HEAT TREATMENT FOR THICK STEEL PLATE

PURPOSE:To provide new property to a thick steel plate without deteriorating characteristic before heat treatment, by heating thick steel plate at =Ar3 transformation point and cooling it. CONSTITUTION:The thick steel plate 2 passed through controlled rolling is charged into a heat treating furnace 1 from a charging hole door 3, gaseous N2 is supplied from a piping 5 to make furnace interior to N2 atmosphere, and the plate is heated to the temp. of =Ar3 transformation point by a heating apparatus 8 such s burner at exit side of the furnace 1. Thereafter the plate 2 is cooled by a cooling apparatus 9 to quench only the surface layer part. In this way, only said part of e.g. high toughness thick steel plate through e.g. controlled rolling is quenched and wear resistance is provided while maintaining high toughness.