Microstructure And Texture Control Of Cr-Ti-B System Microalloyed Low Carbon Double Phase Steel

Lightweight is to become the inevitable trend of its development of the automobile manufacturing industry.The main way of lightweight is the thinning of the steel plate,and it must be ensured that the safety performance at the same time.Most automobile structural parts use cold-rolled dual-phase steel,which can increase the strength by increasing the carbon content.However,the solid solution carbon(C)restricts the development of favorable textures.In this paper,containing Cr,Ti and B low carbon steel as the research object.The second phase precipitations law were analyzed in the hot-rolled sheet by TEM and JMat Pro software,the warm rolling,cold rolling and heat treatment are carried out in the laboratory.The microstructure and deformation texture were observed under different rolling conditions through metallography,SEM and EBSD,etc.And the influence of rolling temperature on the interaction between carbon atoms and dislocations was analyzed through the internal friction,and explore the connection between temperature,interaction,and deformation texture;the evolution of microstructure and texture of the warm-rolled steel and cold-rolled steel under different heat treatment conditions are systematically analyzed,and finally,the mechanism of shear band induced nucleation is discussed.The relevant results are as follows:(1)The temperatures of A_c1and A_c3are 771.9°C and 923.4°C respectively.The hot rolled microstructure is composed of ferrite and some pearlite at the grain boundary,and the average grain size is 39.6?m,the hot-rolled textures are mainly<001>//ND and<110>//RD types.(2)In the warm-rolled steel,the?-fiber,{001}<110>and{554}<225>components are the main texture,the shear band and the?-fiber intensity first increasing and then decreasing as the rolling temperature increases,and the peak at 450°C,some fine recrystallized grains appeared at 650?.The Snoek peak is mainly caused by carbon atoms,the peak is lower and the resistance to texture development is weakest at 450?.(3)During slow heating in ferrite region,the intensity of Goss texture will be weakened when raising temperature or extend soaking time.The hardness of the annealed plate is about90 HV₃.During rapid heating in the critical region,the hardness value has an increase of10-20%;there will be obvious transformation texture{112}<253>at overtemperature or long soaking time.Compared with the former,the Goss texture is less affected by the heat treatment conditions and the?-fiber decreases.(4)After cold rolling(?=0.11)of the warm-rolled steel,the contents of shear band increased by 7%,and the?-fiber intensity also increased.Compared with annealing after warm rolling,the hardness and?texture strength of the critical region after annealing are increased.(5)During annealing,the shear band preferentially recrystallizes,and the deform band is the last.The{110}<001>grains appears in the recover microstructure and grow by merging adjacent deformation microstructure.