| 摘要 |
PROBLEM TO BE SOLVED: To obtain an excellent hot rolled steel sheet with high baking hardenability and low room temperature aging effect without performing any expensive and special treatment by specifying the contents of C and N and average crystal grain size. SOLUTION: Content of C is 0.01-0.12wt.% to raise baking hardenablility(BH) and that of N is 0.0001-0.01wt.% considering both of press formability and BH. At the time of hot rolling of slab with adjusted components, the heating temperature of the slab is 950-1,180 deg.C. After hot rolling, the hot finish rolling is completed with the final finishing temperature at (Ar3 +100 deg.C) to (Ar3 +10 deg.C) and the final stand draft >=10%. After that, the hot rolled sheet is cooled at a cooling velocity >=20 deg.C/sec within 0.5sec and then is coiled in a range of 700-350 deg.C. With the combined effects of low temperature slab heating, final stand high draft rolling and nearest rapid cooling, the average particle grain size of final hot rolled sheet is refined <=8μm and then a high level HB of >=80MPa and a low room temperature aging effect of <=45MPa are realized.
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