Effect Of Niobium On Microstructure And Properties Of B220P2Cold-rolled Automobile Sheet

With the development of the current car to the light weight direction, it is demanded thatthe vehicle body has a higher strength,Nb is used as the alloying element in the steel, canimprove the steel processing and microstructure, improve the mechanical properties and theuse of properties.In this paper, the B220P2cold rolled car plate is used as the research object,and the effect of Nb on the mechanical properties, mechanical properties and microstructure ofB220P2is studied.This paper introduces the car at home and abroad with the development process andcurrent situation of steel, and introduced the toughness of each element in the mechanism andsteel role for automobile.The comparison of two steels with vacuum induction furnace ismade:One steel is joined by0.015%Nb B220P2, another steel without Nb B220P2.And usinggleeble-1500d thermal simulation testing machine, scanning electron microscope,metallographic microscope and universal electronic testing machine, and other equipment oftwo kinds of steel dynamic recrystallization rules, microstructure, tensile and impact fracturemorphology of were observed and compared.The effect of on the properties and tissues of Nbafter B220P2was studied, and the mechanism of Nb in B220P2was analyzed.Through theexperiment and analysis results:(1)B220P2during hot compression deformation, increase of heat processing temperatureor reduce the strain rate can be conducive to dynamic recrystallization; Nb added to theB220P2can suppress deformation of austenite dynamic recovery recrystallization, the dynamicrecovery and recrystallization of resistance to change, the dynamic recovery andrecrystallization rate becomes slower.(2)Add to the B220P20.015%Nb can significantly refine the hot rolled strip grain, getmore uniform organization; Nb can improve carbon atoms from the over cooled austenitediffusion activation energy, increasing subcooling pearlite transformation, making the pearlitespacing smaller; Nb is added after the B220P2hot-rolled plate yield strength rel increased by 37.3%, tensile strength RM increased by53.8%, elongation and section shrinkage rate has littlescope to improve, shock absorption function to improve the52.1J, and improve the appearanceof the fracture, the dimple distribution more uniform.(3)B220P2with the increase of the rolling reduction rate, the distortion of the crystallattice is more obvious, and the effect of hardening is also greater;After the addition of B220P2,the effect of the cold rolling on the cold rolling is more than that of the B220P2Nb;After therecrystallization annealing, the recovery and recrystallization occurred between the two steelsat the540~720, the dislocation density decreased significantly,After810DEG annealing180scan fully recrystallized microstructure and cold rolling reduction amount is large, B220P2recrystallization after annealing is smaller, the addition of Nb B220P2after annealed grain oforganization of smaller;Nb significantly increased the recrystallization temperature of B220P2.