Patent ID: 11913089
Assignee: POSCO CO., LTD
Field: Materials, metallurgy (Chemistry)
Classification: CPC B  C | IPC B  C

Claim 10:
11. A method of manufacturing a steel sheet, the method comprising:
preparing a base material, a ferrite-austenitic duplex steel sheet including, by weight %, C: 0.3-0.7%, Mn: 2.0-9.0%, Al: 4.5-8.0%, and a balance of Fe and inevitable impurities;
preparing a clad material, ferrite carbon steel including, by weight %, C: 0.0005-0.2%, Mn: 0.05-2.5%, and a balance of Fe and inevitable impurities;
obtaining a laminate by disposing the base material between the two clad materials;
welding an edge of the laminate and heating the laminate in a temperature range of 1050-1350° C.;
obtaining a hot rolled steel sheet by finish-rolling the heated laminate in a temperature range of 750-1050° C.;
coiling the hot rolled steel sheet at 350-700° C.;
obtaining a cold rolled steel sheet by pickling the coiled hot rolled steel sheet and performing cold-rolling by applying a cold rolling reduction ratio of 35-90%; and
annealing the cold rolled steel sheet in a temperature range of 550° C. or higher and A3+50° C. or lower of the clad material.