METHOD FOR MANUFACTURING TENSILE STRENGTH 1.5GPA CLASS STEEL SHEET

摘要

PURPOSE: A manufacturing method of ultra-high strength steel panels with a tensile strength of 1.5 GPa is provided to have poly phase complex tissue, tensile strength of higher than 1.5GPa, and to minimize shape defects. CONSTITUTION: A manufacturing method of ultra-high strength steel panels with a tensile strength of 1.5 GPa comprises the following steps: manufacturing a slab by continuously casting molten steel in which alloy element satisfies the relative formula of Si + Al + P/Mn <= 0.5, 5 <= C + 1.5Mn + 2Cr + Mo + B <= 12 and C + Mn/20 + Si/30 +2*P + 4*S <= 0.52; reheating the slab and reeling the same at 400-700 deg. Celsius after hot rolling the same so that the temperature at finishing rolling can be Ar3 transformation point - 950°C; cold rolling the reeled strip cold with a reduction rate of 30 - 70% after pickling; first cooling the cold rolled strip down to the temperature range of 500-750 deg. Celsius with a cooling speed of 1 - 3°C/s after heating the same to the temperature range of (Ac3 - 90°C)-(Ac3±15°C) with a heating speed of 1-5°C/s; and maintaining isothermal transformation for 6-500 seconds or annealing with a cooling speed of 1°C/s or less after second cooling down to the temperature range of[(Ms -120) - 460°C with a cooling speed of 3-50°C/s. [Reference numerals] (AA) Temperature(°C); (BB) Time(second)