Research On Microstructure Of Non Quenched Steel TL1438 During Hot Forming

To save energy and reduce consumption,in the automotive industry,the forging ratio of using non-quenched and tempered steel has been gradually increased,and this kind of steel is widely used especially in the crankshaft,connecting rods and other parts which have more complex shape.These parts will be withstood constantly impact loads and inertia forces during its work processing,so not only high strength,hardness and wear resistance,but also good toughness is a must requirement for the materials after its forming.Excellent mechanical properties is determined by the microstructure evolution during forging process and the subsequent cooling results,however,traditional manufacture is relied on prior experiences and based on huge and increased costs of human and material resources.So it has important practical significance for improving mechanical properties of the non-quenched and tempered steel parts and enhancing production efficiency of company that microstructure evolution can be predicted,the actual number of tests in production is reduced,and process parameters are optimized.In this paper,non-quenched and tempered steel TL1438 is considered as a object of study.By means of combining physical experiments and theory,the microstructure evolution at different deformation condition during its hot forging and subsequent cooling conditions is seriously studied,dynamic recrystallization,Meta-dynamic recrystallization,static recrystallization and the precipitation of intragranular ferrite are included in microstructure evolution research.The conclusion of the study is that recrystallization behavior is effected by deformation temperature,strain rate and inter-pass time,while dynamic recrystallization and static recrystallization are influenced more by strain than that of Meta-recrystallization.On the basis of the conclusion,deformation temperature,strain rate,inter-pass time,the amount of deformation,the cooling rate and other external factors are considered separately to quantitatively analyze the relationship between TL1438 and them.At the same time,the high-temperature flow stress constitutive equation of TL143 8,kinetics and grain size models of recrystallization during microstructure evolution had been established,and through physical experiments in different deformation conditions,grain growth mode of TL 143 8 steel is also established.Besides,from physical testing,some results about intragranular ferrite are obtained:when the cooling rate is about 0.5?/s-5?/s and cooling to 600??700?,TL1438 will be precipitated more intragranular ferrite,and this cooling process can reach the finial target to refine grain,improve forging strength and toughness..In this paper,the mathematical description of recrystallization microstructure evolution has been obtained by a combination of theoretical and experimental methods.The purpose is to provide effective guidance in future for microstructure evolution simulation of TL143 8 steel,as well as the actual production process parameters to be optimized and forecasting microstructure evolution state of TL143 8 steel parts in the production process.