Patent ID: 8337643

Claim:
A hot rolled steel sheet comprising: (a) a dual phase microstructure comprising a martensite phase between 11% and 28% by volume and a ferrite phase formed by hot rolling and cooling a steel sheet; (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% weight, silicon in a range from about 0.2% by weight to about 2% by weight, chromium and nickel in combination from about 0.2% by weight to about 2% by weight where chromium if present in a range from about 0.1% by weight to about 2% by weight and nickel if present is in an amount up to about 1% by weight, aluminum in a range from about 0.01% by weight to about 0.10% by weight and nitrogen less than about 0.02% by weight, where the ratio of Al/N is more than about 2, molybdenum less than 0.2% by weight, copper less than about 0.4%, 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 more than about 590 megapascals and a hole expansion ratio more than about 70%.