｘ線残留応力測定装置を用いて測定を行った。測定では、表面の残留応力測定後、電解研磨にて２５μｍずつエッチングを行い、深さ方向の残留応力を測定した。残留応力測定は、任意の３箇所を測定し、その平均値を用いた。 The residual stress was measured using an X-ray residual stress measuring device. In the measurement, after measuring the residual stress on the surface, etching was performed by 25 μm by electrolytic polishing, and the residual stress in the depth direction was measured. Residual stress measurement was performed at three arbitrary locations and the average value was used.
侵入水素量は、図５示したパターンで腐食試験を３０サイクル行った後、サンドブラストにて表面の腐食層を除去し、昇温法で水素分析を行い、室温から４００℃までに測定された水素量である。 The amount of intrusion hydrogen was determined by measuring 30 cycles of the corrosion test with the pattern shown in FIG. 5, removing the corrosive layer on the surface with sand blasting, performing hydrogen analysis with a temperature rising method, and measuring hydrogen from room temperature to 400 ° C. Amount.
また、遅れ破壊の限界拡散性水素量は、図３の試験片に水素チャージし、表面にＣｄめっきして室温で３時間放置し、図４に示す試験機で引張強さの９０％の荷重をかけた定荷重遅れ破壊試験を行い、図６に模式的に示した破断時間−拡散性水素量のグラフにおいて、１００時間以上で破断しなかった試験片の拡散性水素量の最大値とした。なお、水素チャージは、電解水素チャージ法を用いて行い、チャージ電流によって水素レベルを変化させた。 The critical diffusible hydrogen content of delayed fracture was determined by charging the test piece of FIG. 3 with hydrogen, plating the surface with Cd, leaving it at room temperature for 3 hours, and using a testing machine shown in FIG. 4 with a load of 90% of the tensile strength. In the graph of rupture time-diffusible hydrogen amount schematically shown in FIG. 6, the maximum diffusible hydrogen amount of the test piece that did not break in 100 hours or more was obtained. . In addition, hydrogen charge was performed using the electrolytic hydrogen charge method, and the hydrogen level was changed by the charge current.
侵入水素量と遅れ破壊の限界拡散性水素量を比較して、侵入水素量より限界拡散性水素量の多い場合は遅れ破壊が発生せず、逆に、限界拡散性水素量の方が少ない場合は遅れ破壊が発生する。したがって、この侵入水素量と限界拡散性水素量の大小で耐遅れ破壊特性を評価した。 Comparing the amount of penetrating hydrogen and the amount of critical diffusible hydrogen for delayed fracture, if the amount of critical diffusible hydrogen is greater than the amount of penetrating hydrogen, delayed fracture does not occur. Conversely, the amount of critical diffusible hydrogen is smaller Will cause delayed fracture. Therefore, the delayed fracture resistance was evaluated based on the amount of invading hydrogen and the amount of critical diffusible hydrogen.
鋼材の試験結果を表２に示す。表２のＮｏ．１〜１５は、表面の窒化層（窒素濃度が平均窒素濃度より０．０２％以上高い層）厚さが２００μｍ以上を有し、平均窒素濃度と深さ２００μｍでの窒素濃度の差が０．０２％以上で、何れも引張強度が１３００ＭＰａ以上であり、腐食促進試験における侵入水素量は０．１ｐｐｍ以下、限界拡散性水素量が０．１５ｐｐｍ以上であり、侵入水素量よりも限界拡散性水素量の方が多い。 Table 2 shows the test results of the steel materials. No. in Table 2 Nos. 1 to 15 have a surface nitride layer (layer whose nitrogen concentration is 0.02% or more higher than the average nitrogen concentration) thickness of 200 μm or more, and the difference between the average nitrogen concentration and the nitrogen concentration at a depth of 200 μm is 0.1. 02% or more, all have tensile strength of 1300 MPa or more, intrusion hydrogen amount in corrosion promotion test is 0.1 ppm or less, limit diffusible hydrogen amount is 0.15 ppm or more, and limit diffusible hydrogen is more than intrusion hydrogen amount. The amount is larger.
これに対して、比較例であるＮｏ．１６は、Ｃ量、Ｓｉ量、Ｍｎ量が少なく強度が低い例である。Ｎｏ．１７はＣ量、Ｎｏ．１８はＭｎ量、Ｎｏ．１９はＣｒ量、Ｎｏ．２０はＣｕ量、Ｎｏ．２１はＮｉ量、Ｎｏ．２２はＢ量が多いため、耐遅れ破壊特性が低下した例である。Ｎｏ．２３は、表面付近の窒素濃度は平均窒素濃度より０．０２％以上高いものの、窒化層の厚さが２００μｍ未満であり、侵入水素量が多く、耐遅れ破壊特性が低下した例である。Ｎｏ．２４は、窒化処理による窒素濃化層の厚さは２００μｍに満たなかった例であり、侵入水素量が多く、耐遅れ破壊特性が低下した。 On the other hand, No. which is a comparative example. No. 16 is an example in which the amount of C, Si, and Mn is small and the strength is low. No. 17 is the amount of C. 18 is the amount of Mn. 19 is the amount of Cr. 20 is the amount of Cu. 21 is the amount of Ni. No. 22 is an example in which the delayed fracture resistance is deteriorated because the amount of B is large. No. No. 23 is an example in which the nitrogen concentration near the surface is 0.02% or more higher than the average nitrogen concentration, but the thickness of the nitride layer is less than 200 μm, the amount of invading hydrogen is large, and the delayed fracture resistance is deteriorated. No. No. 24 is an example in which the thickness of the nitrogen enriched layer by nitriding treatment was less than 200 μm, and the amount of invading hydrogen was large and the delayed fracture resistance was deteriorated.
更に、ボルトの試験結果を表３に示す。なお、ボルトの焼戻しマルテンサイト比率、引張強度、窒化層深さ、残留応力、水素侵入量、遅れ破壊の限界拡散水素量の測定は、鋼材と同様にして行った。表２及び表３から、Ｎｏ．１〜１５の線材をボルトに加工後、窒化したＮｏ．２６〜４０は、線材に比べて、更に侵入水素量が抑制されていることがわかる。 Furthermore, the test results of the bolts are shown in Table 3. The tempered martensite ratio, tensile strength, nitrided layer depth, residual stress, hydrogen penetration amount, and critical diffusion hydrogen amount of delayed fracture were measured in the same manner as steel materials. From Table 2 and Table 3, No. No. 1 to 15 were processed into bolts and then nitrided. 26 to 40 show that the amount of invading hydrogen is further suppressed as compared with the wire.
１ 試験片
２ バランスウェイト
３ 支点
1
Claims (10)
Ｃ ：０．１０〜０．５５％、
Ｓｉ：０．０１〜３％、
Ｍｎ：０．１〜２％
を含有し、さらに、
Ｃｒ：０．０５〜１．５％、
Ｖ ：０．０５〜０．２％、
Ｍｏ：０．０５〜０．４％、
Ｎｂ：０．００１〜０．０５％、
Ｃｕ：０．０１〜４％、
Ｎｉ：０．０１〜４％、
Ｂ ：０．０００１〜０．００５％
の１種又は２種以上を含有し、残部がＦｅ及び不可避的不純物からなり、焼戻しマルテンサイトの面積率が８５％以上である組織で、表面から少なくとも２００μｍ深さまでの窒素濃度が平均窒素濃度より０．０２％以上高いことを特徴とする耐遅れ破壊特性に優れた高強度鋼材。 % By mass
C: 0.10 to 0.55%,
Si: 0.01 to 3%,
Mn: 0.1 to 2%
In addition,
Cr: 0.05 to 1.5%,
V: 0.05-0.2%
Mo: 0.05-0.4%
Nb: 0.001 to 0.05%,
Cu: 0.01 to 4%,
Ni: 0.01-4%,
B: 0.0001 to 0.005%
In which the balance is composed of Fe and unavoidable impurities, and the area ratio of tempered martensite is 85% or more, the nitrogen concentration from the surface to at least 200 μm depth is higher than the average nitrogen concentration A high-strength steel material excellent in delayed fracture resistance, characterized by being 0.02% or more.
Ａｌ：０．００３〜０．１％、
Ｔｉ：０．００３〜０．０５％、
Ｍｇ：０．０００３〜０．０１％、
Ｃａ：０．０００３〜０．０１％、
Ｚｒ：０．０００３〜０．０１％
の１種又は２種以上を含有することを特徴とする請求項１記載の耐遅れ破壊特性に優れた高強度鋼材。 further,
Al: 0.003 to 0.1%,
Ti: 0.003 to 0.05%,
Mg: 0.0003 to 0.01%
Ca: 0.0003 to 0.01%,
Zr: 0.0003 to 0.01%
The high-strength steel material having excellent delayed fracture resistance according to claim 1, comprising one or more of the following.
Ｃ ：０．１０〜０．５５％、
Ｓｉ：０．０１〜３％、
Ｍｎ：０．１〜２％
を含有し、さらに、
Ｃｒ：０．０５〜１．５％、
Ｖ ：０．０５〜０．２％、
Ｍｏ：０．０５〜０．４％、
Ｎｂ：０．００１〜０．０５％、
Ｃｕ：０．０１〜４％、
Ｎｉ：０．０１〜４％、
Ｂ ：０．０００１〜０．００５％
の１種又は２種以上を含有し、残部がＦｅ及び不可避的不純物からなり、焼戻しマルテンサイトの面積率が８５％以上である組織で、表面から少なくとも２００μｍ深さまでの窒素濃度が平均窒素濃度より０．０２％以上高いことを特徴とする耐遅れ破壊特性に優れた高強度ボルト。 % By mass
C: 0.10 to 0.55%,
Si: 0.01 to 3%,
Mn: 0.1 to 2%
In addition,
Cr: 0.05 to 1.5%,
V: 0.05-0.2%
Mo: 0.05-0.4%
Nb: 0.001 to 0.05%,
Cu: 0.01 to 4%,
Ni: 0.01-4%,
B: 0.0001 to 0.005%
In which the balance is composed of Fe and unavoidable impurities, and the area ratio of tempered martensite is 85% or more, the nitrogen concentration from the surface to at least 200 μm depth is higher than the average nitrogen concentration A high-strength bolt with excellent delayed fracture resistance, characterized by 0.02% or more.
Ａｌ：０．００３〜０．１％、
Ｔｉ：０．００３〜０．０５％、
Ｍｇ：０．０００３〜０．０１％、
Ｃａ：０．０００３〜０．０１％、
Ｚｒ：０．０００３〜０．０１％
の１種又は２種以上を含有することを特徴とする請求項５記載の耐遅れ破壊特性に優れた高強度ボルト。 further,
Al: 0.003 to 0.1%,
Ti: 0.003 to 0.05%,
Mg: 0.0003 to 0.01%
Ca: 0.0003 to 0.01%,
Zr: 0.0003 to 0.01%
The high-strength bolt excellent in delayed fracture resistance according to claim 5 , comprising one or more of the following.
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