JPH1129836A - Steel for machine structural use for induction hardening - Google Patents
Steel for machine structural use for induction hardeningInfo
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- JPH1129836A JPH1129836A JP17852797A JP17852797A JPH1129836A JP H1129836 A JPH1129836 A JP H1129836A JP 17852797 A JP17852797 A JP 17852797A JP 17852797 A JP17852797 A JP 17852797A JP H1129836 A JPH1129836 A JP H1129836A
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- steel
- torsional
- strength
- induction hardening
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Abstract
Description
【０００１】[0001]
【発明の属する技術分野】本発明は、機械構造用鋼に関
し、とくに高周波焼入れを施し使用される自動車用ドラ
イブシャフトあるいは等速ジョイント等に適用されて好
適な機械構造用鋼に関する。BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a steel for a machine structure, and more particularly to a steel for a machine structure suitably applied to a drive shaft or a constant velocity joint for an automobile which is used after being subjected to induction hardening.
【０００２】[0002]
【従来の技術】近年、環境規制問題から、自動車部材に
対し部材の軽量化の要求が強い。軽量化のためには、部
材の高強度化が必要であり、この点から自動車の動力伝
達系を構成する機械構造用部材（軸部品）ではねじり強
度、ねじり疲労強度の向上が要望されている。2. Description of the Related Art In recent years, there has been a strong demand for automobile members to be lighter due to environmental regulations. In order to reduce the weight, it is necessary to increase the strength of the members, and from this point, there is a demand for improvement in torsional strength and torsional fatigue strength of mechanical structural members (shaft parts) constituting a power transmission system of an automobile. .
【０００３】従来から、自動車用ドライブシャフトある
いは等速ジョイント等の軸部品は、熱間圧延棒鋼を熱間
鍛造、切削、冷間鍛造等により所定の形状に加工したの
ち、高周波焼入れ・焼戻し処理を施し、軸部品としての
重要な特性であるねじり強度、ねじり疲労強度を確保し
ている。例えば、特開平7-90484 号公報には、Ｃ：0.35
〜0.70％、Ｓ：0.005 〜0.15％、Al：0.0005〜0.05％、
Ti：0.005 〜0.05％、Ｂ：0.0005〜0.005 ％、Ｎ：0.00
2 〜0.02％と特定量のSi、Mn、を含み、Ｐ、Cu、Ｏを特
定量以下に規制し、さらにまたは特定量のCr、Mo、Ni、
Nb、Ｖ等を含有し特定の式で定義される断面内平均硬さ
が560 以上とする、焼割れを防止し160kgf/mm2以上のね
じり強度を有する高強度高周波焼入れ軸部品が提案され
ている。Conventionally, shaft parts such as drive shafts or constant velocity joints for automobiles are manufactured by hot forging, cutting, cold forging, etc., into a predetermined shape, and then subjected to induction hardening and tempering. The torsional strength and torsional fatigue strength, which are important characteristics of shaft parts, are secured. For example, JP-A-7-90484 discloses that C: 0.35
~ 0.70%, S: 0.005 ~ 0.15%, Al: 0.0005 ~ 0.05%,
Ti: 0.005 to 0.05%, B: 0.0005 to 0.005%, N: 0.00
2 to 0.02% containing specific amounts of Si and Mn, regulating P, Cu, and O to a specific amount or less, and further or a specific amount of Cr, Mo, Ni,
A high-strength induction hardened shaft part containing Nb, V, etc., having an average hardness in a cross section defined by a specific formula of 560 or more, preventing quench cracks and having a torsional strength of 160 kgf / mm 2 or more has been proposed. I have.
【０００４】また、特開平8-253842号公報には、Ｃ：0.
35〜0.65％、Si：0.35〜2.5 ％、Mn：1.0 〜1.8 ％、M
o：0.05〜0.8 ％、Ｓ：0.01〜0.15％、Al：0.015 〜0.0
5％、Ti：0.005 〜0.05％、Ｂ：0.0005〜0.005 ％、
Ｎ：0.002 〜0.01％を含み、Ｐ、Cu、Ｏを特定量以下に
規制し、さらにまたは特定量のNb、Ｖの１種または２
種、またはさらに特定量のCr、Niの１種または２種を含
有し、かつフェライトの組織分率が35％以下で、フェラ
イト結晶粒径が20μm 以下とするねじり疲労強度の優れ
た高周波焼入れ軸部材用鋼材が提案されている。[0004] Japanese Patent Application Laid-Open No. 8-253842 discloses that C: 0.
35-0.65%, Si: 0.35-2.5%, Mn: 1.0-1.8%, M
o: 0.05-0.8%, S: 0.01-0.15%, Al: 0.015-0.0
5%, Ti: 0.005-0.05%, B: 0.0005-0.005%,
N: contains 0.002 to 0.01%, restricts P, Cu, and O to a specific amount or less, and further or a specific amount of one or two of Nb and V
Induction-hardened shaft with excellent torsional fatigue strength, containing one or two or more specific amounts of Cr and Ni, and having a ferrite structure fraction of 35% or less and a ferrite crystal grain size of 20 μm or less. Steel members have been proposed.
【０００５】[0005]
【発明が解決しようとする課題】しかしながら、特開平
7-90484 号公報に記載された技術では、焼割れと静的ね
じり強度については言及されているものの、ねじり疲労
強度については全く配慮されていない。また、特開平8-
253842号公報に記載された技術では、静的ねじり強度と
ねじり疲労強度については言及されているが、機械構造
用部材として重要な高周波焼入れ時の耐焼割れ性につい
ては配慮が不足している。本発明者らの検討によれば、
特開平8-253842号公報に記載された鋼材では、焼割れに
対する配慮がなされていないため、高周波焼入れ・焼戻
し後の有効硬化層深さ（JIS G 0559参照）が５mm超える
と多数の焼割れが発生し、また有効硬化層深さが５mm程
度でも焼割れの発生が避けられないという問題が残され
ていた。SUMMARY OF THE INVENTION
In the technology described in Japanese Patent Application Laid-Open No. 7-90484, although cracking and static torsional strength are mentioned, no consideration is given to torsional fatigue strength. Also, JP-A-8-
In the technique described in Japanese Patent No. 253842, static torsional strength and torsional fatigue strength are mentioned, but consideration is not given to quenching crack resistance during induction hardening, which is important as a member for machine structures. According to the study of the present inventors,
In the steel described in Japanese Patent Application Laid-Open No. 8-253842, no consideration is given to quenching. If the effective hardened layer depth after induction hardening / tempering (see JIS G 0559) exceeds 5 mm, many The problem remains that even when the effective hardened layer depth is about 5 mm, the occurrence of sintering cracks is unavoidable.
【０００６】本発明は、上記した問題を有利に解決し、
高周波焼入れ焼戻し後のねじり強度、ねじり疲労強度お
よび耐焼割れ性に優れた高周波焼入れ用機械構造用鋼お
よびその製造方法を提案することを目的とする。The present invention advantageously solves the above problems,
An object of the present invention is to propose a steel for machine structural use for induction hardening having excellent torsional strength, torsional fatigue strength and resistance to quenching cracking after induction hardening and tempering, and a method for producing the same.
【０００７】[0007]
【課題を解決するための手段】本発明者らは、上記した
課題を達成するために、鋭意検討した結果、機械構造用
鋼材の高周波焼入れ焼戻し後のねじり強度、ねじり疲労
強度および耐焼割れ性をともに向上させるには、Al含有
量を増加することが極めて有効であるという知見を得
た。これは、Al含有量の増加により、 AlN 量が増加し、高周波焼入れ加熱時にオーステナイ
ト粒が微細化し、その結果焼入れ硬化層の組織が微細化
する、 その焼入れ硬化層組織の微細化により粒界面積が増加
し、粒界脆化を起こすＰ、Ｓ、Cu、Ｏの粒界における偏
析量が減少し、耐焼割れ性が向上する、 ＯをAl2O3 として固定し、粒界脆化を起こす酸素量を
低下させ、ねじり強度およびねじり疲労強度が向上す
る、 ＮをAlN として固定し、Ｎ固定のためのTi添加量を低
減でき、その結果、ねじり疲労強度に悪影響を及ぼすTi
N を低減でき、ねじり疲労強度が向上し、また靱性の低
下を防止できる、ためであると推察された。Means for Solving the Problems The present inventors have conducted intensive studies in order to achieve the above-mentioned object, and as a result, have determined the torsional strength, torsional fatigue strength and torsional cracking resistance of steel for machine structural use after induction hardening and tempering. It has been found that increasing the Al content is extremely effective in improving both. This is because the Al content increases due to the increase in Al content, the austenite grains become finer during induction quenching heating, and the structure of the quenched hardened layer becomes finer. Increases, the amount of segregation of P, S, Cu, O causing grain boundary embrittlement decreases at the grain boundaries, and the resistance to sintering cracks improves. O is fixed as Al 2 O 3 , causing grain boundary embrittlement. Reduces the amount of oxygen, improves torsional strength and torsional fatigue strength. Fixes N as AlN, reduces the amount of Ti added for N fixation, and as a result, adversely affects torsional fatigue strength.
It is presumed that this is because N can be reduced, torsional fatigue strength can be improved, and a decrease in toughness can be prevented.
【０００８】本発明は、上記した知見に基づいて構成さ
れたものである。すなわち、本発明は、重量％で、Ｃ：
0.45〜0.70％、Si：0.01〜0.40％、Mn：0.2 〜2.5 ％、
Ｐ：0.020 ％以下、Ｓ：0.06％以下、Al：0.05超〜0.25
％、Ｎ：0.0020〜0.025 ％、Ｏ：0.0020％以下、Ｂ：0.
0003〜0.0060％を含有し、残部Feおよび不可避的不純物
よりなることを特徴とする高周波焼入れ焼戻し後のねじ
り強度、ねじり疲労強度および耐焼割れ性に優れる高周
波焼入れ用機械構造用鋼であり、上記した主組成に加え
てさらに重量％で、Ti：0.005 〜0.05％を含有してもよ
く、また主組成に加えてさらに重量％で、Mo：0.05〜1.
0 ％、Cr：0.01〜1.0 ％、Cu：1.0 ％以下、Ni：0.1 〜
3.5 ％のうちから選ばれた１種または２種以上を含有し
てもよく、また上記主組成に加えてさらに重量％で、
Ｖ：0.05〜0.5％、Nb：0.01〜0.05％のうちから選ばれ
た１種または２種を含有してもよい。また、上記主組成
に加えてTi：0.005 〜0.05％と、Mo：0.05〜1.0 ％、C
r：0.01〜1.0 ％、Cu：1.0 ％以下、Ni：0.1 〜3.5 ％
のうちから選ばれた１種または２種以上を含有してもよ
い。また、上記主組成に加えてTi：0.005 〜0.05％と、
Ｖ：0.05〜0.5 ％、Nb：0.01〜0.05％のうちから選ばれ
た１種または２種を含有してもよい。また、上記主組成
に加えてMo：0.05〜1.0 ％、Cr：0.01〜1.0 ％、Cu：1.
0 ％以下、Ni：0.1 〜3.5 ％のうちから選ばれた１種ま
たは２種以上と、Ｖ：0.05〜0.5 ％、Nb：0.01〜0.05％
のうちから選ばれた１種または２種を含有してもよい。
また、上記主組成に加えてTi：0.005 〜0.05％と、Mo：
0.05〜1.0 ％、Cr：0.01〜1.0 ％、Cu：1.0 ％以下、N
i：0.1 〜3.5 ％のうちから選ばれた１種または２種以
上、およびＶ：0.05〜0.5 ％、Nb：0.01〜0.05％のうち
から選ばれた１種または２種を含有してもよい。The present invention has been made based on the above findings. That is, the present invention provides a method for preparing C:
0.45 to 0.70%, Si: 0.01 to 0.40%, Mn: 0.2 to 2.5%,
P: 0.020% or less, S: 0.06% or less, Al: more than 0.05 to 0.25
%, N: 0.0020 to 0.025%, O: 0.0020% or less, B: 0.
A steel for machine structural use for induction hardening having excellent torsional strength, torsional fatigue strength and resistance to quenching cracking after induction hardening and tempering, characterized by containing 0003 to 0.0060% and the balance being Fe and inevitable impurities. In addition to the main composition, it may further contain Ti: 0.005 to 0.05% by weight, and also in addition to the main composition, Mo: 0.05 to 1.
0%, Cr: 0.01-1.0%, Cu: 1.0% or less, Ni: 0.1-
One or more selected from 3.5% may be contained, and in addition to the above main composition, in weight%,
V: 0.05 to 0.5%, Nb: One to two selected from 0.01 to 0.05% may be contained. Further, in addition to the above main composition, Ti: 0.005 to 0.05%, Mo: 0.05 to 1.0%, C
r: 0.01 to 1.0%, Cu: 1.0% or less, Ni: 0.1 to 3.5%
One or two or more selected from the above may be contained. Further, in addition to the above main composition, Ti: 0.005 to 0.05%,
V: 0.05 to 0.5%, Nb: 0.01 to 0.05%, may contain one or two selected from the group. Further, in addition to the above main composition, Mo: 0.05 to 1.0%, Cr: 0.01 to 1.0%, Cu: 1.
0% or less, Ni: 0.1 to 3.5%, one or more selected from among them, V: 0.05 to 0.5%, Nb: 0.01 to 0.05%
One or two selected from the above may be contained.
Further, in addition to the above main composition, Ti: 0.005 to 0.05%, and Mo:
0.05-1.0%, Cr: 0.01-1.0%, Cu: 1.0% or less, N
i: may contain one or more selected from 0.1 to 3.5%, and one or two selected from V: 0.05 to 0.5% and Nb: 0.01 to 0.05%. .
【０００９】また、本発明では、次（１）式 Ｍs 値＝538-317 ( ％Ｃ) -11(％ Si)-33(％ Mn)-28(％Cr)-11( ％Mo)-17( ％ Ni)-11( ％Cu)+6(％Ｖ)+10( ％Al) ……（１） （ここに、％Ｃ、％ Si 、％ Mn ％Cr、％Mo、％Ni、％
Cu、％Ｖ、％Al：各元素の含有量（重量％））で定義さ
れるＭs 値が315 以上とするのが好ましい。Further, in the present invention, the following equation (1): Ms value = 538-317 (% C) -11 (% Si) -33 (% Mn) -28 (% Cr) -11 (% Mo) -17 (% Ni) -11 (% Cu) +6 (% V) +10 (% Al) (1) (where% C,% Si,% Mn% Cr,% Mo,% Ni,%
It is preferable that the Ms value defined by Cu,% V, and% Al: the content (% by weight) of each element is 315 or more.
【００１０】また、本発明は、上記したいずれかの組成
の鋼素材を切削加工あるいは冷間加工により所定の形状
に加工し、高周波焼入れを行ったのち焼戻し処理として
175℃以上の温度で10min 以上の加熱を施すことを特徴
とする高周波焼入れ焼戻し後のねじり強度、ねじり疲労
強度および耐焼割れ性に優れる高周波焼入れ用鋼の製造
方法である。[0010] The present invention is also directed to a steel material having any one of the above-mentioned compositions, which is formed into a predetermined shape by cutting or cold working, subjected to induction hardening, and then tempered.
A method for producing induction hardening steel having excellent torsional strength, torsional fatigue strength and resistance to quenching cracking after induction hardening and tempering, characterized in that heating is performed at a temperature of 175 ° C. or more for 10 minutes or more.
【００１１】[0011]
【発明の実施の形態】まず、本発明鋼の組成の限定理由
について説明する。 Ｃ：0.45〜0.70％ Ｃは、高周波焼入れ性に最も大きな影響を及ぼす元素で
あり、焼入れ硬化層の硬さ、深さを増加し、ねじり強度
を向上させる。しかし、0.45％未満では、焼入れ硬化層
の硬さが低く、必要なねじり強度を得るためには焼入れ
硬化深さを飛躍的に大きくする必要があるが、焼入れ硬
化深さを大きくすると、焼割れの発生が顕著となる。一
方、0.70％を超えると、切削性、冷間鍛造性が低下する
とともに、ねじり試験時に脆性破壊を起こし、ねじり強
度が低下するうえ、耐焼割れ性も低下する。このような
ことから、Ｃは0.45〜0.70％の範囲に限定した。First, the reasons for limiting the composition of the steel of the present invention will be described. C: 0.45 to 0.70% C is an element that has the greatest effect on induction hardening, and increases the hardness and depth of the hardened hardened layer and improves the torsional strength. However, if it is less than 0.45%, the hardness of the quench hardened layer is low, and it is necessary to dramatically increase the quench hardening depth to obtain the required torsional strength. The occurrence of is remarkable. On the other hand, when the content exceeds 0.70%, the machinability and the cold forgeability deteriorate, and brittle fracture occurs during the torsional test, so that the torsional strength decreases and the sintering crack resistance also decreases. For these reasons, C is limited to the range of 0.45 to 0.70%.
【００１２】Si：0.01〜0.40％ Siは、脱酸元素として作用するほか、フェライト中に固
溶して基地を強化するとともに、高周波焼入れ後の焼戻
し軟化抵抗を向上させねじり強度を向上させる元素であ
る。このような効果は、0.01％以上の添加で認められる
が、0.4 ％を超えて添加するとフェライトの固溶硬化に
より硬さが上昇し切削性、冷間鍛造性が低下する。この
ため、Siは0.01〜0.40％の範囲に限定した。なお、好ま
しくは、0.01〜0.30％の範囲である。Si: 0.01 to 0.40% Si acts as a deoxidizing element, and also forms a solid solution in ferrite to strengthen the matrix, and also improves the tempering softening resistance after induction hardening and improves the torsional strength. is there. Such an effect is observed when the content is 0.01% or more. However, when the content exceeds 0.4%, the hardness increases due to solid solution hardening of the ferrite, and the machinability and the cold forgeability decrease. For this reason, Si was limited to the range of 0.01 to 0.40%. In addition, Preferably, it is the range of 0.01 to 0.30%.
【００１３】Mn：0.2 〜2.5 ％ Mnは、焼入れ性を向上させ、高周波焼入れ時の硬化深さ
を深くする元素で積極的に添加するが、0.2 ％未満の添
加ではその効果が小さい。一方、2.5 ％を超える添加
は、高周波焼入れ時に残留オーステナイトを増加させ、
表面硬さを低下させる。このため、ねじり強度、ねじり
疲労強度が低下する。このようなことから、Mnは0.2 〜
2.5 ％の範囲に限定した。なお、好ましくは0.2 〜2.0
％である。Mn: 0.2 to 2.5% Mn is an element which improves the hardenability and deepens the hardening depth during induction hardening, but its effect is small when added less than 0.2%. On the other hand, the addition exceeding 2.5% increases the retained austenite during induction hardening,
Decreases surface hardness. For this reason, torsional strength and torsional fatigue strength decrease. Therefore, Mn is 0.2 ~
Limited to the 2.5% range. Preferably, 0.2 to 2.0
%.
【００１４】Ｐ：0.020 ％以下 Ｐは、オーステナイト粒界に偏析し、粒界強度を低下さ
せ、ねじり強度、ねじり疲労強度を低下させるとともに
焼割れを助長する。このようなことから、Ｐ含有量は極
力低減するのが望ましいが、0.020 ％までは許容できる
ので、0.020 ％を上限とした。P: not more than 0.020% P segregates at austenite grain boundaries, reduces grain boundary strength, reduces torsional strength and torsional fatigue strength, and promotes quenching cracking. For this reason, it is desirable to reduce the P content as much as possible. However, since the P content is acceptable up to 0.020%, the upper limit is made 0.020%.
【００１５】Ｓ：0.06％以下 Ｓは、鋼中でMnS を形成し、切削性を向上させるが、0.
06％を超えて添加すると、粒界に偏析し粒界強度を低下
させる。このため、Ｓは0.06％を上限とした。なお、好
ましくは0.01〜0.04％である。 Al：0.05超〜0.25％ Alは、本発明で重要な元素であり積極的に添加する。Al
は、脱酸元素として低酸素化のために作用するほか、Ｎ
と結合してAlN を形成し高周波焼入れ加熱時のオーステ
ナイト粒の成長を抑制することにより、ねじり強度、ね
じり疲労強度を向上させる。0.05％以下では、上記した
効果が小さく、一方、0.25％を超えて添加しても、効果
が飽和するうえ、コストの上昇を招くため、Alは0.05超
〜0.25％の範囲に限定した。なお、コストの点から、好
ましくは0.05〜0.10％である。S: 0.06% or less S forms MnS in steel and improves machinability.
If added in excess of 06%, segregation occurs at the grain boundaries and the grain boundary strength decreases. Therefore, the upper limit of S is set to 0.06%. In addition, it is preferably 0.01 to 0.04%. Al: more than 0.05 to 0.25% Al is an important element in the present invention and is positively added. Al
Acts as a deoxidizing element for lowering oxygen, and N
To form AlN and suppress the growth of austenite grains during induction quenching heating, thereby improving torsional strength and torsional fatigue strength. If the content is 0.05% or less, the above-described effect is small. On the other hand, if the content exceeds 0.25%, the effect is saturated and the cost is increased. In addition, from a point of cost, it is preferably 0.05 to 0.10%.
【００１６】Ｎ：0.0020〜0.025 ％ Ｎは、Alと結合してAlN を形成し高周波焼入れ加熱時の
オーステナイト粒の成長を抑制し、ねじり強度、ねじり
疲労強度を向上させる。0.0020％未満では、この効果が
認められず、一方、0.025 ％を超えて含有すると、熱間
変形能を低下させ連続鋳造時に鋳片の表面欠陥を著しく
増加させる。このため、Ｎは0.0020〜0.025 ％の範囲に
限定した。なお、好ましくは0.0030〜0.010 ％の範囲で
ある。N: 0.0020 to 0.025% N combines with Al to form AlN, suppresses the growth of austenite grains during induction hardening heating, and improves torsional strength and torsional fatigue strength. If it is less than 0.0020%, this effect is not recognized, while if it exceeds 0.025%, the hot deformability is reduced and the surface defects of the slab are significantly increased during continuous casting. For this reason, N is limited to the range of 0.0020 to 0.025%. Incidentally, the content is preferably in the range of 0.0030 to 0.010%.
【００１７】Ｏ：0.0020％以下 Ｏは、硬質の酸化物系非金属介在物として存在するとと
もに、粒界に偏析し粒界強度を低下させる。さらにＯ量
の増加は酸化物系非金属介在物を粗大化させる。粗大化
した酸化物系非金属介在物は、とくにねじり疲労強度を
低下させるため、できるだけ低減するのが望ましいが、
0.0020％までは許容できる。このようなことから、Ｏは
0.0020％以下に限定した。O: 0.0020% or less O exists as hard oxide-based nonmetallic inclusions and segregates at the grain boundaries to lower the grain boundary strength. Further, an increase in the amount of O coarsens oxide-based nonmetallic inclusions. The coarser oxide-based nonmetallic inclusions reduce the torsional fatigue strength, so it is desirable to reduce as much as possible.
Up to 0.0020% is acceptable. Because of this, O
Limited to 0.0020% or less.
【００１８】Ｂ：0.0003〜0.0060％ Ｂは、微量の添加量で焼入れ性を向上させる元素であ
り、高周波焼入れ時の焼入れ深さを増加させる作用を有
している。また、Ｂは粒界に優先的に偏析し、粒界に偏
析しやすいＰの粒界濃度を低減させ粒界強度を高める作
用を有している。焼入れ深さの増加によるねじり強度の
増加と、粒界強度の増加によるねじり強度とねじり疲労
強度の増加が期待できるため、本発明では積極的に添加
する。0.0003％未満ではその効果が少なく、また0.0060
％を超えて添加しても、添加量に見合う効果が期待でき
ずコストの上昇を招くため、Ｂは0.0003〜0.0060％の範
囲に限定した。B: 0.0003% to 0.0060% B is an element that improves the hardenability with a small amount of addition, and has the effect of increasing the quenching depth during induction hardening. In addition, B preferentially segregates at the grain boundaries, has the effect of reducing the grain boundary concentration of P, which tends to segregate at the grain boundaries, and increasing the grain boundary strength. In the present invention, since the increase in torsional strength due to the increase in the quenching depth and the increase in torsional strength and torsional fatigue strength due to the increase in the grain boundary strength can be expected. Less than 0.0003% has little effect, and 0.0060%
%, The effect corresponding to the added amount cannot be expected and the cost is increased. Therefore, B is limited to the range of 0.0003 to 0.0060%.
【００１９】Ti：0.005 〜0.05％ Tiは、ＢよりＮと結合しやすく、ＢがＮと結合するのを
防止しＢの焼入れ性向上効果を発揮させるために添加す
ることができる。0.005 ％未満の添加では、その効果は
認められない。一方、TiとＮが結合し形成されたTiN
は、疲労破壊の起点となりねじり疲労強度を低下させ
る。0.05％を超えてTiを添加すると、TiN が多量に形成
され、ねじり疲労強度が著しく低下する。このため、Ti
は0.005 〜0.05％の範囲に限定した。Ti: 0.005 to 0.05% Ti is more easily bonded to N than B, and can be added to prevent B from being bonded to N and exhibit the effect of improving the hardenability of B. If less than 0.005% is added, the effect is not observed. On the other hand, TiN formed by combining Ti and N
Becomes the starting point of fatigue fracture and lowers the torsional fatigue strength. If more than 0.05% of Ti is added, a large amount of TiN is formed, and the torsional fatigue strength is significantly reduced. For this reason, Ti
Is limited to the range of 0.005 to 0.05%.
【００２０】Mo：0.05〜1.0 ％、Cr：0.01〜1.0 ％、C
u：1.0 ％以下、Ni：0.1 〜3.5 ％のうちから選ばれた
１種または２種以上 Mo：0.05〜1.0 ％ Moは、焼入れ性および焼戻し軟化抵抗を向上させる元素
である。鋼材の焼入れ性を調整するために添加すること
ができる。また、Moは粒界に偏析するＰ等の不純物元素
を低減させ、粒界強度を高め、粒界破壊を抑制する作用
を有している。Moは、これらの作用によりねじり強度お
よびねじり疲労強度を向上させる。0.05％未満の添加で
は、その効果が認められない。一方、1.0 ％を超えて添
加すると、高周波加熱のような短時間の加熱ではオース
テナイト中への溶解が困難な炭化物を形成し、ねじり疲
労強度が劣化する。このため、Moは0.05〜1.0 ％の範囲
に限定した。Mo: 0.05-1.0%, Cr: 0.01-1.0%, C
u: 1.0% or less, Ni: one or more selected from 0.1 to 3.5% Mo: 0.05 to 1.0% Mo is an element that improves the hardenability and the tempering softening resistance. It can be added to adjust the hardenability of steel. Mo has the effect of reducing impurity elements such as P segregated at the grain boundaries, increasing the grain boundary strength, and suppressing grain boundary destruction. Mo improves torsional strength and torsional fatigue strength by these actions. If less than 0.05% is added, the effect is not recognized. On the other hand, if it is added in excess of 1.0%, carbides that are difficult to dissolve in austenite by short-time heating such as high-frequency heating are formed, and the torsional fatigue strength deteriorates. For this reason, Mo was limited to the range of 0.05 to 1.0%.
【００２１】Cr：0.01〜1.0 ％ Crは、焼入れ性を向上させる元素であり、鋼材の焼入れ
性を調整するために添加できる。しかし、Crは高価な元
素であり、1.0 ％を超えて添加すると経済的に不利とな
る。 Cu：1.0 ％以下 Cuは、焼入れ性を向上させる元素であり、鋼材の焼入れ
性を調整するために添加できる。またCuは、基地中に固
溶あるいは析出して鋼の強度を増加させ、ねじり強度を
高める。しかし、1.0 ％を超えて添加すると熱間加工性
が劣化するため、Cuは1.0 ％以下に限定した。Cr: 0.01 to 1.0% Cr is an element that improves the hardenability and can be added to adjust the hardenability of steel. However, Cr is an expensive element, and it is economically disadvantageous to add more than 1.0%. Cu: 1.0% or less Cu is an element that improves hardenability and can be added to adjust the hardenability of steel. Further, Cu forms a solid solution or precipitates in the matrix to increase the strength of the steel and increase the torsional strength. However, if added in excess of 1.0%, the hot workability deteriorates, so Cu was limited to 1.0% or less.
【００２２】Ni：0.1 〜3.5 ％ Niは、焼入れ性を向上させる元素であり、鋼材の焼入れ
性を調整するために添加できる。しかし、0.1 ％未満の
添加では、期待した効果が認められない。一方、Niは極
めて高価な元素であるため、多量添加は経済的に不利と
なる。このためNiの添加は3.5 ％以下に限定した。Ni: 0.1-3.5% Ni is an element for improving the hardenability, and can be added to adjust the hardenability of the steel material. However, the addition of less than 0.1% does not provide the expected effect. On the other hand, Ni is an extremely expensive element, so that large amount addition is economically disadvantageous. Therefore, the addition of Ni is limited to 3.5% or less.
【００２３】Ｖ：0.05〜0.5 ％、Nb：0.01〜0.05％のう
ちから選ばれた１種または２種 Ｖ：0.05〜0.5 ％ Ｖは、析出硬化により鋼の強度を増加させ、また焼戻し
軟化抵抗を増加させる元素であり、ねじり強度を高め
る。しかし、0.05％未満の添加では、強度の増加が少な
く、一方、0.5 ％を超えて添加しても添加量に見合う強
度の増加が認められない。このため、Ｖは0.05〜0.5 ％
の範囲に限定した。V: 0.05 to 0.5%, Nb: one or two selected from 0.01 to 0.05% V: 0.05 to 0.5% V increases the strength of the steel by precipitation hardening and also has a resistance to temper softening. Is an element that increases torsional strength. However, when the addition is less than 0.05%, the increase in strength is small, while when the addition exceeds 0.5%, the increase in strength corresponding to the added amount is not observed. Therefore, V is 0.05-0.5%
Limited to the range.
【００２４】Nb：0.01〜0.05％ Nbは、析出硬化により鋼の強度を増加させ、また焼戻し
軟化抵抗を増加させる元素であり、ねじり強度を高め
る。しかし、0.01％未満の添加では、強度の増加が少な
く、一方、0.05％を超えて添加しても強度増加が飽和す
る。このため、Ｖは0.01〜0.05％の範囲に限定した。Nb: 0.01-0.05% Nb is an element that increases the strength of steel by precipitation hardening and also increases the tempering softening resistance, and increases the torsional strength. However, if the addition is less than 0.01%, the increase in strength is small, while if it exceeds 0.05%, the increase in strength is saturated. For this reason, V was limited to the range of 0.01 to 0.05%.
【００２５】また、本発明では、次（１）式 Ｍs 値＝538-317 ( ％Ｃ) -11(％ Si)-33(％ Mn)-28(％Cr)-11( ％Mo)-17( ％ Ni)-11( ％Cu)+6(％Ｖ)+10( ％Al) ……（１） （ここに、％Ｃ、％ Si 、％ Mn ％Cr、％Mo、％Ni、％
Cu、％Ｖ、％Al：各元素の含有量（重量％））で定義さ
れるＭs 値が315 以上とするのが好ましい。In the present invention, the following equation (1): Ms value = 538-317 (% C) -11 (% Si) -33 (% Mn) -28 (% Cr) -11 (% Mo) -17 (% Ni) -11 (% Cu) +6 (% V) +10 (% Al) (1) (where% C,% Si,% Mn% Cr,% Mo,% Ni,%
It is preferable that the Ms value defined by Cu,% V, and% Al: the content (% by weight) of each element is 315 or more.
【００２６】Ｍs 値は耐焼割れ性とよい相関を有し、Ｍ
s 値が315 以上であれば、耐焼割れ性が顕著に向上す
る。また、本発明では、上記したいずれかの組成の鋼素
材を切削加工あるいは冷間加工により所定の形状に加工
し、高周波焼入れを行ったのち焼戻し処理として175 ℃
以上の温度で10min 以上の加熱を施す。The Ms value has a good correlation with the resistance to burning cracking.
If the s value is 315 or more, the resistance to burning cracking is remarkably improved. Further, in the present invention, a steel material having any one of the above-described compositions is processed into a predetermined shape by cutting or cold working, induction hardening is performed, and then tempering is performed at 175 ° C.
Heat at the above temperature for 10min or more.
【００２７】焼戻しが不十分で、焼入れ硬化層の硬さが
高い場合には、ねじり試験で材料が脆性破壊し、ねじり
強度が低下する。このようなねじり試験での脆性破壊を
防止するためには、175 ℃以上の温度で10min 以上の保
持時間の焼戻し処理を行う必要がある。焼戻し処理が17
5 ℃未満の温度では、焼入れ硬化層の焼戻しの進行が遅
く生産性が劣化する。また、焼戻し処理時間が10min 未
満では、炭化物の分解が十分に進まないため、焼戻しが
不十分となる。If the tempering is insufficient and the hardness of the quenched hardened layer is high, the material is brittlely fractured in a torsion test, and the torsional strength is reduced. In order to prevent brittle fracture in such a torsion test, it is necessary to perform a tempering treatment at a temperature of 175 ° C. or more for a holding time of 10 minutes or more. 17 tempering
If the temperature is less than 5 ° C., the tempering of the quenched and hardened layer proceeds slowly, and the productivity is deteriorated. On the other hand, if the tempering treatment time is less than 10 minutes, the decomposition of the carbide will not proceed sufficiently, and the tempering will be insufficient.
【００２８】[0028]
【実施例】表１に示す組成の鋼を転炉により溶製し、連
続鋳造法で300 ×400mm 断面の鋳片とした。この鋳片を
ブレークダウン工程で150mm 角のビレットとしたのち、
φ26mmの棒鋼に圧延した。これら棒鋼から、平行部20mm
φの切欠き付きねじり試験片（切欠き部の応力集中係数
α＝1.5 ）を採取した。この試験片に周波数15kHz の高
周波焼入れ装置を用いて焼入れ処理を施したのち、表２
に示す条件で焼戻し処理を行ってねじり強度試験および
ねじり疲労試験を実施した。なお、焼入れ深さは、高周
波焼入れ装置の出力により調整した。EXAMPLES Steel having the composition shown in Table 1 was melted by a converter and cast into a slab having a cross section of 300 × 400 mm by a continuous casting method. After making this slab into a 150mm square billet in the breakdown process,
Rolled to φ26 mm steel bars. From these bars, the parallel part 20mm
A torsion test piece with a notch of φ (a stress concentration coefficient of the notch portion α = 1.5) was collected. The test pieces were quenched using a 15 kHz frequency induction hardening apparatus.
Tempering treatment was performed under the conditions shown in (1), and a torsional strength test and a torsional fatigue test were performed. The quenching depth was adjusted by the output of the induction hardening device.
【００２９】ねじり強度試験は、500kgf・m のねじり試
験機を用い、最大ねじり剪断応力をもとめ、ねじり強度
とした。ねじり疲労試験は、500kgf・m のねじり試験機
を用いて、両振りで応力条件を変えて行い、1 ×106 回
の寿命となる応力を疲労強度として評価した。また、こ
れら棒鋼から、表面に軸方向のＶ字溝を有する22mmφの
丸棒試験片を採取し、焼割れ性試験を実施した。In the torsional strength test, the maximum torsional shear stress was determined by using a torsional tester of 500 kgf · m, and the torsional strength was determined. The torsional fatigue test was carried out using a 500 kgf · m torsional tester while changing the stress conditions in both swings, and the stress at which the life was 1 × 10 6 times was evaluated as the fatigue strength. In addition, a round bar test piece of 22 mmφ having an axial V-shaped groove on the surface thereof was sampled from these steel bars and subjected to a quench cracking test.
【００３０】焼割れ性試験は、この試験片に周波数15kH
z の高周波焼入れ装置を用いて焼入れ処理を施したの
ち、丸棒試験片の軸方向に垂直な断面（Ｃ断面）10箇所
について、断面を研磨観察して割れの発生個数を測定し
た。測定した10箇所の割れ発生個数の合計で耐焼割れ性
を評価した。これらの結果を表２に示す。[0030] The sintering cracking test was conducted by applying a frequency of 15 kHz to this test piece.
After the quenching treatment was performed using the induction hardening apparatus of z, the cross section was polished and observed at 10 sections (C section) perpendicular to the axial direction of the round bar test piece, and the number of cracks generated was measured. The burning cracking resistance was evaluated based on the total of the measured number of cracks generated at 10 places. Table 2 shows the results.
【００３１】[0031]
【表１】 [Table 1]
【００３２】[0032]
【表２】 [Table 2]
【００３３】表２から、本発明例（試験No.1〜No.12 ）
はいずれも、本発明の範囲を外れる比較例に比べ、耐焼
割れ性、ねじり強度およびねじり疲労強度に優れている
ことがわかる。これに対し、焼戻し条件が本発明の範囲
を外れる比較例の試験No.13 、No.14は、ねじり強度お
よびねじり疲労強度が低下している。From Table 2, it can be seen that the examples of the present invention (test Nos. 1 to 12).
It can be seen that each of them is superior in the resistance to fire cracking, the torsional strength and the torsional fatigue strength as compared with the comparative examples out of the range of the present invention. On the other hand, in tests No. 13 and No. 14 of the comparative examples in which the tempering conditions are out of the range of the present invention, the torsional strength and the torsional fatigue strength are reduced.
【００３４】また、Al、Si含有量が本発明の範囲を外れ
る比較例の試験No.15 、No.16 は、耐焼割れ性、ねじり
強度およびねじり疲労強度が低下している。試験No.16
は試験No.15 にくらべ、焼入れ深さが４mmと浅く、焼割
れに対して有利となる方向であるが化学組成が本発明の
範囲から大きく外れているため、試験No.15 より焼割れ
個数は減少しているが本発明例に比べ耐焼割れ性が劣化
している。In Comparative Examples No. 15 and No. 16 in which the Al and Si contents are out of the range of the present invention, the resistance to burning cracking, torsional strength and torsional fatigue strength are reduced. Test No.16
Is a shallower quenching depth of 4 mm compared to Test No. 15, which is advantageous for quenching. However, since the chemical composition is far out of the range of the present invention, the number of quenching cracks is smaller than that of Test No. 15. Is decreased, but the fire cracking resistance is deteriorated as compared with the examples of the present invention.
【００３５】また、Al、Si含有量が本発明の範囲を外れ
る比較例の試験No.17 は、耐焼割れ性、ねじり強度およ
びねじり疲労強度が低下している。また、Ｃ、Al含有量
が本発明の範囲を外れる比較例の試験No.18 は、耐焼割
れ性、ねじり強度およびねじり疲労強度が低下してい
る。また、Ｃ、Ｓ、Ｎ含有量が本発明の範囲を外れる比
較例の試験No.19 は、耐焼割れ性、ねじり強度およびね
じり疲労強度が低下している。とくに、Ｍs 値が315 未
満であるため、耐焼割れ性の劣化が著しい。In the test No. 17 of the comparative example in which the Al and Si contents are out of the range of the present invention, the resistance to burning cracking, the torsional strength and the torsional fatigue strength are reduced. In Test No. 18 of Comparative Example in which the contents of C and Al were out of the range of the present invention, the resistance to burning cracking, torsional strength and torsional fatigue strength were reduced. Further, in Test No. 19 of Comparative Example in which the contents of C, S, and N are out of the range of the present invention, the resistance to sintering cracking, torsional strength and torsional fatigue strength are reduced. In particular, since the Ms value is less than 315, the resistance to burn cracking is significantly reduced.
【００３６】また、Ｏ、Mn含有量が本発明の範囲を外れ
る比較例の試験No.20 は、耐焼割れ性、ねじり強度およ
びねじり疲労強度が低下している。とくに、Ｍs 値が31
5 未満であるため、耐焼割れ性の劣化が著しい。また、
Ｃ、Ｐ含有量が本発明の範囲を外れる比較例の試験No.2
1 は、耐焼割れ性、ねじり強度およびねじり疲労強度が
低下している。とくに、Ｍs 値が315 未満であるため、
耐焼割れ性の劣化が著しい。Further, in Test No. 20, which is a comparative example in which the contents of O and Mn are out of the range of the present invention, the resistance to burning cracking, the torsional strength and the torsional fatigue strength are reduced. In particular, if the Ms value is 31
Since it is less than 5, the deterioration of resistance to burning cracking is remarkable. Also,
Test No. 2 of Comparative Example in which C and P contents are out of the range of the present invention
In No. 1, the fire cracking resistance, torsional strength and torsional fatigue strength are reduced. In particular, since the Ms value is less than 315,
Deterioration of fire cracking resistance is remarkable.
【００３７】また、Ti含有量が多く本発明の範囲を外れ
る比較例の試験No.22 は、ねじり疲労強度が低下してい
る。本発明の範囲内の機械構造用鋼は、高周波焼入れ後
の耐焼割れ性、高周波焼入れ焼戻し後のねじり強度、ね
じり疲労強度が優れた鋼材であることがわかる。In Test No. 22, which is a comparative example having a large Ti content and deviating from the range of the present invention, the torsional fatigue strength is low. It can be seen that the steel for machine structural use within the scope of the present invention is a steel material having excellent quench cracking resistance after induction hardening, torsional strength after induction hardening and tempering, and torsional fatigue strength.
【００３８】[0038]
【発明の効果】本発明によれば、高周波焼入れ焼戻し後
のねじり強度、ねじり疲労強度および耐焼割れ性に優れ
た機械構造用鋼を容易に製造でき、産業上格別の効果を
奏する。According to the present invention, steel for machine structural use having excellent torsional strength, torsional fatigue strength and resistance to quenching cracking after induction quenching and tempering can be easily produced, and it has an industrially outstanding effect.
Claims (6)
特徴とする高周波焼入れ焼戻し後のねじり強度、ねじり
疲労強度および耐焼割れ性に優れる高周波焼入れ用機械
構造用鋼。C. 0.45 to 0.70%, Si: 0.01 to 0.40%, Mn: 0.2 to 2.5%, P: 0.020% or less, S: 0.06% or less, Al: more than 0.05 to 0.25% by weight%. N: 0.0020-0.025%, O: 0.0020% or less, B: 0.0003-0.0060%, characterized by the balance of Fe and inevitable impurities, torsional strength, torsional fatigue strength, and torsion cracking after induction hardening and tempering. Steel for machine structural use for induction hardening with excellent heat resistance.
含有することを特徴とする請求項１記載の高周波焼入れ
用機械構造用鋼。2. The steel according to claim 1, further comprising 0.005 to 0.05% by weight of Ti.
r：0.01〜1.0 ％、Cu：1.0 ％以下、Ni：0.1 〜3.5 ％
のうちから選ばれた１種または２種以上を含有すること
を特徴とする請求項１または２記載の高周波焼入れ用機
械構造用鋼。3. Mo%: 0.05-1.0%, C:
r: 0.01 to 1.0%, Cu: 1.0% or less, Ni: 0.1 to 3.5%
The steel for machine structural use for induction hardening according to claim 1, comprising one or more selected from the group consisting of:
b：0.01〜0.05％のうちから選ばれた１種または２種を
含有することを特徴とする請求項１ないし３のいずれか
に記載の高周波焼入れ用機械構造用鋼。4. V: 0.05-0.5% by weight, N
The steel for machine structural use for induction hardening according to any one of claims 1 to 3, wherein the steel contains one or two kinds selected from b: 0.01 to 0.05%.
以上である請求項１ないし４のいずれかに記載の高周波
焼入れ用機械構造用鋼。 記 Ｍs 値＝538-317 （％Ｃ) -11(％ Si)-33(％ Mn)-28(％Cr)-11( ％Mo)-17（％ Ni)-11( ％Cu)+6(％Ｖ)+10（％Al）……（１） ここに、％Ｃ、％ Si 、％ Mn ％Cr、％Mo、％Ni、％C
u、％Ｖ、％Al：各元素の含有量（重量％）5. The Ms value defined by the following equation (1) is 315.
The steel for machine structural use for induction hardening according to any one of claims 1 to 4, which is as described above. Ms value = 538-317 (% C) -11 (% Si) -33 (% Mn) -28 (% Cr) -11 (% Mo) -17 (% Ni) -11 (% Cu) +6 ( % V) +10 (% Al) (1) where% C,% Si,% Mn% Cr,% Mo,% Ni,% C
u,% V,% Al: Content of each element (% by weight)
成の鋼素材を切削加工あるいは冷間加工により所定の形
状に加工し高周波焼入れを行ったのち、焼戻し処理とし
て175 ℃以上の温度で10min 以上の加熱を施すことを特
徴とする高周波焼入れ焼戻し後のねじり強度、ねじり疲
労強度および耐焼割れ性に優れる高周波焼入れ用機械構
造用鋼の製造方法。6. A steel material having a composition according to any one of claims 1 to 5, which is formed into a predetermined shape by cutting or cold working, induction hardening is performed, and then tempering is performed at a temperature of 175 ° C. or more. A method for producing steel for machine structural use for induction hardening having excellent torsional strength, torsional fatigue strength and resistance to quenching cracking after induction hardening and tempering, characterized in that heating is performed for 10 minutes or more.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP17852797A JPH1129836A (en) | 1997-05-13 | 1997-07-03 | Steel for machine structural use for induction hardening |
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP9-121846 | 1997-05-13 | ||
| JP12184697 | 1997-05-13 | ||
| JP17852797A JPH1129836A (en) | 1997-05-13 | 1997-07-03 | Steel for machine structural use for induction hardening |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| JPH1129836A true JPH1129836A (en) | 1999-02-02 |
Family
ID=26459113
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP17852797A Pending JPH1129836A (en) | 1997-05-13 | 1997-07-03 | Steel for machine structural use for induction hardening |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JPH1129836A (en) |
Cited By (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR2850399A1 (en) * | 2003-01-23 | 2004-07-30 | Koyo Seiko Co | Steel for use in a high strength pinion shaft for a motor vehicle guidance system after high frequency hardening |
| WO2006008960A1 (en) * | 2004-07-16 | 2006-01-26 | Jfe Steel Corporation | Component for machine structure, method for producing same, and material for high-frequency hardening |
| JP2007246975A (en) * | 2006-03-15 | 2007-09-27 | Komatsu Ltd | Method of manufacturing steel shaft |
| WO2010082454A1 (en) * | 2009-01-16 | 2010-07-22 | 新日本製鐵株式会社 | Steel for high-frequency hardening |
| WO2010140596A1 (en) * | 2009-06-05 | 2010-12-09 | 株式会社神戸製鋼所 | Steel for mechanical structuring |
| JP2012201983A (en) * | 2011-03-28 | 2012-10-22 | Kobe Steel Ltd | Steel for induction hardening excellent in torsional strength and toughness, and method of manufacturing the same |
| US8802005B2 (en) * | 2009-01-16 | 2014-08-12 | Nippon Steel & Sumitomo Metal Corporation | Steel for surface hardening for machine structural use and part for machine structural use |
-
1997
- 1997-07-03 JP JP17852797A patent/JPH1129836A/en active Pending
Cited By (13)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR2850399A1 (en) * | 2003-01-23 | 2004-07-30 | Koyo Seiko Co | Steel for use in a high strength pinion shaft for a motor vehicle guidance system after high frequency hardening |
| US7740722B2 (en) | 2003-01-23 | 2010-06-22 | Jtekt Corporation | Steel for use in high strength pinion shaft and manufacturing method thereof |
| WO2006008960A1 (en) * | 2004-07-16 | 2006-01-26 | Jfe Steel Corporation | Component for machine structure, method for producing same, and material for high-frequency hardening |
| JP2007246975A (en) * | 2006-03-15 | 2007-09-27 | Komatsu Ltd | Method of manufacturing steel shaft |
| JP4659139B2 (en) * | 2009-01-16 | 2011-03-30 | 新日本製鐵株式会社 | Induction hardening steel |
| WO2010082454A1 (en) * | 2009-01-16 | 2010-07-22 | 新日本製鐵株式会社 | Steel for high-frequency hardening |
| KR101340729B1 (en) * | 2009-01-16 | 2013-12-12 | 신닛테츠스미킨 카부시키카이샤 | Steel for high-frequency hardening |
| US8802005B2 (en) * | 2009-01-16 | 2014-08-12 | Nippon Steel & Sumitomo Metal Corporation | Steel for surface hardening for machine structural use and part for machine structural use |
| CN104726798A (en) * | 2009-01-16 | 2015-06-24 | 新日铁住金株式会社 | STEEL FOR high-frequency hardening |
| US9777343B2 (en) | 2009-01-16 | 2017-10-03 | Nippon Steel & Sumitomo Metal Corporation | Steel for surface hardening for machine structural use and part for machine structural use |
| WO2010140596A1 (en) * | 2009-06-05 | 2010-12-09 | 株式会社神戸製鋼所 | Steel for mechanical structuring |
| US9062360B2 (en) | 2009-06-05 | 2015-06-23 | Kobe Steel, Ltd. | Steel for machine structural use |
| JP2012201983A (en) * | 2011-03-28 | 2012-10-22 | Kobe Steel Ltd | Steel for induction hardening excellent in torsional strength and toughness, and method of manufacturing the same |
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