WO2017170435A1 - Environment-resistant bearing steel excellent in producibility and resistance to hydrogen embrittlement - Google Patents

Environment-resistant bearing steel excellent in producibility and resistance to hydrogen embrittlement Download PDF

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WO2017170435A1
WO2017170435A1 PCT/JP2017/012451 JP2017012451W WO2017170435A1 WO 2017170435 A1 WO2017170435 A1 WO 2017170435A1 JP 2017012451 W JP2017012451 W JP 2017012451W WO 2017170435 A1 WO2017170435 A1 WO 2017170435A1
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steel
layer
hardness
hydrogen embrittlement
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木南 俊哉
良典 杉崎
工 藤田
悠 銭本
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大同特殊鋼株式会社
Ntn株式会社
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    • CCHEMISTRY; METALLURGY
    • C22METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22CALLOYS
    • C22C38/00Ferrous alloys, e.g. steel alloys
    • CCHEMISTRY; METALLURGY
    • C22METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22CALLOYS
    • C22C38/00Ferrous alloys, e.g. steel alloys
    • C22C38/18Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/28Ferrous alloys, e.g. steel alloys containing chromium with titanium or zirconium
    • CCHEMISTRY; METALLURGY
    • C22METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22CALLOYS
    • C22C38/00Ferrous alloys, e.g. steel alloys
    • C22C38/18Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/50Ferrous alloys, e.g. steel alloys containing chromium with nickel with titanium or zirconium
    • CCHEMISTRY; METALLURGY
    • C21METALLURGY OF IRON
    • C21DMODIFYING 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
    • C21D8/00Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/06Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of rods or wires

Abstract

The present invention provides an environment-resistant bearing steel excellent in terms of producibility and resistance to hydrogen embrittlement, the bearing steel being characterized by having a composition which contains, in terms of mass%, 0.5-1.0% C, up to 0.1% Si, 0.4-1.5% Mn, up to 0.03% P, up to 0.03% S, 1.5-3.5% Cr, up to 0.050% Al, up to 0.0015% O, up to 0.003% Ti, and up to 0.015% N, with the remainder comprising Fe and unavoidable impurities. The bearing steel is further characterized in that after spheroidizing annealing, the steel has a hardness of 92 HRB or less and that after carbonitriding, the steel has a surface-layer N concentration of 0.1-1.0%, a surface-layer C concentration of 0.8-1.5%, and a surface-layer hardness of 58 or greater but less than 64 in terms of HRC, the number density of coarse nitride grains of CrN or MnSiN2 which have grain diameters of 2 µm or larger being 103 grains/mm2 or less. The bearing steel is characterized in that fine nitride grains have been dispersed and precipitated.

Description

製造性と耐水素脆性に優れた耐環境用軸受鋼Environmentally resistant bearing steel with excellent manufacturability and hydrogen embrittlement resistance
 本発明は製造性(浸炭時間および加工性)に優れ、かつ水素脆性剥離による寿命低下を抑制し、長寿命を有する耐環境用軸受鋼に関する。従来、自動車、産業機器等の軸受部品において高振動・高荷重、急加減速等の厳しい負荷条件下でかつ特定の潤滑油や水混入条件等が複合した場合に、通常の転がり疲労寿命より著しく短寿命の早期剥離が発生する問題があり、この早期剥離の原因は、転がり過程において転動面に水素が発生し、それが内部に侵入することにより水素脆性を生じ、著しく剥離寿命が低下すると考えられている。本発明はこのような問題を解決する手段を提供するものである。 The present invention relates to an environmentally resistant bearing steel that has excellent manufacturability (carburizing time and workability), suppresses a decrease in life due to hydrogen embrittlement peeling, and has a long life. Conventionally, bearing parts such as automobiles, industrial equipment, etc., under severe load conditions such as high vibration, high load, sudden acceleration / deceleration, etc. and combined with specific lubricating oil and water mixing conditions, etc. There is a problem that short-lived early peeling occurs, and the cause of this early peeling is that hydrogen is generated on the rolling surface in the rolling process, and when it enters the inside, hydrogen embrittlement occurs and the peeling life is significantly reduced. It is considered. The present invention provides means for solving such problems.
 近年、自動車や産業機器に用いられる軸受部品は高性能化、高速化に伴い使用条件が過酷化している。新しい変速機CVT(コンティニュアスリー・バリアブル・トランスミッション)をはじめ潤滑油の種類も多様化しており、従来とは異なる剥離形態による早期剥離を生じる場合があり、問題となっている。 In recent years, bearing parts used in automobiles and industrial equipment have become severer in terms of performance with higher performance and higher speed. There are various types of lubricating oil including a new transmission CVT (continuous variable transmission), and there is a case in which early peeling due to a peeling form different from the conventional one occurs.
 たとえば、自動車のオルタネーター用軸受で、従来型の組織変化であるホワイトバンドとは異なる粒界に沿った樹木状の白色層の組織変化を伴う早期剥離が生じる場合がある。これは、高振動・高荷重の厳しい負荷条件下で潤滑油が分解し、転動面に水素が発生し、内部に侵入することにより水素脆性剥離が生じたためと考えられている。
 これに対して、オルタネーター用軸受では潤滑油を変えることにより、この早期剥離を防止してきた。しかし、軸受部品の使用条件の過酷化および多様化により、従来軸受鋼の転動疲労破壊においてほとんど問題にならなかった、水素脆性剥離が発生する条件が増加する傾向にあり、単に潤滑油を変えるだけでは抑制できなくなりつつある。このため、このような転動疲労における水素脆性剥離に対して長寿命の材料が求められていた。
For example, in an automobile alternator bearing, early peeling may occur with a change in the structure of a dendritic white layer along a grain boundary different from a white band that is a conventional change in structure. This is thought to be because hydrogen embrittlement peeling occurred due to the decomposition of the lubricating oil under severe load conditions of high vibration and high load, generation of hydrogen on the rolling surface, and penetration into the interior.
On the other hand, in the alternator bearing, this early peeling has been prevented by changing the lubricating oil. However, due to the harsh and diversified use conditions of bearing parts, there is a tendency to increase the conditions under which hydrogen embrittlement delamination occurs, a problem that has hardly become a problem in rolling fatigue failure of conventional bearing steel. It is becoming impossible to suppress by itself. For this reason, a material having a long life against hydrogen embrittlement delamination in such rolling fatigue has been demanded.
 以前より水素脆性による材料強度低下現象は知られている。たとえば、ばねやボルト部品では水等の分解により暴露環境から侵入する拡散性水素が遅れ破壊の原因となっている。耐遅れ破壊性に優れたばね、ボルト用鋼として、微細な炭(窒)化物を多数析出させ、拡散性水素をトラップして、粒界や応力集中部への水素の拡散を抑えた鋼が用いられている。本願発明者は、既に特許文献1において開示したように、SUJ2をベースに種々の合金元素の組み合わせを検討した結果、Vを添加することにより、数十から数百nm程度の微細なV系炭化物を多数生成して、繰り返し疲労条件下での水素脆性による寿命低下を抑えることを見出した。 The material strength reduction phenomenon due to hydrogen embrittlement has been known for some time. For example, in springs and bolt parts, diffusible hydrogen entering from the exposure environment due to decomposition of water or the like causes delayed destruction. As steel for springs and bolts with excellent delayed fracture resistance, steel with a large amount of fine carbonitrides precipitated, trapping diffusible hydrogen, and suppressing diffusion of hydrogen to grain boundaries and stress concentration parts is used. It has been. As already disclosed in Patent Document 1, the present inventor has studied the combination of various alloy elements based on SUJ2, and as a result, by adding V, a fine V-based carbide of about several tens to several hundreds of nanometers is added. It has been found that a decrease in life due to hydrogen embrittlement under repeated fatigue conditions is suppressed.
 また、特許文献2に開示したように、Cr添加した軸受鋼でCrの酸化被膜を形成させることで水素侵入を抑制し、水素脆性寿命を長寿命化することができる。 Also, as disclosed in Patent Document 2, by forming a Cr oxide film with Cr-added bearing steel, hydrogen penetration can be suppressed and the hydrogen embrittlement life can be extended.
 さらなる長寿命化には特許文献3に開示したようにCr,Mn等を添加した肌焼鋼を浸炭窒化処理することにより表層に析出したCrNやMnSiN2などの微細窒化物の水素トラップにより水素脆性寿命を長寿命化することが必要である。 As further disclosed in Patent Document 3, hydrogen embrittlement is achieved by hydrogen trapping of fine nitrides such as CrN and MnSiN 2 deposited on the surface layer by carbonitriding the case-hardened steel to which Cr, Mn, etc. are added as disclosed in Patent Document 3. It is necessary to extend the service life.
 しかしながら、SCM440等の肌焼鋼を浸炭窒化処理する場合は、所定の表層C濃度およびC濃度深さ分布を得るために長時間の浸炭処理が必要となり生産性が低下する。浸炭時間を短時間化し生産性を高めるためには、初期C濃度の高いSUJ2に代表される軸受鋼に浸炭窒化することが求められていた。 However, when carburizing and nitriding a case-hardened steel such as SCM440, a long-time carburizing process is required to obtain a predetermined surface C concentration and C concentration depth distribution, and productivity is lowered. In order to shorten the carburizing time and increase the productivity, it has been required to perform carbonitriding on bearing steel represented by SUJ2 having a high initial C concentration.
 しかし、SUJ2に代表される軸受鋼にCr,Mn等の合金元素を添加するだけでは素材硬さが上昇し、被削性や冷間鍛造等の加工性が低下してしまう。 However, just adding an alloying element such as Cr or Mn to bearing steel represented by SUJ2 increases the material hardness and decreases the workability such as machinability and cold forging.
 以上のことから、短時間の浸炭窒化処理が可能な軸受鋼を用いて水素脆性寿命を長寿命化するためCr,Mn等の合金元素を添加し、かつ所定の加工性を確保するために素材硬さを抑制した鋼の開発が求められていた。 Based on the above, using bearing steel that can be carbonitrided in a short time, adding alloy elements such as Cr and Mn in order to prolong the hydrogen embrittlement life, and ensuring the desired workability Development of steel with reduced hardness has been demanded.
日本国特開2006-213981号公報Japanese Unexamined Patent Publication No. 2006-213981 日本国特開平5-26244号公報Japanese Laid-Open Patent Publication No. 5-26244 日本国特開2011-225936号公報Japanese Unexamined Patent Publication No. 2011-225936
 本発明は、上記のような事情を背景としてなされたもので、本発明の目的は浸炭窒化時間の短時間化のためSUJ2に代表される軸受鋼をベースとして合金元素(化学成分の組成比率)を適正化し、浸炭窒化処理することで、従来、水素脆性剥離が生じていた雰囲気条件において使用したとしても、優れた転動疲労寿命を有し、かつ冷間鍛造性や被削性等の加工性に優れた耐環境用軸受鋼を提供することにある。 The present invention has been made in the background as described above, and an object of the present invention is an alloy element (composition ratio of chemical components) based on bearing steel represented by SUJ2 for shortening the carbonitriding time. Optimized and carbonitrided to have excellent rolling fatigue life and work such as cold forgeability and machinability even when used under atmospheric conditions where hydrogen brittle exfoliation has occurred in the past The object is to provide an environmentally resistant bearing steel having excellent properties.
 浸炭窒化による水素脆性寿命の改善は、表層に析出する微細窒化物の水素トラップによる。微細窒化物はCrNとMnSiN2が生成しており、その改善にはCr、Mn量を増加することが有効である。
 しかし、軸受鋼でCr、Mn量を増加するだけでは球状化焼なまし後の素材硬さが93HRB以上と高くなる。素材硬さを低減するためにはC濃度を下げることが有効だが、C濃度を下げすぎると浸炭窒化時間が長時間化して製造性を低下してしまう。
 一方、Si低減は硬さ低減に効果があると共に生成窒化物数を増加し耐水素脆性を改善することを見出した。これは、Si低減することにより生成窒化物がMnSiN2からCrNに変化することで総窒化物数が増加することおよび母層の靱性が向上するためと考えられる。
The improvement of the hydrogen embrittlement life by carbonitriding is due to the hydrogen trap of fine nitride deposited on the surface layer. The fine nitride is produced by CrN and MnSiN 2, and it is effective to increase the amount of Cr and Mn for the improvement.
However, just increasing the amount of Cr and Mn in the bearing steel increases the material hardness after spheroidizing annealing to 93HRB or higher. In order to reduce the material hardness, it is effective to lower the C concentration. However, if the C concentration is lowered too much, the carbonitriding time becomes longer and the productivity is lowered.
On the other hand, it has been found that Si reduction is effective in reducing hardness and increases the number of formed nitrides to improve hydrogen embrittlement resistance. This is presumably because the total number of nitrides is increased and the toughness of the mother layer is improved by changing the generated nitride from MnSiN 2 to CrN by reducing Si.
 本願発明者は種々の試験を行い、製造性(浸炭時間および加工性)と耐水素脆性を両立できるC量とSi量の成分範囲を見出した。
 また、Si量低減により焼入性は低下するが、Mn量を添加することで耐水素脆性を改善しかつ焼入性も補完できることを見出した。
The inventor of the present application conducted various tests and found a component range of C amount and Si amount capable of achieving both manufacturability (carburizing time and workability) and hydrogen embrittlement resistance.
Moreover, although hardenability fell by Si amount reduction, it discovered that hydrogen embrittlement resistance was improved and hardenability could be supplemented by adding Mn amount.
 すなわち、本発明の軸受鋼は、合金元素の含有率が質量%表示で、C:0.5~1.0%、Si:0.1%以下、Mn:0.4~1.5%、P:0.03%以下、S:0.03%以下、Cr:1.5~3.5%、Al:0.050%以下、O:0.0015%以下、Ti:0.003%以下、N:0.015%以下、残部Fe及び不可避的不純物の組成からなり、球状化焼なまし後の硬さが92HRB以下、浸炭窒化後の表層N濃度0.1~1.0%、表層C濃度0.8~1.5%、表層硬さがHRC58以上64未満で、粒径2μm以上の粗大なCrNまたはMnSiN2の窒化物の個数密度が103個/mm2以下であって、微細な窒化物が分散析出していることを特徴とする製造性と耐水素脆性に優れた耐環境用軸受鋼である。 That is, in the bearing steel of the present invention, the alloy element content is expressed by mass%, C: 0.5 to 1.0%, Si: 0.1% or less, Mn: 0.4 to 1.5%, P: 0.03% or less, S: 0.03% or less, Cr: 1.5 to 3.5%, Al: 0.050% or less, O: 0.0015% or less, Ti: 0.003% or less , N: 0.015% or less, balance Fe and inevitable impurities composition, hardness after spheroidizing annealing is 92 HRB or less, surface layer N concentration after carbonitriding 0.1-1.0%, surface layer The number density of coarse CrN or MnSiN 2 nitride having a C concentration of 0.8 to 1.5%, a surface hardness of 58 to less than 64, and a particle size of 2 μm or more is 10 3 pieces / mm 2 or less, It is an environmentally resistant bearing steel excellent in manufacturability and hydrogen embrittlement resistance, characterized in that fine nitrides are dispersed and precipitated.
 また、本発明の軸受鋼は、上記合金元素に加えてV:0.05~2.0%、Ni:0.1~3.0%、Mo:0.05~2.0%のうち1種または2種以上をさらに含むことが好ましい。
 すなわち、本発明の軸受鋼は、質量%表示で、C:0.5~1.0%、Si:0.1%以下、Mn:0.4~1.5%、P:0.03%以下、S:0.03%以下、Cr:1.5~3.5%、Al:0.050%以下、O:0.0015%以下、Ti:0.003%以下、N:0.015%以下であって、V:0.05~2.0%、Ni:0.1~3.0%、Mo:0.05~2.0%のうち1種または2種以上をさらに含み、残部Fe及び不可避的不純物の組成からなるものであることが好ましい。
In addition to the alloy elements described above, the bearing steel of the present invention includes V: 0.05 to 2.0%, Ni: 0.1 to 3.0%, Mo: 0.05 to 2.0%. It is preferable to further include seeds or two or more kinds.
That is, the bearing steel of the present invention is expressed by mass%, C: 0.5 to 1.0%, Si: 0.1% or less, Mn: 0.4 to 1.5%, P: 0.03% S: 0.03% or less, Cr: 1.5 to 3.5%, Al: 0.050% or less, O: 0.0015% or less, Ti: 0.003% or less, N: 0.015 %: V: 0.05 to 2.0%, Ni: 0.1 to 3.0%, Mo: 0.05 to 2.0%, and further including one or more of them, The composition is preferably composed of the balance Fe and inevitable impurities.
 本発明によれば、製造性(浸炭時間および加工性)に優れかつ水素脆性剥離による寿命低下を抑制し、長寿命を有する耐環境用軸受鋼を提供することができる。 According to the present invention, it is possible to provide an environmentally resistant bearing steel that has excellent manufacturability (carburizing time and workability), suppresses a decrease in life due to hydrogen embrittlement peeling, and has a long life.
実施例における浸炭窒化条件の一例を示した図である。It is the figure which showed an example of the carbonitriding conditions in an Example. 2円筒ころがり疲労試験の方法の説明図である。It is explanatory drawing of the method of a 2-cylinder rolling fatigue test.
 本発明の軸受鋼について説明する。
 本発明の軸受鋼は、後述する化学成分(組成)からなる鋼材であり、少なくとも球状化焼なまし処理および浸炭窒化焼入れ焼戻し処理の2つの処理を行うことで、優れた製造性と耐水素脆性とを備える耐環境用軸受鋼として用いることができるものである。
 本発明の軸受鋼は、後述する特定の化学成分(組成)からなる鋼材であって、球状化焼なましを行った場合に、その直後の硬さが92HRB以下であり、浸炭窒化を行った場合に、その直後の表層N濃度が0.1~1.0%、表層C濃度が0.8~1.5%、表層硬さがHRC58以上64未満であり、粒径2μm以上の粗大なCrNまたはMnSiN2の窒化物の個数密度が103個/mm2以下である鋼材であれば、球状化焼なまし処理および浸炭窒化焼入れ焼戻し処理の2つの処理を行った後の鋼材であっても、これら2つの処理のうち少なくとも1つの処理を行う前の鋼材であってもよい。
 いずれであっても、本発明の軸受鋼に相当する。
The bearing steel of the present invention will be described.
The bearing steel of the present invention is a steel material composed of a chemical component (composition) described later, and has excellent manufacturability and hydrogen embrittlement resistance by performing at least two treatments of spheroidizing annealing and carbonitriding and quenching and tempering. Can be used as environmentally resistant bearing steel.
The bearing steel of the present invention is a steel material having a specific chemical composition (composition) described later, and when spheroidizing annealing is performed, the hardness immediately after that is 92 HRB or less, and carbonitriding was performed. In this case, the surface layer N concentration immediately after that is 0.1 to 1.0%, the surface layer C concentration is 0.8 to 1.5%, the surface layer hardness is HRC 58 or more and less than 64, and the grain size is 2 μm or more. If the number density of the nitride of CrN or MnSiN 2 is 10 3 pieces / mm 2 or less, the steel material after performing two treatments, spheroidizing annealing treatment and carbonitriding quenching and tempering treatment, Alternatively, it may be a steel material before performing at least one of these two treatments.
Any of these corresponds to the bearing steel of the present invention.
 本発明の耐環境用軸受鋼の化学成分の限定理由について説明する。以下、特に断りがない限り、「%」は「質量%」を意味するものとする。 The reason for limiting the chemical composition of the environmentally resistant bearing steel of the present invention will be described. Hereinafter, unless otherwise specified, “%” means “mass%”.
 Cの含有量(0.5~1.0%)について、Cは転がり軸受として強度を確保するために必須の元素である。しかし、C量が0.5%を下回ると強度を維持するために必要な表面C濃度およびC濃度深さ分布を得るために長時間の浸炭処理が必要となり製造性が低下するため、C含有量の下限を0.5%に限定した。しかし、C量が1.0%を超えて含有された場合、球状化焼なまし後の素材硬さが高くなり、冷間鍛造性や被削性等の加工性の低下が生じることが判明したため、C量の上限値は1.0%とした。 C Regarding the content of C (0.5 to 1.0%), C is an essential element for securing strength as a rolling bearing. However, if the amount of C is less than 0.5%, a long time carburizing treatment is required to obtain the surface C concentration and C concentration depth distribution necessary for maintaining the strength, and the productivity is lowered. The lower limit of the amount was limited to 0.5%. However, when the C content exceeds 1.0%, the material hardness after spheroidizing annealing is increased, and it is found that workability such as cold forgeability and machinability is deteriorated. Therefore, the upper limit of the C amount is set to 1.0%.
 Siの含有量(0.1%以下)について、Siは鋼を製造する際に脱酸剤として用いられる。しかし、0.1%を超えて添加すると球状化焼なまし後の素材硬さを高め、被削性や冷間鍛造性を低下させるとともに、浸炭窒化後の窒化物形態がCrNからMnSiN2に変化することで水素トラップサイトとなる総窒化物数が減少し、耐水素脆性も低下させるため、その上限値を0.1%とした。 With respect to the Si content (0.1% or less), Si is used as a deoxidizing agent when producing steel. However, adding over 0.1% increases the material hardness after spheroidizing annealing, lowers the machinability and cold forgeability, and the nitride form after carbonitriding changes from CrN to MnSiN 2 By changing, the total number of nitrides serving as hydrogen trap sites is reduced and the hydrogen embrittlement resistance is also lowered. Therefore, the upper limit is set to 0.1%.
 Mnの含有量(0.4~1.5%)について、Mnは鋼を製造する際に脱酸に用いられる元素である。Mnは焼入れ性を改善する元素であり、冷間鍛造性や被削性のためにCやSi量を抑制したことによる焼入れ性の低下を補完するとともに、浸炭窒化後の水素トラップサイトとなるMnSiN2を微細に、増加析出することで耐水素脆性を改善することができるが、この効果を得るためには0.4%以上のMn量が必要なためMnの下限値を0.4%とした。しかし、1.5%を超えて多量にMnを含有すると球状化焼なまし後の素材硬さを高め被削性や冷間鍛造性を低下させるため、Mn含有量の上限を1.5%に限定した。 Regarding the Mn content (0.4 to 1.5%), Mn is an element used for deoxidation when manufacturing steel. Mn is an element that improves hardenability, and complements the decrease in hardenability due to the suppression of the amount of C and Si for cold forgeability and machinability, and MnSiN that becomes a hydrogen trap site after carbonitriding The hydrogen embrittlement resistance can be improved by finely increasing 2 to precipitate 2. However, in order to obtain this effect, an Mn amount of 0.4% or more is required, so the lower limit of Mn is 0.4%. did. However, if Mn is contained in a large amount exceeding 1.5%, the material hardness after spheroidizing annealing is increased and the machinability and cold forgeability are lowered, so the upper limit of Mn content is 1.5%. Limited to.
 Pの含有量(0.03%以下)について、Pは鋼のオーステナイト粒界に偏析し、靭性や転動疲労寿命の低下を招くため、0.03%をP含有量の上限とした。 Regarding the P content (0.03% or less), P segregates at the austenite grain boundaries of the steel, leading to a decrease in toughness and rolling fatigue life, so 0.03% was made the upper limit of the P content.
 Sの含有量(0.03%以下)について、Sは鋼の熱間加工性を害し、鋼中での非金属介在物を形成して靭性や転動寿命を低下させるため、可及的に少なくすることが望ましいが、Sは切削加工性を向上する効果も有しているため、0.03%をSの上限値とした。 Regarding S content (0.03% or less), S impairs hot workability of steel and forms non-metallic inclusions in the steel to reduce toughness and rolling life. Although it is desirable to reduce it, since S also has the effect of improving the machinability, 0.03% was made the upper limit of S.
 Crの含有量(1.5~3.5%)について、Crは焼入れ性の改善と炭化物による硬さの確保と寿命改善とのために添加される。さらに、浸炭窒化後にCrNを析出することで水素トラップサイトとなり耐水素脆性を改善することができる。この効果を得るためには1.5%以上の添加が必要であるため、Cr含有量の下限値を1.5%に限定した。しかし、3.5%を超えて含有すると、球状化焼なまし後の素材硬さを高め被削性や冷間鍛造性を低下させるとともに大型の炭窒化物が生成し、転動疲労寿命の低下が生じるためCr含有量の上限を3.5%とした。 Regarding the Cr content (1.5 to 3.5%), Cr is added to improve hardenability, ensure hardness by carbides and improve life. Furthermore, by depositing CrN after carbonitriding, it becomes a hydrogen trap site and can improve hydrogen embrittlement resistance. In order to obtain this effect, addition of 1.5% or more is necessary, so the lower limit value of the Cr content is limited to 1.5%. However, if the content exceeds 3.5%, the material hardness after spheroidizing annealing is increased, and the machinability and cold forgeability are reduced, and a large carbonitride is formed, which has a rolling fatigue life. Since the reduction occurs, the upper limit of the Cr content is set to 3.5%.
 Alの含有量(0.050%以下)について、Alは鋼の製造時の脱酸剤として使用されるが、硬質の非金属介在物を生成し、転動疲労寿命を低下させるため低減することが望ましい。0.050%を超えてAlが多量に含有されると顕著な転動疲労寿命の低下が認められるため、Al含有量の上限を0.050%とした。
 なお、Al含有量を0.005%未満とするためには鋼製造コストの上昇が生じるため、Alの含有量の下限を0.005%にすることが好ましい。
Regarding Al content (0.050% or less), Al is used as a deoxidizer during steel production, but it is reduced to produce hard non-metallic inclusions and reduce rolling fatigue life. Is desirable. When the Al content exceeds 0.050%, a significant decrease in rolling fatigue life is observed. Therefore, the upper limit of the Al content is set to 0.050%.
In order to reduce the Al content to less than 0.005%, the steel manufacturing cost increases, so the lower limit of the Al content is preferably set to 0.005%.
 Tiの含有量(0.003%以下)、O(酸素)の含有量(0.0015%以下)、Nの含有量(0.015%以下)について、Ti、OおよびNは鋼中に酸化物、窒化物を形成し非金属介在物として疲労破壊の起点となり、転動疲労寿命を低下させるため、Ti:0.003%、O:0.0015%、N:0.015%を各元素の上限とした。 Regarding Ti content (0.003% or less), O (oxygen) content (0.0015% or less), and N content (0.015% or less), Ti, O and N are oxidized in steel. Ti, 0.003%, O: 0.0015%, and N: 0.015% are included in each element in order to reduce fatigue life as non-metallic inclusions by forming oxides and nitrides. The upper limit.
 Vの含有量(0.05~2.0%)について、Vは粒径数百nm以下の微細なV系炭化物を析出し、鋼中で拡散性水素をトラップすることにより水素脆性剥離を抑制する効果がある。この効果を得るためにはV含有量は0.05%以上であることが好ましい。しかし、2.0%を超えて多量に含有すると被削性や鍛造性等の加工性が低下するため、V含有量の上限値は2.0%であることが好ましい。 For V content (0.05 to 2.0%), V precipitates fine V-based carbides with a particle size of several hundred nanometers or less, and suppresses hydrogen embrittlement delamination by trapping diffusible hydrogen in steel. There is an effect to. In order to obtain this effect, the V content is preferably 0.05% or more. However, if the content exceeds 2.0%, the workability such as machinability and forgeability deteriorates, so the upper limit of the V content is preferably 2.0%.
 Niの含有量(0.1~3.0%)について、Niは転動疲労過程での組織変化を抑制、転動疲労寿命を向上する。また、Niの添加は靭性および耐食性の改善にも効果がある。これらの効果を得るために、Ni含有量が0.1%以上であると好ましい。しかし、3.0%を超えて多量に含有すると鋼の焼入れ時に多量の残留オーステナイトを生成し、所定の硬さが得られなくなるとともに、鋼材のコストが上昇する可能性があるため、Ni含有量の上限値は3.0%であることが好ましい。 Regarding the Ni content (0.1-3.0%), Ni suppresses the structural change during the rolling fatigue process and improves the rolling fatigue life. Further, the addition of Ni is effective in improving toughness and corrosion resistance. In order to obtain these effects, the Ni content is preferably 0.1% or more. However, if it is contained in a large amount exceeding 3.0%, a large amount of retained austenite is generated at the time of quenching the steel, and the predetermined hardness cannot be obtained, and the cost of the steel material may increase, so the Ni content Is preferably 3.0%.
 Moの含有量(0.05~2.0%)について、Moは鋼の焼入れ性を改善するとともに、炭化物中に固溶することにより焼戻し時の硬さの低下を抑制する効果がある。この効果を得るためには、Mo含有量が0.05%以上であると好ましい。しかし、2.0%を超えて多量に含有すると鋼材のコストが上昇し、熱間加工性や切削性が低下する可能性があるため、Moの上限値は2.0%であることが好ましい。 Regarding the Mo content (0.05 to 2.0%), Mo has the effect of improving the hardenability of the steel and suppressing the decrease in hardness during tempering by dissolving in the carbide. In order to obtain this effect, the Mo content is preferably 0.05% or more. However, if the content exceeds 2.0%, the cost of the steel material is increased, and hot workability and machinability may be reduced. Therefore, the upper limit value of Mo is preferably 2.0%. .
 このように本発明の軸受鋼は、特定比率でC、Si、Mn、P、S、Cr、Al、O、Ti、Nを含む鋼材であって、さらにV、Ni、Moのうち1種または2種以上を含むものであることが好ましく、残部は、Feおよび不可避的不純物であってよい。
 Fe中に含まれ得る不可避的不純物として、従来公知の成分を挙げられる。例えば、Cu等が挙げられる。不可避的不純物の含有率は少ないほど好ましい。
As described above, the bearing steel of the present invention is a steel material containing C, Si, Mn, P, S, Cr, Al, O, Ti, and N at a specific ratio, and one or more of V, Ni, and Mo It is preferable that it contains 2 or more types, and the balance may be Fe and inevitable impurities.
Examples of inevitable impurities that can be contained in Fe include conventionally known components. For example, Cu etc. are mentioned. The smaller the content of inevitable impurities, the better.
 次に、本発明の耐環境軸受用鋼の表面硬さおよびCrNまたはMnSiN2窒化物について言及する。 Next, the surface hardness and CrN or MnSiN 2 nitride of the environmental bearing steel of the present invention will be mentioned.
<表面硬さHRC58以上64未満について>
 焼戻し後の表面硬さと転動疲労寿命には相関が認められ、表面硬さが高いほど転動疲労寿命は長くなる傾向がある。特に、焼戻し処理後の表面硬さがHRC58以下になると急激に転動疲労寿命が低下し、寿命のばらつきも大きくなるため、焼戻し処理後の表面硬さを58HRC以上とした。また、HRC64未満とする理由は、表面硬さが高くなると水素脆性に対する感受性が高くなり、水素脆性剥離により著しく転動疲労寿命が低下するためである。
 なお、表面硬さ(HRC)の測定方法は、後述する。
<Surface hardness HRC 58 or more and less than 64>
There is a correlation between the surface hardness after tempering and the rolling fatigue life, and the higher the surface hardness, the longer the rolling fatigue life. In particular, when the surface hardness after tempering is HRC58 or less, the rolling fatigue life is abruptly reduced and the variation in the life is increased, so the surface hardness after tempering is set to 58 HRC or more. Moreover, the reason for setting it to less than HRC64 is that when the surface hardness is increased, the sensitivity to hydrogen embrittlement is increased, and the rolling fatigue life is significantly reduced by hydrogen embrittlement delamination.
In addition, the measuring method of surface hardness (HRC) is mentioned later.
<粒径2μm以上の粗大なCrNまたはMnSiN2窒化物の個数が103個/mm2以下について>
 水素脆性型面疲労強度の改善には、微細窒化物を多数析出させることが必要である。すなわち、窒化物のうち水素トラップに有効な窒化物は、粒径300nm以下の微細なCr窒化物(例えばCrN)、及びMnとSiの複合窒化物(例えばMnSiN2)である。しかし、表層N濃度や合金元素を高めると、粒径の大きい粗大な窒化物が形成されやすくなり、強度低下の要因となる。粒径2μm以上の粗大なCrNまたはMnSiN2の窒化物の個数割合が103個/mm2を超えると、著しく水素脆性型面疲労強度が低下するため、粒径2μm以上の粗大な窒化物の個数割合の上限を103個/mm2とした。
 なお、粒径2μm以上の粗大なCrNまたはMnSiN2窒化物の個数の測定方法は、後述する。
<When the number of coarse CrN or MnSiN 2 nitride having a particle size of 2 μm or more is 10 3 pieces / mm 2 or less>
In order to improve the hydrogen embrittlement surface fatigue strength, it is necessary to precipitate a large number of fine nitrides. That is, of the nitrides, nitrides effective for hydrogen trapping are fine Cr nitrides (eg, CrN) having a particle size of 300 nm or less, and composite nitrides of Mn and Si (eg, MnSiN 2 ). However, increasing the surface layer N concentration and the alloy element facilitates the formation of coarse nitrides having a large particle size, which causes a decrease in strength. If the number ratio of coarse CrN or MnSiN 2 nitride having a particle size of 2 μm or more exceeds 10 3 pieces / mm 2 , the hydrogen embrittlement type surface fatigue strength is significantly reduced. The upper limit of the number ratio was 10 3 pieces / mm 2 .
A method for measuring the number of coarse CrN or MnSiN 2 nitride having a particle diameter of 2 μm or more will be described later.
<表層C濃度(表層炭素濃度):0.8~1.5%>
 表層Cは、転がり軸受として強度を確保するために必須の元素であり、所定の熱処理後硬さを維持するためには表層C濃度が0.8%以上は必要であるため、表層C濃度の下限を0.80%に規定した。一方、表層C濃度が1.5%を超えると、大型の炭化物が生成し、転動疲労寿命の低下が生じることが判明したため、表層C濃度の上限を1.5%とした。
 なお、表層C濃度の測定方法は、後述する。
<Surface layer C concentration (surface layer carbon concentration): 0.8 to 1.5%>
The surface layer C is an essential element for securing the strength as a rolling bearing, and the surface layer C concentration of 0.8% or more is necessary to maintain the hardness after a predetermined heat treatment. The lower limit was defined as 0.80%. On the other hand, when the surface layer C concentration exceeds 1.5%, it was found that large carbides are generated and the rolling fatigue life is reduced, so the upper limit of the surface layer C concentration was 1.5%.
In addition, the measuring method of surface layer C density | concentration is mentioned later.
<表層N濃度(表層窒素濃度):0.1~1.0%>
 表層Nは、微細な窒化物を表層に生成することにより水素トラップサイトとして働き、耐水素脆性を改善する。また、鋼の軟化抵抗性を改善することにより転動寿命を向上させる。これらの効果を得るためには表層N濃度が0.1%以上は必要であるため、表層N濃度の下限を0.1%とした。一方、表層N濃度が1.0%を超えると、残留オーステナイトの生成により表面硬さを低下させ、所定の表面硬さが得られなくなるため、表層N濃度の上限を1.0%とした。
 なお、表層N濃度の測定方法は、後述する。
<Surface layer N concentration (surface layer nitrogen concentration): 0.1 to 1.0%>
The surface layer N works as a hydrogen trap site by generating fine nitride in the surface layer, and improves hydrogen embrittlement resistance. It also improves the rolling life by improving the softening resistance of the steel. In order to obtain these effects, the surface layer N concentration needs to be 0.1% or more, so the lower limit of the surface layer N concentration was set to 0.1%. On the other hand, when the surface layer N concentration exceeds 1.0%, the surface hardness is lowered due to the formation of retained austenite, and a predetermined surface hardness cannot be obtained. Therefore, the upper limit of the surface layer N concentration is set to 1.0%.
A method for measuring the surface layer N concentration will be described later.
 本発明の軸受鋼の製造方法は特に限定されない。前述のような特定の化学成分(組成)を含むように原料を調整し、従来公知の方法で溶解し、固化することで本発明の軸受鋼を得ることができる。 The method for producing the bearing steel of the present invention is not particularly limited. The bearing steel of the present invention can be obtained by adjusting the raw materials so as to contain the specific chemical component (composition) as described above, and dissolving and solidifying by a conventionally known method.
 また、本発明の軸受鋼が前述のような特定の化学成分(組成)を含むように原料を調整し、従来公知の方法で溶解し、固化した後、圧延し、球状化焼なまし処理を行い、さらに浸炭窒化焼入れ焼戻し処理を行うことで、優れた製造性と耐水素脆性とを備える耐環境用軸受鋼となる。
 ここで圧延は、熱間圧延および低温圧延であることが好ましい。例えば1000~1200℃での熱間圧延を行った後、700~900℃での冷間圧延を行うことが好ましい。
 また、球状化焼なまし処理は、700~800℃に加熱し、1~10時間保持した後、-5~-30℃/時間で450~700℃まで冷却し、その後、空冷する処理が例示される。
 また、浸炭窒化焼入れ焼戻し処理は、後述する図1に示す処理が例示される。
In addition, the raw material is adjusted so that the bearing steel of the present invention contains the specific chemical component (composition) as described above, melted and solidified by a conventionally known method, and then rolled and subjected to spheroidizing annealing treatment. By performing the carbonitriding quenching and tempering process, the bearing steel for environment resistance having excellent manufacturability and hydrogen embrittlement resistance is obtained.
Here, the rolling is preferably hot rolling and low temperature rolling. For example, it is preferable to perform hot rolling at 1000 to 1200 ° C. and then cold rolling at 700 to 900 ° C.
In addition, the spheroidizing annealing treatment includes heating to 700 to 800 ° C., holding for 1 to 10 hours, cooling to 450 to 700 ° C. at −5 to −30 ° C./hour, and then air cooling. Is done.
The carbonitriding quenching and tempering process is exemplified by the process shown in FIG.
 以下、本発明の実施例について説明する。表1に示す化学成分の材料を150kgの真空溶解で溶製し、加熱温度1200℃で3時間保持した後、鍛造温度1200℃、終止温度900℃で熱間鍛造により直径32mmと直径65mmの棒鋼を製造した。この後、焼ならし処理として920℃に加熱し、2時間保持した後空冷し、さらに球状化焼なまし処理として760℃に加熱し、3時間保持した後、-15℃/時間で650℃まで冷却した後空冷し、各試験の素材(以下「球状化焼なまし材」ともいう)とした。 Hereinafter, examples of the present invention will be described. Bar material with diameters of 32 mm and 65 mm by hot forging at a forging temperature of 1200 ° C. and a final temperature of 900 ° C. after melting the materials of chemical components shown in Table 1 by vacuum melting of 150 kg and holding at a heating temperature of 1200 ° C. for 3 hours. Manufactured. Thereafter, it is heated to 920 ° C. as a normalizing treatment, held for 2 hours, then air-cooled, further heated to 760 ° C. as a spheroidizing annealing treatment, held for 3 hours, and then 650 ° C. at −15 ° C./hour. After cooling to room temperature, it was air-cooled and used as a material for each test (hereinafter also referred to as “spheroidizing annealing material”).
 ここで球状化焼なまし硬さを測定した。球状化焼なまし硬さは、直径32mmの球状化焼なまし材の横断面(棒鋼の長手方向の軸に垂直な面)が露出した硬さ試験片を作製し、横断面の1/2半径部位をロックウエル硬さ計でHRB硬さ(JIS Z2245)を4点平均で求めた。
 表2の「球状化焼なまし硬さ(HRB)」の欄に測定結果を示す。
Here, the spheroidizing hardness was measured. The spheroidizing annealing hardness is a hardness test piece in which the cross section of the spheroidizing annealing material having a diameter of 32 mm (surface perpendicular to the longitudinal axis of the steel bar) is exposed, and is ½ of the cross section The HRB hardness (JIS Z2245) was obtained from the radius part with a Rockwell hardness tester by an average of 4 points.
The measurement results are shown in the column of “spheroidizing annealing hardness (HRB)” in Table 2.
 次に、直径32mmの球状化焼なまし材から断面直径25mm、長さ100mmの試験片を削り出し、種々の浸炭窒化条件で処理を行った。浸炭窒化処理は浸炭ガスにアンモニアガスを加えた混合雰囲気中で、種々の浸炭窒化条件(浸炭温度、浸炭時間、カーボンポテンシャル、アンモニア濃度)で処理を行い、焼入れ焼戻し処理を行った。図1は、用いた浸炭窒化条件の一例である。
 なお、表1のNo.5およびNo.12の鋼材については、オーステナイト中のN濃度が高くなるとマルテンサイト変態開始温度(Ms点)が低下し、焼入れ後の残留オーステナイト量が増加し、表層硬さが不足する可能性があったため、650℃で1時間保持する中間焼鈍を行ない、840℃で2次焼入れを行なった。
Next, a test piece having a cross-sectional diameter of 25 mm and a length of 100 mm was cut out from a spheroidized annealed material having a diameter of 32 mm and treated under various carbonitriding conditions. The carbonitriding treatment was performed under various carbonitriding conditions (carburizing temperature, carburizing time, carbon potential, ammonia concentration) in a mixed atmosphere in which ammonia gas was added to carburizing gas, followed by quenching and tempering treatment. FIG. 1 is an example of the carbonitriding conditions used.
In Table 1, No. 5 and no. As for the steel No. 12, when the N concentration in austenite increases, the martensite transformation start temperature (Ms point) decreases, the amount of retained austenite after quenching increases, and the surface hardness may be insufficient. The intermediate annealing which hold | maintains at 1 degreeC for 1 hour was performed, and the secondary quenching was performed at 840 degreeC.
 上記のような浸炭窒化焼入れ焼戻し処理を行なって得た試験片について外周を深さ0.15mm研削し、その外周部について5点平均でロックウエル硬さ(JIS Z2245に準拠)を求めた。
 表2の「表層硬さ(HRC)」の欄に結果を示す。
The test piece obtained by performing the carbonitriding quenching and tempering treatment as described above was ground at a depth of 0.15 mm, and the Rockwell hardness (conforming to JIS Z2245) was determined for the outer peripheral portion with an average of 5 points.
The results are shown in the column of “surface hardness (HRC)” in Table 2.
 その後、上記のような浸炭窒化焼入れ焼戻し処理を行なって得た試験片を横断面(棒鋼の長手方向の軸に垂直な面)が露出するように樹脂内に埋め込み、横断面を研磨仕上げし、表層部のC、N濃度をEPMAで分析した。
 結果を表2の「表層C濃度」、「表層N濃度」の欄に示す。
 ここで、表層C、N濃度は最表層から深さ10μm位置までのC、N濃度の最大値(ピーク値)とした。
Thereafter, the test piece obtained by performing the carbonitriding quenching and tempering treatment as described above was embedded in the resin so that the cross section (surface perpendicular to the longitudinal axis of the steel bar) was exposed, and the cross section was polished and finished. The C and N concentrations in the surface layer were analyzed by EPMA.
The results are shown in the columns of “surface layer C concentration” and “surface layer N concentration” in Table 2.
Here, the surface layer C and N concentrations were the maximum values (peak values) of the C and N concentrations from the outermost layer to a depth of 10 μm.
 さらに、同試験片について、FE-SEMおよび元素分析(EDX)を用いて表層から深さ100μmまでの深さ領域に存在する粒径2μm以上の窒化物の個数を測定し、観察領域の面積で除して、粒径2μm以上の粗大な窒化物の個数密度(個/mm2)を求めた。
 結果を表2に示す。
Further, for the test piece, the number of nitrides having a particle diameter of 2 μm or more existing in the depth region from the surface layer to a depth of 100 μm was measured using FE-SEM and elemental analysis (EDX). The number density (pieces / mm 2 ) of coarse nitrides having a particle size of 2 μm or more was determined.
The results are shown in Table 2.
 また、直径32mmの球状化焼なまし材から、断面直径26.3mmの円筒粗加工試験片を得た後、各々の試験片について前述の浸炭窒化処理を行ない、その後、表面の0.15mmを研削仕上げする粗加工を行って、試験面直径26mmの円筒試験片を作製した。そして、この円筒試験片について、図2に示すローラーピッチング試験機(ニッコークリエイト社製)を用いて2円筒ころがり疲労試験を行った。図2において18は円筒の試験片で、この図2に示す方法では、試験片18に対してJIS SUJ2の焼入れ焼戻し材から成る相手円筒20を所定面圧で押し付け、その状態でモータ22により軸24を介して試験片18を回転させるとともに、モータ22の回転をギア26,28を介して軸30に伝達して、相手円筒20を回転させることにより行った。
 ここで相手円筒はSUJ2の焼入れ焼戻し材で、形状は軸方向に曲率半径150mmのクラウニングを有する直径130mmの円筒である。試験条件は水素脆性型の面疲労剥離を再現する条件で行った。水素脆性を生じる潤滑油を用い、水素脆性型の早期転動疲労破壊が生じる試験条件(油温90℃、すべり率-60%、面圧3Gpa、回転数1500rpm)で試験を行なった。ここで、すべり率とは試験円筒と相手円筒の周速の差と試験円筒の周速の比率である。試験は同一条件で4点行い、平均寿命を求めた。
 表2に試験結果を示す。
Further, after obtaining a cylindrical roughing test piece having a cross-sectional diameter of 26.3 mm from a spheroidized annealing material having a diameter of 32 mm, the above-mentioned carbonitriding treatment was performed on each test piece, and thereafter 0.15 mm of the surface was reduced. Roughing to finish grinding was performed to produce a cylindrical test piece with a test surface diameter of 26 mm. And about this cylindrical test piece, the 2-cylinder rolling fatigue test was done using the roller pitching testing machine (made by Nikko Create) shown in FIG. In FIG. 2, reference numeral 18 denotes a cylindrical test piece. In the method shown in FIG. 2, a mating cylinder 20 made of a tempered tempering material of JIS SUJ2 is pressed against the test piece 18 with a predetermined surface pressure. The test piece 18 was rotated through 24 and the rotation of the motor 22 was transmitted to the shaft 30 through the gears 26 and 28 to rotate the counterpart cylinder 20.
Here, the counterpart cylinder is a SUJ2 quenching and tempering material, and the shape is a cylinder with a diameter of 130 mm having a crowning with a curvature radius of 150 mm in the axial direction. The test conditions were such that the hydrogen embrittlement type surface fatigue peeling was reproduced. The test was performed under the test conditions (oil temperature 90 ° C., slip rate −60%, surface pressure 3 Gpa, rotation speed 1500 rpm) in which a hydrogen embrittlement type lubricating oil was used and an early rolling fatigue failure of the hydrogen embrittlement type occurred. Here, the slip ratio is a ratio of the difference between the peripheral speeds of the test cylinder and the counterpart cylinder and the peripheral speed of the test cylinder. The test was performed at four points under the same conditions, and the average life was obtained.
Table 2 shows the test results.
Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000002
Figure JPOXMLDOC01-appb-T000002
 表2に示すように本発明に相当する本発明鋼は、いずれも表面硬さ(HRC)は58以上64未満であり、表層C量は0.8~1.5%の範囲、表層N量は0.1~1.0%の範囲であり、粒径2μm以上の粗大な窒化物数が103個/mm2以下である。
 また、本発明鋼の2円筒試験の平均寿命は10.6~19.3×106回と優れる。一方、比較鋼では鋼種No.13、15、1、2において同平均寿命が0.5~4.7×106回と、いずれも水素脆性により低寿命である。
As shown in Table 2, the steels of the present invention corresponding to the present invention each have a surface hardness (HRC) of 58 or more and less than 64, the surface layer C content in the range of 0.8 to 1.5%, and the surface layer N content. Is in the range of 0.1 to 1.0%, and the number of coarse nitrides having a particle size of 2 μm or more is 10 3 pieces / mm 2 or less.
Further, the average life of the two-cylinder test of the steel of the present invention is excellent at 10.6 to 19.3 × 10 6 times. On the other hand, in the comparative steel, the steel type No. The average lifespans of 13, 15, 1, and 2 are 0.5 to 4.7 × 10 6 times, which are all low due to hydrogen embrittlement.
 なお、比較鋼における鋼種No.1および2は、化学成分は本発明鋼における鋼種No.1および2と同じであるが、浸炭窒化後の表層C,N濃度あるいは表層硬さが範囲外となった例である。一方、鋼種No.14,16は同寿命が10.4~12.1×106回と長寿命であるが、球状化焼なまし後の素材硬さが93,94HRBと高く製造性に劣る。
 表2の比較鋼のうち鋼種No.13は化学成分の内Siが高く、粗大な窒化物が生成し低寿命となった例である。
 No.14はC量が高いため素材硬さが高くなった例である。
 No.15はMn量が低いため低寿命となった例である。
 No.16はCr量が高く素材硬さが高くなった例である。
In addition, steel type No. in the comparative steel. Nos. 1 and 2 have the chemical composition No. Although it is the same as 1 and 2, it is an example in which the surface layer C, N concentration or surface layer hardness after carbonitriding is out of the range. On the other hand, steel type No. Nos. 14 and 16 have a long life of 10.4 to 12.1 × 10 6 times, but the material hardness after spheroidizing annealing is as high as 93,94 HRB and is inferior in manufacturability.
Among the comparative steels in Table 2, the steel type No. No. 13 is an example in which Si is a high chemical component and coarse nitrides are produced, resulting in a short life.
No. No. 14 is an example in which the material hardness is increased due to the high amount of C.
No. No. 15 is an example in which the lifetime is reduced due to the low amount of Mn.
No. 16 is an example in which the Cr content is high and the material hardness is high.
 比較例のうち鋼種No.1,2を用いた例は、化学成分は本発明鋼における鋼種No.1および2と同じであるが、以下の理由により低寿命となった例である。
 鋼種No.1は浸炭窒化時のカーボンポテンシャルが低く(Cp=0.7%程度)、そのため表層C濃度が低く、表層硬さが低下し低寿命となった例である。
 鋼種No.2は窒化を行わず表層N濃度が低く、低寿命となった例である。
Among the comparative examples, steel type No. In the examples using Nos. 1 and 2, the chemical composition is the steel type No. in the steel of the present invention. Although it is the same as 1 and 2, it is an example in which the lifetime is reduced for the following reason.
Steel type no. No. 1 is an example in which the carbon potential at the time of carbonitriding is low (Cp = about 0.7%), so the surface layer C concentration is low, the surface layer hardness is lowered, and the life is shortened.
Steel type no. No. 2 is an example in which nitriding is not performed and the surface layer N concentration is low, resulting in a short life.
 本発明によれば、製造性(浸炭時間および加工性)に優れかつ水素脆性剥離による寿命低下を抑制し、長寿命を有する耐環境用軸受鋼を提供することができる。 According to the present invention, it is possible to provide an environmentally resistant bearing steel that has excellent manufacturability (carburizing time and workability), suppresses a decrease in life due to hydrogen embrittlement peeling, and has a long life.
 本発明を詳細にまた特定の実施態様を参照して説明したが、本発明の精神と範囲を逸脱することなく様々な変更や修正を加えることができることは当業者にとって明らかである。
 本出願は、2016年3月30日出願の日本特許出願(特願2016-069716)に基づくものであり、その内容はここに参照として取り込まれる。
Although the present invention has been described in detail and with reference to specific embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the invention.
This application is based on a Japanese patent application filed on March 30, 2016 (Japanese Patent Application No. 2016-069716), the contents of which are incorporated herein by reference.

Claims (2)

  1.  質量%表示で、
     C:0.5~1.0%
     Si:0.1%以下
     Mn:0.4~1.5%
     P:0.03%以下
     S:0.03%以下
     Cr:1.5~3.5%
     Al:0.050%以下
     O:0.0015%以下
     Ti:0.003%以下
     N:0.015%以下
     残部Fe及び不可避的不純物の組成からなり、球状化焼なまし後の硬さが92HRB以下、浸炭窒化後の表層N濃度0.1~1.0%、表層C濃度0.8~1.5%、表層硬さがHRC58以上64未満で、粒径2μm以上の粗大なCrNまたはMnSiN2の窒化物の個数密度が103個/mm2以下であって、微細な窒化物が分散析出していることを特徴とする製造性と耐水素脆性に優れた耐環境用軸受鋼。
    In mass% display,
    C: 0.5 to 1.0%
    Si: 0.1% or less Mn: 0.4 to 1.5%
    P: 0.03% or less S: 0.03% or less Cr: 1.5 to 3.5%
    Al: 0.050% or less O: 0.0015% or less Ti: 0.003% or less N: 0.015% or less The composition is composed of the balance Fe and inevitable impurities, and the hardness after spheroidizing annealing is 92HRB. Hereinafter, coarse CrN or MnSiN having a surface layer N concentration of 0.1 to 1.0% after carbonitriding, a surface layer C concentration of 0.8 to 1.5%, a surface layer hardness of HRC 58 or more and less than 64, and a particle size of 2 μm or more. 2 is a bearing steel for environment resistance excellent in manufacturability and resistance to hydrogen embrittlement, wherein the number density of nitrides of 2 is 10 3 pieces / mm 2 or less, and fine nitrides are dispersed and precipitated.
  2.  V:0.05~2.0%
     Ni:0.1~3.0%
     Mo:0.05~2.0%
    のうち1種または2種以上をさらに含む、請求項1に記載の製造性と耐水素脆性に優れた耐環境用軸受鋼。
    V: 0.05-2.0%
    Ni: 0.1-3.0%
    Mo: 0.05-2.0%
    The environmentally resistant bearing steel excellent in manufacturability and hydrogen embrittlement resistance according to claim 1, further comprising one or more of them.
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JP2013234702A (en) * 2012-05-08 2013-11-21 Nsk Ltd Planetary gear device
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