Metal treatment – Process of modifying or maintaining internal physical... – With casting or solidifying from melt
Patent
1993-12-16
1994-12-27
Yee, Deborah
Metal treatment
Process of modifying or maintaining internal physical...
With casting or solidifying from melt
148544, 148325, 148327, C21D 802, C22C 3840
Patent
active
053761952
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to an austenitic stainless steel sheet having excellent surface quality which is produced by casting a slab having a thickness approximate to that of a product produced by a so-called "synchronous continuous casting process" in which a mold and a slab move in synchronism with each other, and the slab is directly cold rolled without being passed through hot rolling, and a production method thereof.
BACKGROUND ART
To produce a stainless steel sheet by a continuous casting method, a conventional production method comprises the steps of casting a slab having a thickness of at least 100 mm while oscillating a mold in a casting direction, treating the surface of the obtained slab, heating the slab to a temperature not lower than 1,000.degree. C. in a heating furnace, hot rolling the slab by a hot strip mill comprising a rough rolling mill and a finish rolling mill and obtaining a hot strip having a thickness of several millimeters.
When the hot strip thus obtained is cold rolled, to secure the shape (flatness), mechanical and surface properties required for the final product, hot rolled sheet annealing is carried out to soften a strongly hot worked hot strip and scale, etc., on the surface is removed therefrom by grinding after pickling.
The conventional process described above requires a great deal of energy for heating and working the materials in a long and large hot rolling facility, and also cannot be said to be a really excellent production process from the aspect of producibility. In the final product, there are many limitations for using, because a texture develops in the product, and therefore, when a user conducts press working, etc., of the product sheet, anisotropy must be taken into account.
To solve the problem that a long and large hot rolling facility and a great deal of energy and rolling power are necessary for rolling a slab having a thickness of at least 100 mm to a hot strip, studies have been carried out in recent years in search of the process which obtains a slab (thin strip) having a thickness equal or approximate to a hot strip during the continuous casting process.
For examples, feature articles in "Iron and Steels", '85, A197-A256 and "CAMP ISIJ", Vol. 1, 1988, 1674-1705, disclose a process for directly obtaining the hot strip by continuous casting.
In such a continuous casting process, the use of a twin drum system is examined when the gauge of the obtained slab (strip) is at a level of 1 to 10 mm and a use of a twin belt system is examined when the gauge of that is at a level of 20 to 50 mm.
The continuous casting process of this kind produces a slab having a shape approximate to the final shape, and omits or reduces intermediate steps such as a hot rolling step, a heat-treatment step, and so forth. Accordingly, it is known that a structure of the slab greatly affects the mechanical and surface properties of the final product.
Conventionally, very small corrugations of from about 0.2 to 0.1 .mu.m, which are referred to as "roping", have often occurred on the surface of the steel sheet as cold rolled, in the austenitic stainless steel sheet produced by the strip casting process described above. Japanese Unexamined Patent Publication (Kokai) No. 2-19426 teaches to first carry out preliminary cold rolling at a reduction ratio of up to 60%, then to carry out intermediate annealing and to thereafter carry out cold rolling to the thickness of the final product, or a so-called "twice cold rolling method", in cold rolling of the cast-strip so as to reduce this "roping". According to this method, plastic working is applied to the strip consisting of coarse .gamma. grains so as to first flatten mechanically the surface of the strip and at the same time, strain induced by distortion is built up in the internal structure so as to promote the progress of recrystallization during intermediate annealing. After the crystal grains are made smaller and the strain is sufficiently released, the surface corrugation is reduced by the second cold rolling operatio
REFERENCES:
patent: 4265679 (1981-05-01), Ohashi et al.
patent: 5030296 (1991-07-01), Ueda et al.
Iron and Steel, 1985, A197-A256.
Camp Isit, 1988, vol. 1, 1674-1705.
International Search Report PCT/JP93/00497, Jul. 20, 1993.
Patent Abstracts of Japan, vol. 7, No. 100, (C-164) (1245), Apr. 28, 1983.
European Search Report EP 93 90 8107.
Inoue Shuichi
Shindo Takuji
Suehiro Toshiyuki
Teraoka Shin-ichi
Ueda Masanori
Nippon Steel Corporation
Yee Deborah
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