Alloys or metallic compositions – Ferrous – Nine percent or more chromium containing
Patent
1996-02-28
1998-01-20
Yee, Deborah
Alloys or metallic compositions
Ferrous
Nine percent or more chromium containing
420 64, 420 68, 420 69, 420428, 420583, C22C 3826, C22C 3828
Patent
active
057098360
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to chromium steel sheets (inclusive of steel strips) having an excellent press formability, particularly excellent deep-drawing formability and resistance to secondary working brittleness.
BACKGROUND ART
As a typical kind of the chromium steel sheets, ferritic stainless steel sheets are usually produced through steps of hot rolling--annealing of hot rolled sheet--cold rolling--finish annealing after the heating of continuously cast slab.
In general, the thus produced ferritic stainless steel is excellent in the resistance to stress corrosion cracking and is cheap, so that it is widely used to applications such as various kitchenwares, automobile parts and the like. However, the steel is often subjected to a severer deep drawing in the application such as fuel filter casing for automobile and the like, so that there is frequently caused a problem of creating cracks due to secondary working brittleness.
Therefore, there have made many attempts in order to improve the deep-drawing formability and the resistance to secondary working brittleness in the ferritic stainless steel sheets.
For example, JP-B-54-11770 has proposed a production technique of ferritic stainless steel sheets aiming at a high cold workability by addition of Ti, while JP-B-57-55787 has proposed a production technique of ferritic stainless steel sheets aiming at a high Lankford value (hereinafter abbreviated as "r-value") by addition of B. Furthermore, JP-B-2-7391 has proposed a production technique for ferritic stainless steel sheets which limits brittle cracks after deep drawing by addition of Ti and B.
However, these techniques have problems as mentioned below. That is, the brittle cracks are frequently observed at the secondary working after severer deep drawing in the technique disclosed in JP-B-54-11770. Further, the technique disclosed in JP-B-57-55787 is unsuitable for severer deep drawing because the deep drawability is insufficient. And also, the addition of Ti and B is conducted in the technique disclosed in JP-B-2-7391, but either deep drawability or resistance to secondary work brittleness is poor and both the properties are not simultaneously satisfied. Moreover, these techniques have a problem in that the plane anisotropy of r-value (hereinafter abbreviated as ".DELTA.r") is not sufficiently improved.
As mentioned above, all of the above techniques improve either the deep-drawing formability or the resistance to secondary work embrittlement, but have the common problem that both the properties are not simultaneously improved. Therefore, the occurrence of brittle cracks in the subsequent secondary working is still a concern after severer deep drawing.
It is, therefore, an object of the invention to provide chromium steel sheets having excellent press formability, particularly deep-drawing formability and resistance to secondary work brittleness.
It is another object of the invention to provide chromium steel sheets having an r-value of not less than 1.5, .DELTA.r of not more than 0.3 and a brittle crack creating temperature of not higher than -50.degree. C.
DISCLOSE OF INVENTION
The inventors have made various studies in order to achieve the above objects and found that the deep-drawing formability and the resistance to secondary work brittleness are simultaneously improved and further the ductility of weld portion is improved by controlling the chemical composition of the chromium steel sheet to a proper range, and as a result the invention has been accomplished.
The chromium steel sheet having the above properties has the following construction: wt % in addition to the main ingredient of the above item (1). 0.0005-0.01 wt % in addition to the main ingredient of the above item (1). 0.0005-0.025 wt % in addition to the main ingredients of the above item (1). wt % and Ca: 0.0005-0.01 wt % in addition to the main ingredient of the above item (1). wt % and Se: 0.0005-0.025 wt % in addition to the main ingredient of the above item (1). 0.0005-0.01 wt % and Se: 0.0005-0.025 wt % in addit
REFERENCES:
By the 19th Committee in Steelmaking of Japan, Society for the Promotion of Science, "Steel and Alloy Elements (upper)" Feb. 28, 1966 (28.02.1966) Seibundo Shinkosha, p. 223.
By the 19th Committee in Steelmaking of Japan, Society for the Promotion of Science, "Steel and Alloy Elements (lower)" Seibundo Shinkosha, p. 281, Feb. 28, 1966.
Fujisawa Mitsuyuki
Kato Yasushi
Satoh Susumu
Ujiro Takumi
Yamato Koji
Kawasaki Steel Corporation
Miller Austin R.
Yee Deborah
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