A Family of Thermomechanically Treated High Strength Sheet Steels

A family of thermomechanically treated (TMT) low carbon steels, with strengths of 400 to 600 MPa, is proposed as an alternative to the high strength low alloy (HSLA) steels being used to reduce the thickness, and thus weight, of selected automotive stampings. The microstructure consists of randomly dispersed martensite in a strain-aged ferrite matrix.

Prior to stamping, the steels are of intermediate strength and microstructurally stable. After stamping, they age rapidly at both ambient and elevated temperatures to attain their final strength. Press formability, fatigue resistance, low temperature impact, and corrosion resistance are at least comparable to HSLA steels.