| 摘要 |
PURPOSE:To manufacture a steel plate excellent in weldability, combining high ductility with high strength, and having composite structure by applying controlled heating treatment and cooling to a steel stock having a specific composition containing C, Si, and Mn to incorporate specific residual amounts of austenite. CONSTITUTION:A steel stock which has a composition consisting of 0.05-0.25% C, 1.00-3.00% Si, 0.20-1.50% Mn, and the balance Fe with inevitable impurities and further containing, if necessary, 0.20-1.00% Ni is heated up to a temp. in the range of Ac1+30 deg.C-Ac3 and held for 30sec-15min. Subsequently, the steel stock is cooled down to a temp. in the range of 350-500 deg.C at 10-500 deg.C/sec cooling rate and held in the above temp. range for 30sec-30min. Then, the steel stock is cooled down to room temp., by which a composite structure containing ferrite and bainite as principal phases and further containing >=10% retained austenite is formed. By this method, the high-strength steel plate having low C content in the range capable of satisfying weldability, excellent in ductility, and having about 60-100kgf/mm<2> strength can be obtained. |
