| 摘要 |
PURPOSE:To prepare a steel plate excellent in hydrogen-induced cracking resistance and stress-corrosion cracking resistance, by processing a low carbon steel material with content of P and S into a plate material by hot rolling and successive cooling treatment under specific conditions. CONSTITUTION:A steel material having composition, which contains C<0.3%, Si<1.0%, 0.5-2.0% Mn and Al<0.05% and prescribed to P<0.03% and S< 0.01%, is hot rolled to obtain a plate material. In this case, rolling is performed so that a total draft at 950 deg.C or less is brought to 50% or more and quenching is performed at a cooling speed of 8-80 deg.C/sec from a temp. region of 800-700 deg.C after rolling is finished to wind up the plate material at 350-550 deg.C. In another case, the steel plate, after rolling is finished, is quenched to a temp. region of 700-750 deg.C at a cooling speed of 8-80 deg.Csec, gradually cooled to 650-700 deg.C at a cooling speed of 8 deg.C/or less and further quenched at a cooling speed of 8-80 deg.C/ sec to be wound up at 350-550 deg.C. By this method, a steel plate having a uniform fine bainite structure and an area ratio of 10-50% and excellent in hydrogen-induced cracking resistance and stress-corrosion craking resistance is obtained. |
