Research On Recrystallization Texture Of Bh Steel By Different Solid Solution Treatment

Bake-hardening steel sheet (BH steel) has lower yield strength before forming processes; however, the yield strength will be increased as a result of the aging treatment at paint baking temperature after stamping or pre-tensile deformation. Strength improvement and then thickness reducing of steel sheet (Light-duty Vehicles) is a main way to reduce vehicle fuel consumption. It is also a most effective strategy to reduce emissions of carbon dioxide and improve the deteriorating environment. However, the result of improving the strength of steel sheet are deteriorating deep-drawing Properties and increasing elastic recovery of steel sheet. Bake-hardening steel sheet emerged because of its excellent combined properties of high strength, deep-drawing property and dent-resistant ability.The microstructure was observed with optical microscope and the X-ray texture analyses were performed to the texture of BH steel sheets after cold rolling, recrystallization annealing. The paper mainly discussed texture evolution of BH steel sheets after high-temperature solid solution treatment and recrystallization annealing at 790℃during three minitus. It also analyzed the effect of carbon solid solution degree in ferrite to BH value. The following general conclusions based on the results of this work can be drawn:(1) after the samples were subjected to cold rolling, Microstructure investigation result show that the crystalline grains were elongated gradually and fibered or were disintegrated. The more severe reduction was, the thinner the fibrous were, and the more disintegrable degree was. Analysis result show that textures are weak and dispersing at the surface and subsurface layer and originally form {112}<110> y-fiber texture and{111}<110>a-fiber texture components with the cold rolling reductions increase, the intensity intensify gradually too; the main components of fiber textures always are{112}<110>,{111}<110> which derive from hot-rolling textures and intensity strengthened gradually with the cold rolling reductions increase at central layer. (2) The microstructure of water-cooled sample is lath martensite; the equiaxed grain of furnace cooled sample is larger than the sample of air-cooled. The degree of carbon solid solution in ferrite of water-cooled samples is largest, followed by air-cooled sample; the smallest is the sample of furnace cooling. (3) Recrystallization process has been completed when the samples of BH steel sheet with different carbon solid-solution degree after recrystallization annealing at 790℃during three minutes.{111}<110>α-fiber texture components are strengthen from surface to central layer and y-fiber texture is fewer in water-cooled sample; Both the a-fiber texture({001}<110>,{112}<110>) and y-fiber texture exit({111}<112>) in air-cooled sample. There is little{001}<110> texture components and more strengthen {111}<112>,{111}<110> y-fiber texture in furnace-cooled sample after recrystallization. (4) The BH value of Tensile Samples of BH steel sheet varies with different carbon solid-solution degree in ferrite, the value of water-cooled sample is largest, followed by air-cooled sample; the smallest value is tested from samples of furnace cooling.