Dynamic Recrystallization And Phase Transformation Behavior Of Vanadium-Nitrogen Microalloyed Steel

In order to meet the high requirements of various industries for the steel industry and fully present the effect of alloying elements,the development of high-performance microalloyed steels has become a hot topic of research today.In this paper,vanadium-nitrogen microalloyed steels were studied.The influence of alloying elements on the dynamic recrystallization behaviors of vanadium-nitrogen microalloyed steels,the regularity of ferrite transformation under isothermal conditions and the influence of hot rolling and tempering process parameters on the microstructure and properties of experimental steel were systematically analyzed,which provided relevant experimental data for industrial production.The main research contents and results are as follows:(1)The dynamic recrystallization behavior of experimental steels was studied by single-pass compression experiments.Then the influence of deformation conditions and alloying elements on the dynamic recrystallization was analyzed.The Arrhenius constitutive equations,dynamic recrystallization critical model and dynamic model were determined.The results showed that Mo element significantly can not only increase the high temperature flow stress of austenite,but also inhibit the dynamic recrystallization.The activation energy of dynamic recrystallization were 337kJ/mol,321kJ/mol,and 356kJ/mol for three experimental steels containing Cr,Ni and Mo,respectively.(2)The isothermal phase transformation experiment was used to study the ferrite phase transformation behavior of experimental steel.The results showed that the ferrite volume fraction and grain size increased with the isothermal time under static isothermal conditions.With the increasing of isothermal temperature and time under dynamic isothermal conditions,the volume fraction and grain size of ferrite increased,while the microhardness of ferrite matrix decreased.The Mo element made the ferrite transformation incubation period much longer and suppressed the ferrite transformation.Deformation can shorten ferrite transformation incubation period and make the microhardness of the ferrite matrix increase.(3)The hot rolling experiment showed that the yield strength and tensile strength of the experimental steel increased first and then decreased with the increasing of the finish rolling temperature.When the finsh rolling temperature was 918?,the mechanical property was optimal.And the yield strength and tensile strength were 990MPa and 1129MPa,respectively,the elongation was 18%,the impact energy at-20? was 75 J.The yield strength and tensile strength of the experimental steel increased with the decreasing of the finish coiling temperature.When the finsh coiling temperature was 212?,the mechanical property was optimal.And the yield strength and tensile strength were 892MPa and 1022MPa,respectively,the elongation was 18%,the impact energy at-20? was 85J.(4)The tempering experiment showed that the tensile strength of the experimental steel increased,and the yield strength decreased at the finishing rolling temperature of 1000? and 918?,and increased under the other processes when the tempering temperature was 200?.the yield strength of the experimental steel increased,and the tensile strength decreased at the finishing rolling temperature of 1000? and 918?,and increased under the other processes When the tempering temperature is 400?.With the increasing of tempering temperature,the yield strength and tensile strength of the experimental steel increased first and then decreased.When the tempering temperature was 400? for 1.5 hours,the yield strength and tensile strength of the experimental steel were optimal,which were 784MPa and 1006MPa,the standard specimen of the impact of the ductile-brittle transition temperature was-60?-80?.