JPH09256045A - Production of steel for soft-nitriding and soft-nitrided parts using the same steel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce soft-nitrided parts having excellent fatigue resistance, wear resistance, pitching resistance and spalling resistance and to provide a method for producing a steel for soft-nitriding as the stock therefor. SOLUTION: As for the method for producing the steel for soft-nitriding, a steel having a compsn. contg. 0.15 to 0.45% C, 0.05 to 0.50% Si, 0.2 to 2.5% Mn, 0.5 to 1.5% Cu, 0.25 to 0.75% Ni so as to satisfy 1.8<=Cu/Ni<=2.2, 0.5 to 2.0% Cr, 0.05 to 0.5% V, 0.01 to 0.3% Al, 0 to 0.3% Mo, 0 to 0.13% S, 0 to 0.35% Pb, 0 to 0.01% Ca, and the balance Fe with impurities is subjected to hot working, is thereafter subjected to spheroidizing annealing to regulate its hardness to <=180Hv and is then subjected to cold working to regulate its hardness to >=250Hv. The soft-nitrided parts are the ones using the steel for soft- nitriding produced by the above method as the stock, and in which the surface hardness after soft-nitriding is regulated to >=600Hv and the effective hardening depth to >=0.1mm.

Description

【発明の詳細な説明】Detailed Description of the Invention

【０００１】[0001]

【発明の属する技術分野】本発明は、軟窒化用鋼材の製
造方法及びその鋼材を用いた軟窒化部品に関し、より詳
しくは耐疲労特性、耐摩耗性、耐ピッチング性や耐スポ
ーリング性に優れた軟窒化部品と、その軟窒化部品の素
材となる軟窒化用鋼材の製造方法に関する。（なお、繰
り返し面圧の負荷により、材料表面が剥離する疲労現象
のうち、剥離が比較的小さなものを「ピッチング」、剥
離が比較的大きなものを「スポーリング」と呼ぶことが
多いので、本明細書においてもこれに倣った。）BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a steel material for nitrocarburizing and a nitrocarburized component using the steel material, and more particularly to a steel sheet having excellent fatigue resistance, wear resistance, pitting resistance and spalling resistance. The present invention relates to a nitrocarburized component and a method for producing a nitrocarburized steel material used as a material for the nitrocarburized component. (Note that among the fatigue phenomena in which the material surface peels off due to the repeated contact pressure load, those with relatively small peeling are often called "pitching", and those with relatively large peeling are often called "spalling". This was also followed in the specification.)

【０００２】[0002]

【従来の技術】自動車や産業機械に使用される多くの部
品、例えば歯車や軸受などには、一般に大きな疲労強度
や耐摩耗性が要求される。そのため前記部品は、所謂
「表面硬化処理」を施して製造されてきた。2. Description of the Related Art Many parts used in automobiles and industrial machines, such as gears and bearings, generally require large fatigue strength and wear resistance. Therefore, the components have been manufactured by performing a so-called “surface hardening treatment”.

【０００３】表面硬化処理としては一般に、浸炭焼入
れ、高周波焼入れ、炎焼入れ、窒化や軟窒化などの処理
が知られている。このうち、浸炭焼入れ、高周波焼入れ
や炎焼入れといったオ−ステナイト状態の高温域から急
冷（焼入れ）して表面を硬化させる処理では、部品に大
きな焼入れ歪が生じてしまう。更に、場合によっては焼
入れした部品に焼割れが生ずることもある。As the surface hardening treatment, generally, carburizing quenching, induction quenching, flame quenching, nitriding and nitrocarburizing are known. Of these, in the process of quenching (quenching) from the high temperature region of the austenite state such as carburizing quenching, induction hardening and flame quenching to harden the surface, a large quenching distortion occurs in the component. Further, in some cases, quenched cracks may occur in the quenched parts.

【０００４】このため、所要部品に対して特に低歪であ
ることが要求される場合には、窒化や軟窒化処理が施さ
れている。Therefore, when required strain is required to be particularly low, nitriding or soft nitriding is applied.

【０００５】しかし、一般の窒化処理は、アンモニアの
気流中で５００〜５５０℃に２０〜１００時間加熱後徐
冷する所謂「ガス窒化」処理であるため生産性が低くコ
ストが嵩む。このため、窒化温度が５５０℃前後の液体
窒化法が開発されているが、この方法の場合にも窒化に
は１２時間程度を要するので、必ずしも量産部品を低コ
ストで効率良く製造するのに適した方法とは言えない。
イオン窒化法によれば短時間で窒化が可能ではあるが、
温度測定が困難なことや、陰極となる被処理部品の配置
や形状、質量などによって温度や窒化層が不安定になっ
たりするので、この方法もやはり量産部品の製造に適し
ているとは言い難い。However, the general nitriding treatment is a so-called "gas nitriding" treatment in which it is heated at 500 to 550 ° C. for 20 to 100 hours in an ammonia stream and then gradually cooled, resulting in low productivity and high cost. For this reason, a liquid nitriding method with a nitriding temperature of around 550 ° C. has been developed. Even in this method, nitriding requires about 12 hours, so that it is not always suitable for mass-produced parts at low cost and efficiently. It can't be said that it was a method.
According to the ion nitriding method, nitriding is possible in a short time,
This method is not suitable for the production of mass-produced parts because it is difficult to measure the temperature, and the temperature and nitrided layer become unstable depending on the arrangement, shape, and mass of the part to be treated as the cathode. hard.

【０００６】一方、軟窒化処理は、５７０℃程度の温度
のシアン系化合物の塩浴、又はＲＸガス（ＲＸガスは吸
熱型変成ガスの商標）にアンモニアを添加したガス中に
保持することにより、鋼材表面からＮ（窒素）とＣ（炭
素）を鋼中に浸入させて表層部を硬化させる方法で、短
時間処理が可能である。このうち前者のシアン系化合物
の塩浴を用いる方法は、廃液の処理にコストが嵩むた
め、後者のガスを用いる「ガス軟窒化法」が、低歪が要
求される量産品に適した表面硬化処理方法として重用さ
れている。On the other hand, the nitrocarburizing treatment is carried out by keeping a salt bath of a cyanide compound at a temperature of about 570 ° C. or a gas obtained by adding ammonia to RX gas (RX gas is a trademark of endothermic modified gas). A method in which N (nitrogen) and C (carbon) penetrate into the steel from the surface of the steel material to harden the surface layer portion enables short-time processing. Of these, the former method using a salt bath of a cyanide compound increases the cost of waste liquid treatment, so the latter gas nitrocarburizing method using gas is a surface hardening method suitable for mass-produced products requiring low distortion. It is heavily used as a processing method.

【０００７】従来、軟窒化用鋼としては、例えば、JIS
G 4105に規定されているクロムモリブデン鋼鋼材（ＳＣ
Ｍ４３５など）やJIS G 4202のアルミニウムクロムモリ
ブデン鋼鋼材（ＳＡＣＭ６４５）が多く使用されてき
た。Conventionally, as steel for nitrocarburizing, for example, JIS
Chromium molybdenum steel (SC) specified in G 4105
M435, etc.) and JIS G 4202 aluminum chrome molybdenum steel (SACM645) have been widely used.

【０００８】しかし、ＳＣＭ４３５を始めとするＪＩＳ
に規定されたクロムモリブデン鋼鋼材を素材鋼とした部
品の場合、軟窒化処理後の表面からビッカース硬度（Ｈ
ｖ）５００の位置までの距離（以下、「有効硬化深さ」
という）は０．０５ｍｍ程度と小さい。更に、表面から
０．０２５ｍｍの位置におけるビッカース硬度（以下、
「表面硬度」という）もＨｖ６００以上にならない場合
が多い。このため、疲労強度や耐摩耗性の点で充分に満
足できるものではなかった。However, JIS such as SCM435
In the case of parts made of chromium molybdenum steel as specified in JIS, the Vickers hardness (H
v) Distance to the position of 500 (hereinafter, "effective curing depth"
Is about 0.05 mm, which is small. Furthermore, Vickers hardness at a position of 0.025 mm from the surface (hereinafter,
The “surface hardness”) often does not exceed Hv600. For this reason, it was not sufficiently satisfactory in terms of fatigue strength and wear resistance.

【０００９】一方、上記の欠点を改良するためにＳＡＣ
Ｍ６４５には窒化特性向上元素であるＡｌ及びＣｒが多
量に添加されている。しかし、ＳＡＣＭ６４５を素材鋼
とした場合も、軟窒化処理によって表面硬度はＨｖで８
００〜１１００と非常に高くなるものの、有効硬化深さ
は０．０８ｍｍ程度と小さい。したがって、表面部から
芯部（以下、軟窒化処理後の表面硬化されていない部分
を「芯部」という）への硬度勾配が急激になりすぎる。
そのため、高負荷の下で運転される歯車や軸受などで
は、表面硬化部と芯部の境界付近から剥離現象が起きや
すく、耐ピッチング性あるいは耐スポーリング性が劣っ
ていた。更に、ＳＡＣＭ６４５は溶製、鋳造、熱間加工
が比較的困難であるし、冷間加工性が悪く複雑な形状の
部品にはプレス成形し難いという問題もあった。On the other hand, in order to improve the above-mentioned disadvantage, SAC
M645 contains a large amount of Al and Cr which are nitriding property improving elements. However, even when SACM645 is used as the material steel, the surface hardness is 8 in Hv by the nitrocarburizing treatment.
Although it is as high as 00 to 1100, the effective hardening depth is as small as about 0.08 mm. Therefore, the hardness gradient from the surface portion to the core portion (hereinafter, the portion that has not been surface-hardened after the soft nitriding treatment is referred to as “core portion”) becomes too steep.
Therefore, in gears and bearings that are operated under a high load, a peeling phenomenon easily occurs near the boundary between the surface-hardened portion and the core portion, and the pitting resistance or spalling resistance is poor. Furthermore, SACM645 has problems that melting, casting, and hot working are relatively difficult, and that cold workability is poor, and it is difficult to press-mold parts having complicated shapes.

【００１０】特公平１−３７４７２号公報には、ＪＩＳ
規格鋼の問題点を解決した「軟窒化用鋼」が開示されて
いる。この公報で提案された鋼を素材鋼として用いれ
ば、確かに疲労強度、耐摩耗性に優れると共に耐ピッチ
ング性、耐スポーリング性にも優れた軟窒化部品を得る
ことは可能である。しかし、Ｓｉなどの強化に有効な元
素の含有量を低減して冷間加工性を向上させた鋼である
ため、軟窒化によって表面部は硬化するものの、逆に芯
部は軟窒化時の加熱で軟化するので、軟窒化後には芯部
硬度が低くなりすぎて疲労特性が劣化する場合もあっ
た。Japanese Patent Publication No. 1-34722 discloses JIS.
"Steel for soft nitriding" that solves the problems of standard steel is disclosed. If the steel proposed in this publication is used as a raw material steel, it is possible to obtain a soft nitrided component which is certainly excellent in fatigue strength and wear resistance as well as in pitting resistance and spalling resistance. However, since the steel is a steel whose cold workability is improved by reducing the content of elements such as Si, which is effective for strengthening, the surface portion is hardened by nitrocarburizing, while the core portion is heated by nitrocarburizing at the time of nitrocarburizing. Since the alloy is softened by, the hardness of the core portion becomes too low after the nitrocarburizing, and the fatigue characteristics may be deteriorated.

【００１１】[0011]

【発明が解決しようとする課題】本発明は、上記現状に
鑑みなされたもので、冷間加工性に優れた鋼を素材鋼と
し、冷間加工後に軟窒化処理するだけで優れた耐疲労特
性、耐摩耗性、耐ピッチング性や耐スポーリング性を呈
する軟窒化部品を提供することを課題とする。更に、本
発明は、上記軟窒化部品の素材となる軟窒化用鋼材の製
造方法を提供することも課題とする。DISCLOSURE OF THE INVENTION The present invention has been made in view of the above-mentioned current situation, in which a steel having excellent cold workability is used as a raw material steel, and excellent fatigue resistance characteristics are obtained only by soft nitriding after cold working. An object of the present invention is to provide a soft-nitrided component exhibiting abrasion resistance, pitting resistance and spalling resistance. Still another object of the present invention is to provide a method for producing a steel material for nitrocarburizing, which is a material for the nitrocarburized component.

【００１２】[0012]

【課題を解決するための手段】本発明者らは、上記の課
題を解決するために、軟窒化部品の素材となる鋼材の化
学組成、並びに各製造工程における適正なミクロ組織や
機械的性質に関して調査・研究を行った。その結果、次
の重要な事項が判明した。In order to solve the above-mentioned problems, the inventors of the present invention are concerned with the chemical composition of the steel material as the material of the soft-nitrided part, and the appropriate microstructure and mechanical properties in each manufacturing process. I conducted a survey and research. As a result, the following important matters were found.

【００１３】軟窒化部品の耐疲労特性や耐ピッチング
性を向上させるには、いずれも表面硬度と有効硬化深さ
を大きくすれば良い。又、耐摩耗性を向上させるには、
表面硬度を大きくすれば良い。一方、耐スポーリング性
を向上させるには、有効硬化深さを大きくすれば良い。In order to improve the fatigue resistance and pitting resistance of the soft-nitrided part, the surface hardness and the effective hardening depth should be increased in both cases. Also, to improve wear resistance,
The surface hardness should be increased. On the other hand, in order to improve the spalling resistance, the effective hardening depth may be increased.

【００１４】軟窒化処理を施し、表面硬度をＨｖ６０
０以上、有効硬化深さを０．１ｍｍ以上とすれば、軟窒
化部品の耐疲労特性、耐摩耗性、耐ピッチング性及び耐
スポーリング性を著しく高めることができる。The surface hardness is Hv60 after soft nitriding.
When the effective hardening depth is 0 or more and the effective hardening depth is 0.1 mm or more, the fatigue resistance, wear resistance, pitting resistance and spalling resistance of the soft nitrided part can be remarkably enhanced.

【００１５】軟窒化後の芯部硬度がＨｖ２５０以上で
あれば、例えば、自動車のミッションギアのように高い
負荷が加わる部品においても、部品内部を起点として曲
げ疲労が生ずることはない。When the core hardness after soft nitriding is Hv 250 or more, bending fatigue does not occur from the inside of the component even in a component to which a high load is applied, such as an automobile transmission gear.

【００１６】鋼材を球状化焼鈍して硬度をＨｖ１８０
以下に低下させれば、冷間加工性が向上して金型寿命を
大幅に改善できる。The steel material is spheroidized and annealed to have a hardness of Hv180.
If it is reduced below, the cold workability is improved and the life of the die can be greatly improved.

【００１７】適正量のＣｕとＮｉとを含有する鋼材を
球状化焼鈍して硬度をＨｖ１８０以下にし、冷間鍛造に
よる加工硬化で硬度をＨｖ２５０以上に上昇させれば、
次に軟窒化処理を施しても、軟窒化時の加熱で軟化して
芯部硬度が低下することはない。すなわち、芯部硬度を
軟窒化前の値に維持、あるいは更に高めることができ
る。このため、軟窒化部品には、Ｈｖ２５０以上の高い
芯部硬度が安定して確保できるので、耐疲労特性、なか
でも耐曲げ疲労特性が大きく向上する。If a steel material containing appropriate amounts of Cu and Ni is spheroidized and annealed to have a hardness of Hv180 or less and work hardening by cold forging to increase the hardness to Hv250 or more,
Next, even if soft nitriding is performed, the core hardness is not lowered by softening by heating during soft nitriding. That is, the core hardness can be maintained at the value before soft nitriding or further increased. Therefore, the soft nitrided component can stably secure a high core hardness of Hv250 or more, and thus the fatigue resistance, especially the bending fatigue resistance, is greatly improved.

【００１８】なお、特に断らない限り、軟窒化する前の
状態（例えば球状化焼鈍後、冷間加工後）の硬度とは、
軟窒化後の芯部に相当する部分（例えば「中心部」）の
硬度のことをいう。Unless otherwise specified, the hardness before soft nitriding (for example, after spheroidizing annealing and after cold working) is the hardness.
It refers to the hardness of a portion (for example, “center”) corresponding to the core after soft nitriding.

【００１９】上記の〜から、優れた冷間加工性を
有する鋼を素材鋼とし、これに冷間加工を施して加工硬
化により充分な硬度を確保し、次に軟窒化して硬く深い
窒化層を形成させるが、この軟窒化のための加熱で前記
の加工硬化による硬度（すなわち芯部硬度）を維持ある
いは更に上昇できれば、軟窒化部品に大きな耐疲労特
性、耐摩耗性、耐ピッチング性及び耐スポーリング性を
付与できる。From the above items (1) to (4), a steel having excellent cold workability is used as a material steel, and cold working is performed to secure sufficient hardness by work hardening, and then soft nitriding is performed to form a hard and deep nitrided layer. However, if the hardness due to work hardening (that is, the core hardness) can be maintained or further increased by the heating for soft nitriding, the soft nitrided parts will have great fatigue resistance, wear resistance, pitting resistance and pitting resistance. Spalling property can be imparted.

【００２０】上記知見に基づく本発明は、下記（１）の
軟窒化用鋼材の製造方法及び（２）のその鋼材を用いた
軟窒化部品を要旨とする。The gist of the present invention based on the above findings is a method for manufacturing a steel material for soft nitriding of the following (1) and a soft nitriding component using the steel material of (2).

【００２１】（１）重量％で、Ｃ：０．１５〜０．４５
％、Ｓｉ：０．０５〜０．５０％、Ｍｎ：０．２〜２．
５％、Ｃｕ：０．５〜１．５％、Ｎｉ：０．２５〜０．
７５％で、且つ１．８≦Ｃｕ／Ｎｉ≦２．２、Ｃｒ：
０．５〜２．０％、Ｖ：０．０５〜０．５％、Ａｌ：
０．０１〜０．３％、Ｍｏ：０〜０．３％、Ｓ：０〜
０．１３％、Ｐｂ：０〜０．３５％、Ｃａ：０〜０．０
１％、残部はＦｅ及び不可避不純物の化学組成からなる
鋼を、熱間加工後に球状化焼鈍して硬度をＨｖ１８０以
下となし、次いで冷間加工して硬度をＨｖ２５０以上と
なすことを特徴とする軟窒化用鋼材の製造方法。(1) C: 0.15 to 0.45% by weight
%, Si: 0.05 to 0.50%, Mn: 0.2 to 2.
5%, Cu: 0.5-1.5%, Ni: 0.25-0.
75% and 1.8 ≦ Cu / Ni ≦ 2.2, Cr:
0.5-2.0%, V: 0.05-0.5%, Al:
0.01-0.3%, Mo: 0-0.3%, S: 0-
0.13%, Pb: 0-0.35%, Ca: 0-0.0
1%, the balance is steel having a chemical composition of Fe and unavoidable impurities, and is spheroidized and annealed after hot working to have a hardness of Hv 180 or less, and then cold worked to have a hardness of Hv 250 or more. Manufacturing method of steel material for soft nitriding.

【００２２】（２）上記（１）に記載の方法で製造した
軟窒化用鋼材を素材とし、軟窒化後の表面硬度がＨｖ６
００以上、且つ、有効硬化深さが０．１ｍｍ以上である
ことを特徴とする軟窒化部品。(2) Using the steel material for soft nitriding manufactured by the method described in (1) above as a raw material, the surface hardness after soft nitriding is Hv6.
00 or more and an effective hardening depth of 0.1 mm or more.

【００２３】以下において、上記（１）、（２）に記載
のものをそれぞれ（１）の発明、（２）の発明という。In the following, the items (1) and (2) are referred to as the invention (1) and the invention (2), respectively.

【００２４】[0024]

【発明の実施の形態】以下に本発明の各要件について詳
しく説明する。なお、成分含有量の「％」は「重量％」
を意味する。BEST MODE FOR CARRYING OUT THE INVENTION Each requirement of the present invention will be described in detail below. In addition, “%” of the component content is “% by weight”.
Means

【００２５】（Ａ）素材鋼の化学組成 Ｃ：Ｃは、静的強度を確保するために必要な元素であ
る。しかし、その含有量が０．１５％未満では所望の静
的強度（冷間加工後に軟窒化処理した後の芯部硬度、す
なわち最終製品である軟窒化部品の芯部硬度としてＨｖ
２５０以上）が確保できない。一方、０．４５％を超え
ると芯部の延性、靭性の低下をきたすと共に、切削性や
冷間加工性を劣化させてしまう。更に、軟窒化後の表面
硬度及び硬化深さが却って減少するようになる。したが
って、Ｃの含有量を０．１５〜０．４５％とした。(A) Chemical composition of raw steel C: C is an element necessary for ensuring static strength. However, if the content is less than 0.15%, the desired static strength (the hardness of the core portion after soft nitriding after cold working, that is, Hv as the hardness of the core portion of the final product, soft nitrided part, is Hv
250 or more) cannot be secured. On the other hand, if it exceeds 0.45%, the ductility and toughness of the core portion are deteriorated, and the machinability and cold workability are deteriorated. Furthermore, the surface hardness and the hardening depth after soft nitriding are rather decreased. Therefore, the content of C is set to 0.15 to 0.45%.

【００２６】Ｓｉ：Ｓｉは、鋼の焼入れ性を高めると共
に静的強度を向上させる作用を有する。しかし、その含
有量が０．０５％未満では、前記した所望の静的強度が
確保できない。一方、０．５０％を超えると靭性の劣化
を招いて、冷間加工性に悪影響を及ぼす。したがって、
Ｓｉの含有量を０．０５〜０．５０％とした。Si: Si has the functions of enhancing the hardenability of steel and the static strength. However, if the content is less than 0.05%, the above-mentioned desired static strength cannot be secured. On the other hand, if it exceeds 0.50%, the toughness is deteriorated and the cold workability is adversely affected. Therefore,
The content of Si was set to 0.05 to 0.50%.

【００２７】Ｍｎ：Ｍｎは、焼入れ性の向上と芯部強度
の確保に有効な元素である。しかし、その含有量が０．
２％未満では添加効果に乏しく、一方、２．５％を超え
て含有すると偏析を生じて冷間加工性の劣化をもたら
す。したがって、Ｍｎの含有量を０．２〜２．５％とし
た。なお、Ｍｎの含有量は０．５〜１．５％とすること
が好ましい。Mn: Mn is an element effective in improving hardenability and ensuring core strength. However, when its content is 0.1.
If it is less than 2%, the effect of addition is poor. On the other hand, if it exceeds 2.5%, segregation occurs and the cold workability deteriorates. Therefore, the Mn content is set to 0.2 to 2.5%. Note that the content of Mn is preferably set to 0.5 to 1.5%.

【００２８】Ｃｕ：Ｃｕは、本発明において重要な元素
であって、軟窒化処理時に微細に析出して鋼を硬化させ
る作用を有する。このため被処理鋼材は、軟窒化のため
の加熱で軟化することがなく軟窒化前の硬度を維持で
き、場合によっては逆に硬化する。前記のＣｕの効果
は、特に、球状化焼鈍して硬度をＨｖ１８０以下にし、
冷間鍛造による加工硬化で硬度をＨｖ２５０以上に上昇
させた鋼材において大きく発揮される。しかし、その含
有量が０．５％未満では充分な量が微細析出しないので
添加効果に乏しい。一方、１．５％を超えて含有させる
と前記の効果が飽和するばかりか熱間加工性の劣化をも
たらす。したがって、Ｃｕ含有量を０．５〜１．５％と
した。Cu: Cu is an important element in the present invention, and has a function of finely precipitating during the soft nitriding treatment to harden the steel. For this reason, the steel material to be treated can maintain the hardness before the soft nitriding without being softened by heating for the soft nitriding, and in some cases, hardens in reverse. As for the effect of Cu, the spheroidizing annealing makes the hardness Hv180 or less,
It is greatly exerted on steel materials whose hardness is increased to Hv250 or more by work hardening by cold forging. However, if the content is less than 0.5%, a sufficient amount is not finely precipitated, so that the effect of addition is poor. On the other hand, when the content exceeds 1.5%, not only the above effect is saturated, but also the hot workability is deteriorated. Therefore, the Cu content is set to 0.5 to 1.5%.

【００２９】Ｎｉ：Ｎｉは、上記のＣｕを基地に完全に
固溶させて、軟窒化処理に際しＣｕの析出硬化作用を充
分発揮させる効果を有する。この作用は後述するＣｕ／
Ｎｉの比が１．８〜２．２の場合に顕著である。しか
し、Ｎｉの含有量が０．２５％未満では添加効果に乏し
く、０．７５％を超えて含有しても前記の効果は飽和す
る。このため、Ｎｉの含有量を０．２５〜０．７５％と
した。Ni: Ni has the effect of completely dissolving the above-mentioned Cu in the matrix and sufficiently exerting the precipitation hardening action of Cu during the soft nitriding treatment. This action is Cu /
This is remarkable when the Ni ratio is 1.8 to 2.2. However, if the Ni content is less than 0.25%, the effect of addition is poor, and if the content of Ni exceeds 0.75%, the effect is saturated. Therefore, the content of Ni is set to 0.25 to 0.75%.

【００３０】Ｃｕ／Ｎｉ：Ｃｕ／Ｎｉの値が１．８〜
２．２の場合に、適正量のＣｕとＮｉの複合添加により
Ｃｕが基地に完全に固溶して、軟窒化処理に際し析出硬
化するＣｕの作用の発現が顕著となる。したがって、Ｃ
ｕ／Ｎｉの値を１．８〜２．２とした。なお、Ｃｕ／Ｎ
ｉの値は１．９〜２．１とすることが好ましい。Cu / Ni: The value of Cu / Ni is 1.8 to
In the case of 2.2, Cu is completely solid-dissolved in the matrix by the combined addition of an appropriate amount of Cu and Ni, and the action of Cu which is precipitation hardened during the soft nitriding treatment becomes remarkable. Therefore, C
The value of u / Ni was set to 1.8 to 2.2. In addition, Cu / N
The value of i is preferably 1.9 to 2.1.

【００３１】Ｃｒ：Ｃｒは、軟窒化時に鋼材表面から浸
入してくるＮと結合して、表面硬度を高めると共に硬化
深さを大きくするのに極めて有効な元素である。しか
し、その含有量が０．５％未満では上記の作用が期待で
きない。一方、Ｃｒを２．０％を超えて含有させると、
軟窒化によって表面硬度が高くなりすぎるために、表面
から芯部にかけての硬度勾配が急激なものとなってしま
い、却って耐スポーリング性や耐ピッチング性が劣化し
てしまう。したがって、Ｃｒの含有量を０．５〜２．０
％とした。Cr: Cr is an extremely effective element that combines with N infiltrating from the surface of the steel during soft nitriding to increase the surface hardness and increase the hardening depth. However, if the content is less than 0.5%, the above effects cannot be expected. On the other hand, if Cr is contained in excess of 2.0%,
Since the surface hardness becomes too high due to the soft nitriding, the hardness gradient from the surface to the core portion becomes abrupt and the spalling resistance and the pitting resistance deteriorate. Therefore, the content of Cr is 0.5 to 2.0.
%.

【００３２】Ｖ：Ｖは、軟窒化処理時に鋼材表面から浸
入してくるＮ及びＣと結合して微細なバナジウム炭窒化
物として析出することにより、表面硬度を高め、更に、
硬化深さを大きくする作用を有する。Ｖ添加鋼において
は上記のＣｒ添加の場合に比べて、表面硬度の上昇割合
が小さいのに対して硬化深さの増大割合は極めて大き
く、且つ前記炭窒化物が析出して芯部硬度を高めるた
め、硬化深さの大きい、表面から芯部への硬度勾配が緩
やかな硬化曲線が得られる。しかし、Ｖ含有量が０．０
５％未満では添加効果に乏しく、一方、０．５％を超え
て含有させても前記の効果が飽和してコストが嵩むばか
りか、却って脆化現象の発現をきたすようになる。した
がって、Ｖ含有量を０．０５〜０．５％とした。なお、
Ｖ含有量は０．１〜０．３％とすることが好ましい。V: V increases the surface hardness by combining with N and C that infiltrate from the surface of the steel material during the soft nitriding treatment to precipitate as fine vanadium carbonitride, and further,
It has the effect of increasing the curing depth. In the case of V-added steel, the rate of increase in the surface hardness is very small, but the rate of increase in the hardening depth is extremely large, and the carbonitride precipitates to increase the core hardness, as compared with the case of the above Cr addition. Therefore, a hardening curve with a large hardening depth and a gentle hardness gradient from the surface to the core can be obtained. However, the V content is 0.0
If it is less than 5%, the effect of addition is poor. On the other hand, if it exceeds 0.5%, the above effect is saturated and the cost is increased, but rather the embrittlement phenomenon is caused. Therefore, the V content is set to 0.05 to 0.5%. In addition,
The V content is preferably 0.1 to 0.3%.

【００３３】Ａｌ：Ａｌは、鋼の脱酸の安定化及び均質
化を図る作用がある。更に、浸入Ｎと結合して表面硬度
を高める効果を有する。しかし、その含有量が０．０１
％未満では上記の作用が期待できない。一方、０．３％
を超えると硬化深さを小さくしてしまう。したがって、
Ａｌの含有量を０．０１〜０．３％とした。なお、Ａｌ
含有量は０．０１〜０．１５％とすることが好ましい。Al: Al has the function of stabilizing and homogenizing deoxidation of steel. Further, it has an effect of increasing the surface hardness by combining with the infiltration N. However, its content is 0.01
If it is less than%, the above effect cannot be expected. On the other hand, 0.3%
If it exceeds, the curing depth will be reduced. Therefore,
The content of Al was set to 0.01 to 0.3%. In addition, Al
The content is preferably 0.01 to 0.15%.

【００３４】Ｍｏ：Ｍｏは添加しなくても良い。添加す
れば、鋼の焼入れ性を高めると共に軟窒化時の芯部の軟
化抵抗を高める作用を有する。この効果を確実に得るに
は、Ｍｏは０．０２％以上の含有量とすることが好まし
い。しかし、その含有量が０．３％を超えると前記効果
が飽和し、コストが嵩むばかりである。したがって、Ｍ
ｏの含有量を０〜０．３％とした。Mo: Mo may not be added. If added, it has the effects of enhancing the hardenability of the steel and enhancing the softening resistance of the core during soft nitriding. In order to surely obtain this effect, it is preferable that the content of Mo is 0.02% or more. However, if the content exceeds 0.3%, the above effect is saturated, and the cost only increases. Therefore, M
The content of o was set to 0 to 0.3%.

【００３５】Ｓ：Ｓは含有させなくても良い。含有させ
れば軟窒化処理前に、冷間加工して成形した部品（軟窒
化用鋼材）を切削して整形する場合の切削性を向上させ
る効果を有する。この効果を確実に得るには、Ｓは０．
０４％以上の含有量とすることが好ましい。しかし、Ｓ
を０．１３％を超えて含有させると熱間加工性及び冷間
加工性の著しい劣化を招く。したがって、Ｓの含有量を
０〜０．１３％とした。S: S may not be contained. If contained, it has the effect of improving the machinability when the cold-formed component (soft nitriding steel material) is cut and shaped before the soft nitriding treatment. To ensure this effect, S is 0.
It is preferable to set the content to be 04% or more. However, S
If it exceeds 0.13%, the hot workability and cold workability are significantly deteriorated. Therefore, the content of S is set to 0 to 0.13%.

【００３６】Ｐｂ：Ｐｂは含有させなくても良い。含有
させれば上記のＳと同様に、冷間加工で成形した部品に
切削整形が必要な場合の切削性を向上させる効果を有す
る。この効果を確実に得るには、Ｐｂは０．０３％以上
の含有量とすることが好ましい。しかし、Ｐｂを０．３
５％を超えて含有させると熱間加工性が劣化して熱間圧
延や熱間鍛造などの熱間加工時に割れの発生を招く。し
たがって、Ｐｂの含有量を０〜０．３５％とした。Pb: Pb may not be contained. If included, similar to S described above, it has the effect of improving the machinability in the case where cutting and shaping is necessary for a component formed by cold working. In order to surely obtain this effect, the content of Pb is preferably set to 0.03% or more. However, Pb is 0.3
If the content exceeds 5%, the hot workability deteriorates and cracks are generated during hot working such as hot rolling and hot forging. Therefore, the Pb content is set to 0 to 0.35%.

【００３７】Ｃａ：Ｃａも含有させなくても良い。含有
させれば、軟窒化処理前に、冷間加工で成形した部品を
切削して整形する場合の切削性を向上させる効果を有す
る。この効果を確実に得るには、Ｃａは０．００１％以
上の含有量とすることが好ましい。一方、Ｃａを０．０
１％を超えて含有させるには特殊な溶製技術や設備を要
してコストが嵩む。したがって、Ｃａの含有量を０〜
０．０１％とした。Ca: Ca may not be contained. If contained, it has the effect of improving the machinability when the cold-formed component is cut and shaped before the soft nitriding treatment. In order to surely obtain this effect, the content of Ca is preferably set to 0.001% or more. On the other hand, Ca is 0.0
If the content exceeds 1%, special melting technology and equipment are required and the cost increases. Therefore, the content of Ca is 0 to
It was set to 0.01%.

【００３８】（Ｂ）球状化焼鈍 球状化焼鈍は上記（Ａ）に示した化学組成を有する鋼材
を、熱間加工（例えば熱間圧延）した後に、その硬度を
低下させて冷間加工性を高めると共に、それによって金
型寿命を大幅に改善し、最終製品である所要の軟窒化部
品の製造コストを低く抑えるのに必須の処理である。(B) Spheroidizing annealing The spheroidizing annealing is performed by hot working (for example, hot rolling) a steel material having the chemical composition shown in (A) above, and then lowering its hardness to improve cold workability. This is an essential process for increasing the mold life and thereby significantly improving the mold life and keeping the manufacturing cost of the required final soft-nitrided component as the final product low.

【００３９】球状化焼鈍後の硬度がＨｖで１８０を超え
ると、金型の寿命が大幅に低下してしまうため、最終製
品である所望の軟窒化部品の製造コストが著しく高くな
る。したがって、球状化焼鈍後の硬度はＨｖ１８０以下
としなければならない。なお、球状化焼鈍後の硬度の下
限値については、特に制限する必要はない。If the hardness after spheroidizing annealing exceeds 180 in Hv, the life of the die is significantly reduced, so that the production cost of the desired soft nitrided component which is the final product is significantly increased. Therefore, the hardness after spheroidizing annealing must be Hv 180 or less. The lower limit of hardness after spheroidizing annealing does not need to be particularly limited.

【００４０】この球状化焼鈍は、通常の方法で行えば良
い。This spheroidizing annealing may be performed by a usual method.

【００４１】（Ｃ）冷間加工 球状化焼鈍して硬度をＨｖ１８０以下に調整した上記
（Ｂ）の鋼材を、次に冷間加工して所望の軟窒化部品形
状に仕上げる。(C) Cold Working The steel material of the above (B) whose hardness is adjusted to Hv 180 or less by spheroidizing annealing is then cold worked to finish it into a desired nitrocarburized part shape.

【００４２】なお、（１）の発明に係る「軟窒化用鋼
材」とは、前記冷間加工によって所望形状に成形された
もののことで、軟窒化される前のものをいう。The "steel material for nitrocarburizing" according to the invention of (1) means a material which has been formed into a desired shape by the cold working, and which has not been nitrocarburized.

【００４３】上記の冷間加工は、例えば、冷間鍛造、冷
間転造や冷間引き抜きなど、通常の方法で行えば良い
が、加工した部品の硬度をＨｖ２５０以上にする必要が
ある。何故ならば、硬度をＨｖ１８０以下に調整された
上記（Ｂ）の鋼材は、冷間での加工を受けて硬度がＨｖ
２５０以上に上昇すれば、これに軟窒化処理を施しても
芯部硬度は低下せず軟窒化前の硬度が維持でき、あるい
は軟窒化前の硬度を高めることさえできるからである。The above-mentioned cold working may be carried out by an ordinary method such as cold forging, cold rolling or cold drawing, but the hardness of the worked part needs to be Hv250 or more. The reason is that the steel material (B), whose hardness is adjusted to Hv 180 or less, has a hardness of Hv after being subjected to cold working.
If the temperature is increased to 250 or more, the core hardness does not decrease even if soft nitriding is applied to the core, the hardness before soft nitriding can be maintained, or the hardness before soft nitriding can be even increased.

【００４４】軟窒化後の芯部硬度がＨｖ２５０以上であ
れば、既に述べたように、例えば、自動車のミッション
ギアのように高い負荷が加わる部品においても、部品内
部を起点として曲げ疲労が生ずることはない。If the core hardness after soft nitriding is Hv250 or more, bending fatigue occurs from the inside of the component even in a component to which a high load is applied, such as an automobile transmission gear, as described above. There is no.

【００４５】上記（Ｂ）に示した球状化焼鈍して硬度を
Ｈｖ１８０以下に調整した鋼材を冷間加工して、硬度を
Ｈｖ２５０以上となすには、減面率で２０％以上の加工
が加わるように寸法調整しておけば良い。In order to obtain a hardness of Hv 250 or more by cold working the steel material having a hardness of Hv 180 or less by spheroidizing annealing shown in (B) above, a reduction of 20% or more is applied to reduce the surface area. Adjust the dimensions so that

【００４６】なお、冷間加工後の硬度の上限値は特に制
限する必要はない。すなわち、設備上加えることが可能
な最高の減面率で加工して、極めて大きな硬度となって
も良い。The upper limit of hardness after cold working does not have to be particularly limited. In other words, the hardness may be extremely high by processing with the highest surface reduction rate that can be added in equipment.

【００４７】これまでに述べた製造方法によって、
（１）の発明に係る「軟窒化用鋼材」が得られる。この
鋼材は、次に述べる軟窒化処理を施されて、（２）の発
明に係る軟窒化部品となる。By the manufacturing method described above,
"Steel for nitrocarburizing" according to the invention of (1) is obtained. This steel material is subjected to the following nitrocarburizing treatment, and becomes the nitrocarburized component according to the invention of (2).

【００４８】（Ｄ）軟窒化 上記（Ｃ）の冷間加工を行って成形した部品（軟窒化用
鋼材）には、この後更に、軟窒化処理が施される。この
軟窒化の方法は何ら制限しなくても良く、通常の方法で
行えば良い。軟窒化処理を施し、表面硬度をＨｖ６００
以上、有効硬化深さを０．１ｍｍ以上とすれば、軟窒化
部品の耐疲労特性、耐摩耗性、耐ピッチング性及び耐ス
ポーリング性を著しく高めることができるのである。(D) Soft nitriding The component (steel material for soft nitriding) formed by performing the cold working of (C) above is further subjected to a soft nitriding treatment. The soft nitriding method may be performed by any ordinary method without any limitation. Soft nitriding treatment applied, surface hardness Hv600
As described above, when the effective hardening depth is 0.1 mm or more, the fatigue resistance, wear resistance, pitting resistance and spalling resistance of the soft nitrided component can be remarkably enhanced.

【００４９】上記（Ｃ）に示した冷間加工を施された部
品（軟窒化用鋼材）を軟窒化して表面硬度をＨｖ６００
以上、有効硬化深さを０．１ｍｍ以上となすには、例え
ば、当該部品を５７０℃程度の温度の、ＲＸガスにアン
モニアを添加したガス中に３〜９時間保持し、その後油
中に冷却すれば良い。The cold-worked part (steel material for nitrocarburizing) shown in (C) above is nitrocarburized to have a surface hardness of Hv600.
As described above, in order to set the effective hardening depth to 0.1 mm or more, for example, the component is held in a gas of about 570 ° C. in which RX gas is added with ammonia for 3 to 9 hours, and then cooled in oil. Just do it.

【００５０】なお、軟窒化後の表面硬度及び有効硬化深
さの上限値は特に制限しなくても良い。しかし、軟窒化
後の表面硬度については、Ｈｖ９００程度を上限とする
ことが好ましい。The upper limits of the surface hardness and the effective hardening depth after nitrocarburizing need not be particularly limited. However, it is preferable that the surface hardness after soft nitriding has an upper limit of about Hv900.

【００５１】（２）の発明に係わる軟窒化部品は、素材
鋼である上記（Ａ）の化学組成を有する鋼を、例えば通
常の方法によって溶製した後、熱間で圧延又は鍛造し、
必要に応じて焼準を施し、（Ｂ）に示した球状化焼鈍を
行い、次いで（Ｃ）に示した冷間加工によって所望の部
品形状に成形し、更に、必要に応じて整形のための加工
を行ってから、軟窒化処理し、この後更に必要に応じて
研削や研磨を施して製造される。The nitrocarburized part according to the invention of (2) is, for example, by melting a steel having the chemical composition of (A), which is a raw material steel, by an ordinary method and then hot rolling or forging,
If necessary, normalization is performed, spheroidizing annealing shown in (B) is performed, and then cold working shown in (C) is performed to form a desired part shape, and further, if necessary, for shaping. After being processed, it is subjected to a soft nitriding treatment, and then, if necessary, further subjected to grinding or polishing to manufacture.

【００５２】ここで、本発明が対象とする化学組成を有
する素材鋼においては、熱間加工後に焼準して、少なく
とも表層から０．５ｍｍを超える深さまでの領域の組織
をベイナイトを含む組織（ベイナイト単相組織、あるい
はベイナイト、並びに、フェライト、パ−ライト及びマ
ルテンサイトの１種以上の混合組織）とすれば、球状化
焼鈍後の炭化物（主としてセメンタイト）の球状化率が
向上する。したがって、球状化焼鈍で冷間加工前の硬度
を大きく低下させることができる。冷間加工前の鋼の硬
度を下げることは、冷間加工性の向上につながり、金型
寿命が延びて金型コストの削減が図れる。更に、球状化
焼鈍時間を短縮することができて、生産性の向上と製造
コストの低減が図れる。このため、（１）の発明の軟窒
化用鋼材の製造方法においては、熱間加工後に焼準して
から球状化焼鈍することが好ましい。Here, in the material steel having the chemical composition targeted by the present invention, normalization is performed after hot working, and at least the structure in the region from the surface layer to a depth exceeding 0.5 mm contains bainite ( A bainite single-phase structure, or bainite, and a mixed structure of one or more of ferrite, pearlite, and martensite) improves the spheroidization rate of carbides (mainly cementite) after spheroidization annealing. Therefore, the hardness before cold working can be greatly reduced by spheroidizing annealing. Reducing the hardness of the steel before cold working leads to an improvement in cold workability, extending the life of the mold, and reducing the cost of the mold. Further, the spheroidizing annealing time can be shortened, so that productivity can be improved and manufacturing cost can be reduced. For this reason, in the method for manufacturing a steel material for soft nitriding of the invention (1), it is preferable to perform normalizing after hot working and then spheroidizing annealing.

【００５３】[0053]

【実施例】表１、２に示す化学組成を有する鋼を通常の
方法によって１８０ｋｇ真空溶製した。表１における鋼
1〜 9は本発明対象鋼（以下、本発明鋼という）、表２
における鋼10〜20は成分のいずれかが本発明で規定する
範囲から外れた比較鋼である。比較鋼のうち鋼19及び20
はそれぞれＪＩＳ規格のＳＣＭ４３５及びＳＡＣＭ６４
５に相当するものである。EXAMPLES Steels having the chemical compositions shown in Tables 1 and 2 were vacuum-melted by 180 kg in a usual manner. Steel in Table 1
1 to 9 are steels of the present invention (hereinafter referred to as the present invention steels), Table 2
Steels 10 to 20 are comparative steels in which any of the components is out of the range specified in the present invention. Steels 19 and 20 of comparative steels
Are JIS standard SCM435 and SACM64, respectively.
It is equivalent to 5.

【００５４】[0054]

【表１】 [Table 1]

【００５５】[0055]

【表２】 [Table 2]

【００５６】次いで、これらの鋼を通常の方法によって
鋼片となした後、１２５０℃に加熱してから、１２５０
〜９５０℃の温度で熱間鍛造して、直径３０ｍｍ及び３
８ｍｍの丸棒とした。この後、Ｃ含有量に応じて８７０
〜９２５℃で焼準し、次いで、図１に示すヒートパター
ンで球状化焼鈍した。Next, these steels were formed into billets by a usual method, heated to 1250 ° C., and then heated to 1250.
Hot forging at a temperature of ~ 950 ° C, diameter 30 mm and 3
An 8 mm round bar was used. After this, depending on the C content, 870
Normalization was performed at ˜925 ° C., and then spheroidizing annealing was performed in the heat pattern shown in FIG.

【００５７】なお、鋼３及び９については、比較のため
に、熱間鍛造のままで、すなわち熱間鍛造後に焼準を行
わないで球状化焼鈍したものも準備した。For comparison, the steels 3 and 9 were prepared by spheroidizing annealing as hot forging, that is, after hot forging without normalizing.

【００５８】（実施例１）上記のようにして得られた直
径が３０ｍｍの丸棒を用いて、下記の各種調査を行っ
た。Example 1 The following various investigations were carried out using the round bar having a diameter of 30 mm obtained as described above.

【００５９】先ず、焼準ままの丸棒からは、直径が３０
ｍｍで厚さが２０ｍｍの試験片を切り出し、光学顕微鏡
による組織観察を行った。First, from the as-normalized round bar, the diameter is 30
A test piece having a thickness of 20 mm and a thickness of 20 mm was cut out and the structure was observed with an optical microscope.

【００６０】一方、球状化焼鈍後の各丸棒からは、直径
が３０ｍｍで厚さが２０ｍｍの硬度試験片と直径が１０
ｍｍで長さが１５ｍｍの冷間加工用試験片を作製した。On the other hand, from each round bar after spheroidizing annealing, a hardness test piece having a diameter of 30 mm and a thickness of 20 mm and a diameter of 10 were obtained.
A test piece for cold working having a size of 15 mm and a length of 15 mm was prepared.

【００６１】上記の硬度試験片を用いて、マイクロビッ
カース硬度計により中央部のＨｖ硬度測定を行った。Using the above hardness test piece, the Hv hardness of the central portion was measured with a micro Vickers hardness meter.

【００６２】又、上記の冷間加工用試験片を用いて、５
００ｔ高速プレス機による通常の方法で冷間（室温）拘
束型据え込み試験を行い、限界据え込み率を測定した。
なお、各条件ごとに３回の据え込み試験を行い、３個の
試験片のすべてに割れが発生しない最大加工率（減面
率）を限界据え込み率として評価した。Also, using the above cold working test piece, 5
A cold (room temperature) constrained upsetting test was conducted by a usual method using a 00t high-speed press to measure the limit upsetting rate.
In addition, three upsetting tests were performed for each condition, and the maximum working rate (area reduction rate) at which cracks did not occur in all three test pieces was evaluated as the limit upsetting rate.

【００６３】一方、前記のようにして得られた球状化焼
鈍後の直径３０ｍｍの各丸棒を、直径２５ｍｍにピーリ
ング加工し、この後、通常の方法によって冷間（室温）
で直径２０．９ｍｍ（減面率３０．１％）までドローベ
ンチを用いて引き抜き加工した。次いで、ＲＸガスにア
ンモニアガスを１：１の割合で添加した温度が５７０℃
のガス中で６時間保持して軟窒化処理を施し、その後油
中へ冷却した。On the other hand, each round bar having a diameter of 30 mm after spheroidizing annealing obtained as described above was peeled to a diameter of 25 mm, and then cold (at room temperature) by a usual method.
Then, it was drawn out to a diameter of 20.9 mm (area reduction ratio 30.1%) using a draw bench. Then, the temperature at which ammonia gas was added to the RX gas at a ratio of 1: 1 was 570 ° C.
It was held in the gas for 6 hours for soft nitriding treatment and then cooled in oil.

【００６４】引き抜きままの丸棒からは、直径が２０．
９ｍｍで厚さが２０ｍｍの硬度試験片を作製し、マイク
ロビッカース硬度計を用いて中央部の硬度測定を行っ
た。又、軟窒化処理した丸棒からも、直径が２０．９ｍ
ｍで厚さが２０ｍｍの硬度試験片を作製し、マイクロビ
ッカース硬度計により表面硬度（表面から０．０２５ｍ
ｍの位置におけるＨｖ硬度）、有効硬化深さ（表面から
Ｈｖ５００の位置までの距離）及び中央部硬度の測定を
行った。From the as-drawn rod, a diameter of 20.
A hardness test piece having a thickness of 9 mm and a thickness of 20 mm was prepared, and the hardness of the central portion was measured using a micro Vickers hardness meter. In addition, the diameter of the soft-nitrided round bar is 20.9 m.
A hardness test piece having a thickness of 20 mm and a thickness of 20 mm was prepared, and the surface hardness (0.025 m from the surface was measured by a micro Vickers hardness meter).
m), the effective hardening depth (distance from the surface to the position of Hv500), and the center hardness were measured.

【００６５】表３に各種の試験結果をまとめて示す。Table 3 shows the results of various tests.

【００６６】表３から、本発明鋼の場合には、球状化焼
鈍後の硬度はいずれもＨｖで１８０を下回り、限界据え
込み率は８０％を超えている。そして、減面率３０．１
％の冷間加工（引き抜き加工）によって、容易にＨｖ２
５０を超える硬度が得られている。更に、軟窒化後には
Ｈｖ６００を超える表面硬度と、０．１ｍｍを超える有
効硬化深さが得られており、しかも軟窒化のための５７
０℃での６時間の熱処理を受けても、中央部硬度（芯部
硬度）は軟窒化前のレベルに維持されているか、あるい
は軟窒化前の硬度より高くなっている。From Table 3, in the case of the steels of the present invention, the hardness after spheroidizing annealing is less than 180 in Hv, and the critical upsetting ratio exceeds 80%. And the reduction rate of 30.1
% Hv2 easily by cold working (drawing)
A hardness of over 50 is obtained. Furthermore, after the nitrocarburizing, a surface hardness of more than Hv600 and an effective hardening depth of more than 0.1 mm were obtained, and 57 for nitrocarburizing was obtained.
Even after being subjected to heat treatment at 0 ° C. for 6 hours, the central part hardness (core part hardness) is maintained at the level before soft nitriding or is higher than the hardness before soft nitriding.

【００６７】これに対して比較鋼の場合には、（イ）球
状化焼鈍後の硬度がＨｖ１８０を超えて限界据え込み率
が低い、（ロ）冷間加工後の硬度が低いために軟窒化後
の芯部硬度も低い、（ハ）冷間加工後の硬度はＨｖ２５
０を超えるものの軟窒化後の芯部硬度はＨｖ２５０を下
回る、（ニ）軟窒化後の表面硬度がＨｖ６００を下回
る、（ホ）軟窒化後の有効硬化深さが０．１ｍｍを下回
る、のいずれか１つ以上に該当する。このため、冷間加
工時の金型寿命が短くて金型コストが嵩むため、所望の
軟窒化部品の製造コストは極めて高いものとなってしま
ったり、製造コストは低くても軟窒化部品の耐疲労特
性、耐摩耗性、耐ピッチング性及び耐スポーリング性は
劣ったものとなってしまう。On the other hand, in the case of the comparative steels, (a) the hardness after spheroidizing annealing exceeds Hv180 and the critical upsetting ratio is low, and (b) the hardness after cold working is low, so that nitrocarburizing is performed. The core hardness afterwards is also low, and the hardness after (c) cold working is Hv25.
The core hardness after soft nitriding of more than 0 is less than Hv250, (d) the surface hardness after soft nitriding is less than Hv600, and (e) the effective hardening depth after soft nitriding is less than 0.1 mm. It corresponds to one or more. For this reason, the mold life during cold working is short, and the mold cost is increased. Therefore, the production cost of the desired nitrocarburized component becomes extremely high. The fatigue properties, abrasion resistance, pitting resistance and spalling resistance are inferior.

【００６８】[0068]

【表３】 [Table 3]

【００６９】（実施例２）前記のようにして得られた直
径が３８ｍｍの丸棒を用いて、下記の各種調査を行っ
た。Example 2 The following various investigations were carried out using the round bar having a diameter of 38 mm obtained as described above.

【００７０】先ず、球状化焼鈍後の各丸棒から、直径が
３８ｍｍで厚さが２０ｍｍの硬度試験片を作製し、これ
を用いて、マイクロビッカース硬度計により中央部のＨ
ｖ硬度測定を行った。First, a hardness test piece having a diameter of 38 mm and a thickness of 20 mm was prepared from each round bar after spheroidizing annealing, and using this, a H part of the central portion was measured by a micro Vickers hardness meter.
v Hardness measurement was performed.

【００７１】更に、球状化焼鈍後の直径３８ｍｍの各丸
棒を、直径３６ｍｍにピーリング加工し、この後、通常
の方法によって冷間（室温）で直径３０ｍｍ（減面率３
０．６％）までドローベンチを用いて引き抜き加工し
た。この後、図２に示す転動疲労試験片（小ローラー）
と環状半円溝付きの小野式回転曲げ疲労試験片（JIS Z2
274のＤ＝１０ｍｍ、ｄ＝８ｍｍ、ρ＝ｔ＝１ｍｍ、Ｄ₀
＝１２ｍｍの試験片）を作製した。Further, each round bar having a diameter of 38 mm after spheroidizing annealing was subjected to a peeling process to a diameter of 36 mm, and thereafter, by a usual method, the diameter was 30 mm (area reduction ratio: 3).
Up to 0.6%), it was drawn using a draw bench. After this, the rolling fatigue test piece (small roller) shown in FIG.
Ono type rotating bending fatigue test piece (JIS Z2
274 D = 10 mm, d = 8 mm, ρ = t = 1 mm, D ₀
= 12 mm test piece) was prepared.

【００７２】次いで、前記の各試験片を、ＲＸガスにア
ンモニアガスを１：１の割合で添加した温度が５７０℃
のガス中で６時間保持して軟窒化処理を施し、その後油
中へ冷却した。なお、直径３０ｍｍ×長さ１００ｍｍの
冷間引き抜きままのものに対しても、同時に上記の処理
を施した。Then, the temperature of each of the test pieces was 570 ° C. when the ammonia gas was added to the RX gas at a ratio of 1: 1.
It was held in the gas for 6 hours for soft nitriding treatment and then cooled in oil. The above treatment was simultaneously applied to a cold drawn product having a diameter of 30 mm and a length of 100 mm.

【００７３】引き抜きままの丸棒からは、直径が３０ｍ
ｍで厚さが２０ｍｍの硬度試験片を作製し、マイクロビ
ッカース硬度計を用いて中央部の硬度測定を行った。
又、軟窒化処理した丸棒からも、直径が３０ｍｍで厚さ
が２０ｍｍの硬度試験片を作製し、マイクロビッカース
硬度計により表面硬度（表面から０．０２５ｍｍの位置
におけるＨｖ硬度）、有効硬化深さ（表面からＨｖ５０
０の位置までの距離）及び中央部硬度の測定を行った。From the as-drawn rod, the diameter is 30m.
A hardness test piece having a thickness of 20 mm and a thickness of 20 mm was prepared, and the hardness of the central portion was measured using a micro Vickers hardness meter.
Further, a hardness test piece having a diameter of 30 mm and a thickness of 20 mm was prepared from a soft-nitrided round bar, and the surface hardness (Hv hardness at a position of 0.025 mm from the surface) and effective curing depth were measured by a micro Vickers hardness meter. Sa (from the surface Hv50
The distance to the position of 0) and the hardness of the central portion were measured.

【００７４】一方、軟窒化処理した小野式回転曲げ疲労
試験片と転動疲労試験片を用いて、疲労特性を調査し
た。On the other hand, the fatigue characteristics were investigated using the Ono-type rotary bending fatigue test piece and the rolling fatigue test piece which had been subjected to the soft nitriding treatment.

【００７５】すなわち、常温（室温）、大気中、回転数
３０００ｒｐｍの条件で小野式回転曲げ疲労試験を行
い、曲げ疲労強度（疲労限）を求めた。That is, an Ono-type rotary bending fatigue test was carried out at room temperature (room temperature) in the air at a rotation speed of 3000 rpm to determine the bending fatigue strength (fatigue limit).

【００７６】又、回転数１０００ｒｐｍ、潤滑油の温度
８０℃、すべり率４０％の条件でローラーピッチング試
験機を用いて、面疲労強度を求めた。なお、相手材とな
る大ローラーには、ＪＩＳのＳＵＪ２を用いて硬度をロ
ックウェルＣ硬度（ＨR Ｃ）で６１に調整し、外径１３
０ｍｍ、内径４５ｍｍ、厚さ１８ｍｍに加工したものを
使用した。そして、前記の試験条件で１０⁷ 回の回転が
可能な面圧を「面疲労強度」として評価した。The surface fatigue strength was determined using a roller pitching tester under the conditions of a rotation speed of 1000 rpm, a lubricating oil temperature of 80 ° C. and a slip ratio of 40%. For the large roller, which is the mating material, the hardness is adjusted to 61 with Rockwell C hardness (HR C) using JIS SUJ2, and the outer diameter is 13
What was processed to 0 mm, an inner diameter of 45 mm, and a thickness of 18 mm was used. Then, the surface pressure capable of being rotated 10 ⁷ times under the above-mentioned test conditions was evaluated as “surface fatigue strength”.

【００７７】表４に各種の試験結果をまとめて示す。Table 4 collectively shows the results of various tests.

【００７８】表４から、本発明鋼の場合には、前記の実
施例１におけると同様に、球状化焼鈍後の硬度はいずれ
もＨｖで１８０を下回っている。そして、減面率で３
０．６％の冷間加工（引き抜き加工）によって、容易に
Ｈｖ２５０を超える硬度が得られている。更に、軟窒化
後にはＨｖ６００を超える表面硬度と、０．１ｍｍを超
える有効硬化深さが得られており、しかも軟窒化のため
の５７０℃での６時間の熱処理を受けても、中央部硬度
（芯部硬度）は軟窒化前のレベルに維持されているか、
あるいは軟窒化前の硬度より高くなっている。From Table 4, in the case of the steels of the present invention, the hardness after spheroidizing is less than 180 in Hv, as in Example 1 above. And the reduction rate is 3
Hardness exceeding Hv250 is easily obtained by cold working (drawing) of 0.6%. Furthermore, after nitrocarburizing, a surface hardness of more than Hv600 and an effective hardening depth of more than 0.1 mm were obtained, and even after undergoing a heat treatment at 570 ° C for 6 hours for nitrocarburizing, the hardness of the central part Is (core hardness) maintained at the level before soft nitriding?
Alternatively, the hardness is higher than that before soft nitriding.

【００７９】更に、曲げ疲労強度は５５ｋｇｆ／ｍｍ²
以上の値を有し、面疲労強度も２４５ｋｇｆ／ｍｍ² を
超える値が得られている。Further, the bending fatigue strength is 55 kgf / mm ²
The above values are obtained, and the surface fatigue strength exceeds 245 kgf / mm ² .

【００８０】これに対して比較鋼の場合には、（イ）球
状化焼鈍後の硬度がＨｖ１８０を超える、（ロ）冷間加
工後の硬度が低いために軟窒化後の芯部硬度も低い、
（ハ）冷間加工後の硬度はＨｖ２５０を超えるものの軟
窒化後の芯部硬度はＨｖ２５０を下回る、（ニ）軟窒化
後の表面硬度がＨｖ６００を下回る、（ホ）軟窒化後の
有効硬化深さが０．１ｍｍを下回る、のいずれか１つ以
上に該当する。更に、曲げ疲労強度は高々４６ｋｇｆ／
ｍｍ² （鋼10と17）であるし、面疲労強度も鋼14の２３
２ｋｇｆ／ｍｍ² が最高で、本発明鋼と比較して明らか
に劣っている。On the other hand, in the case of the comparative steel, (a) the hardness after spheroidizing exceeds 180, and (b) the hardness after cold working is low, so the core hardness after nitrocarburizing is also low. ,
(C) The hardness after cold working exceeds Hv250, but the core hardness after nitrocarburizing is less than Hv250, (d) the surface hardness after nitrocarburizing is less than Hv600, (e) the effective hardening depth after nitrocarburizing. Falls below 0.1 mm, and corresponds to any one or more of. Furthermore, the bending fatigue strength is at most 46 kgf /
mm ² (steels 10 and 17) and the surface fatigue strength is 23 of steel 14
2 kgf / mm ² is the highest, which is clearly inferior to the steel of the present invention.

【００８１】[0081]

【表４】 [Table 4]

【００８２】[0082]

【発明の効果】本発明の軟窒化部品は、耐疲労特性、耐
摩耗性、耐ピッチング性及び耐スポーリング性に優れる
ことから、自動車用や産業機械用の歯車など大きな疲労
強度や耐摩耗性が要求される部品として利用することが
できる。なお、Ｈｖ２５０以上の高い芯部硬度が安定し
て確保できるので、特に大きな曲げ疲労強度が要求され
る部品にも用いることができる。この軟窒化部品の素材
となる軟窒化用鋼材は、本発明の方法によって比較的容
易に製造することができる。The nitrocarburized parts of the present invention are excellent in fatigue resistance, wear resistance, pitting resistance and spalling resistance, so that they have great fatigue strength and wear resistance in gears for automobiles and industrial machines. Can be used as required parts. Since a high core hardness of Hv250 or more can be stably ensured, it can be used for a component that requires particularly large bending fatigue strength. The steel material for nitrocarburizing, which is the material of the nitrocarburized component, can be produced relatively easily by the method of the present invention.

【図面の簡単な説明】[Brief description of drawings]

【図１】実施例における球状化焼鈍のヒートパターンを
示す図である。FIG. 1 is a diagram showing a heat pattern of spheroidizing annealing in an example.

【図２】実施例で用いた転動疲労試験片の形状を示す図
である。FIG. 2 is a diagram showing a shape of a rolling fatigue test piece used in Examples.

───────────────────────────────────────────────────── フロントページの続き (51)Int.Cl.⁶ 識別記号 庁内整理番号 ＦＩ 技術表示箇所 Ｃ２３Ｃ 8/32 Ｃ２３Ｃ 8/32 ─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical indication C23C 8/32 C23C 8/32

Claims (2)

【特許請求の範囲】[Claims] 【請求項１】重量％で、Ｃ：０．１５〜０．４５％、Ｓ
ｉ：０．０５〜０．５０％、Ｍｎ：０．２〜２．５％、
Ｃｕ：０．５〜１．５％、Ｎｉ：０．２５〜０．７５％
で、且つ１．８≦Ｃｕ／Ｎｉ≦２．２、Ｃｒ：０．５〜
２．０％、Ｖ：０．０５〜０．５％、Ａｌ：０．０１〜
０．３％、Ｍｏ：０〜０．３％、Ｓ：０〜０．１３％、
Ｐｂ：０〜０．３５％、Ｃａ：０〜０．０１％、残部は
Ｆｅ及び不可避不純物の化学組成からなる鋼を、熱間加
工後に球状化焼鈍して硬度をＨｖ１８０以下となし、次
いで冷間加工して硬度をＨｖ２５０以上となすことを特
徴とする軟窒化用鋼材の製造方法。C. 0.15 to 0.45% by weight, S
i: 0.05 to 0.50%, Mn: 0.2 to 2.5%,
Cu: 0.5 to 1.5%, Ni: 0.25 to 0.75%
And 1.8 ≦ Cu / Ni ≦ 2.2, Cr: 0.5 to
2.0%, V: 0.05 to 0.5%, Al: 0.01 to
0.3%, Mo: 0 to 0.3%, S: 0 to 0.13%,
Pb: 0 to 0.35%, Ca: 0 to 0.01%, the balance being steel having a chemical composition of Fe and unavoidable impurities, and spheroidizing annealing after hot working to make the hardness Hv 180 or less, and then cooling. A method for manufacturing a steel material for soft nitriding, which comprises subjecting the steel to a hardness of Hv250 or more by hot working. 【請求項２】請求項１に記載の方法で製造した軟窒化用
鋼材を素材とし、軟窒化後の表面硬度がＨｖ６００以
上、且つ、有効硬化深さが０．１ｍｍ以上であることを
特徴とする軟窒化部品。2. A steel material for soft nitriding manufactured by the method according to claim 1, which has a surface hardness after soft nitriding of Hv 600 or more and an effective hardening depth of 0.1 mm or more. Soft-nitrided parts that do.