Study On Cold-rolled And Annealing Process Of Low-carbon High Strength Steel With Al

Though the iron and steel industry,as the traditional industry,has experienced its best Period, the intrinsic advantages of steel with good utilizing and processing property leads to the more developing interspaced in the world. The improvement in the properties of the steel material is the eternal subject to gain this superiority. It is also the only way for the iron and steel enterprises to survive and development. In this paper, a type of low-carbon high strength steel with Mn,Al and Si is designed and proceeded by melting,forging and rolling . The character of recrystallization and the effect of cold-rolled annealing processes on microstructure,Mechanicals properties and texture are discussed with details. The research contents show that:(1)The effect of different reduction rate on microstructure and Mechanicals Properties:The steel acquires relatively uniform recrystallization, but when continue to increase the reduction rate under pressure, Ferrite grains appear merged phenomenon and become large, resulting in reducing plastic and the value of r ;The strength of steel increased with the cold rolling pressure increasing, and the ratio of Rel/Rm increases, too .(2)The effect of different annealing temperature on microstructure and Mechani- cals Properties: Ferrite grains form ideal equated crystal under the temperature of 730℃,but some Ferrite grains appear thick under the temperature of 780℃.the strength of steel decreases with the annealing temperature increasing; The ratio of Rel/Rm increases at first ,then decreases, and it reaches the maximum under the temperature of 730℃. Elongation increases at first, then decreases, and the tendency of plastic strain ratio r is the same.(3)The effect of different annealing time on microstructure and Mechanicals Properties: Ferrite grains increases slowly with the time of annealing;Intensity decrease gradually with annealing time increasing, and the rates of extension increases, too. The value of r increases at first with the annealing time,and then decline gradually ,and reach the maximum value at the annealing time of 3h.(4)The relationship between steel fracture morphology and material plasticity as follows: the fracture of steel which has good plasticity has rather deep, uniform and oval-shaped hole, and it is relatively large.(5)The difference of texture on different thickness of the layer are investigated with the technology of electron backscatter diffraction(EBSD):On the one-fourth thickness of the layer, the texture of {001}<110> onα-fiber appears weak, and the intensity of < 110 > fiber texture decreases, which is parallel to the rolling direction; the texture of {111}<111> onγ-fiber appears strong, and the intensity of < 111 > fiber texture increases. By contrast, the texture on the surface layer is basically the opposite.