| 摘要 |
PURPOSE:To obtain the titled nonaging steel plate having a low yield ratio as well as high burning hardenability, r-value, ductility and tensile strength by restricting the N and B contents of a dead soft steel having a specified composition, the coiling temp. after hot rolling, the annealing temp. after cold rolling, and the cooling rate. CONSTITUTION:A steel contg., by weight, <=0.009% C, 0.03-1.0% Si, 0.1-0.8% Mn, <=0.1% P, 0.01-0.1% Al, <=0.01% N, Nb and B satisfying Nb=(2-10)C and B>=0.3N is hot rolled and coiled at <=700 deg.C. The coil is cold rolled and annealed at a temp. at which alpha- andgamma-phases coexist, and cooling to 600 deg.C is carried out at >=4 deg.C/sec average cooling rate. The titled steel plate having about 35-50kg f/mm.<2> tensile strength is obtd. |
