Study On The Influence Of Mo And Al On Ferrite Precipitation Behavior And Transformation Of Complex Microalloyed Containing Ti And V

Due to the needs of automobile lightweight,energy saving and emission reduction,the development of high strength and high ductility automotive steel has become an important research direction for steel materials.In this paper,the experimental steel was added microalloying of Mo?Ti and V micro-alloying elements to achieve nanoscale composite precipitation on the ferrite matrix,combined with the high content of Al added to promote the bainite and residual austenite body and other multi-phase formation.The aim was to produce both precipitation strengthening and phase transformation strengthened multiphase steel.Work content and experimental results are as follows:(1)According to thermodynamic calculation software Thermo-Calc,the thermodynamic equilibrium phase diagrams of the three kinds of experimental steels were drawn.It was found that the addition of Al element strongly enhanced the Ae3 point.When Al content increases from 0.5%to 1.83%,Ae3 point changes from 896? to high temperature.(2)The effect of isothermal temperature and isothermal time on ??? transformation of experimental steel was studied by static isothermal quenching experiment.The results show that with the increase of isothermal time,the microhardness of ferrite grain increases firstly then decrease.The hardness of Ti-V steel reaches a maximum of 205 HV at isothermal 60 min,while the Mo-Ti-V steel reaches the maximum of 367 HV at 600? for 60 min.Al-Ti-V steel 600?isothermal 60 min can be up to 336 HV.Hardness of Mo-Ti-V steel is the highest,and the hardness value reaches 318 HV when Mo-Ti-V steel has been isothermal for 480 min,the precipitation strengthening effect is the best.(3)TEM observation detected the isothermal specimens of Mo-Ti-V microalloyed steel at different temperatures for characterization of the composition and structure of the precipitates and the roughening kinetics was calculated.The results show that the precipitated particles are(Mo,Ti,V)C composite precipitate,which has a B-N relationship with the ferrite matrix.When the isothermal time was extended from 60 min to 480 min,the precipitation behavior disappeared and the size of precipitated particles was still less than 10 nm.Complex precipitates anti-roughening ability was perfect.(4)High-temperature quenching experiment and static-dynamic continuous cooling experiment of Al-Ti-V steel were carried out by means of thermal simulation experiment machine.The effects of deformation parameters,deformation temperature and isothermal temperature of bainite on the microstructures of ?-Fe and y was studied.The results show that the lower the deformation temperature is,the larger the deformation is and the smaller the cooling rate is,the more favorable the austenite to ferrite transformation is.During the deformation,?-Fe recrystallizes.The lower deformation temperature is and the large deformation is,the larger the recrystallization fraction of ?-Fe is.