JP3990213B2 - Bearing parts and rolling bearings - Google Patents

Description

【００２４】
（試料Ａ〜Ｄ；本発明例）：温度８５０℃で１５０分間保持して浸炭窒化処理を施した。その浸炭窒化処理時の雰囲気は、ＲＸガスとアンモニアガスとの混合ガスとした。図２に示す熱処理パターンにおいて、浸炭窒化処理温度８５０℃から１次焼入れを行ない、次いで浸炭窒化処理温度より低い温度域７８０℃〜８３０℃に加熱して２次焼入れを行った。ただし、２次焼入れ温度７８０℃の試料Ａは焼入れ不足のため試験の対象から外した。
（試料Ｅ、Ｆ；本発明例）：浸炭窒化処理は、本発明例Ａ〜Ｄと同じ履歴で行い、２次焼入れ温度を浸炭窒素処理温度（８５０℃）以上の８５０℃〜８７０℃で行った。
（従来浸炭窒化処理品；比較例）：温度８５０℃で１５０分間保持して浸炭窒化処理を施した。その浸炭窒化処理時の雰囲気は、ＲＸガスとアンモニアガスとの混合ガスとした。その浸炭窒化処理時の温度からそのまま焼入れを行ない、２次焼入れは行わなかった。
（普通焼入れ品；比較例）：浸炭窒化処理を行なわずに、８５０℃に加熱して焼入れた。２次焼入れは行わなかった。
【００２５】
上記の各試料に対して、（１）水素量の測定、（２）結晶粒度の測定、（３）シャルピー衝撃試験、（４）破壊応力値の測定、（５）転動疲労試験、の各々を行った。その結果を表１に合わせて示す。
【００２６】
次にこれらの測定方法および試験方法について説明する。
（１）水素量の測定
水素量は、ＬＥＣＯ社製ＤＨ−１０３型水素分析装置により、鋼中の非拡散性水素量を分析した。拡散性水素量は測定してない。このＬＥＣＯ社製ＤＨ−１０３型水素分析装置の仕様を下記に示す。
【００２７】
分析範囲：０．０１〜５０．００ｐｐｍ
分析精度：±０．１ｐｐｍまたは±３％Ｈ（いずれか大なるほう）
分析感度：０．０１ｐｐｍ
検出方式：熱伝導度法
試料重量サイズ：１０ｍｇ〜３５ｇ（最大：直径１２ｍｍ×長さ１００ｍｍ）
加熱炉温度範囲：５０℃〜１１００℃
試薬：アンハイドロン（Ｍｇ（ＣｌＯ₄）₂）、アスカライト（ＮａＯＨ）
キャリアガス：窒素ガス、ガスドージングガス（水素ガス）、いずれのガスも純度９９．９９％以上、圧力４０ＰＳＩ（２．８ｋｇｆ／ｃｍ²）である。
【００２８】
測定手順の概要は以下のとおりである。専用のサンプラーで採取した試料をサンプラーごとに上記の水素分析装置に挿入する。内部の拡散性水素は窒素キャリアガスによって熱伝導度検出器に導かれる。この拡散性水素は本実施例では測定しない。次に、サンプラーから試料を取出し抵抗加熱炉内で加熱し、非拡散性水素を窒素キャリアガスによって熱伝導度検出器に導く。熱伝導度検出器において熱伝導度を測定することによって非拡散性水素量を知ることができる。
（２）結晶粒度の測定
結晶粒度の測定は、ＪＩＳ Ｇ ０５５１の鋼のオーステナイト結晶粒度試験方法に基づいて行った。
（３）シャルピー衝撃試験
シャルピー衝撃試験は、ＪＩＳ Ｚ ２２４２の金属材料のシャルピー衝撃試験方法に基づいて行った。試験片には、ＪＩＳ Ｚ ２２０２に示されたＵノッチ試験片（ＪＩＳ３号試験片）を用いた。なお、シャルピー衝撃値は、次式の吸収エネルギーＥを断面積（０．８ｃｍ²）で除した値である。
【００２９】
吸収エネルギー：Ｅ＝ＷｇＲ（ｃｏｓβ−ｃｏｓα）
Ｗ：ハンマー重量（＝２５．４３８ｋｇ）
ｇ：重力加速度（＝９．８０６６５ｍ／ｓｅｃ²）
Ｒ：ハンマー回転軸中心から重心までの距離（＝０．６５６９ｍ）
α：ハンマー持ち上げ角度（＝１４６°）、β：ハンマー降り上がり角度
（４）破壊応力値の測定
図６に破壊応力値の測定に用いた試験片を示す。アムスラー万能試験機を用いて図中のＰ方向に荷重を負荷して試験片が破壊されるまでの荷重を測定する。その後、得られた破壊荷重を、下記に示す曲がり梁の応力計算式により応力値に換算する。なお、試験片は図６に示す試験片に限られず、他の形状の試験片を用いてもよい。
【００３０】
図６の試験片の凸表面における繊維応力をσ₁、凹表面における繊維応力をσ₂とすると、σ₁およびσ₂は下記の式によって求められる（機械工学便覧Ａ４編材料力学Ａ４−４０）。ここで、Ｎは円環状試験片の軸を含む断面の軸力、Ａは横断面積、ｅ₁は外半径、ｅ₂は内半径を表す。また、κは曲がり梁の断面係数である。
【００３１】
σ₁＝（Ｎ／Ａ）＋｛Ｍ／（Ａρ_o）｝［１＋ｅ₁／｛κ（ρ_o＋ｅ₁）｝］
σ₂＝（Ｎ／Ａ）＋｛Ｍ／（Ａρ_o）｝［１−ｅ₂／｛κ（ρ_o−ｅ₂）｝］
κ＝−（１／Ａ）∫_A ｛η／（ρ_o＋η）｝ｄＡ
（５）転動疲労試験、
転動疲労寿命試験の試験条件および試験装置の略図を、表２および図７に示す。図７において、転動疲労寿命試験片２１は、駆動ロール１１によって駆動され、ボール１３と接触して回転している。ボール１３は、（3/4）”のボールであり、案内ロール１２にガイドされて、転動疲労寿命試験片２１との間で高い面圧を及ぼし合いながら転動する。
【００３２】
次に上記の測定結果および試験結果について説明する。
（１） 水素量
表１より、浸炭窒化処理したままの従来浸炭窒化処理品の鋼中水素量は、０．７２ｐｐｍと非常に高い値となっている。これは、浸炭窒化処理の雰囲気に含まれるアンモニア（ＮＨ₃）が分解して水素が鋼中に侵入したためと考えられる。これに対して、試料Ｂ〜Ｆの鋼中水素量は０．３７〜０．４２ｐｐｍとなっており、従来浸炭窒化処理品の半分近くにまで減少している。この鋼中水素量は普通焼入れ品と同じレベルである。
【００３３】
上記の鋼中水素量の低減により、水素の固溶に起因する鋼の脆化を軽減することができる。すなわち、水素量の低減により、本発明例の試料Ｂ〜Ｆのシャルピー衝撃値および破壊応力値は大きく改善されている。
（２） 結晶粒度
表１より、結晶粒度は、２次焼入れ温度が浸炭窒化処理時の焼入れ（１次焼入れ）の温度より低い場合、すなわち試料Ｂ〜Ｄの場合、オーステナイト粒は、結晶粒度番号１１〜１２と顕著に微細化されている。試料ＥおよびＦならびに従来浸炭窒化処理品および普通焼入品のオーステナイト粒は、結晶粒度番号１０であり、試料Ｂ〜Ｄより粗大な結晶粒となっている。
（３） シャルピー衝撃値
表１によれば、従来浸炭窒化処理品のシャルピー衝撃値は５．３３Ｊ／ｃｍ²であるのに比して、本発明例の試料Ｂ〜Ｆのシャルピー衝撃値は６．２０〜６．６５Ｊ／ｃｍ²と高い値が得られている。この中でも、２次焼入れ温度が低いほうがシャルピー衝撃値が高くなる傾向を示す。なお、普通焼入品のシャルピー衝撃値は６．７０Ｊ／ｃｍ²と高い。
（４） 破壊応力値
上記破壊応力値は、耐割れ強度に相当する。表１によれば、従来浸炭窒化処理品は２３３０ＭＰａの破壊応力値となっている。これに比して、試料Ｂ〜Ｆの破壊応力値は２６５０〜２８４０ＭＰａと改善されている。普通焼入品の破壊応力値は２７７０ＭＰａであり、試料Ｂ〜Ｆの破壊応力値と同等である。このような、試料Ｂ〜Ｆの改良された耐割れ強度は、オーステナイト結晶粒の微細化と並んで、水素含有率の低減による効果が大きいと推定される。
（５） 転動疲労試験
表１によれば、普通焼入品は浸炭窒化層を表層部に有しないことを反映して、転動疲労寿命Ｌ₁₀は最も低い。これに比して従来浸炭窒化処理品の転動疲労寿命は３．１倍となる。試料Ｂ〜Ｄの転動疲労寿命は従来浸炭窒化処理品より大幅に向上する。試料Ｅ，Ｆは、従来浸炭窒化処理品とほぼ同等であった。
【００３４】
上記をまとめると、本発明例の試料Ｂ〜Ｆでは、鋼中水素量が低くなり、破壊応力値やシャルピー衝撃値が向上する。しかし、転動疲労寿命まで含めて改良しうるのは、さらにオーステナイト結晶粒度を粒度番号で１１番程度以上に微細化した試料Ｂ〜Ｄである。したがって、本発明例に該当するのは試料Ｂ〜Ｆであるが、より望ましい本発明の範囲は、２次焼入れ温度を浸炭窒化処理温度より低くして結晶粒の微細化をさらに図った試料Ｂ〜Ｄの範囲である。
【００３５】
（実施例２）
次に実施例２について説明する。
【００３６】
下記のＡ材、Ｂ材およびＣ材について、一連の試験を行った。熱処理用素材には、ＪＩＳ規格ＳＵＪ２材（１．０重量％Ｃ−０．２５重量％Ｓｉ−０．４重量％Ｍｎ−１．５重量％Ｃｒ）を用い、Ａ材〜Ｃ材に共通とした。Ａ材〜Ｃ材の製造履歴は次のとおりである。
（Ａ材：比較例）：普通焼入れのみを行なった（浸炭窒化処理せず）。
（Ｂ材：比較例）：浸炭窒化処理後にそのまま焼き入れた（従来の浸炭窒化焼入れ）。浸炭窒化処理の温度を８４５℃とし、保持時間を１５０分間とした。また浸炭窒化処理の雰囲気を、ＲＸガス＋アンモニアガスとした。
（Ｃ材：本発明例）：軸受鋼に図２の熱処理パターンを施した。浸炭窒化処理の温度を８４５℃とし、保持時間を１５０分間とし、雰囲気をＲＸガス＋アンモニアガスとした。また、最終焼入れ温度を８００℃とした。
【００３７】
（１） 転動疲労寿命
転動疲労寿命試験の試験装置には上述した図７の装置を用い、試験条件は表２に示す条件とした。この転動疲労寿命試験結果を表３に示す。
【００３８】
【表２】

【００３９】
【表３】

【００４０】
表３によれば、浸炭窒化処理を施したＢ材（比較例）のＬ₁₀寿命は、普通焼入れのみを施したＡ材（比較例）のＬ₁₀寿命（試験片１０個中１個が破損する寿命）の３.１倍を示し、浸炭窒化処理による長寿命化の効果が認められる。これに対して、本発明例のＣ材は、Ｂ材の１．７４倍、またＡ材の５．４倍の長寿命を示している。この改良の主因はミクロ組織の微細化によるものと考えられる。
【００４１】
（２） シャルピー衝撃試験
シャルピー衝撃試験は、Ｕノッチ試験片を用いて、上述のＪＩＳ Ｚ ２２４２に準じた方法により行なった。試験結果を表４に示す。
【００４２】
【表４】

【００４３】
本発明例のＣ材では、普通焼入れのみを施したＡ材（比較例）と同等で、かつ浸炭窒化処理を施したＢ材（比較例）よりも高いシャルピー衝撃値が得られた。
【００４４】
（３） 静的破壊靭性値の試験
静的破壊靭性試験の試験片には、図８に示す試験体を用い、亀裂を予め約１ｍｍ導入した後に、３点曲げによる静的荷重Ｐを加え、破壊荷重を求めた。破壊靭性値（Ｋ_IC値）の算出には次に示す次式を用いた。また、試験結果を表５に示す。
【００４５】
Ｋ_IC＝（ＰＬ√ａ／ＢＷ²）｛５．８−９．２（ａ／Ｗ）＋４３．６（ａ／Ｗ）²−７５．３（ａ／Ｗ）³＋７７．５（ａ／Ｗ）⁴｝
【００４６】
【表５】

【００４７】
予め導入した亀裂の深さが浸炭窒化層深さよりも大きくなったため、比較例のＡ材とＢ材とには違いはない。しかし、本発明例のＣ材では比較例のＡ材およびＢ材に対して約１．２倍の破壊靭性値（Ｋ_IC値）を得ることができた。
【００４８】
（４） 静圧壊強度試験（破壊応力値の測定）
静圧壊強度試験片には、上述のように図６に示す形状のものを用いた。図中、Ｐ方向に荷重を付加して、上記と同様にして静圧壊強度試験を行なった。試験結果を表６に示す。
【００４９】
【表６】

【００５０】
浸炭窒化処理を施したＢ材（比較例）の静圧壊強度は普通焼入れのみを施したＡ材（比較例）の静圧壊強度よりもやや低い値である。しかしながら、本発明例のＣ材の静圧壊強度は、Ｂ材の静圧壊強度よりも向上し、Ａ材の静圧壊強度よりもわずかに高いレベルになっている。
【００５１】
（５） 経年寸法変化率
温度１３０℃で５００時間保持した場合の経年寸法変化率を測定した。その測定結果を、表面硬度、残留オーステナイト量（表面から０．１ｍｍ深さでの）とともに表７に示す。
【００５２】
【表７】

【００５３】
残留オーステナイト量の多いＢ材の寸法変化率に比べて、本発明例のＣ材の寸法変化率は低く抑えられていることがわかる。
【００５４】
（６） 異物混入潤滑下における寿命試験
玉軸受６２０６を用い、標準異物を所定量混入させた異物混入潤滑下での転動疲労寿命を評価した。試験条件を表８に、また試験結果を表９に示す。
【００５５】
【表８】

【００５６】
【表９】

【００５７】
Ａ材に比べ、浸炭窒化処理を施したＢ材（比較例）では約２．５倍の、また本発明例のＣ材では約２．３倍の長寿命が得られた。本発明例のＣ材では、比較例のＢ材に比べて残留オーステナイトが少ないものの、窒素の侵入と微細化されたミクロ組織の影響とによりほぼ同等の長寿命が得られている。
【００５８】
上記の結果より、本発明例のＣ材、すなわち本発明の熱処理方法によって製造された軸受部品は、従来の浸炭窒化処理では困難であった転動疲労寿命の長寿命化、割れ強度の向上、経年寸法変化率の低減の３項目を同時に満足することができることがわかった。
【００５９】
今回開示された実施の形態および実施例はすべての点で例示であって制限的なものではないと考えられるべきである。本発明の範囲は上記した説明ではなくて特許請求の範囲によって示され、特許請求の範囲と均等の意味および範囲内でのすべての変更が含まれることが意図される。
【００６０】
【発明の効果】
本発明の軸受部品および転がり軸受を用いることにより、浸炭窒化処理層を形成した上で、これまでにない優れた破壊応力値を得ることができるため、優れた耐割れ強度などを得ることができる。
【図面の簡単な説明】
【図１】 本発明の実施の形態における転がり軸受を示す概略断面図である。
【図２】 本発明の実施の形態における熱処理方法を説明する図である。
【図３】 本発明の実施の形態における熱処理方法の変形例を説明する図である。
【図４】 軸受部品のミクロ組織、とくにオーステナイト粒を示す図である。(ａ)は本発明例の軸受部品であり、（ｂ）は従来の軸受部品である。
【図５】 （ａ）は図４（ａ）を図解したオーステナイト粒界を示し、（ｂ）は図４（ｂ）を図解したオーステナイト粒界を示す。
【図６】 静圧壊強度試験（破壊応力値の測定）の試験片を示す図である。
【図７】 転動疲労寿命試験機の概略図である。(ａ)は正面図であり、(ｂ)は側面図である。
【図８】 静的破壊靭性試験の試験片を示す図である。
【符号の説明】
１ 外輪、２ 内輪、３ 転動体、１０ 転がり軸受、１１ 駆動ロール、１２ 案内ロール、１３ （3/4）”ボール、２１ 転動疲労寿命試験片、Ｔ₁ 浸炭窒化処理温度、Ｔ₂ 焼入れ加熱温度。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to bearing parts and rolling bearings used for reduction gears, drive pinions, transmission bearings, etc., and relates to bearing parts and rolling bearings that have a long rolling fatigue characteristic and have high cracking resistance and aging-resistant dimensional changes. It is about.
[0002]
[Prior art]
As a heat treatment method that gives a long life against rolling fatigue of a bearing component, a method of performing a carbonitriding process on the surface layer portion of the bearing component by adding ammonia gas to the atmosphere RX gas during quenching heating, etc. (For example, JP-A-8-4774, JP-A-11-101247). By using this carbonitriding treatment method, the surface layer portion can be hardened, retained austenite can be generated in the microstructure, and the rolling fatigue life can be improved.
[0003]
[Problems to be solved by the invention]
However, since the carbonitriding method described above is a diffusion treatment that diffuses carbon and nitrogen, it must be kept at a high temperature for a long time. For this reason, it is difficult to improve the cracking resistance due to the coarsening of the structure. In addition, an increase in the dimensional change rate due to increase in retained austenite is also a problem.
[0004]
On the other hand, in order to ensure a long life against rolling fatigue, improve crack strength, and prevent an increase in the rate of dimensional change over time, it is possible to cope with the problem by adjusting the composition by the alloy design of steel. However, the alloy design causes problems such as an increase in raw material costs.
[0005]
Future bearing parts are required to have characteristics that can be used under larger load conditions and at higher temperatures than in the past as the usage environment increases in load and temperature. For this reason, a bearing component having high strength, long rolling fatigue characteristics, high cracking strength and dimensional stability is required.
[0006]
It is an object of the present invention to provide a bearing component and a rolling bearing that have high cracking resistance and dimensional stability and are excellent in rolling fatigue life.
[0007]
[Means for Solving the Problems]
Rolling bearing of the present invention, the inner ring, the rolling bearing having an outer ring and a plurality of rolling elements, the inner ring, at least one of member of the outer ring and the rolling elements have a carbonitrided layer, the fracture stress value of the member der least 2650MPa is, the grain size number of austenite crystal grains of the member is in the range exceeding number 10, the members are those characterized that you have made a JIS standard SUJ2.
[0008]
The present inventors, after the steel for the bearing parts were carbonitrided in the carbonitriding temperature exceeding the A ₁ transformation point, cooled to a temperature below the A ₁ transformation point, then the A ₁ transformation point or above the hardening temperature It was found that the fracture stress value of the steel having the carbonitriding layer can be increased to 2650 MPa or higher, which has not been obtained conventionally, by reheating and quenching the zone. Thereby, it is possible to obtain a rolling bearing having a higher fracture strength than that of the conventional one and thereby a higher strength.
[0009]
The bearing component of the present invention is a bearing component to be incorporated in the rolling bearing, and have a carbonitrided layer, the fracture stress value of Ri der least 2650 MPa, in a range grain size number of austenite crystal grains exceeds number 10 Yes, it is an feature that you have made from the JIS standard SUJ2.
[0010]
Also in this bearing part, like the above-mentioned rolling bearing, it is possible to obtain a bearing part that has an excellent fracture stress value compared to the conventional one and thereby has a high cracking strength.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0012]
FIG. 1 is a schematic cross-sectional view showing a rolling bearing in an embodiment of the present invention. In FIG. 1, this rolling bearing 10 mainly has an outer ring 1, an inner ring 2, and rolling elements 3. The drawings show radial ball bearings, but the same applies to ball bearings, tapered roller bearings, roller bearings, and needle roller bearings. The rolling element 3 is supported by a cage disposed between the outer ring 1 and the inner ring 2 so as to be able to roll.
[0013]
At least one member of the outer ring 1, the inner ring 2 and the rolling element 3 includes steel having a carbonitriding layer and has a fracture stress value of 2650 MPa or more.
[0014]
In addition, at least one member of the outer ring 1, the inner ring 2 and the rolling element 3 includes steel having a carbonitriding layer, and the hydrogen content in the steel is 0.5 ppm or less.
[0015]
Further, at least one member of the outer ring 1, the inner ring 2 and the rolling element 3 includes steel having a carbonitriding layer, and the grain size number of the austenite crystal grains of the member is in the range exceeding # 10.
[0016]
In addition, at least one member of the outer ring 1, the inner ring 2 and the rolling element 3 includes steel having a carbonitriding layer and has a Charpy impact value of 6.2 J / cm ² or more.
[0017]
Next, heat treatment including carbonitriding performed on at least one bearing component of the outer ring, the inner ring and the rolling element of the rolling bearing will be described.
[0018]
2 and 3 show a heat treatment method according to the embodiment of the present invention. FIG. 2 is a heat treatment pattern showing a method of performing primary quenching and secondary quenching, and FIG. 3 is a method of cooling the material to below the A ₁ transformation point temperature during quenching, and then re-heating and finally quenching. It is the heat processing pattern which shows. Both are exemplary embodiments of the present invention. In these figures, in treatment T ₁ , carbon and nitrogen are diffused in the steel base, and after sufficient carbon penetration, the steel is cooled to below the A ₁ transformation point. Next, in the process T ₂ of the in the figure, than the processing T ₁ is reheated to a low temperature, subjected to oil quenching from there.
[0019]
Rather than performing normal quenching, that is, carbonitriding once after the carbonitriding treatment, the crack strength can be improved and the aging change rate can be reduced while carbonitriding the surface layer portion. As described above, according to the above heat treatment method, it is possible to obtain a microstructure in which the grain size of austenite crystal grains is ½ or less of the conventional one. The bearing parts subjected to the above heat treatment have a long rolling fatigue characteristic, can improve the cracking strength, and can also reduce the rate of dimensional change over time.
[0020]
FIG. 4A shows the austenite grain size of the bearing steel to which the heat treatment pattern shown in FIG. 2 is applied. For comparison, FIG. 4B shows the austenite grain size of the bearing steel obtained by the conventional heat treatment method. FIGS. 5 (a) and 5 (b) show the austenite grain sizes illustrated in FIGS. 4 (a) and 4 (b). From the structure showing the austenite crystal grain size, the conventional austenite grain size is No. 10 in the JIS standard grain size number, and according to the heat treatment method of the present invention, No. 12 fine grains can be obtained. Moreover, the average particle diameter of Fig.4 (a) was 5.6 micrometers as a result of measuring by the intercept method.
[0021]
【Example】
Next, examples of the present invention will be described.
[0022]
Example 1
Example 1 of the present invention was performed using JIS standard SUJ2 material (1.0 wt% C-0.25 wt% Si-0.4 wt% Mn-1.5 wt% Cr). The manufacturing history of each sample shown in Table 1 is shown below.
[0023]
[Table 1]

[0024]
(Samples A to D; examples of the present invention): Carbonitriding was performed by holding at a temperature of 850 ° C. for 150 minutes. The atmosphere during the carbonitriding process was a mixed gas of RX gas and ammonia gas. In the heat treatment pattern shown in FIG. 2, primary quenching was performed from a carbonitriding temperature of 850 ° C., and then secondary quenching was performed by heating to a temperature range of 780 ° C. to 830 ° C. lower than the carbonitriding temperature. However, Sample A having a secondary quenching temperature of 780 ° C. was excluded from the test because of insufficient quenching.
(Samples E and F; Example of the present invention): The carbonitriding process is performed with the same history as that of Examples A to D of the present invention, and the secondary quenching temperature is performed at 850 ° C. to 870 ° C. which is equal to or higher than the carburizing nitrogen treatment temperature (850 ° C.) It was.
(Conventional carbonitrided product; comparative example): Carbonitriding was performed by holding at a temperature of 850 ° C. for 150 minutes. The atmosphere during the carbonitriding process was a mixed gas of RX gas and ammonia gas. Quenching was performed as it was from the temperature during the carbonitriding treatment, and secondary quenching was not performed.
(Normally hardened product; comparative example): It was quenched by heating to 850 ° C. without performing carbonitriding. Secondary quenching was not performed.
[0025]
For each of the above samples, (1) measurement of hydrogen content, (2) measurement of crystal grain size, (3) Charpy impact test, (4) measurement of fracture stress value, (5) rolling fatigue test Went. The results are also shown in Table 1.
[0026]
Next, these measurement methods and test methods will be described.
(1) Measurement of hydrogen amount The amount of hydrogen was determined by analyzing the amount of non-diffusible hydrogen in the steel using a DH-103 hydrogen analyzer manufactured by LECO. The amount of diffusible hydrogen is not measured. The specification of this LECO DH-103 type hydrogen analyzer is shown below.
[0027]
Analysis range: 0.01 to 50.00 ppm
Analysis accuracy: ± 0.1 ppm or ± 3% H (whichever is greater)
Analysis sensitivity: 0.01ppm
Detection method: Thermal conductivity method Sample weight size: 10 mg to 35 g (maximum: diameter 12 mm × length 100 mm)
Heating furnace temperature range: 50 ° C to 1100 ° C
Reagents: Anhydrone (Mg (ClO ₄ ) ₂ ), Ascarite (NaOH)
Carrier gas: Nitrogen gas, gas dosing gas (hydrogen gas), all of which have a purity of 99.99% or more and a pressure of 40 PSI (2.8 kgf / cm ² ).
[0028]
The outline of the measurement procedure is as follows. Samples collected with a dedicated sampler are inserted into the hydrogen analyzer for each sampler. Internal diffusible hydrogen is directed to the thermal conductivity detector by a nitrogen carrier gas. This diffusible hydrogen is not measured in this example. Next, the sample is taken out from the sampler and heated in a resistance heating furnace, and non-diffusible hydrogen is guided to the thermal conductivity detector by nitrogen carrier gas. The amount of non-diffusible hydrogen can be known by measuring the thermal conductivity with a thermal conductivity detector.
(2) Measurement of crystal grain size The crystal grain size was measured based on the JIS G 0551 steel austenite grain size test method.
(3) Charpy impact test The Charpy impact test was performed based on the Charpy impact test method of a metal material of JIS Z 2242. As a test piece, a U-notch test piece (JIS No. 3 test piece) shown in JIS Z 2202 was used. The Charpy impact value is a value obtained by dividing the absorbed energy E of the following formula by the cross-sectional area (0.8 cm ² ).
[0029]
Absorbed energy: E = WgR (cosβ-cosα)
W: Hammer weight (= 25.438 kg)
g: Gravitational acceleration (= 9.80665 m / sec ² )
R: Distance from the center of rotation of the hammer to the center of gravity (= 0.6569m)
α: Hammer lifting angle (= 146 °), β: Hammer descending angle (4) Measurement of fracture stress value FIG. 6 shows a test piece used for measurement of the fracture stress value. Using an Amsler universal testing machine, load is applied in the direction P in the figure and the load until the test piece is broken is measured. Thereafter, the obtained fracture load is converted into a stress value by the following bending beam stress calculation formula. In addition, a test piece is not restricted to the test piece shown in FIG. 6, You may use the test piece of another shape.
[0030]
Assuming that the fiber stress on the convex surface of the test piece of FIG. 6 is σ ₁ and the fiber stress on the concave surface is σ ₂ , σ ₁ and σ ₂ are obtained by the following formulas (Mechanical Engineering Handbook A4 Knitting Material Dynamics A4-40) . Here, N is the axial force of the cross section including the axis of the annular specimen, A is the cross-sectional area, e ₁ is the outer radius, and e ₂ is the inner radius. Further, κ is a section modulus of the curved beam.
[0031]
σ ₁ = (N / A) + {M / (Aρ _o )} [1 + e ₁ / {κ (ρ _o + e ₁ )}]
σ ₂ = (N / A) + {M / (Aρ _o )} [1-e ₂ / {κ (ρ _o −e ₂ )}]
κ = − (1 / A) ∫ _A {η / (ρ _o + η)} dA
(5) Rolling fatigue test,
Table 2 and FIG. 7 show test conditions for the rolling fatigue life test and a schematic diagram of the test apparatus. In FIG. 7, the rolling fatigue life test piece 21 is driven by the drive roll 11 and rotates in contact with the ball 13. The ball 13 is a (3/4) ″ ball, which is guided by the guide roll 12 and rolls while exerting a high surface pressure with the rolling fatigue life test piece 21.
[0032]
Next, the measurement results and test results will be described.
(1) Hydrogen amount From Table 1, the amount of hydrogen in steel of the conventional carbonitrided product as it is carbonitrided is a very high value of 0.72 ppm. This is presumably because ammonia (NH ₃ ) contained in the carbonitriding atmosphere decomposed and hydrogen entered the steel. On the other hand, the amount of hydrogen in steel of Samples B to F is 0.37 to 0.42 ppm, which is reduced to nearly half that of the conventional carbonitrided product. The amount of hydrogen in this steel is at the same level as that of ordinary quenched products.
[0033]
By reducing the amount of hydrogen in the steel, embrittlement of the steel due to hydrogen solid solution can be reduced. That is, by reducing the amount of hydrogen, the Charpy impact value and the fracture stress value of the samples BF of the present invention example are greatly improved.
(2) Crystal grain size From Table 1, the crystal grain size is the crystal grain size number when the secondary quenching temperature is lower than the quenching (primary quenching) temperature during carbonitriding, that is, in the case of Samples BD. It is remarkably miniaturized as 11-12. The austenite grains of Samples E and F, the conventional carbonitrided product and the normal quenching product have a crystal grain size number 10, and are coarser than Samples B to D.
(3) Charpy impact value According to Table 1, the Charpy impact value of the samples B to F of the present invention example is 6 compared with the Charpy impact value of the conventional carbonitrided product being 5.33 J / cm ^2. A high value of .20 to 6.65 J / cm ² is obtained. Among these, the lower the secondary quenching temperature, the higher the Charpy impact value tends to be. In addition, the Charpy impact value of the normally quenched product is as high as 6.70 J / cm ² .
(4) Fracture stress value The above-mentioned fracture stress value corresponds to the crack resistance strength. According to Table 1, the conventional carbonitrided product has a fracture stress value of 2330 MPa. Compared to this, the fracture stress values of Samples B to F are improved to 2650 to 2840 MPa. The fracture stress value of the normally quenched product is 2770 MPa, which is equivalent to the fracture stress values of Samples B to F. Such improved crack resistance strength of Samples B to F is presumed to have a great effect by reducing the hydrogen content, along with the refinement of austenite crystal grains.
(5) According to the rolling contact fatigue test Table 1, usually sintered Irihin is reflecting that does not have a carbonitrided layer in the surface layer portion, the rolling fatigue life L ₁₀ is the lowest. Compared to this, the rolling fatigue life of the conventional carbonitrided product is 3.1 times. The rolling fatigue life of Samples B to D is significantly improved as compared with the conventional carbonitrided product. Samples E and F were almost equivalent to conventional carbonitrided products.
[0034]
In summary, in Samples B to F of the present invention example, the amount of hydrogen in the steel is lowered, and the fracture stress value and Charpy impact value are improved. However, what can be improved including the rolling fatigue life is the samples B to D in which the austenite crystal grain size is further refined to about 11 or more in the grain size number. Therefore, samples B to F correspond to the examples of the present invention, but a more desirable range of the present invention is sample B in which the secondary quenching temperature is made lower than the carbonitriding temperature to further refine the crystal grains. It is the range of -D.
[0035]
(Example 2)
Next, Example 2 will be described.
[0036]
A series of tests were performed on the following A material, B material, and C material. JIS standard SUJ2 material (1.0% by weight C-0.25% by weight Si-0.4% by weight Mn-1.5% by weight Cr) is used for the heat treatment material, which is common to A material to C material. did. The manufacturing histories of the A material to the C material are as follows.
(A material: Comparative example): Only normal quenching was performed (without carbonitriding).
(B material: comparative example): It hardened as it was after carbonitriding (conventional carbonitriding quenching). The temperature of carbonitriding was 845 ° C., and the holding time was 150 minutes. The atmosphere of carbonitriding was RX gas + ammonia gas.
(C material: Example of the present invention): The heat treatment pattern of FIG. 2 was applied to the bearing steel. The carbonitriding temperature was 845 ° C., the holding time was 150 minutes, and the atmosphere was RX gas + ammonia gas. The final quenching temperature was 800 ° C.
[0037]
(1) Rolling fatigue life The above-described apparatus shown in FIG. 7 was used as a rolling fatigue life test apparatus, and the test conditions were as shown in Table 2. The rolling fatigue life test results are shown in Table 3.
[0038]
[Table 2]

[0039]
[Table 3]

[0040]
According to Table 3, L ₁₀ life of B material subjected to carbonitriding treatment (comparative example), normally hardened only alms was A material (Comparative Example) of L ₁₀ life (the test piece 10 in one damaged Life) is 3.1 times longer, and the effect of extending the life by carbonitriding is recognized. On the other hand, the C material of the present invention example has a long life of 1.74 times that of the B material and 5.4 times that of the A material. The main reason for this improvement is thought to be the refinement of the microstructure.
[0041]
(2) Charpy impact test The Charpy impact test was performed by the method according to the above-mentioned JIS Z 2242 using a U-notch test piece. The test results are shown in Table 4.
[0042]
[Table 4]

[0043]
In the C material of the present invention example, a Charpy impact value equivalent to the A material (comparative example) subjected only to normal quenching and higher than that of the B material (comparative example) subjected to carbonitriding was obtained.
[0044]
(3) Test of static fracture toughness value The test piece shown in FIG. 8 was used as a test piece for static fracture toughness test. After introducing a crack of about 1 mm in advance, a static load P by three-point bending was applied, The breaking load was determined. The following equation was used to calculate the fracture toughness value (K _IC value). The test results are shown in Table 5.
[0045]
K _IC = (PL√a / BW ² ) {5.8−9.2 (a / W) +43.6 (a / W) ² −75.3 (a / W) ³ +77.5 (a / W ⁴ }
[0046]
[Table 5]

[0047]
Since the depth of the crack introduced in advance is larger than the depth of the carbonitriding layer, there is no difference between the A material and the B material of the comparative example. However, in the C material of the present invention, a fracture toughness value (K _IC value) about 1.2 times that of the A material and B material of the comparative example could be obtained.
[0048]
(4) Static crush strength test (measurement of fracture stress value)
As described above, the static crushing strength test piece having the shape shown in FIG. 6 was used. In the figure, a load was applied in the P direction, and a static crushing strength test was performed in the same manner as described above. The test results are shown in Table 6.
[0049]
[Table 6]

[0050]
The static crushing strength of the B material (comparative example) subjected to the carbonitriding treatment is slightly lower than the static crushing strength of the A material (comparative example) subjected only to normal quenching. However, the static crushing strength of the C material of the present invention example is higher than the static crushing strength of the B material, and is slightly higher than the static crushing strength of the A material.
[0051]
(5) Aged dimensional change rate Aged dimensional change rate was measured at a temperature of 130 ° C. for 500 hours. The measurement results are shown in Table 7 together with the surface hardness and the amount of retained austenite (at a depth of 0.1 mm from the surface).
[0052]
[Table 7]

[0053]
It can be seen that the dimensional change rate of the C material of the present invention example is kept low compared to the dimensional change rate of the B material having a large amount of retained austenite.
[0054]
(6) Life test under lubrication mixed with foreign matter Using a ball bearing 6206, a rolling fatigue life under lubrication mixed with a predetermined amount of standard foreign matter was evaluated. The test conditions are shown in Table 8, and the test results are shown in Table 9.
[0055]
[Table 8]

[0056]
[Table 9]

[0057]
Compared to the A material, a long life was obtained about 2.5 times longer in the B material (comparative example) subjected to carbonitriding, and about 2.3 times longer in the C material of the present invention example. In the C material of the present invention, although the retained austenite is less than that in the B material of the comparative example, a substantially equivalent long life is obtained due to the intrusion of nitrogen and the influence of the refined microstructure.
[0058]
From the above results, the material C of the example of the present invention, that is, the bearing part produced by the heat treatment method of the present invention, has a long rolling fatigue life, which is difficult with the conventional carbonitriding process, and an improved crack strength. It was found that the three items of reduction of the aging dimensional change rate can be satisfied simultaneously.
[0059]
It should be understood that the embodiments and examples disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.
[0060]
【The invention's effect】
By using the bearing component and the rolling bearing of the present invention, it is possible to obtain an unprecedented excellent fracture stress value after forming a carbonitriding layer, and therefore, it is possible to obtain excellent cracking resistance and the like. .
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view showing a rolling bearing in an embodiment of the present invention.
FIG. 2 is a diagram illustrating a heat treatment method according to an embodiment of the present invention.
FIG. 3 is a diagram for explaining a modification of the heat treatment method in the embodiment of the present invention.
FIG. 4 is a diagram showing the microstructure of bearing parts, particularly austenite grains. (a) is a bearing part of the example of the present invention, and (b) is a conventional bearing part.
5A shows an austenite grain boundary illustrated in FIG. 4A, and FIG. 5B shows an austenite grain boundary illustrated in FIG. 4B.
FIG. 6 is a view showing a test piece of a static crushing strength test (measurement of a breaking stress value).
FIG. 7 is a schematic view of a rolling fatigue life tester. (a) is a front view, (b) is a side view.
FIG. 8 is a view showing a test piece of a static fracture toughness test.
[Explanation of symbols]
1 outer ring, 2 inner ring, 3 rolling element, 10 rolling bearing, 11 drive roll, 12 guide roll, 13 (3/4) "ball, 21 rolling fatigue life test piece, T ₁ carbonitriding temperature, T ₂ quenching heating temperature.

Claims (2)

In a rolling bearing having an inner ring, an outer ring and a plurality of rolling elements,
The inner ring, at least one of the members have a carbonitrided layer in the outer ring and rolling elements,
Fracture stress of the member Ri der least 2650 MPa,
The particle number number of the austenite crystal grains of the member is in the range exceeding 10
The member that consisted of JIS standard SUJ2, the rolling bearing. A bearing component incorporated in a rolling bearing,
The carbonitrided layer possess,
Fracture stress value of Ri der more than 2650MPa,
The austenite grain size number is in the range exceeding 10;
That consisted of JIS standard SUJ2, bearing components.

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