METHOD FOR SLOWLY COOLING 13% CR STAINLESS STEEL

PURPOSE:To prevent the development of crack after slow cooling by making the surface temp. of 13% Cr stainless steel cast bloom the specific temp. blooming-rolled and starting the slow cooling to lower the hardness. CONSTITUTION:The blooming-rolled 13% Cr stainless steel blooms 1 are charged in slow cooling pit formed with bottom wall, side walls and cover 4 arranging refractory layer 3 at inside of the iron shell 2 in order after rolling and slowly cooled during the long time and lowered to the temp. near the room temp. and taken out and sent to working process of tube-making process, etc. At the time of executing the slow cooling, the surface temp. of the above steel bloom 1 starting the slow cooling is made to >=650 deg.C. The 13% Cr stainless steel bloom 1 obtd. with this has low hardness and crack during treating after slow cooling is not developed. Further, in the working process by using this as the raw material, the development of the surface defect caused by crack of the steel bloom is prevented and the yield of the product is improved.