Metal treatment – Process of modifying or maintaining internal physical... – Heating or cooling of solid metal
Patent
1991-08-19
1994-02-08
Yee, Deborah
Metal treatment
Process of modifying or maintaining internal physical...
Heating or cooling of solid metal
148611, 148542, 148546, 164477, C21D 802
Patent
active
052845354
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a method of manufacturing an austenitic stainless steel sheet, and more particularly, to a method of manufacturing an austenitic stainless steel sheet, including cold-rolling a cast plate having a thickness nearly equal to that of a part to be formed and prepared by a synchronous continuous casting process in the technical parlance, in which the speed of the cast plate relative to the inner surface of the mold is zero, and to a manufacturing system for carrying out the same.
BACKGROUND ART
A conventional method of manufacturing a thin stainless steel sheet employing a continuous casting process comprises casting a cast plate having a thickness of not less than 100 mm while the mold is vibrated in the casting direction, cleaning the surfaces of the cast plate, hot-rolling the cast plate into a hot strip of a thickness on the order of several millimeters by a hot strip mill consisting of roughing stands and finishing stands arranged in series, after heating the cast plate to a temperature not lower than 1000.degree. C., descaling the hot strip, if needed, after annealing the same, cold-rolling the descaled hot strip, and finish-annealing the cold-rolled strip.
Such a conventional method has problems in that a very long hot strip mill must be used for hot-rolling the cast plate of a thickness not less than 100 mm, and a large quantity of energy must be used for the specific gravity of the cast plate and rolling the cast plate.
To solve such problems, studies have been made to develop an improved continuous casting process capable of producing a cast plate having a thickness equal to or nearly equal to that of the hot strip. Synchronous continuous casting processes of a twin-roll system and a twin-belt system, in which the speed of the cast plate relative to the inner surface of the mold is zero, are reported in papers inserted in the special edition of "Tetsu to Hagane", '85-A197 -'85-A256.
In a first method employing the continuous casting process of a twin-roll system, a thin cast plate of a thickness in the range of 0.5 to 10 mm is produced. Then, a sheet of a desired thickness is produced only by cold-rolling after subjecting the cast plate to an annealing process and a pickling process for descaling.
In a second method employing the continuous casting process of a twin-roll system, a thin cast plate of a thickness in the range of 0.5 to 10 mm is produced. Then, the cast plate is hot-rolled to produce a hot-rolled strip, the hot-rolled strip is descaled by pickling, and then the descaled strip is cold-rolled in a sheet of a desired thickness.
The cast plate produced in accordance with the above prior methods has a coarse crystal grain microstructure and, then to produce a cold-rolled sheet of a satisfactory surface quality by rolling the cast plate, the draft of the cold-rolling process in the first method must be considerably large, and the second method requires that the cast plate be hot-rolled before the cold-rolling process. Accordingly, these previously proposed methods have problems a long processing time and a significant increase of the cost of the sheet.
DISCLOSURE OF THE INVENTION
Accordingly, an object of the present invention is to provide a method of manufacturing an austenitic stainless steel sheet having insignificant minute surface concavities and convexties, insignificant roping, and a negligible uneven gloss.
According to the present invention, the foregoing problems can be solved by a method of manufacturing an austenitic stainless steel sheet comprising:
(a) a process of casting a molten austenitic (.gamma.) stainless steel by a thin plate producing process of a twin-roll system employing a pair of opposite cooling rolls to produce a thin cast plate,
(b) a cooling process of cooling the thin cast plate to form a .gamma.-phase solid solution,
(c) a heat-treating process comprising heating the thin cast plate to maintain the thin cast plate in the .delta. and .gamma. dual phase or the .delta. phase, and cooling the heated thin cast
REFERENCES:
Supplementary European Search Report EP 9190 0936.
Tetsu To Hagane, 1985--A197 A256.
J. Singh et al., Metallurgical Transaction A, "Microstructural and Microchemical Aspects of the Solid-State Decomposition of Delta Ferrite in Austenitic Stainless Steels" vol. 16 A, Aug. 1985, pp. 1363-1369.
Abe Masayuki
Miyazawa Kenichi
Mizoguchi Toshiaki
Ueshima Yoshiyuki
Nippon Steel Corporation
Yee Deborah
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