Niobium containing hot rolled steel sheet with high strength and good deep-drawing properties, and process for its manufacture

摘要

Steel sheet comprises 0.5-1.5wt.% Mn, 0.01-0.10, pref. 0.010-0.020% Nb, 0.01-0.1% Al and up to 0.12% C, 0.3% Si, 0.1% P, 0.05% S, 1% Cr, also up to 0.05% of Ti not in the form of nitrides, sulphides or oxides. The structure comprises at least 75% of ferrite hardened by precipitation of carbides or carbonitrides of Nb or of Nb and Ti, the remainder comprising at least 10% martensite and possibly bainite and austenite. Also claimed are methods of making the steel sheet by hot-rolling followed by controlled cooling.