JPH089754B2 - Case hardening steel - Google Patents
Case hardening steelInfo
- Publication number
- JPH089754B2 JPH089754B2 JP32535988A JP32535988A JPH089754B2 JP H089754 B2 JPH089754 B2 JP H089754B2 JP 32535988 A JP32535988 A JP 32535988A JP 32535988 A JP32535988 A JP 32535988A JP H089754 B2 JPH089754 B2 JP H089754B2
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- grain boundary
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- steel
- case
- carburized layer
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Description
【発明の詳細な説明】 ［産業上の利用分野］ 本発明は、浸炭焼入に用いられる肌焼鋼、特に浸炭焼
入後の曲げ疲労強度と転動疲労強度に優れた肌焼鋼に関
する。TECHNICAL FIELD The present invention relates to a case-hardening steel used for carburizing and quenching, and particularly to a case-hardening steel having excellent bending fatigue strength and rolling fatigue strength after carburizing and quenching.
［従来の技術］ 近年、産業界では機械材料の高強度化への期待がます
ます強くなっている。特に、歯車、各種シャフト等に使
用される肌焼鋼においては浸炭焼入後、高い曲げ疲労強
度および転動疲労強度が要求されるようになっている。[Prior Art] In recent years, expectations for higher strength of mechanical materials have become stronger in the industrial world. In particular, case hardening steels used for gears, various shafts, etc. are required to have high bending fatigue strength and rolling fatigue strength after carburizing and quenching.
しかし、従来一般に用いられている肌焼鋼、たとえば
JIS規格SCR420,SCM420では、次のような難点があった。However, case-hardening steels that are commonly used in the past, for example,
The JIS standards SCR420 and SCM420 had the following problems.
肌焼鋼の浸炭において、浸炭雰囲気中の酸化性ガス
（CO2、H2O）中のＯが、浸炭中に鋼のオーステナイト粒
界に侵入して、Feよりも酸化されやすい、Si、Mn、Crの
ような元素と結合して、オーステナイト粒界に酸化物を
形成する。さらにこれに付随して、オーステナイト粒界
近傍の焼入性が低下して、不完全焼入層か生成する。こ
の不完全な焼入層は、浸炭層表面に10μｍ〜20μｍ程度
生成するが、不完全な焼入組織であるために、硬度が低
く、曲げ疲労強度および転動疲労強度を劣化させる。In carburizing of case-hardening steel, O in oxidizing gas (CO 2 , H 2 O) in the carburizing atmosphere penetrates into the austenite grain boundary of the steel during carburizing and is more easily oxidized than Fe. Si, Mn , Combines with elements such as Cr to form oxides at austenite grain boundaries. Further to this, the hardenability in the vicinity of the austenite grain boundaries deteriorates and an incompletely hardened layer is formed. This incompletely hardened layer is formed on the surface of the carburized layer by about 10 μm to 20 μm, but since it has an incompletely hardened structure, it has low hardness and deteriorates bending fatigue strength and rolling fatigue strength.
同じく肌焼鋼の浸炭において、旧オーステナイト粒
界でのＰの偏析および上記に記載した旧オーステナイ
ト粒界のSi、Mn、Crの酸化物により旧オーステナイト粒
界が脆弱化し、曲げ疲労強度および転勤疲労強度が劣化
する。Similarly, in carburizing of case-hardening steel, segregation of P at the former austenite grain boundary and the oxides of Si, Mn, and Cr at the former austenite grain boundary weaken the former austenite grain boundary, resulting in bending fatigue strength and transfer fatigue. Strength deteriorates.
そこで、上記、を改善しようとして、特開昭60−
243252号において新たな肌焼鋼が開示されている。この
肌焼鋼では粒界酸化を低減させるため、Feよりも酸化さ
れやすい、Si、Mn、Crを低減させている。また粒界酸化
に付随して生成する不完全焼入層を低減させるため、Fe
よりも酸化されにくく、かつ鋼の焼入性を向上させるM
o、Niを添加している。さらに、Ｐの粒界偏析を防止す
るため、低Ｐ化に加えて、Ｐの粒界偏析を助長するMnを
減らすとともに、Ｐの粒界偏析を軽減させるMoを添加し
たものである。Therefore, in order to improve the above, Japanese Patent Laid-Open No.
No. 243252 discloses a new case hardening steel. In this case-hardening steel, since grain boundary oxidation is reduced, Si, Mn, and Cr, which are more easily oxidized than Fe, are reduced. In order to reduce the incompletely hardened layer that accompanies grain boundary oxidation, Fe
M that is harder to oxidize and improves the hardenability of steel
o, Ni is added. Furthermore, in order to prevent the grain boundary segregation of P, in addition to lowering the P content, Mn that promotes the grain boundary segregation of P is reduced and Mo that reduces the grain boundary segregation of P is added.
［発明が解決しようとする課題］ しかしながら、上記公報に開示の肌焼鋼では、従来技
術の欠点の１つである浸炭層中の旧オーステナイト粒界
の脆弱化については十分に改善されていない。すなわ
ち、この肌焼鋼について曲げ疲労、転動疲労後の浸炭層
の破面を調べてみると、依然として粒界破壊が観察され
ており、曲げ疲労強度および転動疲労強度は大幅に改善
されるに至っていない。[Problems to be Solved by the Invention] However, in the case-hardening steel disclosed in the above publication, the weakening of the former austenite grain boundaries in the carburized layer, which is one of the drawbacks of the prior art, has not been sufficiently improved. That is, when examining the fracture surface of the carburized layer after bending fatigue and rolling fatigue of this case-hardening steel, intergranular fracture is still observed, and bending fatigue strength and rolling fatigue strength are significantly improved. Has not reached.
そこで本発明の主目的は、浸炭焼入後の曲げ疲労強度
および転動疲労強度が大幅に向上した肌焼鋼を提供する
ことにある。Therefore, a main object of the present invention is to provide a case-hardening steel having significantly improved bending fatigue strength and rolling fatigue strength after carburizing and quenching.
［課題を解決するための手段］ 上記課題を解決するための本第１発明は、重量比で、
C:0.1〜0.4％、Si:0.15％未満、Mn:0.5％未満、P:0.015
未満、Cr:0.30％未満、Mo:0.20〜2.5％、Ni:5.0未満、
B:0.0010〜0.0050％、Sol.Al:0.010〜0.060％、N:0.006
0〜0.0200％を含有し、残部がFeおよび不可避的不純物
からなることを特徴とするものである。[Means for Solving the Problems] The first aspect of the present invention for solving the above problems is, in terms of weight ratio,
C: 0.1-0.4%, Si: less than 0.15%, Mn: less than 0.5%, P: 0.015
Less than, Cr: less than 0.30%, Mo: 0.20 to 2.5%, Ni: less than 5.0,
B: 0.0010-0.0050%, Sol.Al:0.010-0.060%, N: 0.006
It is characterized in that it contains 0 to 0.0200% and the balance is Fe and inevitable impurities.
また，本第２発明は，重量比で、C:0.1〜0.4％、Si:
0.15％未満、Mn:0.5％未満、P:0.015未満、Cr:0.30％未
満、Mo:0.20〜2.5％、Ni:5.0％未満、B:0.0010〜0.0050
％、Sol.Al:0.010〜0.060％、N:0.0060〜0.0200％を含
有し、さらに、Nb:0.01〜0.10％、V:0.01〜0.10％、Ti:
0.01〜0.10％のいずれか１種または２種以上を含有し、
残部がFeおよび不可避的不純物からなることを特徴とす
るものである。In addition, the second aspect of the present invention is, by weight ratio, C: 0.1 to 0.4%, Si:
Less than 0.15%, Mn: less than 0.5%, P: less than 0.015, Cr: less than 0.30%, Mo: 0.20-2.5%, Ni: less than 5.0%, B: 0.0010-0.0050
%, Sol.Al: 0.010 to 0.060%, N: 0.0060 to 0.0200%, and Nb: 0.01 to 0.10%, V: 0.01 to 0.10%, Ti:
Contains any one or more of 0.01 ~ 0.10%,
The balance is Fe and inevitable impurities.
従来、Ｂは経済性向上のため、高価な焼入性向上用の
合金元素であるCr、Mn、Niの代わりに添加されていた
（特開昭53−147616号等）。本発明では、Ｂ添加の添加
を焼入性の向上ではなく、浸炭層の粒界強化の目的をも
って添加している。Conventionally, B has been added in place of expensive alloying elements Cr, Mn, and Ni for improving hardenability in order to improve economic efficiency (JP-A-53-147616, etc.). In the present invention, the addition of B is added not for improving the hardenability but for the purpose of strengthening the grain boundary of the carburized layer.
［作用］ 一般に、浸炭を行った肌焼鋼の曲げ疲労および転動疲
労に関しては、次のような基礎的な事実が知られてい
る。[Operation] In general, the following basic facts are known regarding bending fatigue and rolling fatigue of case-hardened case-hardened steel.
（ａ）曲げ疲労の破面については、表面部から中心部に
向かって、旧オーステナイト粒界破壊→粒内疲労破壊→
機械的最終破壊へと変化し、浸炭層中では旧オーステナ
イト粒界破壊が支配的である。(A) Regarding the fracture surface of bending fatigue, the former austenite grain boundary fracture → intragranular fatigue fracture →
Old austenite intergranular fractures are dominant in the carburized layer, changing to mechanical final fractures.
（ｂ）転動疲労による破面については、浸炭層中での破
面は部分的に粒界破壊を呈し、その破面の周辺に多数存
在するクラックも部分的に旧オーステナイト粒界に沿っ
ている。(B) Regarding the fracture surface due to rolling fatigue, the fracture surface in the carburized layer partially exhibits grain boundary fracture, and many cracks around the fracture surface also partially extend along the former austenite grain boundary. There is.
これらの事実に基づき、本発明者は肌焼鋼の浸炭層の
粒界を強化して肌焼鋼の浸炭後の曲げ疲労強度および転
動疲労強度を向上させることを目的として詳細な調査を
行った結果、次の知見を得た。Based on these facts, the present inventor conducted a detailed investigation for the purpose of strengthening the grain boundary of the carburized layer of case-hardening steel and improving the bending fatigue strength and rolling fatigue strength of the case-hardening steel after carburization. As a result, we obtained the following findings.
すなわち、不完全焼入層、粒界酸化およびＰの粒界偏
析を低減した肌焼鋼にホウ素（Ｂ）を微量添加すると、
浸炭層の粒界破壊が抑制され、曲げ疲労強度よび転動疲
労強度が上昇することである。That is, when a small amount of boron (B) is added to case-hardening steel in which an incompletely hardened layer, grain boundary oxidation and grain boundary segregation of P are reduced,
This is to suppress the grain boundary fracture of the carburized layer and increase the bending fatigue strength and rolling fatigue strength.
本発明は上記知見をもとに完成されたもので、肌焼鋼
中にＢを所定量添加することを主要点とするものであ
る。The present invention was completed based on the above findings, and its main point is to add a predetermined amount of B to case-hardening steel.
Ｂの添加により浸炭層の粒界破壊が抑制され、粒界が
強化するメカニズムについては、浸炭中の鋼のオーステ
ナイト粒界へ、固溶Ｂが偏析し、粒界の歪エネルギーが
低減して、オーステナイト結晶粒界が整合化するためで
あると考えられる。Regarding the mechanism that the grain boundary destruction of the carburized layer is suppressed by the addition of B and the grain boundary is strengthened, the solid solution B segregates to the austenite grain boundary of the steel during carburization, and the strain energy of the grain boundary is reduced, It is considered that this is because the austenite grain boundaries are matched.
また焼入性向上は、主にCr、Mo、Niが負担するように
しており、かつＢの添加に伴う粒界の強化の効果をさら
に大きくするために、Crを0.30％以下添加することとし
ている。In addition, hardenability is mainly borne by Cr, Mo and Ni, and in order to further enhance the effect of strengthening the grain boundaries accompanying the addition of B, it is necessary to add Cr by 0.30% or less. There is.
［発明の具体的構成］ 次に本発明にかかる肌焼鋼の成分範囲（重量％）の限
定理由について元素別に説明する。[Specific Structure of the Invention] The reasons for limiting the component range (% by weight) of the case-hardening steel according to the present invention will be described element by element.
C:0.1〜0.4％ Ｃは肌焼鋼の芯部の強度を上昇させる作用がある。下
限を0.1％としたのは、芯部の強度確保のためである。
肌焼鋼の浸炭焼入、焼戻の後、芯部の硬さは少なくとも
HRC25は必要である。C: 0.1 to 0.4% C has the effect of increasing the strength of the core of case-hardening steel. The lower limit of 0.1% is to ensure the strength of the core.
After case hardening and tempering of case hardening steel, the hardness of the core is at least
HRC25 is required.
HRC25を得るための炭素量は少なくとも0.1％は必要で
ある。また、0.4％を超えると、機械構造用鋼として必
要な耐衝撃性、被削性を劣化させるから、0.4％を上限
とした。At least 0.1% of carbon is required to obtain HRC25. Further, when it exceeds 0.4%, the impact resistance and machinability required for steel for machine structural use are deteriorated, so 0.4% was made the upper limit.
Si:0.15％以下 SiはFeよりも酸化されやすい元素であり、浸炭部の表
層部で粒界酸化物を生成し、浸炭層の粒界強度を低下さ
せる作用がある。0.15％以下であれば、浸炭後の粒界酸
化を無視できる程度に低減させることができるのでこの
値を上限とした。Si: 0.15% or less Si is an element that is more easily oxidized than Fe, and has the action of forming grain boundary oxides in the surface layer portion of the carburized portion and lowering the grain boundary strength of the carburized layer. If it is 0.15% or less, grain boundary oxidation after carburization can be reduced to a negligible level, so this value was made the upper limit.
他方、Siが少ない程粒界酸化を低減できるので下限は
設けない。On the other hand, the lower limit is not set because grain boundary oxidation can be reduced as the amount of Si decreases.
Mn:0.5％未満 MnはSiほどではないがFeよりも酸化されやすい元素で
あり、浸炭部の表層部で粒界酸化物を生成させ、浸炭層
の粒界強度を低下させる作用がある。またMnはＰの粒界
偏析を助長し、浸炭層の粒界強度を低下させる作用もあ
る。Mn: less than 0.5% Mn is an element that is less likely to be oxidized than Si but is more easily oxidized than Fe, and has the action of forming grain boundary oxides in the surface layer portion of the carburized portion and lowering the grain boundary strength of the carburized layer. In addition, Mn also promotes the segregation of P at the grain boundaries, and also has the effect of lowering the grain boundary strength of the carburized layer.
上限を0.5％未満としたのは、0.5％未満であれば、粒
界酸化は無視できる程度に低減でき、さらにＰの粒界偏
析も低減でき、曲げ疲労限、転動疲労限の向上に寄与す
るためである。The upper limit of less than 0.5% is that if it is less than 0.5%, grain boundary oxidation can be reduced to a negligible degree, and grain boundary segregation of P can be reduced, contributing to improvement of bending fatigue limit and rolling fatigue limit. This is because
他方、Mnが少ない程、粒界酸化を低減でき、Ｐの粒界
偏析も低減できるので下限は設けない。On the other hand, the lower Mn is, the more the grain boundary oxidation can be reduced and the grain boundary segregation of P can be reduced.
P:0.015％未満 Ｐは浸炭時にオーステナイト粒界に偏析し、浸炭層の
旧オーステナイト粒界の強度を著しく低下させる作用が
ある。そこで、上記粒界偏析による旧オーステナイト粒
界脆化の影響を少くし、曲げ疲労限、転動疲労限の低下
を防止するため0.015％を上限とした。P: less than 0.015% P segregates at the austenite grain boundaries during carburization and has the effect of significantly reducing the strength of the former austenite grain boundaries in the carburized layer. Therefore, in order to reduce the influence of the former austenite grain boundary embrittlement due to the grain boundary segregation and prevent the bending fatigue limit and rolling fatigue limit from lowering, 0.015% was made the upper limit.
Cr:0.35％未満 CrはFeよりも酸化されやすい元素であり、Si、Mnと同
様に、浸炭層の表層部で、粒界酸化物を生成し、浸炭層
の粒界強度を低下させる作用がある。またCrは炭化物生
成元素であり、浸炭中にオーステナイト粒界で粗大な板
状の炭化物を生成し、浸炭層の粒界強度を低下させる作
用もある。またこの粒界の粗大炭化物により、Ｂの粒界
での整合強化を低下させる作用もある。Cr: less than 0.35% Cr is an element that is more easily oxidized than Fe and, like Si and Mn, has the function of forming grain boundary oxides in the surface layer of the carburized layer and lowering the grain boundary strength of the carburized layer. is there. In addition, Cr is a carbide-forming element, and also has a function of forming coarse plate-shaped carbides at austenite grain boundaries during carburization and lowering the grain boundary strength of the carburized layer. Further, the coarse carbides at the grain boundaries also have the effect of lowering the matching strengthening of B at the grain boundaries.
上限を0.35％としたのは、0.35％未満であれば、粒界
酸化は無視でき、浸炭中のオーステナイト粒界への炭化
物の析出も軽減でき、さらにはＢの粒界強化作用も十分
に発揮でき、曲げ疲労強度、転動疲労強度を向上するこ
とができるからである。The upper limit of 0.35% is that if it is less than 0.35%, the grain boundary oxidation can be ignored, the precipitation of carbides at the austenite grain boundaries during carburization can be reduced, and the grain boundary strengthening effect of B is sufficiently exerted. This is because the bending fatigue strength and the rolling fatigue strength can be improved.
Mo:0.20〜2.5％ Moは浸炭層の旧オーステナイト粒界でのＰの偏析を低
減させる作用がある。またFeよりも酸化されにくい元素
であり、粒界酸化を生成することなく、鋼の焼入性を上
昇させる作用がある。Mo: 0.20-2.5% Mo has the effect of reducing the segregation of P at the former austenite grain boundaries in the carburized layer. In addition, it is an element that is less likely to be oxidized than Fe, and has the effect of increasing the hardenability of steel without generating intergranular oxidation.
上限を2.5％としたのは、Moの炭化物の析出を防止
し、この値を超えて添加する場合に、浸炭層ではMo炭化
物が析出し、浸炭層の焼入性が低下して、硬化特性が劣
化することを防止するためである。The upper limit of 2.5% is to prevent the precipitation of Mo carbide, and when added in excess of this value, Mo carbide precipitates in the carburized layer, which reduces the hardenability of the carburized layer, resulting in hardening characteristics. This is to prevent the deterioration of.
他方、浸炭層の旧オーステナイト粒界でのＰの偏析の
低減を十分に発揮するためには0.20％以上である必要が
あり、0.20％を下限値とした。On the other hand, in order to sufficiently exert the reduction of P segregation at the former austenite grain boundary of the carburized layer, it is necessary to be 0.20% or more, and 0.20% was made the lower limit value.
Ni:5.0％未満 NiはFeよりも酸化されにくい元素であり、粒界酸化物
を生成することなく、鋼の焼入性を上昇させる作用があ
る。また浸炭層および非浸炭層の基地を強靱化する作用
もある。Ni: less than 5.0% Ni is an element that is less likely to be oxidized than Fe, and has the effect of increasing the hardenability of steel without forming intergranular oxides. It also acts to strengthen the bases of the carburized and non-carburized layers.
5.0％以上添加すると浸炭性は低下し、浸炭層のＣ量
が不足する結果、浸炭層の硬化が十分に上昇しない。ま
た機械構造用鋼として必要な切削性も大幅に劣化するた
め、5.0％未満とした。If it is added in an amount of 5.0% or more, the carburizing property is deteriorated and the amount of C in the carburized layer is insufficient, so that the hardening of the carburized layer is not sufficiently increased. In addition, the machinability required for machine structural steel is significantly deteriorated, so the content was made less than 5.0%.
B:0.0010〜0.0050％ Ｂは浸炭層の旧オーステナイト粒界に偏析して、浸炭
層の旧オーステナイト粒界を強化する作用がある。B: 0.0010 to 0.0050% B segregates at the former austenite grain boundaries of the carburized layer to strengthen the former austenite grain boundaries of the carburized layer.
上限を設けた理由は、Ｂが0.0050を超えると、AlN＋
Ｂ→BN＋Alの反応によって、AlNが低減し、浸炭中にオ
ーステナイトの粗粒化が生じ、曲げ疲労限と転動疲労限
を劣化させるからである。The reason for setting the upper limit is that when B exceeds 0.0050, AlN +
This is because the reaction of B → BN + Al reduces AlN, causes austenite coarsening during carburization, and deteriorates the bending fatigue limit and rolling fatigue limit.
他方、0.0010％未満では、浸炭層の粒界強化の効果が
小さくなってしまうため、0.0010％を下限とした。On the other hand, if it is less than 0.0010%, the effect of strengthening the grain boundary of the carburized layer becomes small, so 0.0010% was made the lower limit.
Sol.Al:0.010〜0.060％ N:0.0060〜0.0200％ Sol.AlとＮはAlNを形成して、浸炭中、オーステナイ
トの粗粒化防止作用がある。Sol.Al:0.010-0.060% N: 0.0060-0.0200% Sol.Al and N form AlN and have an action of preventing austenite coarsening during carburization.
Sol.Al、0.010％未満、Ｎ、0.0060％未満では上記粗
粒化防止効果が十分でない。他方、Sol.Al、0.060％、
Ｎ、0.0200％を超えると、上記粗粒化防止効果が飽和状
態となり、さらにAlについては地キズ、Ｎについては冷
間加工性に悪影響を及ぼす。そこでそれぞれ上記範囲と
した。If Sol.Al is less than 0.010% and N is less than 0.0060%, the effect of preventing coarsening is not sufficient. On the other hand, Sol.Al, 0.060%,
If the N content exceeds 0.0200%, the effect of preventing coarsening is saturated, and further, Al has a ground flaw and N has an adverse effect on the cold workability. Therefore, the above ranges are set respectively.
Nb:0.01〜0.1％ V:0.01〜0.1％ NbとＶは鋼中のＣおよびＮと結合して炭窒化物を形成
して、浸炭中のオーステナイトの粗粒化を防止して、曲
げ疲労限、転動疲労限を向上させる効果がある。Nb: 0.01-0.1% V: 0.01-0.1% Nb and V combine with C and N in steel to form carbonitrides, prevent austenite coarsening during carburization, and prevent bending fatigue limit. , Has the effect of improving the rolling fatigue limit.
0.01％未満では、その粗粒化防止効果が十分でない一
方、0.1％を超えると、その効果が飽和状態になるため
上記範囲とした。If it is less than 0.01%, the effect of preventing coarsening is not sufficient, while if it exceeds 0.1%, the effect is saturated, so the above range was made.
Ti:0.01〜0.1％ Tiは鋼中のＮと結合して、窒化物を形成して、粒界強
化に寄与しないBNの生成を抑えて、Ｂの粒界強化の効果
を大きくする作用がある。Ti: 0.01-0.1% Ti has a function of combining with N in the steel to form a nitride, suppressing the formation of BN that does not contribute to grain boundary strengthening, and enhancing the effect of strengthening the grain boundary of B. .
0.01未満ではこの作用が小さく、0.1％を超えると、
鋼の靱性を著しく劣化させるため、上記範囲としたもの
である。If it is less than 0.01, this effect is small, and if it exceeds 0.1%,
The above range is set because the toughness of steel is significantly deteriorated.
［実施例］ 次に実施例を説明する。[Example] Next, an example will be described.
第１表に示す化学成分の鋼を真空溶製し、鍛造、焼準
しの後、機械加工を行い、小野式回転曲げ疲労試験片お
よび転動疲労試験片を製作した。次に各々の試験片を、
930℃×2hr（カーボンポテンシャル0.9〜1.0％）で浸炭
し、油焼入した後、170℃×2hrで焼き戻した後、空冷し
た。以上の処理により得られた試験片に対し、小野式回
転曲げ疲労試験および転動疲労試験を行った。Steel having the chemical composition shown in Table 1 was vacuum-melted, forged and normalized, and then machined to produce Ono-type rotary bending fatigue test pieces and rolling fatigue test pieces. Next, each test piece,
After carburizing at 930 ° C x 2 hr (carbon potential 0.9 to 1.0%), oil quenching, tempering at 170 ° C x 2 hr, air cooling was performed. Ono type rotary bending fatigue tests and rolling fatigue tests were performed on the test pieces obtained by the above treatment.
一方、浸炭焼入―焼戻し処理後の粒界酸化および不完
全焼入層を調べるために、未試験の小野式回転曲げ疲労
試験片の平行部よりミクロ試料を切出し、顕微鏡観察を
行った。また、試験片の浸炭焼入、焼戻し後の硬度分布
については、表面硬さが、Hv740〜780、芯部硬さHv430
〜470、硬化深さ0.6〜0.7mm（Hv550）であり、各鋼種と
も大きな差異はなく、疲労限におよぼす硬度分布の影響
は小さかった。On the other hand, in order to investigate the grain boundary oxidation and the incompletely hardened layer after the carburizing and quenching-tempering treatment, a micro sample was cut out from the parallel part of the untested Ono-type rotary bending fatigue test piece and observed under a microscope. Further, regarding the hardness distribution after carburizing and tempering of the test piece, the surface hardness is H v 740 to 780, the core hardness is H v 430.
〜470, hardening depth 0.6〜0.7mm (H v 550), there was no big difference between each steel type, and the effect of hardness distribution on fatigue limit was small.
以下の試験結果を第１表に示す。 The following test results are shown in Table 1.
（考察） （１）小野式回転曲げ疲労試験、転動疲労試験結果 曲げ疲労、転動疲労に及ぼすＢの硬化は大きく、従来
の浸炭層粒界強化した鋼にＢを添加すると、曲げ疲労で
15％、転動疲労で５％の上昇が認められた（ただし、高
Crにすると、Ｂの効果は小さくなった）。 (Discussion) (1) Results of Ono-type rotary bending fatigue test and rolling fatigue test B hardening greatly affects bending fatigue and rolling fatigue, and when B is added to conventional carburized layer grain boundary strengthened steel, bending fatigue
An increase of 15% and 5% due to rolling fatigue was observed (however,
When Cr was used, the effect of B became smaller).
また粒界強化に悪影響を及ぼすSi、Mn、Ｐ、Cr添加量
が増えると、粒界が脆弱化して疲労限が下がるが、本発
明の請求の範囲内に制限すれば疲労限は従来鋼に比べ、
確実に上昇することがわかった。When the amount of addition of Si, Mn, P, and Cr, which has an adverse effect on grain boundary strengthening, increases, the grain boundary becomes weak and the fatigue limit lowers. compared,
It turns out that it will definitely rise.
（２）粒界酸化および不完全焼入層 本発明による成分範囲内では、曲げ疲労および転動疲
労に悪影響を及ぼす粒界酸化と不完全焼入層の厚さは非
常に小さい。粒界酸化の軽減については、浸炭層の粒界
脆化が軽減し、また不完全焼入層の低減は浸炭層の表層
部の軟化層を低減して、いずれも曲げ疲労、転動疲労強
度を向上した。(2) Grain Boundary Oxidation and Incompletely Quenched Layer Within the range of the composition according to the present invention, the thickness of the grain boundary oxidation and incompletely quenched layer, which adversely affects bending fatigue and rolling fatigue, is very small. Regarding the reduction of intergranular oxidation, the intergranular embrittlement of the carburized layer is reduced, and the reduction of the incompletely hardened layer reduces the softened layer at the surface of the carburized layer. Improved.
［発明の効果］ 以上の通り、本発明によれば、浸炭焼入後の曲げ疲労
強度および転動疲労強度が大幅に向上した肌焼鋼を提供
することができる。[Effects of the Invention] As described above, according to the present invention, it is possible to provide a case-hardening steel in which bending fatigue strength and rolling fatigue strength after carburizing and quenching are significantly improved.
Claims (2)
満、Mn:0.5％未満、P:0.015未満、Cr:0.30％未満、Mo:
0.20〜2.5％、Ni:5.0未満、B:0.0010〜0.0050％、Sol.A
l:0.010〜0.060％、N:0.0060〜0.0200％を含有し、残部
がFeおよび不可避的不純物からなることを特徴とする肌
焼鋼。1. By weight ratio, C: 0.1 to 0.4%, Si: less than 0.15%, Mn: less than 0.5%, P: less than 0.015, Cr: less than 0.30%, Mo:
0.20-2.5%, Ni: less than 5.0, B: 0.0010-0.0050%, Sol.A
A case-hardening steel containing l: 0.010 to 0.060% and N: 0.0060 to 0.0200%, the balance being Fe and inevitable impurities.
満、Mn:0.5％未満、P:0.015未満、Cr:0.30％未満、Mo:
0.20〜2.5％、Ni:5.0未満、B:0.0010〜0.0050％、Sol.A
l:0.010〜0.060％、N:0.0060〜0.0200％を含有し、さら
に、Nb:0.01〜0.10％、V:0.01〜0.10％、Ti:0.01〜0.10
％のいずれか１種または２種以上を含有し、残部がFeお
よび不可避的不純物からなることを特徴とする肌焼鋼。2. By weight ratio, C: 0.1 to 0.4%, Si: less than 0.15%, Mn: less than 0.5%, P: less than 0.015, Cr: less than 0.30%, Mo:
0.20-2.5%, Ni: less than 5.0, B: 0.0010-0.0050%, Sol.A
l: 0.010 to 0.060%, N: 0.0060 to 0.0200%, Nb: 0.01 to 0.10%, V: 0.01 to 0.10%, Ti: 0.01 to 0.10.
%, And the balance consists of Fe and unavoidable impurities, and the case-hardening steel.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP32535988A JPH089754B2 (en) | 1988-12-23 | 1988-12-23 | Case hardening steel |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP32535988A JPH089754B2 (en) | 1988-12-23 | 1988-12-23 | Case hardening steel |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPH02170944A JPH02170944A (en) | 1990-07-02 |
| JPH089754B2 true JPH089754B2 (en) | 1996-01-31 |
Family
ID=18175944
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP32535988A Expired - Fee Related JPH089754B2 (en) | 1988-12-23 | 1988-12-23 | Case hardening steel |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JPH089754B2 (en) |
Families Citing this family (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5853502A (en) * | 1995-08-11 | 1998-12-29 | Sumitomo Metal Industries, Ltd. | Carburizing steel and steel products manufactured making use of the carburizing steel |
| JP3311949B2 (en) * | 1996-12-18 | 2002-08-05 | 有限会社金属技術研究所 | Surface hardened chain |
| SE9701594L (en) * | 1997-04-29 | 1998-10-05 | Ovako Steel Ab | Hardened steel |
-
1988
- 1988-12-23 JP JP32535988A patent/JPH089754B2/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| JPH02170944A (en) | 1990-07-02 |
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