| 摘要 |
<p>PROBLEM TO BE SOLVED: To provide a cold-rolled high-tensile-strength steel sheet having excellent ductility, work hardening properties and stretch flange property.SOLUTION: There is provided a cold rolled steel sheet which contains more than 0.010% and less than 0.080% of C, more than 0.20% and 2.00% or less of Si, more than 1.50% and 3.50% or less of Mn, more than 0.10% and less than 1.00% of sol.Al, 0.001% or more and less than 0.100% Nb, optionally one or more of Ti, V, Cr, Mo, B, Ca, Mg, TEM and Bi, the balance of Fe and impurities, 0.10% or less of P, 0.010% or less of S and 0.010% or less of N, where the main phase is ferrite, residual austenite is contained in the second phase, the average crystal particle diameter of the ferrite is less than 5.0μm, the volume fraction of residual austenite is more than 1.0% and less than 7.0%, the X-ray integrated intensity ratios of (200) plane, (211) plane and (222) plane in a direction parallel to a rolling surface of anαphase satisfy I/(I+I)>0.70.</p> |
