| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a high carbon high manganese steel material capable of preventing bottom cracks, and hook cracks in welded portions, occurring in a case of producing a steel pipe by bending and welding a steel sheet. <P>SOLUTION: A steel raw material is casted which has a composition including, by mass%, 0.40 to 0.50% C, 0.10 to 0.30% Si, 1.50 to 1.70% Mn, ≤0.08% P, ≤0.01% S, 0.010 to 0.030% Al, 0.0015 to 0.0035% Ca, further Ca/S being 0.3 to 0.6, and the balance of Fe and inevitable impurities. Then, the steel raw material is gradually cooled down to 450°C or lower in such a manner that a cooling rate of the steel raw material is 10°C/h or lower in a time average in a range of from 700 to 450°C at a surface temperature of the steel raw material when measuring the temperature at the surface of the steel raw material, and, thereafter, hot rolling is successively performed. <P>COPYRIGHT: (C)2012,JPO&INPIT |
