JP2006097096A - Bearing steel component subjected to carburizing or carbonitriding - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a carburized bearing component having excellent wear resistance and seizure resistance and having a rolling fatigue life even under the condition where contact fatigue accompanied by slipping lies or in a environment where lubricating oil is dilute. <P>SOLUTION: The bearing steel component is obtained by forming a steel having an alloy composition comprising, by weight, 0.1 to <0.3% C, 0.4 to 2% Si, ≤1.5% Mn, ≤0.03% P, ≤0.03% S, 0.3 to 2.5% Cr and 0.005 to 0.050% Al, and comprising ≤0.003% Ti, ≤0.0015% O and ≤0.025% N, and the balance substantially Fe into a component shape. Its surface hardness after carburizing quenching and tempering or carbonitriding quenching and tempering treatment is ≥58 HRC, and 300°C tempering softening resistance defined as (the surface hardness after carburizing quenching and tempering or carbonitriding quenching and tempering treatment)-(the surface hardness after tempering treatment at 300°C) is ≤130 Hv. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

本発明は、すべりを伴う接触が生じる環境または潤滑油が希薄な環境の下で、すぐれた耐摩耗性と耐焼付き性を示し、長い転動疲労寿命を有する浸炭または浸炭窒化した軸受鋼部品に関する。 The present invention relates to a carburized or carbonitrided bearing steel part that exhibits excellent wear resistance and seizure resistance and has a long rolling fatigue life in an environment where contact with sliding occurs or in an environment where the lubricating oil is dilute. .

従来、一般的な軸受の製造には、ＪＩＳのＳＵＪ２、ＳＣｒ４２０、ＳＣＭ４２０等に代表される軸受鋼が用いられてきた。しかし、近年、軸受の使用条件が過酷になり、軸受を使用する温度が上昇して潤滑油の粘度が低下したり、高速回転に伴って接触時に生じるすべりが多くなったりして、軸受の焼付きを生じる危険が増加している。そこで、軸受に関して、転動疲労寿命のみならず、耐焼付き性にすぐれた製品の出現が要望されていた。 Conventionally, bearing steels represented by JIS SUJ2, SCr420, SCM420 and the like have been used for the manufacture of general bearings. However, in recent years, the bearing usage conditions have become severe, the temperature at which the bearing is used increases, the viscosity of the lubricating oil decreases, and slippage that occurs during contact with high-speed rotation increases. There is an increased risk of sticking. Thus, there has been a demand for bearings that have not only rolling fatigue life but also excellent seizure resistance.

耐焼付き性が要求される軸受にとしては、セラミック軸受が知られているが、一般に製造コストが高いという問題があるため、実用化は特殊な用途の軸受に限られている。今後増加すると考えられる使用条件の一層の過酷化に対応するため、ＪＩＳ軸受鋼のもつ製造性および加工性を維持したまま、耐焼付き性および転動疲労寿命に関して改善された軸受鋼ないし軸受を開発する努力がなされている。 Ceramic bearings are known as bearings that require seizure resistance, but their practical application is limited to bearings for special applications due to the high manufacturing cost. Developed bearing steels and bearings with improved seizure resistance and rolling fatigue life, while maintaining the manufacturability and workability of JIS bearing steels, in order to cope with further severe usage conditions that are expected to increase in the future. Efforts are being made.

焼付きは、すべりに伴う表面温度上昇に起因して油膜が破断することにより金属間の直接の接触が生じ、接触した金属どうしの凝着が生じる現象である。一般に、油膜厚さｈと表面粗さσの比である油膜パラメターｈ／σが２以下になると，焼付きの危険性が増加し、すべりに伴う接触表面での閃光温度が約１４０℃を超えると、焼付きが発生するといわれている。耐焼付き性を改善するためには、すべりに伴う温度上昇に起因する凝着と、その拡大を抑制することが効果的である。凝着は、接触部の塑性変形により拡大するため、塑性変形を抑制する高い表面硬さと高い降伏強度が望ましく、また、凝着部の拡大を防止する意味で、凝着部の破断が促進されることが有効と考えられている。 Seizure is a phenomenon in which an oil film breaks due to an increase in surface temperature caused by slipping, whereby direct contact between metals occurs, and adhesion between the metals in contact occurs. Generally, when the oil film parameter h / σ, which is the ratio of the oil film thickness h to the surface roughness σ, becomes 2 or less, the risk of seizure increases, and the flash temperature on the contact surface due to slip exceeds 140 ° C. It is said that seizure occurs. In order to improve the seizure resistance, it is effective to suppress the adhesion caused by the temperature rise accompanying the slip and the expansion thereof. Adhesion expands due to plastic deformation of the contact area, so high surface hardness and high yield strength to suppress plastic deformation are desirable, and fracture of the adhesion area is promoted to prevent the adhesion area from expanding. Is considered effective.

歯車に関しては、浸炭後、焼入れしても芯部にフェライトを発生せず、かつ、再加熱しても軟化抵抗を有するものが開発された（特許文献１）。この浸炭歯車用鋼は、重量で、Ｃ：０．１８〜０．２５％、Ｓｉ：０．４５〜１．００％、Ｍｎ：０．４〜０．７％、Ｎｉ：０．３〜０．７％、Ｃｒ：１．０〜１．５％、Ｍｏ：０．３〜０．７％、Ｃｕ：０．７０％以下、Ａｌ：０．０１５〜０．０３０％、Ｖ：０．０３〜０．３０％、Ｎｂ：０．０１〜０．０３％、Ｏ：０．００１５％以下およびＮ：０．０１〜０．０２％を含有し、残部が実質上Ｆｅからなる合金組成を有し、浸炭層の硬さが、浸炭焼入れ焼戻し後の硬さに比べてＨＶ５０以上低下しないものである。 As for the gear, a gear that does not generate ferrite in the core portion even after quenching after carburizing and has a softening resistance even after reheating has been developed (Patent Document 1). This carburized gear steel is C: 0.18-0.25%, Si: 0.45-1.00%, Mn: 0.4-0.7%, Ni: 0.3-0 by weight. 0.7%, Cr: 1.0 to 1.5%, Mo: 0.3 to 0.7%, Cu: 0.70% or less, Al: 0.015 to 0.030%, V: 0.03 -0.30%, Nb: 0.01-0.03%, O: 0.0015% or less and N: 0.01-0.02%, with the balance being substantially composed of Fe However, the hardness of the carburized layer does not decrease by HV50 or more compared to the hardness after carburizing, quenching and tempering.

軸受を対象とする発明では、すべり接触を伴う転がり軸受において、すべり接触する部品を黒鉛、セメンタイトおよびフェライトを主成分とする素材で製作し、黒鉛の平均粒径が１〜５μｍ、黒鉛の総含有量が面積率で０．１〜２．５％となるように均一に分散させたものがある（特許文献２）。この転がり軸受の材料とする鋼は、黒鉛を析出させるために、０．４５〜０．８０％という多量のＣを含有する。 In the invention for bearings, in rolling bearings with sliding contact, the parts that make sliding contact are made of materials mainly composed of graphite, cementite and ferrite, the average particle size of graphite is 1-5 μm, and the total content of graphite Some are uniformly dispersed so that the amount is 0.1 to 2.5% in area ratio (Patent Document 2). The steel used as the material for this rolling bearing contains a large amount of C of 0.45 to 0.80% in order to precipitate graphite.

やはり転がり軸受に属する支持装置において、焼付き寿命特性にすぐれたものとして、針状ころ軸受の外輪に、重量で、Ｃ：０．３〜１．１％、Ｓｉ：０．１５〜１．５％、Ｃｒ：０．５〜１．８％、Ｍｎ：０．１５〜１．８％を含有し、残部Ｆｅおよび不可避の不純物からなる合金を用い、浸炭窒化および焼入れ焼戻しを施して、表面のＳｉ濃度とＮ濃度（ともに重量％）との積が０．０８〜０．９１となるようにした、耐焼き付き材料を使用することが提案された（特許文献３）。
特開平７−２５８７９３ 特開平１１−８０８３８ 特開２００４−２２５７４３ In the support device that also belongs to the rolling bearing, the outer ring of the needle roller bearing has C: 0.3 to 1.1% by weight, Si: 0.15 to 1.5, as having excellent seizure life characteristics. %, Cr: 0.5 to 1.8%, Mn: 0.15 to 1.8%, an alloy composed of the remainder Fe and inevitable impurities, carbonitrided and quenched and tempered, It has been proposed to use an anti-seizure material in which the product of the Si concentration and the N concentration (both by weight) is 0.08 to 0.91 (Patent Document 3).
JP-A-7-258793 JP-A-11-80838 JP 2004-225743 A

発明者らは、ＳＣｒ４２０鋼に代表される浸炭鋼をベースとする軸受鋼および軸受部品の改良を意図し、検討の結果、浸炭焼入れ・焼戻しまたは浸炭窒化焼入れ・焼戻し処理により形成された表面硬さが、３００℃での焼戻し処理によりどの程度低下するかという度合い（これを本発明において「３００℃焼戻軟化抵抗」と呼ぶ）が、耐焼付き性と高い相関を示すことを見出した。これは、焼付き発生時の表面温度が２００〜３００℃であること、すべりに起因した閃光温度による瞬間的温度上昇時に表面硬さが低下する程度が大きい鋼ほど、温度上昇に伴う塑性変形の変化量も大きく、油膜破断を生じやすくなるためと考えられる。 The inventors intend to improve bearing steel and bearing parts based on carburized steel typified by SCr420 steel, and as a result of investigation, surface hardness formed by carburizing quenching / tempering or carbonitriding quenching / tempering treatment. However, it has been found that the degree of reduction by tempering at 300 ° C. (this is referred to as “300 ° C. temper softening resistance” in the present invention) is highly correlated with seizure resistance. This is because the surface temperature at the time of seizure occurrence is 200 to 300 ° C., and the steel whose degree of surface hardness is large when the instantaneous temperature rise due to flash temperature due to slip is large, the plastic deformation accompanying the temperature rise It is considered that the amount of change is large and oil film breakage tends to occur.

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、すべりを伴う接触疲労あるいは潤滑油が希薄な環境下においても、すぐれた耐摩耗性と耐焼付き性、および転動疲労寿命を有する浸炭軸受部品を提供することにある。 The present invention has been made in the background as described above, and the object of the present invention is to provide excellent wear resistance and seizure resistance, as well as rolling resistance even in an environment where slipping contact fatigue or lubricating oil is scarce. It is to provide a carburized bearing part having a dynamic fatigue life.

上記の目的を達成する本発明の浸炭または浸炭窒化した軸受鋼部品は、重量基準で、Ｃ：０．１％以上０．３％未満、Ｓｉ：０．４〜２％、Ｍｎ：１．５％以下、Ｐ：０．０３％以下、Ｓ：０．０３％以下、Ｃｒ：０．３〜２．５％およびＡｌ：０．００５〜０．０５０％を含有し、Ｔｉ：０．００３％以下、Ｏ：０．００１５％以下、Ｎ：０．０２５％以下であって、残部が実質上Ｆｅからなる合金組成を有する鋼を部品形状に成形してなり、浸炭焼入れ・焼戻しまたは浸炭窒化焼入れ・焼戻し処理後の表面硬さが５８ＨＲＣ以上であって、（浸炭焼入れ・焼戻しまたは浸炭窒化焼入れ・焼戻し処理後の表面硬さ）−（３００℃での焼戻し処理後の表面硬さ）として定義される３００℃焼戻し軟化抵抗が１３０Ｈｖ以下であることを特徴とする軸受鋼部品である。 The carburized or carbonitrided bearing steel part of the present invention that achieves the above object is C: 0.1% or more and less than 0.3%, Si: 0.4-2%, Mn: 1.5 based on weight. %: P: 0.03% or less, S: 0.03% or less, Cr: 0.3 to 2.5% and Al: 0.005 to 0.050%, Ti: 0.003% Hereinafter, steel having an alloy composition of O: 0.0015% or less and N: 0.025% or less, the balance being substantially made of Fe, is formed into a part shape, and carburized, tempered, or carbonitrided. -The surface hardness after tempering is 58HRC or more, and is defined as (surface hardness after tempering at 300 ° C)-(surface hardness after carburizing and tempering or carbonitriding and quenching and tempering) 300 ° C. temper softening resistance is 130 Hv or less That is bearing steel parts.

本発明によれば、固有の合金組成の選択によって浸炭処理あるいは浸炭窒化処理を行なうことにより、すべりを伴う接触疲労が生じる環境、あるいは潤滑油が希薄な環境下で、すぐれた耐摩耗性と耐焼付き性を有し、転動疲労寿命が長い浸炭または浸炭窒化した軸受鋼部品を提供することができる。 According to the present invention, by performing carburizing treatment or carbonitriding treatment by selecting a specific alloy composition, excellent wear resistance and calcination resistance can be obtained in an environment in which contact fatigue accompanied by slip occurs or an environment where the lubricating oil is dilute. It is possible to provide a carburized or carbonitrided bearing steel part having a sticking property and a long rolling fatigue life.

本発明の浸炭または浸炭窒化した軸受鋼部品の材料としては、前記した合金成分に加えて、Ｎｉ：０．２５〜３．５％、Ｍｏ：０．０３〜２．５％、Ｖ：０．０５〜１．０％およびＮｂ：０．１％以下の１種または２種以上を含有し、残部が実質上Ｆｅからなる合金組成を有する鋼を使用することができる。 In addition to the alloy components described above, Ni: 0.25 to 3.5%, Mo: 0.03 to 2.5%, and V: 0.00. It is possible to use steel having an alloy composition that contains one or two or more of 05 to 1.0% and Nb: 0.1% or less, and the balance substantially consists of Fe.

以下に、本発明の軸受鋼部品の材料とする浸炭または浸炭窒化して使用する鋼の合金組成を、上記のように選択した理由を説明する。 The reason why the alloy composition of the steel used by carburizing or carbonitriding as the material of the bearing steel part of the present invention is selected as described above will be described below.

Ｃ：０．１％以上０．３％未満
Ｃは軸受として必要な強度を得るとともに、浸炭処理後に十分な表面硬さを確保する上で０．１％以上必要である。ただし、０．３％以上になると靭性および被削性が低下する。 C: 0.1% or more and less than 0.3% C needs to be 0.1% or more for obtaining sufficient strength as a bearing and securing sufficient surface hardness after carburizing treatment. However, when it is 0.3% or more, toughness and machinability are lowered.

Ｓｉ：０．４〜２％
Ｓｉは、焼き入れマルテンサイト組織を緻密なものとし、鋼の靭性や耐疲労特性を向上させる上で有用である。発明者らの見出したところでは、３００℃軟化抵抗はＳｉ量と相関があり、軟化抵抗を改善する合金元素としてＳｉを添加することが有効であり、それによって耐焼付き性が向上する。Ｓｉ量が０．４％より少ないと、そのような効果が得られない。一方、２％を超えると、靭性および加工性が低下する。窒化によっても３００℃軟化抵抗は改善されるため、浸炭窒化処理によっても耐焼付性を向上させることができる。 Si: 0.4-2%
Si is useful for improving the toughness and fatigue resistance of steel by making the quenched martensite structure dense. As found by the inventors, the 300 ° C. softening resistance has a correlation with the amount of Si, and it is effective to add Si as an alloy element that improves the softening resistance, thereby improving seizure resistance. If the Si amount is less than 0.4%, such an effect cannot be obtained. On the other hand, if it exceeds 2%, toughness and workability are lowered. Since the softening resistance at 300 ° C. is improved by nitriding, seizure resistance can be improved by carbonitriding.

Ｍｎ：１．５％以下
Ｍｎは、鋼の溶製時に脱酸および脱硫元素として作用するとともに、鋼の焼入れ性を高める上で有効な元素である。ただし、１．５％を超えると加工性および被削性が低下する。 Mn: 1.5% or less Mn acts as a deoxidation and desulfurization element during the melting of steel and is an element effective in enhancing the hardenability of steel. However, if it exceeds 1.5%, the workability and machinability deteriorate.

Ｐ：０．０３％以下、Ｓ：０．０３％以下
ＰおよびＳは、軸受部品の強度を低下させる。そこで、含有量をそれぞれ上記の限度以下に規制する。 P: 0.03% or less, S: 0.03% or less P and S lower the strength of the bearing component. Therefore, each content is regulated to the above limit or less.

Ｃｒ：０．３〜２．５％
Ｃｒは鋼の焼入れ性および焼入れ・焼戻し後の靭性を向上させるのに有効な元素であり、そのために０．３％以上含有させる。２．５％を超えると鋼の靭性および加工性を低下させるので、この値を上限とした。 Cr: 0.3-2.5%
Cr is an element effective for improving the hardenability of steel and the toughness after quenching and tempering. For this purpose, it is contained in an amount of 0.3% or more. If it exceeds 2.5%, the toughness and workability of the steel are lowered, so this value was made the upper limit.

Ａｌ：０．００５〜０．０５０％
ＡｌはＡｌＮとなって結晶粒を微細化する効果があり、この目的で０．００５％以上添加する。０．０５０％を超えて多量に含有させると、鋼の清浄度が低下するとともに、結晶粒の粗大化防止効果がかえって低下する。 Al: 0.005 to 0.050%
Al becomes AlN and has an effect of refining crystal grains. For this purpose, 0.005% or more is added. When it is contained in a large amount exceeding 0.050%, the cleanliness of the steel is lowered and the effect of preventing the coarsening of the crystal grains is lowered.

Ｔｉ：０．００３％以下
Ｔｉは、鋼の原料を吟味しないと混入する成分であって、硬質析出物ＴｉＮを生成し、それが転動疲労破壊の起点となって、疲労寿命の低下を引き起こす。そこで、Ｔｉの含有量を０．００３％以下に規制する。 Ti: 0.003% or less Ti is a component to be mixed unless the steel raw materials are examined, and produces a hard precipitate TiN, which becomes a starting point of rolling fatigue failure and causes a decrease in fatigue life. . Therefore, the Ti content is restricted to 0.003% or less.

Ｏ：０．００１５％以下
Ｏは鋼の清浄度を低下させ、疲労寿命を低下させる原因となる。そこでＯの含有量を０．００１５％以下に規制する。 O: 0.0015% or less O decreases the cleanliness of steel and decreases the fatigue life. Therefore, the O content is regulated to 0.0015% or less.

Ｎ：０．０２５％以下
ＮはＡｌと結合してＡｌＮを生成し、結晶粒を微細化する働きをする。多量に含有させると、かえって鋼の強度を低下させる。そこで、Ｎの含有量の上限を０．０２５％とする。好ましい範囲は、０．０１〜０．０２％である。 N: 0.025% or less N combines with Al to produce AlN, and serves to refine crystal grains. If contained in a large amount, the strength of the steel is lowered. Therefore, the upper limit of the N content is 0.025%. A preferable range is 0.01 to 0.02%.

Ｎｉ：０．２５〜３．５％
Ｎｉは鋼の焼入れ性および焼入れ・焼戻し後の強度および靭性を向上させるのに有効な元素であり、所望により０．２５％以上含有させるとよい。３．５％を超えると、鋼の靭性および加工性を低下させる。 Ni: 0.25 to 3.5%
Ni is an element effective for improving the hardenability of steel and the strength and toughness after quenching and tempering, and it may be contained in an amount of 0.25% or more if desired. When it exceeds 3.5%, the toughness and workability of steel are reduced.

Ｍｏ：０．０３〜２．５％、
Ｍｏは鋼の強度を向上させる上で有用な元素であり、選択元素として添加する場合には、この効果が確実に得られる０．０３％以上の添加量を選ぶ。２．５％よりも多く含有させると、焼き入れ性が低下すると同時に被削性も低下するので、この値を上限とした。Ｍｏはまた、軟化抵抗を改善するとともに、微細な炭（窒）化物が析出することにより、耐焼付き性の改善にも寄与する。 Mo: 0.03-2.5%,
Mo is an element useful for improving the strength of the steel, and when added as a selective element, an addition amount of 0.03% or more is selected so that this effect can be surely obtained. If the content is more than 2.5%, the hardenability is lowered and the machinability is also lowered. Therefore, this value is set as the upper limit. Mo also improves softening resistance and contributes to improvement of seizure resistance by precipitation of fine charcoal (nitride).

Ｖ：０．０５〜１．０％、Ｎｂ：０．１％以下
ＶおよびＮｂは、結晶粒の微細化に寄与する元素であるが、含有量が多すぎるとその効果が小さくなるため、選択元素として添加する場合に、Ｖについては０．０５〜１．０％、Ｎｂについては０．１％以下の範囲の添加量を選ぶ。Ｖの添加は、耐焼付き性の一層の改善をもたらす。これは、微細炭化物の分散析出により凝着部の破断が促進されることにより、凝着部の拡大が抑制されるためと考えられる。 V: 0.05 to 1.0%, Nb: 0.1% or less V and Nb are elements that contribute to the refinement of crystal grains. However, if the content is too large, the effect is reduced. When adding as an element, the addition amount is selected in the range of 0.05 to 1.0% for V and 0.1% or less for Nb. Addition of V brings about further improvement of seizure resistance. This is considered to be because expansion of the adhesion portion is suppressed by accelerating the breakage of the adhesion portion due to the dispersion and precipitation of fine carbides.

表１（実施例）および表２（比較例）に示す化学組成の浸炭軸受鋼を溶製し、熱間圧延鋼材を試験用の素材とした。この素材から試験部の直径が５５mm、厚さが５mmのディスク型摩耗試験片を削り出し、図１に示す条件下に、カーボンポテンシャル０．８％で浸炭処理を行なった。つづいて機械加工を行ない、焼付き試験に供した。表面処理を浸炭窒化処理とした場合については、同様にディスク型摩耗試験片を図２に示した条件で浸炭窒化処理した後、図３に示した条件の二次焼入れ・焼戻しを行ない、つづいて機械加工を行なったものを、焼付き試験に供した。 Carburized bearing steels having chemical compositions shown in Table 1 (Examples) and Table 2 (Comparative Examples) were melted, and hot-rolled steel materials were used as test materials. A disk-type wear test piece having a test portion diameter of 55 mm and a thickness of 5 mm was cut out from this material, and carburized at a carbon potential of 0.8% under the conditions shown in FIG. Subsequently, it was machined and subjected to a seizure test. When the surface treatment is carbonitriding, similarly, after subjecting the disk-type wear test piece to carbonitriding under the conditions shown in FIG. 2, secondary quenching and tempering under the conditions shown in FIG. 3 are performed. The machined product was subjected to a seizure test.

上記の試験片の試験面を、ロックウェル硬さ計を用いてＨＲＣ表面硬さを測定し、５点の平均を算出した。同じ試験片の縦断面を埋め込んで研磨し、ビッカース硬さ計を用いて表面硬さを測定した。さらに、この試験片に対して３００℃×６０分間の焼戻しを行ない、同様に表面のビッカース硬さを測定して、３００℃焼戻し前の表面硬さから３００℃焼戻し後の表面硬さの値を引いて、３００℃焼戻軟化抵抗を求めた。 The test surface of the test piece was measured for HRC surface hardness using a Rockwell hardness tester, and an average of 5 points was calculated. A vertical section of the same specimen was embedded and polished, and the surface hardness was measured using a Vickers hardness tester. Further, the test piece was tempered at 300 ° C. for 60 minutes, and the surface Vickers hardness was measured in the same manner, and the surface hardness value after tempering at 300 ° C. was calculated from the surface hardness before tempering at 300 ° C. By subtracting, 300 ° C. temper softening resistance was obtained.

焼付き試験にはピンオンディスク試験機を用い、回転するディスク試験片に、相手材として直径８mm×長さ２０mmのＳＵＪ２ピン（２本）を押し付けて行なった。試験は、すべり速度５ｍ/ｓ、タービン＃６８連続潤滑の条件下である。荷重負荷条件は、初期荷重１０kgfから１分間隔で１０kgfづつ漸増した。試験中にディスクとピンとの間の摩擦により生じるトルクを連続的に測定し、このトルクの急激な上昇によって焼付きを判定し、焼付き発生時の荷重を求めた。 The seizure test was performed by using a pin-on-disk tester and pressing two SUJ2 pins having a diameter of 8 mm and a length of 20 mm as a mating member against a rotating disk test piece. The test was performed under conditions of a sliding speed of 5 m / s and turbine # 68 continuous lubrication. The load condition increased gradually from the initial load of 10 kgf by 10 kgf at 1 minute intervals. During the test, the torque generated by the friction between the disk and the pin was continuously measured, and seizure was judged by the rapid increase in torque, and the load at the time of seizure was obtained.

この素材から試験部の直径が６３mmのスラスト型転動疲労試験片を削り出し、図１に示す条件下にカーボンポテンシャル０．８％で浸炭処理を行なった後、機械加工およびラッピング加工によって表面研磨を行ない、転動疲労試験に供した。スラスト転動疲労試験条件は、つぎのとおりである。
試験片形状： φ６３×φ２８．７×ｔ８．８（mm）
転動体： ３／８インチＳＵＪ２ボール３個
接触応力： Ｐmax＝５．５ＧＰａ
負荷回転速度：１８００rpm
潤滑： タービン油＃６８油浴給油
試験温度： 常温 A thrust type rolling fatigue test piece having a diameter of 63 mm is cut out from this material, carburized at a carbon potential of 0.8% under the conditions shown in FIG. 1, and then polished by machining and lapping. And subjected to a rolling fatigue test. The thrust rolling fatigue test conditions are as follows.
Test piece shape: φ63 × φ28.7 × t8.8 (mm)
Rolling element: 3/8 inch SUJ2 3 balls Contact stress: Pmax = 5.5 GPa
Load rotation speed: 1800rpm
Lubrication: Turbine oil # 68 oil bath lubrication test temperature: normal temperature

浸炭窒化処理については、同様にスラスト型転動疲労試験片を、図２に示す条件で浸炭窒化処理後、図３に示した二次焼入れ・焼戻しを行ない、その後機械加工を行なったものを転動疲労試験に供した。表３（実施例）および表４（比較例）に浸炭処理した場合の、表５（実施例）および表６（比較例）に浸炭窒化処理した場合の、それぞれ表面硬さ、３００℃焼戻軟化抵抗、焼付き荷重および転動寿命試験でのＬ₁₀寿命を示す。 Similarly, for carbonitriding, a thrust type rolling fatigue test piece was subjected to carbonitriding under the conditions shown in FIG. 2 and then subjected to secondary quenching and tempering as shown in FIG. 3, followed by machining. It was subjected to a dynamic fatigue test. Table 3 (Example) and Table 4 (Comparative Example) when carburized, and Table 5 (Example) and Table 6 (Comparative Example) when carbonitrided, surface hardness and 300 ° C. tempered, respectively. L ₁₀ life in softening resistance, seizure load and rolling life test is shown.

浸炭処理材においては、表３および表４にみるように、本発明に従った鋼の表層硬さは５８ＨＲＣ以上である。３００℃焼戻軟化抵抗は１３０Ｈｖ以下であって、この限界を超える軟化傾向を示す比較鋼にくらべて軟化抵抗性がすぐれており、それに伴って耐焼付き荷重も高い。転動疲労寿命においても、本発明のものは、比較鋼にくらべてすぐれた性能を有する。 In the carburized material, as shown in Table 3 and Table 4, the surface hardness of the steel according to the present invention is 58 HRC or more. The temper softening resistance at 300 ° C. is 130 Hv or less, and the softening resistance is superior to the comparative steel showing a softening tendency exceeding this limit, and accordingly, the seizure load is high. Also in rolling fatigue life, the thing of this invention has the outstanding performance compared with comparative steel.

一方、浸炭窒化処理材に関しては、表５および表６のデータが示すように、浸炭材と比較したとき、窒化により焼戻し軟化抵抗が一層高まっている。このため、浸炭窒化材では、本発明の実施例も比較例も、耐焼付き性が浸炭材にくらべて向上している。しかし、本発明の実施例は、焼戻し軟化抵抗、耐焼付き荷重、転動疲労寿命のいずれに関しても比較例よりすぐれていることは、浸炭材と同様である。 On the other hand, regarding the carbonitrided material, as shown in the data in Tables 5 and 6, when compared with the carburized material, the temper softening resistance is further increased by nitriding. For this reason, in the carbonitrided material, the seizure resistance is improved compared to the carburized material in both the examples and comparative examples of the present invention. However, the examples of the present invention are superior to the comparative examples in terms of temper softening resistance, seizure resistance load, and rolling fatigue life, similar to the carburized material.

上述の試験結果について、３００℃焼戻し軟化抵抗と焼付き荷重との関係を、図４にまとめて示す。焼付き荷重は軟化抵抗の値が小さいほど増大し、両者の間に明瞭な相関が認められる。この図に見るように、本発明で限定した軟化抵抗１３０Ｈｖ以下の領域においては、焼付き荷重１００kgf以上という、本発明で目標としたレベルが維持されている。 About the above-mentioned test result, the relationship between 300 degreeC temper softening resistance and a seizing load is put together in FIG. The seizure load increases as the softening resistance value decreases, and a clear correlation is observed between the two. As shown in this figure, in the region of the softening resistance of 130 Hv or less limited in the present invention, the target level in the present invention of seizing load of 100 kgf or more is maintained.

同じく本発明の実施データから得た、焼戻し軟化抵抗とＳｉ量との関係を、図５にまとめて示す。軟化抵抗はＳｉ量と高い相関があること、および、窒化により軟化抵抗の値が改善されることがわかる。この試験結果は、すべり速度５ｍ／ｓの条件における結果であるが、焼付き性はすべり速度Ｖと接触面圧ｐの積ｐＶ値でほぼ決定されるから、本発明に従った軸受に関して、広いすべり速度範囲で同様の効果が期待できることが確認された。





























Similarly, the relationship between the temper softening resistance and the Si amount obtained from the implementation data of the present invention is shown in FIG. It can be seen that the softening resistance has a high correlation with the amount of Si, and that the value of the softening resistance is improved by nitriding. Although this test result is a result under the condition of a sliding speed of 5 m / s, the seizure property is almost determined by the product pV value of the sliding speed V and the contact surface pressure p. It was confirmed that the same effect can be expected in the sliding speed range.

本発明の実施例における、供試材の浸炭処理すなわち浸炭焼き入れ・焼戻しの条件（温度、保持時間および冷却方法）を観念的に示す図。The figure which shows notionally the carburizing process of the test material in the Example of this invention, ie, the conditions (temperature, holding time, and cooling method) of carburizing quenching and tempering. 本発明の実施例における、供試材の浸炭窒化処理すなわち浸炭窒化焼き入れ・焼戻しの条件（温度、保持時間および冷却方法）を観念的に示す図。The figure which shows notionally the carbonitriding process of the test material in the Example of this invention, ie, the carbonitriding quenching and tempering conditions (temperature, holding time, and cooling method). 本発明の実施例における、供試材の二次焼入れ・焼戻し処理の条件（温度、保持時間および冷却方法）を観念的に示す図。The figure which shows notionally the conditions (temperature, holding | maintenance time, and cooling method) of the secondary quenching and tempering process of the test material in the Example of this invention. 本発明の実施例のデータをまとめたものであって、３００℃焼戻軟化抵抗と焼付き荷重との関係を示すグラフ。The data which summarized the data of the Example of this invention, Comprising: The graph which shows the relationship between 300 degreeC temper softening resistance and seizure load. 本発明の実施例のデータをまとめたものであって、３００℃焼戻軟化抵抗とＳｉ含有量との関係を示すグラフ。The data which summarized the data of the Example of this invention, Comprising: The graph which shows the relationship between 300 degreeC temper softening resistance and Si content.

Claims (2)

重量基準で、Ｃ：０．１％以上０．３％未満、Ｓｉ：０．４〜２％、Ｍｎ：１．５％以下、Ｐ：０．０３％以下、Ｓ：０．０３％以下、Ｃｒ:０．３〜２．５％およびＡｌ：０．００５〜０．０５０％を含有し、Ｔｉ：０．００３％以下、Ｏ：０．００１５％以下、Ｎ:０．０２５％以下であって、残部が実質上Ｆｅからなる合金組成を有する鋼を部品形状に成形してなり、浸炭焼入れ・焼戻しまたは浸炭窒化焼入れ・焼戻し処理後の表面硬さが５８ＨＲＣ以上であって、（浸炭焼入れ・焼戻しまたは浸炭窒化焼入れ・焼戻し処理後の表面硬さ）−（３００℃での焼戻し処理後の表面硬さ）として定義される３００℃焼戻し軟化抵抗が１３０Ｈｖ以下であることを特徴とする浸炭または浸炭窒化した軸受鋼部品。 On the basis of weight, C: 0.1% or more and less than 0.3%, Si: 0.4-2%, Mn: 1.5% or less, P: 0.03% or less, S: 0.03% or less, Cr: 0.3 to 2.5% and Al: 0.005 to 0.050%, Ti: 0.003% or less, O: 0.0015% or less, N: 0.025% or less The balance is formed into a part shape of steel having an alloy composition substantially consisting of Fe, and the surface hardness after carburizing / tempering or carbonitriding / quenching / tempering treatment is 58 HRC or more, Carburization or carburization characterized by having a 300 ° C. temper softening resistance of 130 Hv or less, defined as (surface hardness after tempering or carbonitriding quenching / tempering treatment) − (surface hardness after tempering treatment at 300 ° C.) Nitrided bearing steel parts. 前記した合金成分に加えて、Ｎｉ：０．２５〜３．５％、Ｍｏ：０．０３〜２．５％、Ｖ:０．０５〜１．０％およびＮｂ:０．１％以下の１種または２種以上を含有し、残部が実質上Ｆｅからなる合金組成を有する鋼を部品形状に成形してなり、前記した表面硬さおよび焼戻し軟化抵抗を有する請求項１の浸炭または浸炭窒化した軸受鋼部品。
In addition to the alloy components described above, Ni: 0.25 to 3.5%, Mo: 0.03 to 2.5%, V: 0.05 to 1.0%, and Nb: 0.1% or less 1 The carburized or carbonitrided carbon steel according to claim 1, which has a surface shape and a temper softening resistance, and is formed of a steel having an alloy composition containing seeds or two or more, the balance being substantially composed of Fe. Bearing steel parts.

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