| 摘要 |
PROBLEM TO BE SOLVED: To provide a high strength steel sheet having ≥590 MPa tensile strength and simultaneously improving uniform extension and bore expandability, and excellent in the workability; and to provide a manufacturing method therefor. SOLUTION: The high strength steel sheet excellent in the workability has the chemical composition composed by mass% of 0.04-0.10% C, 0.5-2.6% Mn, 0.8-2.0% Si and ≥0.05 to <0.10 C/Si, the ratio of C content to Si content, and limited to the contents of Al, P, S, N and metallic structure composed by volume ratio of 90-95% ferrite and 5-10% tempered martensite. After hot-rolling this steel, a primary water-cooling is applied into the range of 600-750°C and after air-cooling, the tempering is applied with a secondary water-cooling or the annealing after cold-rolling is applied in the temperature range of Ac<SB>1</SB>point to Ac<SB>1</SB>point+100[°C], and a primary cooling is performed in the temperature range of 600-700°C at ≤20°C/s cooling speed, and after secondary cooling, the tempering is applied to manufacture this steel sheet. As substitution of the tempering, a galvanizing or an alloying treatment can be applied. COPYRIGHT: (C)2011,JPO&INPIT
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