Super strong and highly ductile low alloy multiphase steels consisting of bainite, ferrite and retained austenite

摘要

A moderately high carbon (0.61%) high silicon steel was subjected to a newly designed heat treatment cycle consisting of continuous cooling for different duration after austenitization followed by austempering at 300, 350 and 400 ℃ to form a very high strength and highly ductile multiphase steels with microstructures consisting of varied amounts of ferrite (formed during continuous cooling), bainite (formed during austempering) and retained austenite. Steels with very high strength up to (tensile strength ～1100-2000 MPa) along with excellent ductility (elongation ～10-32%) were obtained. Effect of continuous cooling duration on ferrite content amount of carbon diffused in the prior austenite grains, variation of carbon content in the retained austenite (c_r) and its volume fraction (V_r) have been analyzed. Finally, structure property correlation has been established.