The Influence Of Vanadium Content On Precipitation Behavior And Microstructure Of Nb-V-Ti Microalloyed Steel

Currently,with the rapid development and progress of the society,the steel industry of China is facing new challenges and opportunities.How to save resources,reduce production costs,and improve product comprehensive competitiveness have caused great attention of enterprises.Therefore,it is imperative to develop a microalloyed high-strength steel which has low cost and excellent comprehensive mechanical properties.In this paper,the Nb-V-Ti composite microalloyed high strength steels with different V content were studied.In order to research the effect of V element on microstructure evolution of Nb-V-Ti composite microalloyed high strength steel,the the addition of V has been controlled.The main research contents and experimental results are as follows:(1)Through the continuous cooling transformation experiment,the effects of deformation,cooling rate and V element on the continuous cooling phase transformation of austenite were studied,and the CCT curves under deformed and undeformed conditions were drawn.Studies have shown that the start and end temperatures of the phase transition of experimental steel decrease with increasing cooling rate.With the increase of the cooling rate,the macroscopic hardness of the experimental steel basically increases,and the volume fraction of ferrite decreases with the increase of the cooling rate.The deformation reduces the austenite stability,increases the phase transition onset temperature,moves the CCT curve to the left,and therefore promote the transition of ferrite and pearlite phase.As the V content increases,the bainite phase transition interval is expanded.(2)According to the study of isothermal phase transition experiments,it is found that as the isothermal time increases,the volume fraction of ferrite increases while the hardness decreases.With the increase of isothermal temperature,the volume fraction and microhardness of ferrite decrease.V element promotes the transformation of austenite to ferrite during isothermal transformation and expands the temperature range from austenite to ferrite transformation.(3)The theoretical calculation of(Nb,V,Ti)C composite precipitation is carried out,and the NrT and PTT curves are plotted.The critical nucleation size and critical nucleation work of(Nb,V,Ti)C increase as the increase of precipitation temperature.At the same temperature,with the increase of V content,the critical core size and critical nucleation work of(Nb,V,Ti)C precipitated in alloy steel gradually increase.(4)The influence of V content on the microstructure performance under different rolling processes was studied through the hot rolling experiment,which provides a theoretical reference for industrial trial production.