Research On Isothermal Compression Behavior And Optimization Of Process Parameters For A100 Ultra-high Strength Steel

A100 ultra-high strength steel is widely used in advanced fighter landing gear and various important bearing components and guards because of its high tensile strength,hardness and fatigue resistance combined with high fracture toughness and ductility.In this paper,the hot compression experiment and the metallographic experiment were performed on A100 ultra-high strength steel using Gleeble-3500 thermal simulator and LEICA metallurgical microscope.The effect of friction and temperature rise on the flow stress,flow stress curve,dynamic recrystallization behavior,microstructure evolution,constitutive model and processing map can be studied in detail,which can provide a theoretical basis for the optimization of hot workable zone and the control of the organizational performance.The main research results are as follows:The effect of friction and temperature rise on flow stress during hot compression is more significant,and the application of correction method can effectively reduce the errors caused by these factors.The flow stress of the steel is sensitive to the deformation temperature and strain rate,and it decreases with increasing deformation temperature or decreasing strain rate.Based on the derivation of Cingara-McQueen equation,the ratio of critical strain to peak strain for dynamic recrystallization was determined to be about0.459.Models of dynamic recrystallization such as model of critical strain/stress,peak strain/stress and steady state strain/stress were characterized by considering Zener-Hollomon parameters.The dynamic recrystallization state diagram was drawn to accurately describe the parameter interval for dynamic recrystallization.According to the analysis of the microstructure evolution of the steel after hot deformation,it is concluded that the occurrence of dynamic recrystallization is improved by the increase of deformation temperature or the decrease of strain rate.Under the same deformation condition and the compressed specimen,the dynamic recrystallization degree during the different compression zone is large deformation zone>small deformation zone>hard deformation zone.Poor organization uniformity tend to appear at low temperature-high strain rate and high temperature-low strain rate,so these zones are not suitable for hot deformation.The functiond_rex?28?80883.16??5?^-0.208exp?95410.22/RT??10?0.198 was the dynamic recrystallization average grain size prediction model of the steel.The predicted values and the experimental values were in good agreement with a average relative error of 8.56%.The flow stress behavior of A100 ultra-high strength steel was characterized by the constitutive model with Arrhenius-type phenomenology and with physical foundation.The influence of the strain was considered though the constitutive models.the effect of deformation temperature on the self-diffusion coefficient and Young's modulus for the steel was reflected by the physical constitutive model,and its constructed method was relatively simple.The results show that the average relative errors of phenomenological and physical constitutive models are 4.99%and 4.89%,respectively.These models have good prediction effect,and the prediction effect of the constitutive model with physical foundation is better.According to energy dissipation coefficients and instability parameters,the processing maps of A100 ultra-high strength steel under different strains were constructed and the microstructure verification was combined.The results show that the domains of flow instability are about(850⁸90°C,0.01¹0 s^-1),(890¹100°C,0.4¹0s^-1)and(1100¹200°C,1.2¹0 s^-1),and the organizational characteristics of flow instability are mechanical instability and local plastic flow.The optimal processing parameters range of A100 steel are about(900¹050°C,0.01⁰.1 s^-1)and(1050¹100°C,0.1¹ s^-1),which has high energy dissipation values and can form fine and uniform dynamic recrystallized structures.