COLD ROLLED DUAL PHASE STEEL SHEET HAVING HIGH FORMABILITY AND METHOD OF MAKING THE SAME

摘要

A steel sheet having (a) a dual phase microstructure with a martensite phase and a ferrite phase and (b) a composition containing by percent weight: 0.01 = C = 0.2; 0.3 = Mn = 3; 0.05 = Si = 2; 0.2 = Cr+Ni = 2; 0.01 = Al = 0.10; 0.0005 = Ca = 0.01, with the balance of the composition being iron and incidental ingredients. Also, the steel sheet is made by a batch annealing method, and has a tensile strength of at least approximately 400 megapascals and an n-value of at least approximately 0.175.