Research On Recrystallization And Microstructural Evolution Of 34CrNiMo Heavy Forging Steel

Heavy forgings are the core components of large-sized equipment and engineering constructions.As the foundation of major equipment manufacturing,heavy forgings are widely used in military,petrification,power and so many other areas.However,the manufacturing process of heavy forgings is complex and difficult.And the performance of it directly affects the quality and safety reliability of the whole related equipment.Thus,in order to control both the macroscopic shape and microstructure inside the materials during the hot processes,plastic deformation is widely used to manufacture the heavy forgings.It is necessary to study the deformation behavior and microstructural evolution of the material during the plastic working process.At the same time,the research will help to improve the quality of plastic processing,explore the potentiality of materials and give full play to the use of products.And it also provides the theoretical basis for the numerical simulation of plastic processing.In this paper,a series of high temperature deformation simulation tests were carried out to study 34 CrNiMo steel,whch is a typical wind power spindle material.The mechanical behavior and microstructural evolution of the material were studied systematically.Then high temperature kinetics model and microstructural evolution model were established.The main work is as following:The heating and holding experiments were conducted.And the effect of heating temperature and holding time on the grian growth behavior of 34 CrNiMo steel was studied by observing the high temperature microstructure.The results show that increasing of the heating temperature and prolonging of the holding time can both promote the grain growth of 34 CrNiMo steel.And based on average austenite grain size,a mathematical model of austenite grain growth during high temperature and short time was established.Based on the results of heating and holding experiments,the single pass compression tests were carried out,and flow stress curve was corrected by considering the effects of friction.The influences of deformation temperature and strain rate on flow stress behavior and dynamic recrystallization(DRX)behavior of the steel were studied.The results show that the friction between specimen and compression hammer deviates the flow stress largely from actual curves.And the corrected curves can represent the deformation behavior of materials more accurately.Meanwhile,three typical equations based on different constitutive models were compared.It is found that the physical constitutive equation concering recrystallization behavior has a better accuracy of prediction in predicting the flow behavior than others.Based on the modified results,the models of DRX kinetics and microstructural evolution of 34 CrNiMo steel were established.Besides,the hot processing maps were established by dynamic materials model,and the ideal processing area of the high-plasticity was given at a deformation temperature range of 1000-1150℃ and a strain rate range of 0.002-0.3s-1.The two pass compression tests were conducted based on the critical strain of DRX.Then meta-dynamic recrystallization(MDRX)and static recrystallization(SRX)behaviors of 34 CrNiMo steel during hot deformation process were studied,respectively.The tests results indicate that increasing deformation temperature and strain rate will promote the MDRX and SRX.With the increasing of prestrain,the SRX process is easy to take place.According to the experimental results,the kinetics models of MDRX and SRX behaviors and their corresponding grain size models were established,respectively.