| 摘要 |
PROBLEM TO BE SOLVED: To produce a steel sheet good in formability in the final stage of working because of small work hardening in the initial stage of the working though it is relatively hard before the working. SOLUTION: This steel sheet is the one in which the content of C is 0.005 to 0.070% wt.%, the crystal grain size is <=10μm, the density of carbides of >=2μm in the optional cross-section of the steel sheet is <=10 pieces per 0.01 mm2, 0.2% proof stress is 200 to 450 MPa, the total elongation is >=15%, and the difference in 0.2% proof stress before and after cold rolling is <=150 MPa. As to the method for producing it, particularly, the hot rolling coiling temp. is controlled to <=500 deg.C, the residence time at >=550 deg.C in an annealing stage is controlled to <=90 sec, and the draft by cold rolling after the annealing is controlled to <=8%.
|
