| With the development of the automotive industry,the automotive materials are facing with serious challenges about safety,environment,resources,energy,and cost.Automobile steel is also facing the fierce competition of Non-Steel materials and the challenge of users.The development of new generation steel requires that the steel should have high safety,light weight,environmental protection and low cost.The advanced high strength automobile steel has high performance price ratio,it is very safe and lightweight.It will be the best suit automobile steel for both conventional fuel-powered vehicles and new energy vehicles.At present,the development of high strength automotive steel has reached the third generation.But the research of the steel is in laboratory,and has not reached the level of practical application.Therefore,the research and development of high strength steel of automobile can provide reference and basis theoretical for production process.It is of great significance for the application of automobile steel.Medium manganese steel is a typical third generation automobile steel,and in this paper new low density and high strength plastic third generation automobile steel Fe5Mn3Al is designed.Systematically analyze the hot deformation mechanism,process of rolling and heat treatment,provide reference for development of high strength steel and automotive steel rolling in industrial production.The main work of this paper is as follows:?1?The temperature and strain rate play important roles in the hot deformation process,the stress decreases with the increase of temperature and the decrease of strain rate.Based on the regression analysis of the flow stress data,the constitutive equation of Fe5Mn3Al steel was developed to describe the hot flow behavior of the steel.The calculated flow stress values show good agreement with the experimental results,and the correlation coefficient is 0.975and the average absolute relative error is 3.25%.?2?In order to obtain the critical strain or stress of dynamic recrystallization?DRX?during hot deformation,the DRX critical strain and stress model considering work hardening and Zener–Hollomon?Z?parameter was established.?3?The 3D processing maps were developed using dynamic material model?DMM?according to the experimental stress-strain data.Then the relatively ideal hot deformation region with the temperature of 1000-1050?and strain rates of 10-20s-1is identified combined with the subsequent microstructural observation.?4?The relatively ideal hot deformation region of microstructure evolution was investigated by EBSD and TEM.The nucleation mechanism of DRX shows both discontinuous dynamic recrystallization?DDRX?and continuous dynamic recrystallization?CDRX?exist while the Fe5Mn3Al steel deformed at the stable region,and the DDRX of austenite is dominant.The microstructure evolution mechanism of ferrite is CDRX.?5?Based on the results of thermal simulation experiment and JMat Pro software simulation phase transition calculation,the rolling experiment is carried out for the test steel where the first rolling temperature of the test steel is1000-1050?and the second rolling temperature is 900-800?.?6?The element diffusion law and phase change temperature were calculated based on JMat Pro software and the optimal annealing temperature was determined.The influence of the two-phase heat treatment process to microstructure and mechanical properties of the test steel was analyzed in this study.The results show that the ideal combination microstructure of experimental steel are?-ferrite,bainite and retained austenite under annealed temperature of 710?and 1hour.The strength-ductility can attain26GPa?%. |
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