Is superior in resistance die drag Characteristic and chemical conversion coating Characteristic the cold rolling steel sheet null for deep drawing

摘要

PURPOSE:To provide the steel sheet with the excellent characteristics such as the elongation of a dead soft steel sheet and r bar value maintained by annealing the cold-rolled dead soft steel sheet having a specified composition and specifying the carbon concn. distribution on the surface and maximum carbon concn. CONSTITUTION:A cold-rolled steel sheet contg., by weight, =0.005% C, =1.0% Si, =1.0% Mn, =0.2% P, =0.05% S, 0.01-0.10% Al =0.005% N and the balance Fe is used as the original sheet. The original sheet is annealed or preferably continuously annealed to limit the C content of the surface layers on both sides of the sheet to conform to the desired characteristic. Accordingly, the C concn. distribution in the thickness direction of the annealed sheet is so adjusted that the average C concn. in the layer having the thickness equivalent to the surface maximum roughness (Rmax) from the surface of the sheet is controlled to 0.005-0.1wt.% and the maximum C concn. to 0.01-0.2wt.%. As a result, a deep drawing cold-rolled steel sheet excellent in galling resistance and chemical convertibility is obtained.