Effect of Hot Band Microstructure on Strength and Ductility of Cold Rolled Dual Phase Steel

Abstract

The strength and ductility of cold rolled dual phase steels produced, from four different hot band structures were investigated for a 0.07%C-1.00% Si-1.54%Mn steel. The hot band microstructures were: spheroidized cementite, ferrite-pearlite, bainite-ferrite and martensite. Following 50% cold rolling these were given simulated water quenching type intercritical continuous annealing treatments to produce cold rolled dual phase steel.
The distribution of low temperature transformation products (LTTP) was affected by hot band microstructure. Bainitic hot band produced the most uniform LTTP distribution with complete ferrite grain boundary coverage resulting in marked stage II work hardening seen in Jaoul-Crussard stress-strain analysis. This structure also had the highest endurance ratio in reverse bending fatigue tests. Bainitic and martensitic hot band structures developed the highest tensile strengths when processing conditions were otherwise the same. No hot band microstructure conferred superior ductility for the strength of the resulting cold rolled dual phase steel,