Effect of Cold Rolling Reduction Rate on Microstructure and Properties of Annealed Cr-Mo Dual-Phase Deep Drawing Steel

A hot-rolled Cr-Mo dual-phase deep drawing steel with thickness of 4.00 mm was cold-rolled at different reduction rates (70%, 75%, and 80%), and annealed at 860 °C for 3 min. The effect of cold rolling reduction rate on the microstructure, tensile properties, and deep drawing formability of the test steel were investigated. The results show that with the increase of cold rolling reduction rate, the ferrite grains in the test steel were refined, the martensite content increased, the orientation density of γ texture 〈111〉//ND (ND was the normal direction of rolling surface) decreased first and then increased, and the distribution of γ texture evolved from a concentrated state at 70% cold rolling reduction rate to a more dispersed state. When the cold rolling reduction rate was no more than 75%, the intensity of η texture 554〈225〉and ε texture 332〈113〉of the test steel was not lower than that of hot rolled test steel, indicating that the cold rolling deformation with the reduction rate not more than 75% was helpful to form and maintain these textures which were beneficial to deep drawing formability. With the increase of cold rolling reduction rate, the tensile strength of the annealed test steel increased, the elongation after fracture, plastic strain ratio, and strain hardening exponent decreased, and the product of strength and plasticity first increased then decreased. When the cold rolling reduction rate was 75%, the product of strength and plasticity was the highest, the plastic strain and strain hardening exponent were moderate, indicating relatively high strength and good deep drawing formability of the steel.