| 摘要 |
PURPOSE: A high strength steel and a producing method thereof are provided to reduce producing cost by producing thick steel plate by high temperature rolling and accelerative cooling. CONSTITUTION: A slab of steel is composed of from 0.01wt% to 0.04wt% of carbon, from 1.2wt% to 2.0 wt% of manganese, from 0.1wt% to 0.3wt% of silicon, from 0.02wt% to 0.06wt% of aluminum, from 0.01wt% to 0.03wt% of titanium, from 0.04wt% to 0.06wt% of niobium, from 0.05wt% to 0.07wt% of vanadium, from 0.15wt% to 0.25wt% of molybdenum, from 0.001wt% to 0.002wt% of solid boron, less than 0.002wt% of sulphur, less than 0.02wt% of phosphor, from 10 to 100 ppm of nitrogen, from 0.01wt% to 0.05wt% of oxygen, from 10 to 100 ppm of calcium, remnant iron and impurities. The slag of steel is heated at temperatures from 1150°C to 1250°C, rolled at temperatures 100°C to 200°C higher than transformation temperature, and cooled by an accelerative cooling method. Thus, steel having 70kgf/mm¬2 of tensile strength is produced.
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