Patent ID: 7879160

Claim:
A steel sheet having been subjected to cold rolling and batch annealing comprising: (a) a dual phase microstructure comprising a tempered martensite phase no more than about 35% by volume embedded in a ferrite matrix phase before cold rolling and batch annealing; (b) a composition comprising: carbon in a range from about 0.01% by weight to about 0.2% by weight, manganese in a range from about 0.3% by weight to about 3% by weight, silicon in a range from about 0.05% by weight to about 2% by weight, chromium in a range from about 0.1% by weight to about 2% by weight, aluminum in a range from about 0.01% by weight to about 0.10% by weight, and calcium in a range from about 0.0005% by weight to about 0.01% by weight, with the balance of the composition comprising iron and incidental ingredients; and (c) properties comprising a tensile strength of at least about 400 MPa and an n-value of at least about 0.175 after cold rolling and batch annealing lower than about the A c1 temperature.