High Strength Dual Phase Steel With Low Yield Ratio, High Toughness and Superior Weldability

摘要

A dual phase, high strength steel having a composite microstructure of soft and hard phases providing a low yield ratio, high strain capacity, superior weldability, and high toughness is provided. The dual phase steel includes from about 10% by volume to about 60% by volume of a first phase or constituent consisting essentially of fine-grained ferrite. The first phase has a ferrite mean grain size of about 5 microns or less. The dual phase steel further includes from about 40% by volume to about 90% by volume of a second phase or constituent comprising fine-grained martensite, fine-grained lower bainite, fine-grained granular bainite, fine-grained degenerate upper bainite, or any mixture thereof. Methods for making the same are also provided.