PURPOSE: To prevent the flaw generation and to improve a yield by taking the S contents of a steel in the specified amt., deciding the billet heating temp. at the piercer piercing time according to the S contents of the steel and taking the piercing start temp. at more than the specified temp.
CONSTITUTION: In case of manufacturing the Cr-Mo steel tube contg. 1.0W12.0% Cr and ≤2% Mo in weight %, the flaw generation of the case of a billet piercing is prevented by taking the S contents of a steel at ≤0.008%. The flaw generation is prevented by taking the billet heating temp. at more than the specified temp. according to the S contents of the steel. The piercer piercing start temp. is taken at ≥1050°C. A flow is generated, when it is below this temp. The flaw generation of the case of making the Cr-Mo steel tube is prevented by executing the piercer piercing of a billet under said conditions. The reduction in yield is thus prevented and the productivity can be improved.
ATSUMI TAKUYA
TAKADA ISAO
