Effect of Ultra-fast Cooling on Microstructure and Mechanical Property of Vanadium Micro-alloyed Steel

Rolling and cooling experiments were conducted under ultra-fast cooling(UFC) condition to investigate the influence of UFC on microstructure(including homogeneity of microstructure) and mechanical property of vanadium micro-alloyed steel.Following UFC process,there is martensite on the surface and bainite and a small amount of martensite in the core of the specimen while with conventional cooling process,there is bainite and a small amount of martensite on the surface and a small amount of massive ferrite,bainite and martensite in the core of the specimen.The tested steel exhibits increase in strength and slight decrease in plasticity after UFC.Different microstructures and inhomogeneous cooling are observed on the surface and in the core of the 20 mm thick rolled pieces subject to UFC.