JP6819504B2 - Steel member - Google Patents
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本発明は、焼入れ焼戻した耐水素脆化特性に優れる鋼部材に関するものである。 The present invention relates to a steel member having excellent hydrogen embrittlement resistance after quenching and tempering.
機械、自動車等に使用される鋼部材のうち、特に高強度を必要とするものは、例えばＪＩＳ Ｇ ４１０４、ＪＩＳ Ｇ ４１０５規定のクロム鋼、クロムモリブデン鋼を焼入れ・焼戻し処理して使用している。歯車のように、浸炭を行ってから焼入れを行い、高強度を得る鋼部材もある。浸炭材は、鋼材をオーステナイト相となる高温に加熱した後に焼入れ、低温で焼戻し、表層を７５０ＨＶ以上の高硬度にすることが普通である。このような表層硬化部材には、歯車、ＣＶＴ、軸受け等があり、潤滑環境下で高い面圧を受けながら使用される。このような環境下では、潤滑油や潤滑油に混入した水分から部材中に水素が浸入し、水素に起因する割れを引き起こす場合がある。 Among the steel members used in machines, automobiles, etc., those that require particularly high strength are used by quenching and tempering, for example, JIS G 4104, JIS G 4105 stipulated chrome steel and chrome molybdenum steel. .. Some steel members, such as gears, are carburized and then hardened to obtain high strength. The carburized material is usually a steel material heated to a high temperature which becomes an austenite phase, then quenched and tempered at a low temperature to make the surface layer having a high hardness of 750 HV or more. Such surface-hardened members include gears, CVTs, bearings, etc., and are used while receiving high surface pressure in a lubricating environment. In such an environment, hydrogen may infiltrate into the member from the lubricating oil or the water mixed in the lubricating oil, causing cracks due to hydrogen.
高強度鋼の耐水素脆化特性に関する従来の知見として、例えば、特許文献１には、Ｖ、Ｎｂ、Ｔｉを鋼に添加して旧オーステナイト粒を微細化させることが耐遅れ破壊特性を向上させることに有効であることが記載されている。 As a conventional finding regarding hydrogen embrittlement resistance of high-strength steel, for example, in Patent Document 1, adding V, Nb, and Ti to steel to make old austenite grains finer improves delayed fracture resistance. It is stated that it is particularly effective.
特許文献２には、焼入れ後に高温焼戻しすることで水素トラップ能を発現する微細析出物を鋼中に分散させて耐遅れ破壊特性を向上させる技術が記載されている。 Patent Document 2 describes a technique for improving delayed fracture resistance by dispersing fine precipitates exhibiting hydrogen trapping ability in steel by tempering at a high temperature after quenching.
一方、従来の技術では、焼入れ後に低温焼戻しを施すような高強度鋼部材の耐遅れ破壊特性を抜本的に向上させることには限界があった。 On the other hand, in the conventional technique, there is a limit in drastically improving the delayed fracture resistance of a high-strength steel member that is tempered at a low temperature after quenching.
本発明は、耐水素脆化特性と靭性に優れた部品、特に、耐水素脆化特性が良好で且つ表層硬さが７５０ＨＶ以上である高強度鋼部材を提供することを課題とする。 An object of the present invention is to provide a component having excellent hydrogen embrittlement resistance and toughness, particularly a high-strength steel member having good hydrogen embrittlement resistance and a surface hardness of 750 HV or more.
浸炭材など高硬度の焼入れ焼き戻し部材を、歯車や軸受として使用した場合、潤滑環境下で高い面圧を受ける。このような環境下では、例えば軸受けでは、白層と呼ばれる組織が出現して早期破壊が発生する事が知られており、白層の出現は潤滑油や潤滑油に混入した水分から部材中に浸入した水素に起因すると考えられている。 When a hardened tempered member such as a carburized material is used as a gear or a bearing, it receives a high surface pressure in a lubricating environment. In such an environment, for example, in bearings, it is known that a structure called a white layer appears and early destruction occurs, and the appearance of the white layer is caused by lubricating oil or moisture mixed in the lubricating oil in the member. It is believed to be due to the infiltrated hydrogen.
本発明者らは、焼入れ焼き戻しした高硬度部材において白層組織の発生を防止するには、二次硬化現象を示すＭＣ系炭化物もしくはＭＣ系炭窒化物を適切に析出させることが有効であると共に、高い面圧を受ける高硬度の表層部を薄くすることが重用であるとの知見を得た。高硬度の表層部を薄くすることは、部材に優れた靱性を与える利点もある。 In order to prevent the formation of a white layer structure in a hardened and tempered high hardness member, the present inventors are effective in appropriately precipitating MC-based carbides or MC-based carbonitrides exhibiting a secondary curing phenomenon. At the same time, it was found that it is important to thin the surface layer of high hardness that receives high surface pressure. Thinning the surface layer portion with high hardness also has an advantage of giving excellent toughness to the member.
さらに、高硬度が必要でない内部については、さらに低Ｃ組成の鋼材として、鋼部材の靱性が向上することも明らかになった。靱性が向上することで、衝撃的な入力による破壊を防止することができると考えられる。 Furthermore, it has been clarified that the toughness of the steel member is improved as a steel material having a lower C composition in the inside where high hardness is not required. It is considered that the improvement in toughness can prevent fracture due to impact input.
本発明は以上の知見に基づいてなされたものであって、その要旨とするところは、下記の通りである。すなわち、
（１）
質量％で、Ｃ ：０．８〜１．２０％、Ｓｉ：０．０２〜２．００％、Ｍｎ：０．０５〜２．０％、Ｃｒ：０．１０〜２．０％、Ａｌ：０．００５〜０．１％、Ｖ：０．２〜２．０％、Ｎ：０．００３〜０．０５％を含有し、残部がＦｅおよび不純物からなり、ビッカース硬さが７５０ＨＶ以上であり、焼戻しマルテンサイト組織の面積率が８０％以上であり、Ｖを含む平均粒径２００ｎｍ以下のＭＣ系炭化物もしくはＭＣ系炭窒化物を、個数密度で１０個／μｍ２以上含有する、表面から厚さ０．５〜２．０ｍｍの表層部と、質量％で、Ｃ：０．１０〜０．５０％、Ｓｉ：０．０２〜２．００％、Ｍｎ：０．０５〜２．０％、Ｃｒ：０．１０〜２．０％、Ａｌ：０．００５〜０．１％、Ｖ：０．１％以下、Ｎ：０．００３〜０．０５％を含有し、残部がＦｅおよび不純物からなり、ビッカース硬さが６００ＨＶ以下、３００ＨＶ以上である内部を有することを特徴とする鋼部材。
（２）
さらに、前記表層部または前記内部の少なくとも一方が、質量％で、Ｎｂ：０．０１〜０．５％、Ｍｏ：０．０１〜１．０％、Ｔｉ：０．０１〜０．５％の１種または２種以上を含有することを特徴とする（１）の鋼部材。
（３）
さらに、前記表層部または前記内部の少なくとも一方が、質量％で、Ｂ：０．０００３〜０．０１％を含有することを特徴とする（１）または（２）の鋼部材。
（４）
さらに、前記表層部または前記内部の少なくとも一方が、耐圧表層部およびまたは内部が、質量％で、Ｎｉ：０．０５〜３．０％、Ｃｕ：０．０５〜２．０％の１種または２種を含有することを特徴とする（１）〜（３）のいずれか一つに記載の鋼部材。
（５）
さらに、前記表層部または前記内部の少なくとも一方が、質量％で、ＲＥＭ：０．００５０％以下（０％を含まない）を含有することを特徴とする（１）〜（４）のいずれか一つに記載の鋼部材。
（６）
ラジアル玉軸受け、スラスト玉軸受け、ラジアルころ軸受け、スラストころ軸受けのいずれかである、（１）〜（５）のいずれか一つに記載の鋼部材。
The present invention has been made based on the above findings, and the gist thereof is as follows. That is,
(1)
By mass%, C: 0.8 to 1.20%, Si: 0.02 to 2.00%, Mn: 0.05 to 2.0%, Cr: 0.10 to 2.0%, Al: It contains 0.005 to 0.1%, V: 0.2 to 2.0%, N: 0.003 to 0.05%, the balance is composed of Fe and impurities, and the Vickers hardness is 750 HV or more. , The area ratio of the tempered martensite structure is 80% or more, and the MC-based carbide or MC-based carbonitride having an average particle size of 200 nm or less including V is contained in a number density of 10 pieces / μm 2 or more. C: 0.10 to 0.50%, Si: 0.02 to 2.00%, Mn: 0.05 to 2.0%, in terms of surface layer portion of 0.5 to 2.0 mm and mass%. It contains Cr: 0.10 to 2.0%, Al: 0.005 to 0.1%, V: 0.1% or less, N: 0.003 to 0.05%, and the balance is from Fe and impurities. A steel member having an internal Vickers hardness of 600 HV or less and 300 HV or more.
(2)
Further, at least one of the surface layer portion or the inside thereof is Nb: 0.01 to 0.5%, Mo: 0.01 to 1.0%, Ti: 0.01 to 0.5% in mass%. The steel member of (1), which contains one kind or two or more kinds.
(3)
Further, the steel member according to (1) or (2), wherein at least one of the surface layer portion or the inside thereof contains B: 0.0003 to 0.01% in mass%.
(4)
Further, at least one of the surface layer portion or the inside thereof, and the pressure resistant surface layer portion and / or the inside, in mass%, Ni: 0.05 to 3.0%, Cu: 0.05 to 2.0%, or one kind or The steel member according to any one of (1) to (3), which is characterized by containing two types.
(5)
Further, any one of (1) to (4), wherein at least one of the surface layer portion and the inside thereof contains REM: 0.0050% or less (not including 0%) in mass%. The steel member described in 1.
(6)
The steel member according to any one of (1) to (5), which is any one of a radial ball bearing, a thrust ball bearing, a radial roller bearing, and a thrust roller bearing.
本発明によれば、耐水素脆化特性と靭性に優れた高強度の鋼部材を提供することが可能となる。 According to the present invention, it is possible to provide a high-strength steel member having excellent hydrogen embrittlement resistance and toughness.
（鋼材成分）
本発明の対象とする鋼部材における成分の限定理由について述べる。成分についての％は、質量％である。
(Steel component)
The reason for limiting the components in the steel member targeted by the present invention will be described. The% for the component is mass%.
Ｃ：０．８０〜１．２０％（表層部）、０．１０〜０．５０％（内部）
Ｃは鋼材の強度を確保する上で必須の元素である。表層部において、７５０ＨＶ以上の硬さを満足するためには０．８０％以上が必要であり、一方、１．２０％を超えると鋳造・圧延時の延性を劣化させるために、表層部（表面から深さ０．５〜２．０ｍｍの領域）においては０．８０〜１．２０％の範囲とした。内部においては、部材としての靭性と硬さのバランスが求められる。硬さとしては３００〜６００ＨＶが必要であり、そのためにはＣ量は０．１０％以上必要である。一方、０．５０％を超えると十分な靭性を満足できないため、内部は０．１０〜０．５０％とする。
C: 0.80 to 1.20% (surface layer), 0.10 to 0.50% (inside)
C is an essential element for ensuring the strength of the steel material. In the surface layer portion, 0.80% or more is required to satisfy the hardness of 750 HV or more, while if it exceeds 1.20%, the ductility during casting / rolling is deteriorated, so that the surface layer portion (surface) In the range of 0.5 to 2.0 mm in depth), the range was 0.80 to 1.20%. Inside, a balance between toughness and hardness as a member is required. The hardness is required to be 300 to 600 HV, and for that purpose, the amount of C is required to be 0.10% or more. On the other hand, if it exceeds 0.50%, sufficient toughness cannot be satisfied, so the content is set to 0.10 to 0.50%.
Ｓｉ：０．０２〜２．０％（表層部および内部）
Ｓｉは固溶体硬化作用によって硬さを高める作用がある。０．０２％未満では前記作用が発揮できず、一方、２．０％を超えると添加量に見合う効果が期待できないこと、加熱時の粒界酸化を促進し、表層のマルテンサイト分率が低下するため、０．０２〜２．０％とする。
Si: 0.02 to 2.0% (surface layer and inside)
Si has an action of increasing hardness by a solid solution hardening action. If it is less than 0.02%, the above-mentioned effect cannot be exhibited, while if it exceeds 2.0%, the effect commensurate with the amount of addition cannot be expected, intergranular oxidation during heating is promoted, and the martensite fraction in the surface layer is lowered. Therefore, it is set to 0.02 to 2.0%.
Ｍｎ：０．０５〜２．０％（表層部および内部）
Ｍｎは脱酸、脱硫のために必要であるばかりでなく、マルテンサイト組織を得るための焼入性を高めるために有効な元素であるが、０．０５％未満では上記の効果が得られず、一方、２．０％を超えるとオーステナイト域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ために、０．０５〜２．０％とする。
Mn: 0.05 to 2.0% (surface layer and inside)
Mn is not only necessary for deoxidation and desulfurization, but is also an effective element for enhancing hardenability to obtain a martensite structure, but if it is less than 0.05%, the above effect cannot be obtained. On the other hand, if it exceeds 2.0%, it segregates at the grain boundaries when heated in the austenite region, making the grain boundaries brittle and deteriorating the delayed fracture resistance, so that the content is set to 0.05 to 2.0%.
Ｃｒ：０．１０〜２．０％（表層部および内部）
Ｃｒは焼入性の向上および焼戻し処理時の軟化抵抗を増加させるために有効な元素であるが、０．１０％未満ではその効果が十分に発揮できず、一方、２．０％を超えると靭性の劣化、冷間加工性の劣化を招く。さらに、過剰に添加するとMs温度が低下し、残留オーステナイトが増加するため、十分な硬さが得られないために、０．１０〜２．０％に限定する。
Cr: 0.10 to 2.0% (surface layer and inside)
Cr is an element effective for improving hardenability and increasing softening resistance during tempering treatment, but if it is less than 0.10%, the effect cannot be sufficiently exhibited, while if it exceeds 2.0%, it cannot be sufficiently exerted. It causes deterioration of toughness and cold workability. Further, if it is added excessively, the Ms temperature is lowered and the retained austenite is increased, so that sufficient hardness cannot be obtained.
Ａｌ：０．００５〜０．１％（表層部および内部）
Ａｌは脱酸および熱処理時においてＡｌＮを形成することによりオーステナイト粒の粗大化を防止する効果とともにＮを固定する効果も有しているが、０．００５％未満ではこれらの効果が発揮されず、０．１％を超えても効果が飽和するのみならず、酸化物が過剰に生成し、疲労や衝撃特性を劣化させるため０．００５〜０．１％に限定する。
Al: 0.005 to 0.1% (surface layer and inside)
Al has an effect of preventing coarsening of austenite grains by forming AlN during deoxidation and heat treatment and also has an effect of fixing N, but these effects are not exhibited when the percentage is less than 0.005%. If it exceeds 0.1%, not only the effect is saturated, but also oxides are excessively generated, which deteriorates fatigue and impact characteristics, so the ratio is limited to 0.005 to 0.1%.
Ｖ：０．２〜２．０％（表層部）、０．１％以下（０％を含む）（内部）
Ｖは、Ｎｂ，Ｍｏなどと共にＦＣＣ構造（面心立方格子構造）の炭化物や炭窒化物を生成することにより、部材に浸入してきた水素のトラップサイトとして機能することで、耐水素脆化特性を向上させる。その効果を発揮するには０．２％以上が必要であり、２．０％以上では飽和するため、特に耐水素脆化特性が求められる表層部においては、０．２〜２．０％とする。
V: 0.2 to 2.0% (surface layer), 0.1% or less (including 0%) (inside)
V functions as a trap site for hydrogen that has penetrated into the member by forming carbides and carbonitrides with an FCC structure (face-centered cubic lattice structure) together with Nb, Mo, etc., thereby providing hydrogen embrittlement resistance. Improve. 0.2% or more is required to exert the effect, and 2.0% or more is saturated. Therefore, it is 0.2 to 2.0% especially in the surface layer portion where hydrogen embrittlement resistance is required. To do.
一方、ＦＣＣ構造の炭化物は靭性を劣化させる要因となるため、上記より内部の部位においては、炭化物の析出量を抑制するため、Ｖを０．１％以下に制限した。 On the other hand, since carbides having an FCC structure cause deterioration of toughness, V was limited to 0.1% or less in order to suppress the amount of carbides precipitated in the internal portion from the above.
Ｎ：０．００３〜０．０５％（表層部および内部）
Ｎは、Ａｌ、Ｖ、Ｎｂ、Ｔｉの窒化物を形成することによって旧オーステナイト粒の微細化、降伏強度の増加の効果がある。０．００３％未満ではその効果が小さく、０．０５％を超えても効果が飽和するのみならず、窒化物が過剰に生成し、疲労や衝撃特性を劣化させるため、０．００３〜０．０５％に限定した。好ましくは０．００３〜０．０２％とする。
N: 0.003 to 0.05% (surface layer and inside)
N has the effect of making the former austenite grains finer and increasing the yield strength by forming nitrides of Al, V, Nb and Ti. If it is less than 0.003%, the effect is small, and if it exceeds 0.05%, not only the effect is saturated, but also nitride is excessively generated, which deteriorates fatigue and impact characteristics. Therefore, 0.003 to 0. Limited to 05%. It is preferably 0.003 to 0.02%.
以上が本発明の対象とする鋼の基本成分であるが、本発明においては、さらにこの鋼部材の表層部または内部の少なくとも一方に、Ｎｂ：０．０１〜０．５％、Ｍｏ：０．０１〜１．０％、Ｔｉ：０．０１〜０．５％の１種または２種以上を含有することができる。また、Ｂ：０．０００３〜０．０１％を含有することができる。また、Ｎｉ：０．０５〜３．０％、Ｃｕ：０．０５〜２．０％の１種または２種を含有することができる。また、ＲＥＭ：０．００５０％以下（０％を含まない）を含有することができる。なお、これらの任意成分は、鋼部材の表層部と内部の両方に含有しても良いし、表層部と内部のどちらか一方のみに含有しても良い。 The above are the basic components of the steel that is the subject of the present invention. In the present invention, Nb: 0.01 to 0.5% and Mo: 0. Are further applied to at least one of the surface layer portion and the inside of the steel member. It can contain one or more of 01 to 1.0% and Ti: 0.01 to 0.5%. Further, B: 0.0003 to 0.01% can be contained. Further, one or two kinds of Ni: 0.05 to 3.0% and Cu: 0.05 to 2.0% can be contained. Further, REM: 0.0050% or less (not including 0%) can be contained. It should be noted that these optional components may be contained in both the surface layer portion and the inside of the steel member, or may be contained in only one of the surface layer portion and the inside.
Ｎｂ：０．０１〜０．５％
ＮｂはＶと炭化物または炭窒化物として複合析出する。Ｎｂは析出物の微細分散に寄与する元素である。また、炭窒化物として析出するとオーステナイト粒を微細化させる。０．０１％未満のＮｂ添加では前記効果を発揮するのに不十分であり、一方、０．５％を超えるとこの効果が飽和するため、０．０１〜０．５％とする。
Nb: 0.01-0.5%
Nb is compound-precipitated with V as a carbide or carbonitride. Nb is an element that contributes to the fine dispersion of precipitates. Further, when it is precipitated as a carbonitride, the austenite grains are made finer. Addition of less than 0.01% of Nb is insufficient to exert the above effect, while if it exceeds 0.5%, this effect is saturated, so it is set to 0.01 to 0.5%.
Ｍｏ：０．０１〜１．０％
ＭｏもＶと炭化物または炭窒化物として複合析出し、析出物の微細分散に寄与する元素である。ただしその効果は０．０１％未満では不十分であり、１．０％で飽和するばかりでなく、それを超えて添加すると、変形抵抗の増大により加工性が損なわれるため、０．０１〜１．０％とする。
Mo: 0.01-1.0%
Mo is also an element that is compound-precipitated with V as a carbide or carbonitride and contributes to fine dispersion of the precipitate. However, the effect is insufficient if it is less than 0.01%, and not only is it saturated at 1.0%, but if it is added in excess of that, workability is impaired due to an increase in deformation resistance, so 0.01 to 1 It is set to 0.0%.
Ｔｉ：０．０１〜０．５％
ＴｉもＶと炭化物または炭窒化物として複合析出し、析出物の微細分散に寄与する元素である。その効果は０．０１％未満では発揮されず、０．５％を超えると、未溶解の粗大な炭化物が残存することで切削性や靭性に悪影響を及ぼすため、０．０１〜０．５％の範囲に限定した。
Ti: 0.01-0.5%
Ti is also an element that is compound-precipitated with V as a carbide or carbonitride and contributes to fine dispersion of the precipitate. The effect is not exhibited when it is less than 0.01%, and when it exceeds 0.5%, undissolved coarse carbide remains, which adversely affects machinability and toughness. Therefore, 0.01 to 0.5%. Limited to the range of.
Ｂ：０．０００３〜０．０１％
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。更に、Ｂはオーステナイト粒界に偏析することにより、焼入性を著しく高めるが、０．０００３％未満では前記の効果が発揮されず、０．０１％を超えても効果が飽和するため、０．０００３〜０．０１％に限定した。
B: 0.0003-0.01%
B has the effect of suppressing grain boundary fracture and improving delayed fracture resistance. Further, B significantly enhances hardenability by segregating at the austenite grain boundaries, but the above effect is not exhibited when it is less than 0.0003%, and the effect is saturated when it exceeds 0.01%. Limited to 0003 to 0.01%.
Ｎｉ：０．０５〜３．０％
一般に高強度化に伴って延性は低下する。Ｎｉは鋼部品を強化すると共に延性を向上させる。また熱処理時の焼入性を向上させる効果がある。０．０５％未満ではこれら効果が小さく、一方、３．０％を超えても添加量に見合う効果が発揮できないため、０．０５〜３．０％に限定した。
Ni: 0.05-3.0%
Generally, the ductility decreases as the strength increases. Ni strengthens steel parts and improves ductility. It also has the effect of improving hardenability during heat treatment. If it is less than 0.05%, these effects are small, and if it exceeds 3.0%, the effect commensurate with the amount of addition cannot be exhibited.
Ｃｕ：０．０５〜２．０％
Ｃｕは焼戻し軟化抵抗を高めるために有効な元素であるが、０．０５％未満では効果が発揮できず、２．０％を超えると熱間加工性が劣化するため、０．０５〜２．０％に限定した。
Cu: 0.05-2.0%
Cu is an element effective for increasing the temper softening resistance, but if it is less than 0.05%, the effect cannot be exhibited, and if it exceeds 2.0%, the hot workability deteriorates. Therefore, 0.05 to 2. Limited to 0%.
ＲＥＭ：０．００５０％以下（０％を含まない）
ＲＥＭは希土類元素（Ｓｃ、Ｙと、原子番号５７から７１までの元素の総称）であり、通常、各種元素が混合された原料で鉄鋼に添加される。アルミナなどの粗大化し易い酸化物は転動負荷時の破壊起点となり易いが、ＲＥＭを添加すると、ＲＥＭを含有した微細な複合酸化物となるため、転動疲労破壊を抑制する。なお、ＲＥＭは希土類元素の何れか１つを０．００５０％以下含有しても良いし、２以上を合計で０．００５０％以下含有しても良い。
REM: 0.0050% or less (not including 0%)
REM is a rare earth element (Sc, Y and a general term for elements having atomic numbers 57 to 71), and is usually added to steel as a raw material in which various elements are mixed. Oxides such as alumina, which tend to be coarsened, tend to be fracture starting points at the time of rolling load, but when REM is added, they become fine composite oxides containing REM, so that rolling fatigue fracture is suppressed. The REM may contain 0.0050% or less of any one of the rare earth elements, or 0.0050% or less in total of two or more.
残部：Ｆｅおよび不純物（表層部および内部）
本発明の鋼部材は、表層部および内部において以上の必須成分と任意成分を含有し、残部は、Ｆｅおよび不純物からなる。不純物には、製造過程において不可避的に混入されるＰ、Ｓなどが含まれる。
Remaining: Fe and impurities (surface and inside)
The steel member of the present invention contains the above essential components and optional components in the surface layer portion and inside, and the balance is composed of Fe and impurities. Impurities include P, S and the like that are inevitably mixed in during the manufacturing process.
（組織形態と硬さ）
本発明の鋼部材を歯車や軸受け等として用いるため、高面圧を受ける表面から０．５〜２．０ｍｍの領域（表層部）において、硬さを７５０ＨＶ以上とする必要がある。この硬さを実現し、優れた転動疲労寿命を得るには、焼戻しマルテンサイト組織の面積率を８０％以上とする必要がある。また、実験の結果より、上記の表層部に、金属成分としてＶを主体とする、平均粒径２００ｎｍ以下のＭＣ系炭化物もしくは炭窒化物を、個数密度で１０個／μｍ２以上含有させることによって、疲労寿命が大幅に改善される。
(Tissue morphology and hardness)
Since the steel member of the present invention is used as a gear, a bearing, or the like, the hardness needs to be 750 HV or more in a region (surface layer portion) of 0.5 to 2.0 mm from the surface subject to high surface pressure. In order to achieve this hardness and obtain an excellent rolling fatigue life, it is necessary to set the area ratio of the tempered martensite structure to 80% or more. In addition, based on the results of the experiment, the above surface layer portion contains 10 pieces / μm 2 or more of MC-based carbides or carbonitrides having an average particle size of 200 nm or less, mainly V as a metal component, in terms of number density. , Fatigue life is greatly improved.
その効果は、表層部の降伏応力を高めることで、塑性変形を抑制し、塑性変形に伴う水素の侵入を抑制することと、侵入してきた水素をこれら析出物がトラップすることで無害化することと推定される。ＭＣ系炭化物もしくは炭窒化物とは、金属原子Ｍと（Ｃ＋Ｎ）が１対１で結合した、ＦＣＣ（面心立方格子）構造の炭化物である。 The effect is to suppress the plastic deformation by increasing the yield stress of the surface layer, suppress the invasion of hydrogen due to the plastic deformation, and detoxify the invading hydrogen by trapping these precipitates. It is estimated to be. The MC-based carbide or carbide is a carbide having an FCC (face-centered cubic) structure in which a metal atom M and (C + N) are bonded in a one-to-one manner.
表層部のＭＣ系炭化物もしくは炭窒化物の観察と個数密度測定は、抽出レプリカ−ＴＥＭ観察により行った。表層部断面を観察するように埋め込み研磨したサンプルを４％ナイタール腐食液で１０秒エッチングした後、カーボンを蒸着させ、蒸着したカーボン膜を塩酸メタノール溶液中で対基準電位７．５Ｖで１分間通電し、その後、蒸留水中で洗浄しつつ遊離させ、Ｃｕメッシュ上に載置し、ＴＥＭ観察に供した。 Observation of MC-based carbides or carbonitrides on the surface layer and measurement of the number density were performed by extraction replica-TEM observation. A sample embedded and polished so as to observe the cross section of the surface layer is etched with a 4% nital corrosive solution for 10 seconds, then carbon is vapor-deposited, and the vapor-deposited carbon film is energized in a hydrochloric acid-methanol solution at a counter-reference potential of 7.5 V for 1 minute. Then, it was released while being washed in distilled water, placed on a Cu mesh, and subjected to TEM observation.
一方、部材全体が上記のような硬さおよび析出物量を有する場合、靭性が低下する。特に過剰な析出物の存在により靭性が低下するため、内部の領域においては、ＭＣ系炭化物を析出させないよう、Ｖの含有量が０．１％以下であり、ビッカース硬さが６００ＨＶ以下であることとする。一方、部材としての強度を確保するため、内部の硬さは３００ＨＶ以上であることとする。 On the other hand, when the entire member has the hardness and the amount of precipitates as described above, the toughness is lowered. In particular, since the toughness decreases due to the presence of excess precipitates, the V content should be 0.1% or less and the Vickers hardness should be 600 HV or less in the internal region so as not to precipitate MC-based carbides. And. On the other hand, in order to secure the strength as a member, the internal hardness is set to 300 HV or more.
（表層部の厚さ）
白層は、表面から厚さ０．２〜０．３ｍｍ程度の部位で生成する事が多いことから、厚みの下限値を０．５ｍｍとした、厚みが大きすぎると、部品としての靭性確保が難しくなることから、実験より上限値を２．０ｍｍとした。
(Thickness of surface layer)
Since the white layer is often formed at a portion having a thickness of about 0.2 to 0.3 mm from the surface, the lower limit of the thickness is set to 0.5 mm, and if the thickness is too large, the toughness of the part can be ensured. Since it becomes difficult, the upper limit was set to 2.0 mm from the experiment.
（製造方法）
本発明の鋼部材の素材となる鋼材においては、部材としての性能を満足するため、耐圧表層と内部で、異なるＣ量およびＶ量を与える必要がある。このような成分分布を有する鋼材の製造方法としては、例えば鋳造時に異鋼種の複合鋳込みを行う、鋼管に丸棒を挿入して、焼きばめ、あるいはリング状の部材と円盤状の部材を組み合わせ、圧入その他の手段で一体化した後に鍛造する等の手段を採る。
(Production method)
In the steel material used as the material of the steel member of the present invention, it is necessary to give different C amounts and V amounts to the pressure-resistant surface layer and the inside in order to satisfy the performance as the member. As a method for producing a steel material having such a component distribution, for example, composite casting of different steel types is performed at the time of casting, a round bar is inserted into a steel pipe, and shrink fitting is performed, or a ring-shaped member and a disk-shaped member are combined. , Press-fitting or other means to integrate and then forge.
（鋼部材の一例）
本発明の鋼部材は、機械、自動車等に使用される鋼部材に広く適用できるが、例えば、ラジアル玉軸受け、スラスト玉軸受け、ラジアルころ軸受け、スラストころ軸受けのいずれかにおいて好適に利用される。
(Example of steel member)
The steel member of the present invention can be widely applied to steel members used in machines, automobiles, etc., and is preferably used in any one of, for example, a radial ball bearing, a thrust ball bearing, a radial roller bearing, and a thrust roller bearing.
以下、実施例により本発明の効果をさらに具体的に説明する。表１の「表層」（表層部）に示す化学組成を有する供試材を外径２２ｍｍ−内径２０〜１４ｍｍのリング状に加工した部材１に、このリングの内径に等しい外径を有する、「内部」に示す化学成分を有する鋼材をディスク状に加工した部材２を嵌め合わせ、９５０℃以上に加熱後、熱間にて直径１３ｍｍに押し出し加工して棒状に成形し圧着させた。その後、一旦２００℃以下に急冷後、再度加熱するに際して６５０℃〜７００℃にて一旦３０〜６０ｓ保持し更に８００〜８６０℃に加熱後焼入れ後、１８０℃にて焼戻を行った。この棒材を用い、転動疲労寿命試験片と衝撃試験片を作製した。 Hereinafter, the effects of the present invention will be described in more detail with reference to Examples. A member 1 obtained by processing a test material having the chemical composition shown in the "surface layer" (surface layer portion) of Table 1 into a ring shape having an outer diameter of 22 mm and an inner diameter of 20 to 14 mm has an outer diameter equal to the inner diameter of this ring. A member 2 made by processing a steel material having a chemical component shown in "Inside" into a disk shape was fitted, heated to 950 ° C. or higher, extruded to a diameter of 13 mm while hot, formed into a rod shape, and crimped. Then, after quenching to 200 ° C. or lower, the mixture was once held at 650 ° C. to 700 ° C. for 30 to 60 seconds, further heated to 800 to 860 ° C., quenched, and then quenched at 180 ° C. Using this bar, a rolling fatigue life test piece and an impact test piece were prepared.
転動疲労寿命試験片として、直径１２ｍｍ×長さ２２ｍｍの円筒形のサンプルを切削加工にて作製した。これに、最大接触面圧荷重を５８８０ＭＰａ、応力負荷速度４６２４０ｃｐｍの条件で転動疲労試験を行った。 As a rolling fatigue life test piece, a cylindrical sample having a diameter of 12 mm and a length of 22 mm was prepared by cutting. A rolling fatigue test was carried out under the conditions of a maximum contact surface pressure load of 5880 MPa and a stress load rate of 46240 cpm.
一方、衝撃試験片として、上記の直径１３ｍｍ押し出し加工材を熱処理した棒材より、４面の内の上面を押し出し材の表面とし、底面の幅が１０ｍｍ、長さが５５ｍｍであるようなサンプルを作製し、押し出し材の表面側の中央部に、長手方向に垂直に、深さ０．５ｍｍ、角度４５度の切り欠きを入れ、シャルピー試験に供した。 On the other hand, as an impact test piece, a sample in which the upper surface of the four surfaces is the surface of the extruded material and the width of the bottom surface is 10 mm and the length is 55 mm is prepared from the bar material obtained by heat-treating the extruded material having a diameter of 13 mm. A notch having a depth of 0.5 mm and an angle of 45 degrees was made in the central portion of the extruded material on the surface side in the longitudinal direction, and the material was subjected to a Charpy test.
表層部のＭＣ系炭化物もしくは炭窒化物の観察と測定は、表層部断面を観察するように埋め込み研磨したサンプルを４％ナイタール腐食液で１０秒エッチングし、カーボン蒸着させ、カーボン膜を、塩酸メタノール溶液中で基準電位に対し７．５Ｖの電位で１分間、通電し、その後に蒸留水中で洗浄することで遊離させ、Ｃｕメッシュでサンプリングし、ＴＥＭ観察に供した。ＴＥＭ観察は、５０００倍の倍率で５視野撮影し、Ｖを含有する析出物のサイズと面積率、個数密度を測定した。 To observe and measure MC-based carbides or carbonitrides on the surface layer, a sample embedded and polished so as to observe the cross section of the surface layer is etched with a 4% nital corrosive solution for 10 seconds, carbon-deposited, and the carbon film is made of methanol hydrochloride. The solution was energized at a potential of 7.5 V with respect to the reference potential for 1 minute, then released by washing in distilled water, sampled with a Cu mesh, and subjected to TEM observation. In the TEM observation, 5 fields of view were taken at a magnification of 5000 times, and the size, area ratio, and number density of the deposit containing V were measured.
表層部分の鋼組織分率の測定はＳＥＭ（走査電子顕微鏡）とＳＥＭ付属のＥＢＳＤ（電子線後方散乱回折法）装置を用いて行った。対象となる表層部断面を観察するように埋め込み、研磨およびナイタールエッチングを行って試験片を作製し、表層部断面の大きさ１００μm×１００μmの領域をＥＢＳＤ解析して、焼戻しマルテンサイト組織と残部組織の各面積率を測定した。 The steel structure fraction of the surface layer was measured using an SEM (scanning electron microscope) and an EBSD (electron backscatter diffraction method) device attached to the SEM. A test piece is prepared by embedding so as to observe the cross section of the surface layer to be observed, polishing and nighting etching, and EBSD analysis is performed on a region having a cross section of the surface layer of 100 μm × 100 μm, and the tempered martensite structure and the balance are obtained. Each area ratio of the tissue was measured.
硬さは、試験力０．９８ｍＮのマクロビッカース試験機を用い、表層部分と表層から３ｍｍの深さの内部において、各々５点測定し、その平均値を試験値とした。なお、本発明では転動疲労によるｆ５０寿命が４０×１０７以上であり、衝撃値が７Ｊ以上である。 The hardness was measured at 5 points each in the surface layer portion and the inside at a depth of 3 mm from the surface layer using a macro Vickers tester having a test force of 0.98 mN, and the average value was used as the test value. In the present invention has at f50 life due rolling fatigue 40 × 10 7 or more, the impact value is greater than or equal to 7J.
表１、２のＮｏ．１〜２１が本発明例で、その他は比較例である。
比較例であるＮｏ．２２は表層のC濃度が高く、残留γ量が多くなったため、所定のマルテンサイト量を確保できず、硬さも低くなった例である。
Ｎｏ．２３は、内部のC濃度が高く、硬さを満足できず、靭性も低下した例である。
Ｎｏ．２４は、表層および内部のＳｉ量が過剰であり、表層のマルテンサイト分率と硬さを満足できず、靭性も低下した例である。
Ｎｏ．２５は、表層のＭｎ濃度が過剰であり、転動疲労寿命が低下した例である。
Ｎｏ．２６は、内部のＭｎ濃度が過剰であり、靭性が低下した例である。
Ｎｏ．２７は、表層のＣｒ量が過剰であり、表層のマルテンサイト分率および硬さを満足できなかった例である。
Ｎｏ．２８は、内部のＣｒ濃度が過剰であり、靭性が低下した例である。
Ｎｏ．２９は、表層および内部のＡｌ量が過剰であり、転動疲労寿命と靭性が低下した例である。
Ｎｏ．３０は、表層のＶ量が過剰であり、転動疲労寿命が低下した例である。
Ｎｏ．３１は、内部のＶ濃度が過剰であり、靭性が低下した例である。
Ｎｏ．３２は、表層のＮ量が過剰であり、転動疲労寿命が低下した例である。
Ｎｏ．３３は、内部のＮ量が過剰であり、靭性が低下した例である。
Ｎｏ．３４は、表層の硬質層深さが所定の値より浅いため、転動疲労試験後に変形が大きかった例である。
Ｎｏ．３５は、内部のＣ量が不足しており、所定の硬さを満足できなかった例である。
Ｎｏ．３６は、表層のＶ量が不足しており、転動疲労寿命が低下した例である。
Ｎｏ．３７は、表層の硬化層厚みが大きすぎ、靭性が低下した例である。
Tables 1 and 2 No. 1 to 21 are examples of the present invention, and the others are comparative examples.
No. which is a comparative example. In No. 22, the C concentration in the surface layer was high and the amount of residual γ was large, so that the predetermined amount of martensite could not be secured and the hardness was also low.
No. No. 23 is an example in which the internal C concentration is high, the hardness cannot be satisfied, and the toughness is also lowered.
No. No. 24 is an example in which the amount of Si in the surface layer and the inside is excessive, the martensite fraction and hardness of the surface layer cannot be satisfied, and the toughness is also lowered.
No. No. 25 is an example in which the Mn concentration in the surface layer is excessive and the rolling fatigue life is reduced.
No. No. 26 is an example in which the internal Mn concentration is excessive and the toughness is lowered.
No. No. 27 is an example in which the amount of Cr in the surface layer was excessive and the martensite fraction and hardness of the surface layer could not be satisfied.
No. No. 28 is an example in which the internal Cr concentration is excessive and the toughness is lowered.
No. No. 29 is an example in which the amount of Al in the surface layer and the inside is excessive, and the rolling fatigue life and toughness are lowered.
No. Reference numeral 30 denotes an example in which the amount of V in the surface layer is excessive and the rolling fatigue life is reduced.
No. No. 31 is an example in which the internal V concentration is excessive and the toughness is lowered.
No. No. 32 is an example in which the amount of N in the surface layer is excessive and the rolling fatigue life is reduced.
No. No. 33 is an example in which the amount of N inside is excessive and the toughness is lowered.
No. Reference numeral 34 denotes an example in which the deformation was large after the rolling fatigue test because the depth of the hard layer on the surface layer was shallower than a predetermined value.
No. Reference numeral 35 denotes an example in which the amount of C inside is insufficient and the predetermined hardness cannot be satisfied.
No. No. 36 is an example in which the amount of V in the surface layer is insufficient and the rolling fatigue life is reduced.
No. No. 37 is an example in which the thickness of the hardened layer on the surface layer is too large and the toughness is lowered.
Claims (6)
Ｃ：０．８０〜１．２０％、
Ｓｉ：０．０２〜２．００％、
Ｍｎ：０．０５〜２．０％、
Ｃｒ：０．１０〜２．０％、
Ａｌ：０．００５〜０．１％、
Ｖ：０．２〜２．０％、
Ｎ：０．００３〜０．０５％
を含有し、残部がＦｅおよび不純物からなり、
ビッカース硬さが７５０ＨＶ以上であり、
焼戻しマルテンサイト組織の面積率が８０％以上であり、
Ｖを含む平均粒径２００ｎｍ以下のＭＣ系炭化物もしくはＭＣ系炭窒化物を、個数密度で１０個／μｍ２以上含有する、表面から厚さ０．５〜２．０ｍｍの表層部と、
質量％で、
Ｃ：０．１０〜０．５０％、
Ｓｉ：０．０２〜２．００％、
Ｍｎ：０．０５〜２．０％、
Ｃｒ：０．１０〜２．０％、
Ａｌ：０．００５〜０．１％、
Ｖ：０．１％以下（０％を含む）、
Ｎ：０．００３〜０．０５％
を含有し、残部がＦｅおよび不純物からなり、
ビッカース硬さが６００ＨＶ以下、３００ＨＶ以上である内部を有することを特徴とする鋼部材。 By mass%
C: 0.80-1.20%,
Si: 0.02-2.00%,
Mn: 0.05-2.0%,
Cr: 0.10 to 2.0%,
Al: 0.005-0.1%,
V: 0.2-2.0%,
N: 0.003 to 0.05%
Containing, the balance consists of Fe and impurities,
Vickers hardness is 750 HV or more,
The area ratio of tempered martensite structure is 80% or more,
A surface layer portion having a thickness of 0.5 to 2.0 mm from the surface, which contains 10 pieces / μm 2 or more of MC-based carbides or MC-based carbonitrides having an average particle size of 200 nm or less including V.
By mass%
C: 0.10 to 0.50%,
Si: 0.02-2.00%,
Mn: 0.05-2.0%,
Cr: 0.10 to 2.0%,
Al: 0.005-0.1%,
V: 0.1% or less (including 0%),
N: 0.003 to 0.05%
Containing, the balance consists of Fe and impurities,
A steel member having an internal Vickers hardness of 600 HV or less and 300 HV or more.
質量％で、
Ｎｂ：０．０１〜０．５％、
Ｍｏ：０．０１〜１．０％、
Ｔｉ：０．０１〜０．５％
の１種または２種以上を含有することを特徴とする請求項１の鋼部材。 Further, at least one of the surface layer portion or the inside thereof
By mass%
Nb: 0.01-0.5%,
Mo: 0.01-1.0%,
Ti: 0.01-0.5%
The steel member according to claim 1, characterized in that it contains one or more of the above.
質量％で、
Ｂ：０．０００３〜０．０１％
を含有することを特徴とする請求項１または２に記載の鋼部材。 Further, at least one of the surface layer portion or the inside thereof
By mass%
B: 0.0003-0.01%
The steel member according to claim 1 or 2, wherein the steel member contains.
質量％で、
Ｎｉ：０．０５〜３．０％、
Ｃｕ：０．０５〜２．０％
の１種または２種を含有することを特徴とする請求項１〜３のいずれか一つに記載の鋼部材。 Further, at least one of the surface layer portion or the inside thereof
By mass%
Ni: 0.05-3.0%,
Cu: 0.05-2.0%
The steel member according to any one of claims 1 to 3, wherein the steel member contains one or two of the above.
質量％で、ＲＥＭ：０．００５０％以下（０％を含まない）を含有することを特徴とする請求項１〜４のいずれか一つに記載の鋼部材。 Further, at least one of the surface layer portion or the inside thereof
The steel member according to any one of claims 1 to 4, wherein the steel member contains REM: 0.0050% or less (not including 0%) in mass%.
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