Effect of Critical Region Heat Treatment Austenitizing Temperature on Microstructure and Properties of Vanadium Dual Phase Steel

Vanadium existential state in the vanadium dual phase steel was analyzed,and its static CCT curve was tested,then the effect of critical region heat treatment austenitizing temperature on microstructure and properties of the steel was studied.The results show that the martensite transformation critical cooling speed increased and the strength reduced with the increase of the critical region austenitizing temperature under the same other process parameters.Martensite transformation critical cooling speed rose up 5℃·s~(-1) when the austenitizing temperature increased from 780℃ to 800℃,the tensile strength reduced down 95 MPa from 780℃ to 820℃. Vanadium in the dual phase steel had two kinds of states,one was precipitate,another was solute in martensite,the main roles of vanadium in the steel were precipitation strength,refining grains and rising hardenability.