| 摘要 |
PROBLEM TO BE SOLVED: To provide a hot rolled steel sheet improved in both baking hardenability and impact resistance in a high strength hot rolled steel sheet having tensile strength of 440 MPa or more and suitable as an automotive interior material and to provide a producing method therefor. SOLUTION: This high tensile strength hot rolled steel sheet excellent in baking hardenability and impact resistance has a composition containing 0.01 to 0.16% C, <=2.0% Si, <=3.0% Mn, 0.005 to 0.2% P, 0.001 to 0.1% Al, >0.0060 to 0.0200% N inclusive of 0.0030 to 0.0100% solid solution N, and the balance Fe with inevitable impurities and a structure composed of ferrite of ferrite with the average crystal grain size of <=7.0μm as the main phase and has tensile strength of 440 to 840 MPa and strain aging strengthening capacity of >80 MPa. In the producing method for the above hot rolled steel sheet, a steel stock containing C, Si, Mn, P, Al and N by the above amounts is heated, is subjected to rough rolling, is thereafter subjected finish rolling in which the total draft of the final three passes is 15 to 65%, and FDT comes to the high temperature side of Ar3 by 10 to 100 deg.C, is rapidly cooled within 0.5 sec after that and is coiled.
|
