Effect Of Annealing Processing On Microstructure And Properties Of If Steel Processed By Asymmetric Rolling

With the rapid development of China's economy,the development trend of the automobile industry is bound to be lighter and safer.The requirement for both strength and plasticity of automotive steel is becoming true.In this paper,IF steel is used as the research object,the metallographic analysis technology was used to analyze the microstructure of IF steel processed by asymmetric rolling and annealing at different temperatures and times;and the tensile test was used to determine the mechanical properties.The Hall-Petch relationship was studied by combining the structure and properties.In addition,the heterogeneous structure IF steel was obtained through double annealing.EBSD analysis was used to study the influence of IF steel on the formation process of recrystallization and heterogeneous structure under different annealing conditions,as well as its structure properties and deformation mechanism.The main research contents are as follows:(1)Ultra-fine-grained IF steel is obtained by asymmetric rolling.The ultimate tensile strength of 773.2 MPa is obtained.The comprehensive mechanical properties are the best after annealing at 600 ? for 1 h,the yield strength is 422 MPa,and the elongation is 13.8%.(2)The grain size(0.53 ?m-513.6 ?m)and the corresponding mechanical properties are fitted to the Hall-Petch relationship.It is found that the UTS conforms to the linear Hall-Petch relationship in the whole range.YS and hardness conform to the Hall-Petch relationship when the grain size is less than about 100 ?m,and deviate when the grain size is greater than 100 ?m.This is due to the grain boundary strengthening effect in the coarse grain and fine grain are different.(3)The heterogeneous IF steel was obtained through the double annealing.The sample shows excellent performance with both high strength and plasticity.The yield strength is 412.1 MPa,and the elongation is 16.1%.(4)It is found that the YS and UTS were significantly larger and deviated from the normal Hall-Petch relationship in the samples of double annealing.It was due to the extra back stress strengthening.