To obtain a steel plate without developing the surface crack thereon even in the case of executing rolling by using a hot slab at temp. as high as possible, by regulating hydrogen sulfide concn. in fuel for combustion used to a heating furnace for steel material to not higher than a specified value and executing heating and rolling to the steel.
The hydrogen sulfide concn. in the fuel for combustion is regulated to ≤50 ppm (containing 0). When the gas for combustion containing H2S burns in the heating furnace for rolling, H2S is decomposed, and SO2 is generated and contained in the atmospheric gas in the heating furnace. SO2 generated in the combustion, causes the concentration to S into grain boundary of the austenite in a cast slab. When H2O concn. contained in the fuel for combustion is lowered, SO2 concn. in the fuel is lowered and the concentration of S into the grain boundary of the austenite in the cast slab is restrained to prevent the development of starting point of crack on the surface of the steel plate. Before or after charging into the heating furnace for rolling, a process, in which the cast slab surface is cooled or reheated to not higher than Ar3 point, is unnecessary.
MITAO SHINJI
SUZUKI MIKIO
AWAJIYA HIROSHI
KAMIOKA SATOSHI
