PROCESS FOR PRODUCING SEAMLESS STEEL PIPE

摘要

A round billet comprising 10.50 to 14.00% by mass of Cr and satisfying a value of not more than 9.0% as determined by a formula [Cr + 4Si - (22C + 0.5Mn + 1.5Ni + 30N)] wherein the symbol of element represents the content (% by mass) of each constituent element in the steel is heated under conditions of a soaking temperature of 1100 to 1250°C and an in-furnace time (min) of not less than "0.5 x diameter of round billet (mm)". Thereafter, piercing and rolling are carried out under conditions of a piercer piercing efficiency of not less than 50%, a value of not more than 8.0 as specified by "{(diameter of round billet - roll spacing at foremost end of plug)/diameter of round billet} x 100", and a plug shape of 0.06 to 0.17 as defined by {radius of foremost end of plug (mm)/diameter of round billet (mm)}". The high Cr seamless steel pipe thus obtained has no significant internal flaw, that is, has excellent internal properties.