PURPOSE: To obtain the titled high tensile steel sheet by heating the steel containing specified amount of C, Si, Mn, Al to the specified temp. range, performing two stage rolling with the specified cumulative draft and cooling at the specified cooling rate.
CONSTITUTION: The steel consists of, by weight %, 0.03W2 C, 0.03W0.6 Si, 0.5W 2 Mn, 0.005W0.06 Al if necessary, one or ≥2 kinds among and the balance Fe with inevitable impurities (where <0.008 S in the inevitable impurities). This steel is heated to 900W1,150°C, then rolled with the cumulative draft R satisfying the equation calculated for the heating temp. T when the heated temp. is above 900°C until it is decreased to 900°C; then rolling is continued with the cumulative draft above 50% during the temp. is reduced from 900°C to Ar3 point and the rolling is finished at below Ar3 temp. This steel is then cooled at the rate of 2W25°C/sec.
SHIGA CHIAKI
HATOMURA TANEO
