HOT ROLLED STEEL SHEET HAVING EXCELLENT HIGH-SPEED DEFORMATION CHARACTERISTIC AND ELONGATION CHARACTERISTIC AND ITS MANUFACTURING METHOD

摘要

PROBLEM TO BE SOLVED: To provide a high-strength hot rolled steel sheet having an excellent high-speed deformation characteristics and elongation characteristics, and to provide its manufacturing method. SOLUTION: A steel blank of a composition containing C, Si, Mn, P, and Al in adequate ranges is subjected to hot finish rolling of heating the steel blank to a heating temperature 1,000 to1,300°C, a finish rolling initiation temperature 1,000 to 1,300°C and a finish rolling end temperature: Ar3transformation point or above, then to primary cooling of cooling the steel blank down to a cooling stop temperature below 650 to 800°C at above 30°C/s, then to secondary cooling of air cooling the steel blank for 3 to 10 s from the primary cooling stop temperature and to ternary cooling of cooling the steel blank at an average cooling rate above A°C/s defined by A=ä(FET)/(C+Mn/6)}/100 (where C, Mn: contents (mass%) of the respective elements) down to the cooling stop temperature of B°C to (B+50)°C at an average cooling rate above A°C/s down to the cooling stop temperature of B to (B+50)°C defined by B=ä(C+Mn/6)×9,000/(FET)}×10 (where C, Mn: contents (mass%) of the respective elements, FET: the finish rolling initiation temperature (°C)), and taking up the steel sheet. As a result, the steel sheet having the excellent high-speed deformation characteristics and the elongation characteristic is obtained. COPYRIGHT: (C)2005,JPO&NCIPI