HIGH TENSILE STRENGTH HOT ROLLED STEEL PLATE EXCELLENT IN BAKING HARDENABILITY, FATIGUE RESISTANCE, IMPACT RESISTANCE AND ORDINARY TEMPERATURE AGING RESISTANCE AND ITS PRODUCTION

摘要

PROBLEM TO BE SOLVED: To produce a hot rolled steel plate improved in baking hardenability, fatigue resistance, impact resistance and ordinary temp. aging resistance and suitable for an automotive interior material and to provide a method for producing it. ;SOLUTION: A rolling stock contg. 0.01 to 0.12% C, ≤2.0% Si, 0.01 to 3.0% Mn, ≤0.2% P, 0.001 to 0.1% Al and 0.003 to 0.02% N is hot-rolled, within 0.5 sec after the completion of the hot rolling, cooling is started at a cooling rate of ≥50°C/s to form a structure composed of ferrite of ≤8 μm average crystal grain size as the main phase, the content of solid solution N is controlled to 0.003 to 0.01%, and the ratio between the average concn. Ngb of solid solution N present on the ferrite crystal grain boundary and the average concn. Ng of solid solution N present in the ferrite crystal grains, i.e., Ngb/Ng is controlled to 100 to 10,000.;COPYRIGHT: (C)2000,JPO