Metal treatment – Stock – Ferrous
Patent
1995-04-14
1997-11-25
Yee, Deborah
Metal treatment
Stock
Ferrous
420 8, C22C 3806
Patent
active
056907532
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
1. Technical Field
The present invention relates to a steel containing super-finely dispersed oxide system inclusions, and provides a steel having superior properties which is not adversely affected by oxide system inclusions.
2. Background of the Invention
Recently, qualities required for steel materials have been gradually becoming more strict in their standards and more diversified, and there has been a strong demand for developing steels of more excellent properties. It has been known that oxide system inclusions in steel materials, especially alumina (Al.sub.2 O.sub.3) system inclusions, cause wire materials such as tire cords to break, or deteriorate rolling-contact fatigue properties of bar steels such as bearing steels, or cause thin sheet steels used for cans to crack during pressing. Consequently, steels have been demanded which have small amounts of alumina system inclusions so as to lessen their adverse affects in steel materials, or which have alumina system inclusions improved in characteristics so as to become not harmful.
In the manufacture of steels with small amounts of alumina system inclusions, removal of alumina system inclusions of steels, attempts have been made to remove such inclusions which are generated in the refining process, as much as possible in the process. A summary of this trial is disclosed in the 126th, 127th Nishiyama Memorial Technology Lectures Report "Highly Clean Steels", pp. 11-15, published by Japan Steel Association in November, 1988, of which the technical abstract is attached (see Table 4 on p. 12). According to this document, technology for removal can be roughly classified into 1) a technique of decreasing alumina, which is a deoxidation product, in molten steel, 2) a technique of restraining or preventing generation of alumina due to oxidation in air or the like, and 3) a technique of decreasing alumina system inclusions introduced from refractories or the like. In the actual industrial process, alumina system inclusions are decreased by combining the above classified techniques appropriately with each other. Thus, the total oxygen (T.O.) amount as the measure of an amount of alumina system inclusions in molten steel can be lowered to the following level:
High carbon steel containing about 1 wt % carbon
Medium carbon steel containing about 0.5 wt % carbon
Low carbon steel containing about 0.1 wt % carbon
On the other hand, as stated above, it has been tried to improve alumina system inclusions in characteristics thereof so as to become not harmful, for example, by a method proposed by the present inventors which is described in JP patent application ser. No. 3-55556. According to the method, molten steel and flux are contacted with each other, the melting point of oxide system inclusions in the molten steel is made not higher than 1500.degree. C., and a slab obtained from the molten steel is heated to 850.degree. to 1350.degree. C. and thereafter rolled. Thus, the inclusions are deformed into oblong shapes in a strict deformation rate-similar to that of the steel, and consequently, stress concentration on the inclusions is restrained, thereby preventing defects caused by inclusions in final products.
However, even if the above-described techniques for removing alumina system inclusions and eliminating their adverse affects are exercised, oxide system inclusions often cause defects in products. Therefore, this problem has been a significant technical obstacle. Meanwhile, it can be predicted that the level of oxide system inclusions required for steel materials will become more strict. There has been a strong desire for developing superior steels from which adverse affects of oxide system inclusions are completely eliminated.
DISCLOSURE OF INVENTION
The present invention is intended to solve the above problems and satisfy the current desires. It is an object of the invention to provide a superior steel from which adverse affects of oxide system inclusions are completely eliminated by a novel idea.
According to the invention, the following stee
REFERENCES:
patent: 5234513 (1993-08-01), Inoue et al.
patent: 5391241 (1995-02-01), Watanabe et al.
126th, 127th Nishiyama Memorial Technology Lectures Report "Highly Clean Steels", pp. 11-15, published by Japan Steel Association in Nov., 1988 (translation of relevant portion).
Kawauchi Yuji
Maede, deceased Hirobumi
Nippon Steel Corporation
Yee Deborah
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