| 摘要 |
PURPOSE:To produce an Al killed base cold rolled high tensile steel plate of superior workability and of the strength improved by baked coating or the like by hot rolling, cold rolling and annealing the Al killed steel contained with a fixed amount of P and defined of an Mn amount under the specific conditions. CONSTITUTION:The Al killed steel slab contg. <0.2% Mn, <=0.15% C, 0.04%<= P<=0.15%, 0.015%<=Al<=0.1%, and 0.002%<=N<=0.008% is hot rolled. The finishing temperature is kept at above the Ar3 transformation point and the coiling temperature is kept at <=700 deg.C, so that it is maintained in a solid solution state without allowing AlN to deposit. Next, scale is removed by pickling or the like, and the plate is cold rolled at >=40% draft, to make tensile strength, surface characteristic and workability highest possible. Further, it is annealed at a high temperature above the recrystallization temperature, after which it is cooled at a cooling rate of >= 0.15T deg.C/hr when the passage temperature during cooling is defined as T deg.C. The workability and baking hardness improve, and consequently, the steel plate of superior dent resistance for automobile planks is obtained. |
