Study On Hot Formability Of 30CrMnSiNi2A High Strength Steel

High-strength steel is used widely in automobile manufacturing.High-strength steel parts with a strength exceeding 1000 MPa are often formed by hot working.There is a critical issue that different steel grades have differences in composition and historical process,and their thermodynamic properties are too complicated to be generalized.So research on the hot forming properties has important significance for hot working process.The thermal compression experiment of 30CrMnSiNi2A high strength steel under different deformation conditions was carried out to investigate the influence of forming conditions on the rheological behavior and microstructure evolution of the material.Based on the constitutive equations and thermal processing maps,the numerical simulation of the thermal processing of 30CrMnSiNi2A steel was conducted to determine the optimized process parameters,and provide a theoretical basis for the development and application of high strength steel hot forming technology.The main research of the thesis is as follows:The 30CrMnSiNi2A high strength steel material was used in the hot compression experiment under the condition of temperature range of 850¹200°C and strain rate of0.1¹0s-1.The true stress-strain curve of 30CrMnSiNi2A high strength steel was obtained and analyzed.The influence of forming conditions on the flow stress during hot compression is as follows:at the same deformation temperature,the high peak stress appeared in the higher the strain rate;in the same strain rate,the higher peak stress appeared in the lower strain rate.The microstructure of 30CrMnSiNi2A high strength steel is make up of martensite and retained austenite.The temperature and strain rate have a obvious influence on the size and shape of martensite.The influence of temperature is mainly through the austenitization process,while the effect of strain rate mainly occurs in the dynamic recrystallization stage.According to the true stress-strain data obtained from thermal compression experiment,the constitutive equation and thermal processing diagram of30CrMnSiNi2A high-strength steel are established.The analysis of the power dissipation coefficient^?and the instability coefficient????5??shows that the plastic deformation instability zone of 30CrMnSiNi2A steel increases with the deformation degree gradually,and the instability mainly occurs in the low temperature with high strain region and the high temperature with high strain region.30CrMnSiNi2A steel has good processing performance in the temperature of 1000¹100°C and the strain of0.1^1-1.The 30CrMnSiNi2A material model was established according to the constitutive equation.The numerical simulation of the hot forging of the head parts was carried out at a temperature of 1100°C and a strain rate of 1 s-1.The complete filled parts were obtained.And the stress field,strain field and temperature field of workpiece show that the 30CrMnSiNi2A high strength steel has good hot forming properties under the process parameters,which proved the selected process parameters are reasonable.