HOT ROLLED STEEL SHEET HAVING EXCELLENT IN-PLANE ANISOTROPY IN r-VALUE, AND METHOD FOR PRODUCING THE SAME

摘要

PROBLEM TO BE SOLVED: To provide a hot rolled steel sheet having reduced in-plane anisotropy of r-value suitable for drawing, and to provide a method for stably producing the same.;SOLUTION: A steel sheet having a steel composition comprising, by mass, 0.01 to 0.10% C, ≤0.10% Si, 0.10 to 0.60% Mn, ≤0.03% P, ≤0.020% S, 0.004 to 0.10% sol.Al and ≤0.0050% N, and the balance Fe with impurities is finished at a temperature which is not lower than dynamic Ar₃ upon hot rolling, thus its in-plane anisotropy is improved in such a manner that it has a steel structure where a difference between the maximum crystal grain size of ferrite in the surface layer part from the surface of the sheet to a depth position of 1/4 in the sheet thickness and the maximum crystal grain size of ferrite in the central part from a depth position of 1/4 in the sheet thickness to the center of the sheet thickness is controlled to ≤10 μm, and further, the absolute value of Δr is controlled to ≤0.25.;COPYRIGHT: (C)2008,JPO&INPIT