| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide a hot stamping molding which is obtained by using a steel plate having a thickness of 4 mm or more, has high strength and good toughness after quenching, and is used for frame members of a truck or the like. <P>SOLUTION: The hot stamping molding is composed of a steel containing, by mass, 0.28-0.35% of C, 1-3% of Mn+Cr, 0.005-0.1% of Ti, 0.005-0.1% of Nb, 0.005-0.03% of REM, and 0.003-0.007% of O, and is characterized in that the ratio of the rolling direction to the thickness direction is 1.3 or more and the average grain diameter is 6 μm or less, in the prior austenite grain diameter after hot stamping, martensite is contained in an amount of 90% or more, and the tensile strength is 1,370 MPa or more. The steel plate for the hot stamping molding is manufactured by heating a slab containing the components to a temperature range of 1,250°C or less, then finishing finish-rolling under conditions that the temperature in the final stand is in the range of 800-900°C and the total rolling reduction in the stands from two preceding stands is 60% or more, starting cooling within 1 s, and winding up the resulting slab at a temperature of 600°C or less. <P>COPYRIGHT: (C)2013,JPO&INPIT |
