Study On Thermal Deformation Behavior And Thermal Simulation Of 42CrMosteel

Large forgings with high strength and complete structure are widely used in electric power,shipbuilding,metallurgy,petrochemical,heavy machinery and national defense and other industrial fields.The manufacturing process of large forgings is one of the key technologies in the major equipment manufacturing industry,and its quality directly affects the reliability of equipment operation and the performance of final products,which is the basis for the development of advanced equipment manufacturing industry.The mechanical properties required by large forgings are relatively high,and these indicators are usually guaranteed by thermal machining and subsequent heat treatment.However,the manufacturing process of large forgings is very complex.Due to the large volume,it is easy to appear defects of structure and stress concentration in the process of machining.From the microscopic point of view,the thermal deformation behavior during hot processing is affected by a variety of deformation mechanisms.The microstructure changes,leading to the change of the final product performance.Numerical simulation is an effective research method to optimize the process parameters due to the software tools and strong computing power that are now available.In this paper,the numerical simulation of thermal deformation and heat treatment process of 42CrMo steel used for large wind power spindle is carried out to establish the constitutive equation of the material and optimize the heat treatment process.With good machinability and excellent performance,42CrMo steel is a common raw material for manufacturing large forgings.In this paper,42CrMo steel is chosen as the reference material,which is isothermally compressed at the deformation temperatures of 850℃,950℃ and 1050℃ and the strain rates of 0.01 s-1,0.1 s-1 and 1 s-1.It is found that work hardening and dynamic softening occur simultaneously in the process of hot deformation.The true stress-strain curves show typical dynamic recrystallization characteristics.At the same amount of deformation,the flow stress of 42CrMo steel increases with the decrease of deformation temperature and the increase of strain rate.According to the true stress-strain curve of 42CrMo steel,two phenomenological constitutive models coupled with the dynamic recovery(DRV)and dynamic recrystallization(DRX)models are built up.A comparative study is conducted to evaluate their accuracy.On the basis of the correlation coefficient(R)analysis,the average absolute relative error(AARE)assessment and the comparison of the DRX volume fraction estimated by optical microscope(OM)maps with that predicted by the established models,it is found that the Arrhenius model coupled with DRV and DRX(A-DRVX)model has better prediction precision.On this basis,the thermal physical parameters,mechanical properties and phase transition parameters are calculated,and a database for the simulation of thermal deformation and heat treatment of 42CrMo steel is established.The thermal compression behavior of 42CrMo steel at 900℃ and the strain rates of 0.01 s-1,0.1 s-1 and 1 s-1 is simulated by Deform-3D software.The simulated true stress-strain curve is in good agreement with the actual experimental curve,and the predicted dynamic recrystallization volume fraction is basically in agreement with the value estimated from the metallographic diagram,which proves that the constructed constitutive equation has high accuracy.The simulation of end quenching is carried out in Deform-HT software.At the end of the workpiece,the temperature decreases rapidly.And there is little difference between the temperatures at the surface and the center of the workpiece.During the simulation process,the austenite transformation occurs.There is more martensite at the end of the workpiece.The predicted volume fraction of retained austenite is close to the experimental result,and the predicted value of hardness agrees with the experimental one.It can be conducted that the simulation result of end quenching process based on 42CrMo steel database is reliable.According to the simulation result,the production and processing parameters can be improved.