Metal treatment – Stock – Carburized or nitrided
Patent
1997-03-07
1998-09-22
Yee, Deborah
Metal treatment
Stock
Carburized or nitrided
148333, 420103, 420104, C22C 3828, C22C 3824, C23C 826
Patent
active
058109480
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a nitriding steel excellent in formability and susceptibility to nitriding and a press formed article which is made of the steel, which is excellent in workability, particularly in deep drawability and wear resistance, and which is used for parts required to have wear resistance, fatigue strength and seizure resistance such as tools, parts for machine structures and parts for automobiles.
BACKGROUND OF THE INVENTION
Tools, parts for machine structures, parts for automobiles, and the like are required to have wear resistance, fatigue strength and seizure resistance. Accordingly, a process termed nitriding, for producing parts (formed articles of steel sheets being excluded) having a high surface hardness and a high internal hardness by making nitrogen invade the steel, has been employed. Since such steels (for example, Japanese Patent Kokai Publication Nos. 59-31850 and 59-50158) used for these parts are made to contain large amounts of nitriding-promoting elements, the steels have high strength but are difficult to work. As a result, a steel bar, or the like steel product is shaped by grinding, and then nitrided to have a high hardness. Shaping such a steel material, therefore, consumes time and becomes costly.
On the other hand, press forming is an easy, low cost forming method, and press formed articles can be produced by applying the method to a steel sheet such as a low carbon steel sheet and an extra low carbon steel sheet (e.g., Japanese Patent Kokai Publication No. 44-18066). Although steel parts having a necessary shape can be formed, the steel parts have been incapable of being made to have a high surface hardness which is important for their properties such as wear resistance, fatigue strength and seizure resistance. As described above, it has been impossible to produce a press formed article which is easily obtained by forming and which has a desired high surface hardness, by conventional methods. The compatibility of both properties has been a problem to be solved.
In such conventional techniques, grinding for shaping a steel material consumes much time and is costly. Even when a steel such as a free-cutting steel which can be easily ground is used, a shaping procedure in which a steel bar is ground to have a necessary shape consumes much time and is very costly. When forming methods often used for a steel sheet, particularly for a thin steel sheet, for example, press forming and bending can be applied to the steel, the cost related to forming steel parts can be greatly reduced, and the production efficiency can be significantly increased. Accordingly, a steel sheet which can be formed by a low cost forming method such as press forming and bending, and which is excellent in susceptibility to nitriding, namely an increase in hardness by nitriding is strongly desired.
The present invention is intended to solve the problems as mentioned above. An object of the present invention is to provide a nitriding steel to which forming such as press forming and bending can be applied and which is excellent in formability, particularly in deep drawability, as well as in susceptibility to nitriding.
A further object of the present invention is to provide a press formed article excellent in economy and productivity as well as in formability and wear resistance by the use of the steel.
A still further object of the present invention is to provide a press formed article having a surface hardness (Hv) of at least 400 and a limiting drawing ratio of at least 1.9.
DISCLOSURE OF THE INVENTION
The present invention has been achieved on the basis of the technical discovery that subjecting a steel sheet to press forming such as deep drawing forms an appropriate amount of dislocation therein, which promotes nitrogen diffusion and nitride formation, a nitride hardened layer thus being formed on the surface thereof to a desired depth in a short period of time.
In the present invention, the steel to be used is classified into a high C content steel containing f
REFERENCES:
patent: Re31251 (1983-05-01), Nakasugi et al.
patent: 5372654 (1994-12-01), Satoh et al.
Hotta Akio
Mine Kouichi
Nishiwaki Takeshi
Shimoda Kenji
Yamazaki Kazumasa
Nippon Steel Corporation
Toyota Jidosha & Kabushiki Kaisha
Yee Deborah
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