US 6,982,012 B2
Method of manufacturing steel sheet having excellent workability and shape accuracy
Shigeki Nomura, Kashima (Japan); Hiroyuki Nakagawa, Anjo (Japan); and Yoshiaki Nakazawa, Takarazuka (Japan)
Assigned to Sumitomo Metal Industries Ltd., Osaka (Japan)
Filed on Apr. 23, 2003, as Appl. No. 10/420,815.
Application 10/420815 is a division of application No. 09/981986, filed on Oct. 19, 2001, granted, now 6,586,117.
Prior Publication US 2003/0190493 A1, Oct. 09, 2003
This patent is subject to a terminal disclaimer.
Int. Cl. C21D 9/46 (2006.01); B32B 31/00 (2006.01); B05D 1/18 (2006.01)
U.S. Cl. 148—540 11 Claims
 
7. A method of manufacturing a high strength steel sheet comprising casting a slab of steel comprising, in mass %, C: 0.02 to 0.04%, Si: at most 0.4%, Mn: 0.5-3.0%, P: at most 0.15%, S: at most 0.03%, Al: at most 0.50%, N: at most 0.01%, and Mo: 0.01-1.0%, performing hot rough rolling either directly or after heating to a temperature of at most 1300° C., commencing hot finish rolling either directly or after reheating or holding, completing finish rolling at a temperature of at least 780° C., performing coiling after cooling to a temperature of 750° C. or below at an average cooling rate of at least 3° C./second, heating to an annealing temperature of at least 700° C. and then cooling to a temperature of 600° C. or below at an average cooling rate of at least 3° C./second, then holding in a temperature range of 250-600° C. for at least 10 seconds, and then cooling.