JP2019049032A - Steel material for carburization processing - Google Patents
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Abstract
Description
本発明は鋼材、浸窒処理用鋼材に関する。 TECHNICAL FIELD The present invention relates to a steel material and a steel material for carbonitriding treatment.
リングギアを代表とする自動車のトランスミッションの中の遊星ギヤの一部品である薄物部品の表面硬化処理法として、高炭素マルテンサイトの形成を利用した浸炭処理や合金窒化物による析出強化を利用した窒化処理が広く用いられている。ここで、浸炭処理では処理ひずみの大きさが、窒化処理では処理時間が長い事や硬化層が浅い事が問題となっており改善が求められている。そのため浸炭処理に比べ処理ひずみが小さく、窒化処理より短時間で比較的厚い硬化層が得られる新たな表面硬化処理法として浸窒焼入れ処理法が開発され、工業的に利用され始めている。 As surface hardening treatment method for thin parts which are one component of planetary gears in transmissions of ring gears, carburizing using high carbon martensite formation and nitriding using precipitation strengthening with alloy nitrides Processing is widely used. Here, in the case of the carburizing treatment, the magnitude of the treatment strain is a problem, and in the nitriding treatment, the problem is that the treatment time is long and the hardened layer is shallow, and an improvement is required. Therefore, as a new surface hardening treatment method in which a treatment strain is smaller than carburizing treatment and a relatively thick hardened layer can be obtained in a short time than nitriding treatment, a nitro-quenching treatment method has been developed and is beginning to be used industrially.
浸窒焼入れ処理法はＡ１点（８６３Ｋ）以上の温度域で鋼表面から窒素を拡散浸透させて高窒素オーステナイトを表層部で得た後に、焼入れて硬質な高窒素マルテンサイトを生成させる表面硬化法である。浸窒焼入れ処理法は浸炭処理に比べ低温で処理を行うため熱ひずみが小さく、母材がオーステナイト化しない温度域では変態ひずみも小さい。また窒化に比べて高温で処理を行うため処理時間が短くなることが期待される。
このような浸窒処理に関する従来法として、例えば特許文献１〜６に記載の方法が提案されている。
In the case of carbonitriding, nitrogen is diffused and infiltrated from the steel surface in a temperature range of A1 point (863 K) or higher to obtain high nitrogen austenite in the surface layer, and then hardening is performed to form hard high nitrogen martensite. It is. In the case of the carbonitriding treatment method, the thermal strain is small because the treatment is performed at a lower temperature than the carburizing treatment, and the transformation strain is also small in a temperature range where the base material is not austenitized. In addition, it is expected that the processing time will be shorter because the processing is performed at a higher temperature than the nitriding.
As a conventional method regarding such nitronitriding treatment, for example, methods described in Patent Documents 1 to 6 have been proposed.
しかしながら、従来の浸窒処理は、浸炭に比べると温度が低いため、有効硬化層を深くすることが困難であった。 However, in the conventional carbonitriding process, it is difficult to deepen the effective hardened layer because the temperature is lower than carburizing.
本発明は上記のような課題を解決することを目的とする。
すなわち、本発明の目的は、低歪かつ有効硬化層を深くでき、かつ、浸窒処理時に発生する窒化物の制御を考慮することで、浸炭材同等の曲げ疲労強度を有することが可能な浸窒処理に適した鋼材を提供することである。
The present invention aims to solve the above-mentioned problems.
That is, it is an object of the present invention to provide a low strain and deep effective hardened layer, and an immersion capable of having the same bending fatigue strength as that of a carburized material by considering the control of the nitride generated at the time of nitriding treatment. It is providing a steel material suitable for nitrogen treatment.
本発明者は上記課題を解決するため鋭意検討し、本発明の鋼材を完成させた。
本発明の鋼材は、
Ｃ：０．０５〜０．２５質量％、
Ｓｉ：０．３０質量％以下、
Ｍｎ：０．６１〜２．０質量％、
Ｐ：０．１質量％以下、
Ｓ：０．１質量％以下、
Ｃｒ：０．７質量％以下、
Ａｌ：１０〜８００ｐｐｍ、
Ｎ：１０〜３００ｐｐｍ、
で含有し、残部はＦｅおよび不可避的不純物からなり、
式１＝−０．２２５×Ｓｉ＋０．０８３×Ｍｎ＋０．０９１×Ｃｒ＋０．０３５×Ｃｕ＋０．０４７×Ｎｉ＋０．０９２×Ｍｏ
と定義した場合に、式１≧０．０４を満たし、
式２＝−２０＋７４×Ｃ＋７×Ｓｉ＋１５×Ｍｎ＋２６×Ｃｒ＋１０×Ｃｕ＋１２Ｎｉ＋３０×Ｍｏ
と定義した場合に、式２≦（６０×Ｃ＋３１）／２を満たし、
式３＝２５．４×Ｓｉ＋２０．３×Ｃｒ＋３２．８×Ｓｉ×Ｍｎ
と定義した場合に、式３≦２２を満たす、浸窒処理用鋼材である。
MEANS TO SOLVE THE PROBLEM This inventor earnestly examined in order to solve the said subject, and completed the steel materials of this invention.
The steel material of the present invention is
C: 0.05 to 0.25 mass%,
Si: 0.30 mass% or less,
Mn: 0.61 to 2.0% by mass,
P: 0.1 mass% or less,
S: 0.1 mass% or less,
Cr: 0.7 mass% or less,
Al: 10 to 800 ppm,
N: 10 to 300 ppm,
And the balance consists of Fe and unavoidable impurities,
Formula 1 = -0.225xSi + 0.083xMn + 0.091xCr + 0.035xCu + 0.047xNi + 0.092xMo
Satisfying the equation 1 ≧ 0.04 when defined as
Formula 2 = -20 + 74 x C + 7 x Si + 15 x Mn + 26 x Cr + 10 x Cu + 12 Ni + 30 x Mo
Satisfying the equation 2 ≦ (60 × C + 31) / 2 when defined as
Formula 3 = 25.4 x Si + 20.3 x Cr + 32.8 x Si x Mn
When it defines as, it is a steel material for nitriding treatment which satisfy | fills Formula 3 <= 22.
本発明の鋼材は、
Ｃ：０．０５〜０．２５質量％、
Ｓｉ：０．３０質量％以下、
Ｍｎ：０．６１〜２．０質量％、
Ｐ：０．１質量％以下、
Ｓ：０．１質量％以下、
Ｃｒ：０．７質量％以下、
Ａｌ：１０〜８００ｐｐｍ、
Ｎ：１０〜３００ｐｐｍ、
で含有し、
さらに、
Ｃｕ：０．３質量％以下、および／または、
Ｎｉ：０．５質量％以下、および／または、
Ｍｏ：０．６質量％以下、および／または、
Ｖ：０．３質量％以下、および／または、
Ｎｂ：０．１質量％以下
含有し、残部はＦｅおよび不可避的不純物からなり、
式１≧０．０４を満たし、
式２≦（６０×Ｃ＋３１）／２を満たし、
式３≦２２を満たす、浸窒処理用鋼材であることが好ましい。
The steel material of the present invention is
C: 0.05 to 0.25 mass%,
Si: 0.30 mass% or less,
Mn: 0.61 to 2.0% by mass,
P: 0.1 mass% or less,
S: 0.1 mass% or less,
Cr: 0.7 mass% or less,
Al: 10 to 800 ppm,
N: 10 to 300 ppm,
Containing
further,
Cu: 0.3% by mass or less, and / or
Ni: 0.5% by mass or less, and / or
Mo: 0.6% by mass or less, and / or
V: 0.3% by mass or less, and / or
Nb: not more than 0.1% by mass, the balance being composed of Fe and unavoidable impurities,
Satisfy the equation 1 ≧ 0.04,
The formula 2 ≦ (60 × C + 31) / 2 is satisfied,
It is preferable that it is a steel material for nitriding treatment that satisfies the formula 3 ≦ 22.
本発明によれば、低歪かつ有効硬化層を深くでき、浸炭材同等の曲げ疲労強度を有することが可能な浸窒処理に適した鋼材を提供することができる。 According to the present invention, it is possible to provide a steel material which is low in strain and capable of deepening the effective hardened layer, and which is capable of having a bending fatigue strength equivalent to that of a carburized material, and which is suitable for the nitriding treatment.
本発明の発明者は、（１）有効硬化層深さ、（２）焼入れ性、（３）窒化物生成量に関して、低歪かつ有効硬化層を深くでき、浸炭材同等の曲げ疲労強度を有することが可能な浸窒処理に適した鋼材の成分について調査した。 The inventor of the present invention has low strain and can deepen the effective hardened layer with respect to (1) effective hardened layer depth, (2) hardenability, and (3) nitride formation amount, and has bending fatigue strength equivalent to carburized material. It investigated about the composition of the steel material suitable for the possible nitriding treatment.
（１）有効硬化層
実用部品への負荷応力を想定した場合、内部でも破損しない程度に硬化層の深さが必要となってくる。よって、内部起点で破損する部位にとって有効硬化深さの増加は、そのまま高強度化につながる。
有効硬化層を深くするための手段として、Ｉ．処理温度を高くする、II．処理時間を長くする、III．鋼材の焼入れ性を上げる、の三種類が挙げられる。
ここでＩ．は温度上昇により歪が増大するため、なるべく低温で処理を実施したい。
II．生産性の観点からなるべく短時間で処理を実施したい。
III．について、これまで有効硬化深さの増加に対する鋼材成分の影響についての検討は、ほぼされていない。
(1) Effective Hardened Layer Assuming stress applied to practical parts, the depth of the hardened layer is required to such an extent that no damage occurs inside. Therefore, the increase in the effective curing depth directly leads to the increase in strength for the portion broken at the internal starting point.
As a means to deepen the effective cured layer, I.1. Raise the processing temperature, II. Increase processing time, III. There are three types to increase the hardenability of steel materials.
Here, I. Since the strain is increased by the temperature rise, it is desirable to carry out the treatment at a temperature as low as possible.
II. We want to carry out processing in as short time as possible from the viewpoint of productivity.
III. So far, the effects of steel components on the increase of effective hardening depth have not been almost considered.
（２）焼入れ性
焼入れ性は有効硬化層の深さを増大するために必要に応じて高くする必要がある。一般的に焼入れ性を向上させるためにはＳｉ、Ｃｒ、Ｍｎ、Ｃｕ、Ｎｉ、Ｍｏなどの元素を添加する。また、添加元素の量を増やせば増やすほど焼入れ性は向上するといわれている。一方で、焼入れ性が高すぎるとマルテンサイト変態量が多くなり、歪が増大する。そのため歪軽減の観点から言えば、焼入れ性は低い方がよい。ここで、焼入れ性のジョミニー試験で測定される各水冷端からの距離はそれぞれ違う冷却速度を持っており、水冷端から遠くなるほど冷却速度は遅くなる。
(2) Hardenability The hardenability needs to be increased as necessary to increase the depth of the effective hardened layer. Generally, in order to improve the hardenability, an element such as Si, Cr, Mn, Cu, Ni, Mo, etc. is added. Further, it is said that the hardenability is improved as the amount of the additive element is increased. On the other hand, when the hardenability is too high, the amount of martensitic transformation increases and strain increases. Therefore, from the viewpoint of strain reduction, the hardenability should be low. Here, the distance from each water cooling end measured in the hardenability test has different cooling rates, and the cooling speed becomes slower as the distance from the water cooling end increases.
（３）窒化物割合
浸窒処理中に窒化物が生成すると、焼入れ性を担保するために添加していた元素が母相から奪われるため、不完全焼入れ組織が形成されたり、Ｎの固溶による焼入れ性の向上効果が十分に得られなかったりするため、疲労強度が低下するものと予想される。そのため、窒化物量は少ない方がよい。しかし、添加元素量と窒化物の生成量の関係および、それが疲労強度に与える影響についてはこれまでに明らかにされていない。
(3) Nitride ratio If nitride is formed during the nitriding treatment, the element added for securing the hardenability is deprived from the matrix phase, so that an incompletely quenched structure is formed or a solid solution of N is formed. It is expected that the fatigue strength is lowered because the effect of improving the hardenability by the above can not be obtained sufficiently. Therefore, the smaller the amount of nitride, the better. However, the relationship between the amount of added elements and the amount of nitride formation and the influence on the fatigue strength have not been clarified so far.
＜式１について＞
本発明の発明者は、ＪＩＳのＳ１５Ｃの中央成分対比１．４倍の有効硬化層を得る成分系を検討した。ＮやＣの拡散深さは、処理時間に対して平方根でしか増えない。つまり、処理時間を２倍に増やすと有効硬化深さは１．４倍となる。鋼成分を制御し有効硬化深さを１．４倍に増加させるとＳ１５Ｃ対比処理時間が半分になることに対応する。
本発明の発明者が検討したところ、Ｉ．合金元素添加量により、Ｎの侵入深さが変化することを明らかにした。具体的にはＳｉとＣｒは窒化物を生成するため、侵入Ｎ深さが減少する。ＭｎはＮの活量を低下させ、鋼材中のＮの安定度が上がるため、侵入Ｎ深さが増加する。II．さらに同一Ｎ濃度の場合でも鋼材の焼入れ性の変化により、硬さは変化する。Ｉ．、II．の影響を考慮し、鋼材成分が有効硬化深さに与える影響を検討した。そして、式１＝−０．２２５×Ｓｉ＋０．０８３×Ｍｎ＋０．０９１×Ｃｒ＋０．０３５×Ｃｕ＋０．０４７×Ｎｉ＋０．０９２×Ｍｏと定義した場合に、式１≧０．０４を満たすと、ＪＩＳ Ｓ１５Ｃ対比１．４倍となる鋼材が得られることがわかった。
なお、Ｓｉ、Ｍｎ、Ｃｒ、Ｃｕ、Ｎｉ、Ｍｏは、Ｓｉ含有率（質量％）、Ｍｎ含有率（質量％）、Ｃｒ含有率（質量％）、Ｃｕ含有率（質量％）、Ｎｉ含有率（質量％）、Ｍｏ含有率（質量％）を意味する。また、後述するように、Ｓｉ、Ｃｒ、Ｃｕ、Ｎｉ、Ｍｏは含有率がゼロである場合がある。この場合は、式１の該当する項にゼロを代入すればよい。後述する式２、式３においても同様である。
<About Formula 1>
The inventor of the present invention examined a component system for obtaining an effective cured layer 1.4 times the central component of JIS S15C. The diffusion depths of N and C increase only by the square root with respect to the processing time. That is, if the treatment time is doubled, the effective curing depth becomes 1.4 times. Controlling the steel composition and increasing the effective hardening depth by 1.4 corresponds to halving the S15C contrast processing time.
As examined by the inventor of the present invention, I.I. It was clarified that the penetration depth of N changes with the addition amount of alloy elements. Specifically, Si and Cr form nitrides, so the penetration N depth decreases. Mn lowers the activity of N and increases the stability of N in steel materials, so the penetration N depth increases. II. Furthermore, even in the case of the same N concentration, the hardness changes due to the change in the hardenability of the steel material. I. , II. The effects of steel components on the effective hardening depth were examined in consideration of the effects of And, when the equation 1 ≧ 0.04 is satisfied in the case that the equation 1 = −0.225 × Si + 0.083 × Mn + 0.091 × Cr + 0.035 × Cu + 0.047 × Ni + 0.092 × Mo is satisfied, the JIS S15 C contrast is satisfied. It turned out that the steel material which becomes 1.4 times is obtained.
In addition, Si, Mn, Cr, Cu, Ni, Mo are Si content (mass%), Mn content (mass%), Cr content (mass%), Cu content (mass%), Ni content (Mass%), Mo content (mass%) is meant. Further, as described later, the content of Si, Cr, Cu, Ni, and Mo may be zero. In this case, zero may be substituted for the corresponding term of equation 1. The same applies to Equations 2 and 3 described later.
＜式２について＞
薄肉部品を想定した場合、薄物部品の芯部の冷却速度はおよそジョミニー値のJ３〜Ｊ５程度であり、本発明の鋼材はこれらの冷却速度でのマルテンサイト量を減らすことで歪が大きく低減できる。
フルマルテンサイトの硬さは炭素量で整理でき、０．０５〜０．３％の範囲では（６０Ｃ＋３１）ＨＲＣと表わせる。Ｊ５値がフルマルテンサイトとなる硬さの半分（６０Ｃ＋３１）／２以下となれば、歪に影響が大きいマルテンサイト組織が発生せず、フェライト＋パーライト＋少量のベイナイト組織となり、歪を十分に小さくすることができる。
このような知見に基づき、鋼材のジョミニー値Ｊ５に対する合金元素の影響を検討し、後述する式２が、式２≦（６０×Ｃ＋３１）／２を満たす場合に、歪を小さくできることを見出した。
<About Formula 2>
When thin parts are assumed, the cooling rate of the core of thin parts is approximately J3 to J5 of the jominy value, and the steel material of the present invention can greatly reduce the strain by reducing the amount of martensite at these cooling rates. .
The hardness of full martensite can be arranged by the amount of carbon, and can be expressed as (60C + 31) HRC in the range of 0.05 to 0.3%. If the J5 value becomes half (60C + 31) / 2 or less of the hardness at which full martensite is formed, a martensitic structure having a large influence on strain does not occur, and ferrite + pearlite + a small amount of bainite structure is formed, and the strain is sufficiently small. can do.
Based on such findings, the inventors examined the influence of the alloying elements on the jominy value J5 of the steel material, and found that the strain can be reduced when the equation 2 described later satisfies the equation 2 ≦ (60 × C + 31) / 2.
＜式３について＞
曲げ疲労強度に対して、侵入した表層Ｎのうち窒化物となるＮ量が一定割合（２２％以上）を超えると不完全焼入れ組織が形成されたり、Ｎの固溶による焼入れ性の向上効果が十分に得られなかったりするため、疲労強度が大きくばらつくことを明らかにし、合金成分添加量を規定した。また、ＳｉとＭｎを同時添加すると、Ｍｎも窒化物として生成することを明らかにした。
そして、式３＝２５．４×Ｓｉ＋２０．３×Ｃｒ＋３２．８×Ｓｉ×Ｍｎとすると、式３≦２２を満たす必要があることを見出した。
<About Equation 3>
If the N content to be nitrided out of the intruded surface layer N exceeds a certain percentage (22% or more) against the bending fatigue strength, an incompletely quenched structure is formed or the hardenability improvement effect by solid solution of N is In order not to be obtained sufficiently, it was clarified that the fatigue strength largely fluctuated, and the alloy component addition amount was specified. In addition, it was revealed that when Si and Mn were simultaneously added, Mn was also formed as a nitride.
And when Formula 3 = 25.4 x Si + 20.3 x Cr + 32.8 x Si x Mn, it was found that Formula 3 を 満 た す 22 needs to be satisfied.
本発明の鋼材の組成について説明する。 The composition of the steel material of the present invention will be described.
Ｃ成分の含有率は０．０５〜０．２５質量％であり、０．０７〜０．２０質量％であることが好ましい。
Ｃ成分の含有率が低すぎると、浸窒焼入後の芯部硬さが低下する傾向がある。
また、逆にＣ成分の含有率が高すぎると、冷間鍛造性、芯部の靭性、加工性が低下する傾向がある。また、Ｃ成分の含有率が高くなると、焼入時の膨張量が増え、歪が増加する傾向がある。
The content of the component C is 0.05 to 0.25% by mass, and preferably 0.07 to 0.20% by mass.
If the content of the C component is too low, the hardness of the core after dip quenching tends to decrease.
On the other hand, if the content of the component C is too high, the cold forgeability, the toughness of the core, and the processability tend to be lowered. In addition, when the content of the C component increases, the amount of expansion at the time of quenching increases, and the distortion tends to increase.
Ｓｉ成分の含有率は０．３０質量％以下であり、０．０１〜０．１５質量％であることが好ましい。
Ｓｉは微量でも窒化物が生成するため、Ｓｉ成分の含有率が高すぎると、窒化物が形成され、疲労強度を低下する傾向があるからである。
The content rate of Si component is 0.30 mass% or less, and it is preferable that it is 0.01-0.15 mass%.
Since a small amount of Si forms nitrides, if the content of the Si component is too high, nitrides are formed and the fatigue strength tends to decrease.
Ｍｎ成分の含有率は０．６１〜２．０質量％であり、０．６５〜１．５質量％であることが好ましい。
Ｍｎは浸窒処理時の有効硬化深さを向上させるために有効である。Ｍｎ成分の含有率が低すぎると、浸窒焼入時の芯部の焼入れ性が低下する傾向がある。
また、逆にＭｎ成分の含有率が高すぎると、被削性や加工性が低下し、焼入性が上昇しすぎる傾向がある。
The content of the Mn component is 0.61 to 2.0% by mass, and preferably 0.65 to 1.5% by mass.
Mn is effective to improve the effective curing depth at the time of nitridation treatment. If the content of the Mn component is too low, the hardenability of the core during nitrocarburizing tends to decrease.
Also, conversely, if the content of the Mn component is too high, the machinability and the workability tend to be reduced, and the hardenability tends to be too high.
Ｐ成分の含有率は０．１質量％以下であり、０．０５質量％以下であることが好ましい。
Ｐ成分の含有率が高すぎると、粒界割れが生じやすくなる傾向があるからである。
The content of the P component is 0.1% by mass or less, and preferably 0.05% by mass or less.
If the content of P component is too high, intergranular cracking tends to occur easily.
Ｓ成分の含有率は０．１質量％以下であり、０．０５質量％以下であることが好ましい。
Ｓ成分の含有率が高すぎると、ＭｎＳ系介在物が生成し、疲労強度が低下する傾向があるからである。
The content rate of S component is 0.1 mass% or less, and it is preferable that it is 0.05 mass% or less.
If the content of the S component is too high, MnS inclusions tend to be generated and the fatigue strength tends to decrease.
Ｃｒ成分の含有率は０．７質量％以下であり、０．０１〜０．５質量％であることが好ましい。
Ｃｒは、浸窒処理後の有効硬化深さを増加させるのに有効な元素である。Ｃｒ成分の含有率が高すぎると、窒化物が形成されやすくなり、疲労強度がばらつきが多くなる。
The content of the Cr component is 0.7% by mass or less, preferably 0.01 to 0.5% by mass.
Cr is an element effective to increase the effective depth of hardening after carbonitriding. If the content of the Cr component is too high, nitrides are likely to be formed, and the variation in fatigue strength increases.
Ａｌ成分の含有率は１０〜８００ｐｐｍであり、５０〜５００ｐｐｍであることが好ましい。
Ａｌ成分の含有率が低すぎると結晶粒粗大化を防止するＡｌＮが十分な量が析出せず、結晶粒粗大化を発生しやすくなるからである。
逆にＡｌ成分の含有率が高すぎると、粗大なＡｌ2Ｏ3系介在物が生じて強度低下を招く傾向があるからである。
The content of the Al component is 10 to 800 ppm, preferably 50 to 500 ppm.
If the content of the Al component is too low, a sufficient amount of AlN for preventing the coarsening of the crystal grains is not precipitated, and the coarsening of the crystal grains is easily generated.
On the other hand, if the content of the Al component is too high, coarse Al 2 O 3 inclusions tend to be generated to cause a reduction in strength.
Ｎ成分の含有率は１０〜３００ｐｐｍであり、１０〜２５０ｐｐｍであることが好ましい。
Ｎ成分の含有率が低すぎると結晶粒粗大化を防止するＡｌＮが十分な量が析出せず、結晶粒粗大化を発生しやすくなるからである。
逆にＮ成分の含有率が高すぎると、鋳造時に空隙（密に埋まっていない部分）が発生する傾向があるからである。
The content of the N component is 10 to 300 ppm, preferably 10 to 250 ppm.
If the content of the N component is too low, a sufficient amount of AlN for preventing the coarsening of the crystal grains is not precipitated, and the coarsening of the crystal grains is easily generated.
Conversely, if the content of the N component is too high, voids (portions not closely filled) tend to occur during casting.
Ｃｕ成分の含有率は０．３質量％以下であり、０．０１〜０．２５質量％であることが好ましい。
Ｃｕ成分の含有率が高すぎると、熱間鍛造性が低下する傾向があるからである。
The content of the Cu component is 0.3% by mass or less, and preferably 0.01 to 0.25% by mass.
If the content of the Cu component is too high, the hot forgeability tends to decrease.
Ｎｉ成分の含有率は０．５質量％以下であり、０．４質量％以下であることが好ましい。
Ｎｉ成分の含有率が高すぎると、加工性が低下する傾向があるからである。
The content of the Ni component is 0.5% by mass or less, and preferably 0.4% by mass or less.
If the content of the Ni component is too high, the processability tends to decrease.
Ｍｏ成分の含有率は０．６質量％以下であり、０．５質量％以下であることが好ましい。
Ｍｏ成分の含有率が高すぎると、加工性および切削性が低下し、焼入性が上昇しすぎる傾向があるからである。
The content of the Mo component is 0.6% by mass or less, and preferably 0.5% by mass or less.
If the content of the Mo component is too high, the processability and the machinability are reduced, and the hardenability tends to be excessively increased.
Ｖ成分の含有率は０．３質量％以下であり、０．２５質量％以下であることが好ましい。
Ｖ成分の含有率が高すぎると、被削性が低下する傾向があるからである。
The content of the V component is 0.3% by mass or less, and preferably 0.25% by mass or less.
If the content of the V component is too high, the machinability tends to decrease.
Ｎｂ成分の含有率は０．１質量％以下であり、０．０５質量％以下であることが好ましい。
Ｎｂ成分の含有率が高すぎると、加工性が低下する傾向があるからである。
The content of the Nb component is 0.1% by mass or less, and preferably 0.05% by mass or less.
If the content of the Nb component is too high, the processability tends to decrease.
本発明の鋼材は、上記のような特定比率でＣ、Ｓｉ、Ｍｎ、Ｐ、Ｓ、Ｃｒ、Ａｌ、Ｎ、Ｃｕ、Ｎｉ、Ｍｏ、Ｖ、Ｎｂを含む鋼材であり（ただし、Ｓｉ、Ｐ、Ｓ、Ｃｒ、Ｃｕ、Ｎｉ、Ｍｏ、Ｖ、Ｎｂは含まない場合がある）、残部は、Ｆｅおよび不可避的不純物である。 The steel material of the present invention is a steel material containing C, Si, Mn, P, S, Cr, Al, N, Cu, Ni, Mo, V, Nb at the specific ratio as described above (with the proviso that Si, P, S, Cr, Cu, Ni, Mo, V, Nb may not be included), the balance is Fe and unavoidable impurities.
本発明の鋼材は、浸窒処理を施すことで、薄肉部品として好ましく利用できる。
ここで薄肉とは、概ね、最も薄い部位の厚みが１〜１５ｍｍの厚さの部品をいう。また、薄肉部品としては、例えばオートマチックトランスミッションに組み込まれているプラネタリギア中のリングギアなどが挙げられる。
The steel material of the present invention can be preferably used as a thin-walled part by subjecting it to a nitriding treatment.
Here, the term “thin-walled” generally refers to a part having a thickness of 1 to 15 mm at the thinnest portion. In addition, as a thin part, for example, a ring gear in a planetary gear incorporated in an automatic transmission can be mentioned.
＜試験片の製造＞
以下、本発明の実施例について説明する。
第１表に示す実施例１〜３８および比較例１〜１５の各々について、第１表に示す組成（残部はＦｅ及び不可避不純物）となるように原料を混合し、１５０ｋｇ高周波誘導炉を用いて溶製し、鋳造して鋼塊Ａを得た。
<Production of test pieces>
Hereinafter, examples of the present invention will be described.
The raw materials were mixed so as to become the composition shown in Table 1 (the balance being Fe and unavoidable impurities) for each of Examples 1 to 38 and Comparative Examples 1 to 15 shown in Table 1, using a 150 kg high frequency induction furnace. It was melted and cast to obtain a steel ingot A.
＜疲労強度の測定＞
鋼塊Ａを熱間圧延または熱間鍛造し、断面直径が１０５ｍｍの丸棒を得た後、さらに熱間鍛造して、断面直径が２２ｍｍの丸棒を得た。そして、焼きならし処理後（９２５℃×１ＨｒＡＣ）、この丸棒から、断面直径１５ｍｍの丸棒（長さ２１０ｍｍ）を切り出し、さらに加工して、図１に示すような、平行部の径がφ１２ｍｍであり、切欠部の径が８ｍｍであり、ノッチ底が０．５Ｒ（半径０．５ｍｍ）である鋼片を得た。
次に、鋼片に浸窒処理Ｘを施して、試験片Ｂを得た。
<Measurement of fatigue strength>
The steel ingot A was hot-rolled or hot-forged to obtain a round bar having a cross-sectional diameter of 105 mm, and further hot forging to obtain a round bar having a cross-sectional diameter of 22 mm. Then, after normalizing treatment (925 ° C. × 1 HrAC), a round bar (length 210 mm) having a cross-sectional diameter of 15 mm is cut out from this round bar and further processed, and the diameter of the parallel portion is as shown in FIG. A piece of steel having a diameter of 12 mm, a notch diameter of 8 mm, and a notch bottom of 0.5 R (radius 0.5 mm) was obtained.
Next, the steel piece was subjected to nitrous treatment X to obtain a test piece B.
なお、以下において浸窒処理Ｘとは、次のような処理を意味するものとする。
ガス浸炭窒化炉へ鋼片を載置し、浸窒ガスとしてアンモニアを供給し、浸炭ガスとしてプロパンガスを供給し、８００℃で１８０分間の浸窒処理を施した。この時、一酸化炭素と二酸化炭素の分圧を調整することでＣＰを０．３に制御した。このような浸窒処理を施すことで、最表面のＣ濃度を０．３質量％とし、母材に含まれているＣ量の変化が有効硬化深さに影響しない様にした。
このような浸窒処理を施した後、試験片を１５０℃のホット油内へ浸漬することで焼入れし、その後、加熱炉を用いて１８０℃で１２０分間の焼戻し処理を施して、試験片を得る。
ただし、比較例１４および比較例１５の場合は、ＣＰを０．７とし、８８０℃で６０分間のガス浸炭処理を施した。
実施例および比較例（ただし比較例１４、１５は除く）における浸窒処理の概要を図２に示す。比較例１４、１５における浸炭処理の概要を図３に示す。
In addition, in the following, the carbonitriding process X shall mean the following processes.
A piece of steel was placed in a gas carbonitriding furnace, ammonia was supplied as a carbonitriding gas, propane gas was supplied as a carburizing gas, and a carbonitriding treatment was performed at 800 ° C. for 180 minutes. At this time, CP was controlled to 0.3 by adjusting the partial pressure of carbon monoxide and carbon dioxide. By performing such a carbonitriding treatment, the C concentration of the outermost surface is set to 0.3% by mass, so that the change in the amount of C contained in the base material does not affect the effective curing depth.
After subjecting to such a nitridation treatment, the specimen is quenched by immersing the specimen in a hot oil of 150 ° C., and thereafter, the specimen is subjected to tempering treatment at 180 ° C. for 120 minutes using a heating furnace. obtain.
However, in the case of Comparative Example 14 and Comparative Example 15, CP was set to 0.7, and gas carburizing treatment was performed at 880 ° C. for 60 minutes.
The outline of the nitridation treatment in Examples and Comparative Examples (except for Comparative Examples 14 and 15) is shown in FIG. The outline of the carburizing process in Comparative Examples 14 and 15 is shown in FIG.
このようにして得た試験片Ｂを用いてＪＩＳ Ｚ ２２７４に準拠した方法で小野式回転曲げ疲労試験を行い、疲労強度を調査した。試験条件は回転数３５００ｒｐｍ、試験温度は室温の条件である。また、疲労強度の値は、繰返し数１０7回で破断しない最大応力である疲労限度を意味している。
結果を第２表に示す。
The Ono type rotational bending fatigue test was performed by the method according to JIS Z 2274 using the test piece B thus obtained, and the fatigue strength was examined. The test conditions are a rotation speed of 3500 rpm, and the test temperature is room temperature. Also, the value of fatigue strength means the fatigue limit which is the maximum stress which does not break after several 10 7 cycles.
The results are shown in Table 2.
＜ジョミニー試験＞
鋼塊Ａを熱間圧延または熱間鍛造し、断面直径が１０５ｍｍの丸棒を得た後、さらに熱間鍛造して、断面直径が３０ｍｍの丸棒を得た。そして、焼きならし処理（９２５℃×１ＨｒＡＣ）を実施した。この丸棒から断面直径が２５ｍｍ、長さ１００ｍｍの試験片Ｃを得た。
そして、このような試験片Ｃを、ＪＩＳ Ｇ０５６１に規定されるジョミニー式一端焼入れ試験（９２５℃、３０分）に供した。そして、焼入れ端から５ｍｍにおけるロックウェル硬さ（Ｊ５）を測定した。
結果を第２表に示す。
<Jomnie test>
The steel ingot A was hot-rolled or hot-forged to obtain a round bar having a cross-sectional diameter of 105 mm, and further hot forging to obtain a round bar having a cross-sectional diameter of 30 mm. Then, a normalizing treatment (925 ° C. × 1 HrAC) was performed. From this round bar, a test piece C having a cross-sectional diameter of 25 mm and a length of 100 mm was obtained.
Then, such a test piece C was subjected to the Jominy type one-end quenching test (925 ° C., 30 minutes) defined in JIS G0561. And Rockwell hardness (J5) in 5 mm from a hardening end was measured.
The results are shown in Table 2.
＜歪み（真円からの変形量）の測定＞
鋼塊Ａを熱間圧延または熱間鍛造し、断面直径が１０５ｍｍの丸棒を得て、焼きならし処理後（９２５℃×１ＨｒＡＣ）、この丸棒を加工して、図４に示すような外径１００ｍｍ、内径９０ｍｍ、厚さ２０ｍｍのリング状の試験片素材を得た。
次に、このリング状の試験片素材に浸窒処理Ｘを施して、試験片Ｄを得た。そして、浸窒前および後の各々において試験片Ｄの内径部分の長さを３点測定し、その平均値を算出し、その平均値から内周長さを求め、浸窒前後の内径長さの平均値の差を計算することで真円からの変形量（歪み）を測定した。
結果を第２表に示す。
<Measurement of distortion (the amount of deformation from a perfect circle)>
The steel ingot A is hot-rolled or hot-forged to obtain a round bar having a cross-sectional diameter of 105 mm, and after normalizing treatment (925 ° C. × 1 HrAC), the round bar is processed to have a shape as shown in FIG. A ring-shaped test piece material having an outer diameter of 100 mm, an inner diameter of 90 mm, and a thickness of 20 mm was obtained.
Next, the ring-shaped test piece material was subjected to a nitridation treatment X to obtain a test piece D. Then, the length of the inner diameter portion of the test piece D is measured at three points before and after carbonitriding, the average value is calculated, the inner circumferential length is determined from the average value, and the inner diameter length before and after carbonitriding The amount of deformation (distortion) from a perfect circle was measured by calculating the difference in the average value of.
The results are shown in Table 2.
＜表面Ｃ濃度＞
鋼塊Ａを熱間圧延により断面直径が１０５ｍｍの丸棒を得た後、熱間鍛造により断面直径を３０ｍｍとし、さらに焼きならし処理（９２５℃×１ＨｒＡＣ）を施した後、この丸棒から断面直径２５ｍｍの丸棒（長さ１００ｍｍ）を切り出して得た試験片素材に浸窒処理Ｘを施し、試験片Ｅを得た。
そして、試験片Ｅについて、その表面から０．０５ｍｍの位置までを削り、得られた切り屑（ダライ粉）におけるＣ濃度を測定した。測定には燃焼−赤外線吸収法を用いた。
結果を第２表に示す。
<Surface C concentration>
The steel ingot A is hot-rolled to obtain a round bar having a cross-sectional diameter of 105 mm, and the hot-forging to make the cross-section diameter 30 mm and subjected to normalizing treatment (925 ° C. × 1HrAC). A test strip material obtained by cutting out a round bar (length 100 mm) having a cross-sectional diameter of 25 mm was subjected to carbonitriding treatment X to obtain a test strip E.
And about the test piece E, it cut | removed to the position of 0.05 mm from the surface, and measured C density | concentration in the obtained chip (darai powder). The combustion-infrared absorption method was used for the measurement.
The results are shown in Table 2.
＜表面Ｎ濃度＞
試験片Ｅの表面から０．０５ｍｍの位置までを削って得られた切り屑（ダライ粉）におけるＮ濃度を測定した。測定には融解−熱伝導度測定を用いた。
結果を第２表に示す。
<Surface N concentration>
The N concentration in the chips (dalai powder) obtained by scraping from the surface of the test piece E to a position of 0.05 mm was measured. Melting-thermal conductivity measurement was used for the measurement.
The results are shown in Table 2.
＜窒化物析出量＞
試験片Ｅの表面から０．０５ｍｍの位置までを削って得られた切り屑（ダライ粉）を臭化メタノールによって溶解し、０．２μｍのフィルターを使い析出物を抽出し、窒化物析出量を測定した。測定には蒸留分離−窒素分析法を用いた。
結果を第２表に示す。
<Nitride precipitation amount>
The chips (Dalai powder) obtained by scraping 0.05 mm from the surface of the test piece E are dissolved with methanol bromide, the precipitate is extracted using a 0.2 μm filter, and the nitride deposition amount is It was measured. A distillation separation-nitrogen analysis method was used for the measurement.
The results are shown in Table 2.
＜有効硬化層深さ測定＞
鋼塊Ａを熱間圧延または熱間鍛造し、断面直径が１０５ｍｍの丸棒を得た後、さらに熱間鍛造して、断面直径が３０ｍｍの丸棒を得て、焼きならし処理後（９２５℃×１ＨｒＡＣ）、この丸棒から、断面直径２５ｍｍの丸棒（長さ１０ｍｍ）を切り出して得た鋼片に浸窒処理Ｘを施し、試験片Ｆを得た。
そして、試験片Ｆについて、その一方端面から厚さ方向へ表層からビッカース硬さ測定を試験力２．９４Ｎで試験を実施した。ここで表層から０．５ｍｍまでは０．０２５ｍｍピッチで進み、それ以降は０．１ｍｍピッチで１ｍｍ位置まで硬さを求めた。そして、得られた各位置での硬さを連続的に結び、有効硬化層深さを求めた。なお、表層硬さとは０．０５ｍｍの位置の硬さとし、有効硬化層深さは５１３ＨＶとなる表面からの深さとする。具体的には５１３ＨＶに最も近く、５１３ＨＶの前後の２点の硬さから計算し、５１３ＨＶにおける有効硬化層深さを算出した。
結果を第２表に示す。
<Measurement of effective hardened layer depth>
The steel ingot A is hot-rolled or hot-forged to obtain a round bar having a cross-sectional diameter of 105 mm, and further hot forged to obtain a round bar having a cross-sectional diameter of 30 mm, and after normalizing treatment (925 A steel piece obtained by cutting out a round bar (10 mm in length) having a cross-sectional diameter of 25 mm from this round bar was subjected to carbonitriding treatment X to obtain a test piece F.
And about the test piece F, the Vickers-hardness measurement was implemented by the test power 2.94N from surface layer from thickness direction from the one end surface. Here, from the surface layer, 0.5 mm was advanced at a pitch of 0.025 mm, and thereafter hardness was obtained to a position of 1 mm at a 0.1 mm pitch. And the hardness in each obtained position was connected continuously, and the effective hardened layer depth was calculated. The surface layer hardness is the hardness at a position of 0.05 mm, and the effective hardened layer depth is the depth from the surface of 513 HV. Specifically, it was the closest to 513 HV, and was calculated from the hardness of two points before and after 513 HV, and the effective hardened layer depth at 513 HV was calculated.
The results are shown in Table 2.
＜ミクロ組織観察＞
試験片Ｆについてミクロ組織観察を行った。試験片を半円状に二等分に割り、切断面を被検面となるように樹脂埋めし、鏡面研磨した。研磨された面をナイタールで腐食し、倍率１００〜４００倍で光学顕微鏡および倍率２０００倍でＳＥＭを用い組織観察をした。また、鏡面研磨後の試料を使ってＦＥ−ＥＰＭＡを用い、倍率２，０００倍で表層の窒化物の析出状態を確認した。
<Microstructure observation>
Microstructure observation was performed on the test piece F. The test piece was divided into two halves in a semicircular shape, and the cut surface was filled with resin so as to be a test surface, and mirror-polished. The polished surface was corroded with nital, and the structure was observed using an optical microscope at a magnification of 100 to 400 and an SEM at a magnification of 2000. Moreover, the deposition state of the nitride of surface layer was confirmed by magnification of 2,000 using FE-EPMA using the sample after mirror polishing.
第２表に示した有効硬化深さと式１の計算結果との関係を図５に示す。
図５から、式１の値が０．０４以上であると、Ｓ１５Ｃの１．４倍の有効硬化深さとなることが理解される。なお、１．４倍は処理時間にすると、同一有効硬化深さを得るためにＪＩＳ １５Ｃ対比処理時間が半分になることに相当する。
したがって本発明の鋼材は、短時間（３〜４ｈ程度）で、必要な有効硬化深さを得ることができる鋼材といえる。
The relationship between the effective curing depth shown in Table 2 and the calculation result of Equation 1 is shown in FIG.
It is understood from FIG. 5 that when the value of Formula 1 is 0.04 or more, the effective curing depth is 1.4 times that of S15C. In addition, if processing time is made into 1.4 time, in order to obtain the same effective hardening depth, it is equivalent to half processing time compared with JIS 15C.
Accordingly, the steel material of the present invention can be said to be a steel material capable of obtaining a necessary effective hardening depth in a short time (about 3 to 4 hours).
第１表に示したロックウェル硬さ（Ｊ５）と真円からの変形量（歪み）との関係を、図６に示す。
図６からロックウェル硬さ（Ｊ５）がおよそ２０ＨＲＣ以下であると変形量が少ないことが分かる。フルマルテンサイトの硬さは炭素量で整理でき、０．０５〜０．３％の範囲では（６０Ｃ＋３１）ＨＲＣと表すことができる。一般的に、ロックウェル硬さ（Ｊ５）がフルマルテンサイトとなる半分（（６０Ｃ＋３１）／２）以下（０．１５％の場合は２０ＨＲＣ）であれば歪（変形量）に影響が大きいマルテンサイト組織が生成せず、フェライト＋パーライト＋少量のベイナイト組織となる。すなわち、式２≦（（６０Ｃ＋３１）／２）を満たすのであれば、マルテンサイト量を減らすことができ、歪を大幅に低下させることができる。また、比較例１４と１５は、それぞれ汎用肌焼鋼であるＳＣＲ４１５とＳＣＲ４２０であるが、それらに対して大幅に歪が低下していることがわかる。
実機の薄肉部品を想定した場合、薄物部品の芯部の冷却速度はおよそジョミニー値のＪ３〜Ｊ５程度であり、本発明の鋼材はこれらの冷却速度でのマルテンサイト量を減らすことで歪が大きく低減できる。
The relationship between the Rockwell hardness (J5) shown in Table 1 and the amount of deformation (distortion) from a perfect circle is shown in FIG.
It can be seen from FIG. 6 that the amount of deformation is small when the Rockwell hardness (J5) is approximately 20 HRC or less. The hardness of full martensite can be arranged by the amount of carbon, and can be expressed as (60C + 31) HRC in the range of 0.05 to 0.3%. In general, martensite having a large influence on strain (deformation amount) if Rockwell hardness (J5) is half ((60C + 31) / 2) or less (20 HRC in the case of 0.15%) at which full martensite is achieved No structure is formed, resulting in ferrite + pearlite + small amount of bainite structure. That is, if the formula 2 ≦ ((60C + 31) / 2) is satisfied, the amount of martensite can be reduced, and the strain can be significantly reduced. Moreover, although comparative example 14 and 15 are SCR 415 and SCR 420 which are general purpose case-hardening steels, respectively, it turns out that distortion is falling sharply to them.
Assuming thin-walled parts of actual machines, the cooling speed of the core of thin parts is approximately J3 to J5 of the jominy value, and the steel of the present invention has a large strain by reducing the amount of martensite at these cooling speeds. It can be reduced.
第２表に示した表面Ｎ濃度および窒化物析出量から、窒化物析出割合（＝窒化物析出量／表面Ｎ濃度×１００（％））を求めた。求められた窒化物析出割合と疲労強度との関係を、図７に示す。
図７から、表層Ｎのうち窒化物となったＮの割合が２２％以上となると、疲労強度のばらつきが大きくなっていることが分かる。組織写真（ＳＥＭ２０００倍、図８）から、窒化物の生成により、焼入れ性を担保するために添加していた元素が母相から奪われ、固溶Ｎの低減により形成された不完全焼入れ組織が確認される。さらにＦＥ−ＥＰＭＡ（２０００倍、図９）から窒化物の生成を見てとることができる。疲労強度が低下した試験片は、すべてはこの様な不完全焼入組織と多量の窒化物生成が確認され、疲労強度との因果関係が明らかになった。
本発明の鋼材は、窒化物析出量を抑制しているため、疲労強度のばらつきや低下が起こらない鋼材であるといえる。
From the surface N concentration and the nitride deposition amount shown in Table 2, the nitride deposition ratio (= nitride deposition amount / surface N concentration × 100 (%)) was determined. The relationship between the nitride precipitation ratio thus determined and the fatigue strength is shown in FIG.
It can be seen from FIG. 7 that when the ratio of N which has become nitride in the surface layer N is 22% or more, the variation in fatigue strength is large. From the microstructure photograph (SEM 2000 times, FIG. 8), due to the formation of nitride, the element added for securing the hardenability is deprived from the matrix phase, and the incompletely quenched structure formed by the reduction of solid solution N is It is confirmed. Furthermore, the formation of nitride can be seen from FE-EPMA (2000 ×, FIG. 9). All the specimens with reduced fatigue strength were confirmed to have such a partially quenched structure and a large amount of nitride formation, revealing a causal relationship with the fatigue strength.
Since the steel material of the present invention suppresses the nitride precipitation amount, it can be said that the steel material of the present invention is a steel material which does not cause variation or reduction in fatigue strength.
Claims (2)
Ｓｉ：０．３０質量％以下、
Ｍｎ：０．６１〜２．０質量％、
Ｐ：０．１質量％以下、
Ｓ：０．１質量％以下、
Ｃｒ：０．７質量％以下、
Ａｌ：１０〜８００ｐｐｍ、
Ｎ：１０〜３００ｐｐｍ、
で含有し、残部はＦｅおよび不可避的不純物からなり、
式１＝−０．２２５×Ｓｉ＋０．０８３×Ｍｎ＋０．０９１×Ｃｒ＋０．０３５×Ｃｕ＋０．０４７×Ｎｉ＋０．０９２×Ｍｏ
と定義した場合に、式１≧０．０４を満たし、
式２＝−２０＋７４×Ｃ＋７×Ｓｉ＋１５×Ｍｎ＋２６×Ｃｒ＋１０×Ｃｕ＋１２Ｎｉ＋３０×Ｍｏ
と定義した場合に、式２≦（６０×Ｃ＋３１）／２を満たし、
式３＝２５．４×Ｓｉ＋２０．３×Ｃｒ＋３２．８×Ｓｉ×Ｍｎ
と定義した場合に、式３≦２２を満たす、浸窒処理用鋼材。 C: 0.05 to 0.25 mass%,
Si: 0.30 mass% or less,
Mn: 0.61 to 2.0% by mass,
P: 0.1 mass% or less,
S: 0.1 mass% or less,
Cr: 0.7 mass% or less,
Al: 10 to 800 ppm,
N: 10 to 300 ppm,
And the balance consists of Fe and unavoidable impurities,
Formula 1 = -0.225xSi + 0.083xMn + 0.091xCr + 0.035xCu + 0.047xNi + 0.092xMo
Satisfying the equation 1 ≧ 0.04 when defined as
Formula 2 = -20 + 74 x C + 7 x Si + 15 x Mn + 26 x Cr + 10 x Cu + 12 Ni + 30 x Mo
Satisfying the equation 2 ≦ (60 × C + 31) / 2 when defined as
Formula 3 = 25.4 x Si + 20.3 x Cr + 32.8 x Si x Mn
A steel material for nitriding treatment that satisfies the formula 3 ≦ 22 when defined as
Ｎｉ：０．５質量％以下、
Ｍｏ：０．６質量％以下、
Ｖ：０．３質量％以下、
Ｎｂ：０．１質量％以下、
からなる群から選ばれる一種または二種以上をさらに含有する、請求項１に記載の浸窒処理用鋼材。 Cu: 0.3 mass% or less,
Ni: 0.5 mass% or less,
Mo: 0.6 mass% or less,
V: 0.3 mass% or less,
Nb: 0.1% by mass or less,
The steel for nitriding treatment according to claim 1, further comprising one or more selected from the group consisting of
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| JP2012036495A (en) * | 2010-07-16 | 2012-02-23 | Sumitomo Metal Ind Ltd | Method for manufacturing nitrided machine part |
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