| 摘要 |
PROBLEM TO BE SOLVED: To provide a hot rolled steel sheet having a tensile strength in a class of 370 to 490 MPa, and combining BH (Bake hardening) properties and stretch flange formability, and to provide its production method. SOLUTION: The hot rolled steel combining BH properties and stretch flange formability is a steel sheet comprising 0.01 to 0.2% C, 0.01 to 2% Si, 0.1 to 2% Mn,≤0.1% P,≤0.03% S, 0.001 to 0.1% Al and≤0.01% N, and the balance Fe with inevitable impurities. Its microstructure is a mainly uniform continuously cooled transformed structure, and the average particle diameter thereof is >8 to 30μm. In the method of producing a hot rolled steel sheet combining BH properties and stretch flange formability, a slab comprising the above components is subjected to rough rolling, is subjected to finish rolling in the temperature range of the Ar<SB>3</SB>transformation point+50°C or higher, is cooled in the temperature range of Ar<SB>3</SB>to 500°C at a cooling rate of≥80°C/s to the temperature range of≤500°C on and after 0.5s after the completion of the finish rolling, and is coiled. COPYRIGHT: (C)2005,JPO&NCIPI |
