PURPOSE: To produce a seamless steel tube excellent in SSC resistance by specifying chemical components and also limiting hot rolling conditions and cooling conditions, respectively.
CONSTITUTION: A steel having specific chemical components is heated to 1000-1250°C and pierced. Forced cooling is applied from the internal surface of a tube stock and homogenizing treatment at Ar3 to 1100°C is done, followed by working at 20-70%. After continuous rolling for shape straightening, reheating to a temp. between Ar and 900°C is applied and hot finish rolling at ≥(Ar3+50°C) is done. After finish rolling, the position of 1-2mm on the hardening side of the tube is cooled down to a temp. right under the Ar1 point at a rate of ≤150°C/s, cooled successively at a rate of ≥150°C/s until the temp. of the opposite side on the tube hardening side becomes 800-400°C, and air- cooled. By this method, the seamless steel tube excellent in SSC resistance can be produced.
UENO MASAKATSU
TANO YASUNORI
NAKAJIMA AKIRA
