Research On Constitutive Model And Microstructure Evolution Of Difficult-To-Deform Metal

Because of the excellent combination properties, difficult-to-deform metal is widely applied in the aviation and aerospace, chemical engineering, medical industry, ships and other field, as the resistance to deformation is high and the work-hardening is serious when forming at room temperature, the plastic forming of difficult-to-deform metal has become a hot research topic of more and more scientists. As the foundation of plastic forming, the constitutive model and microstructure evolution of difficult-to-deform metal is necessary to be studied.The research subject is supported by National Natural Science Foundation of China “Research on forming mechanism and precision/property integrated control of difficult-to-deform metal in hot power spinning”(51375172), the Specialized Research Fund for the Doctoral Program of Higher Education “Research on forming mechanism and magnetic property recovery of magnetically soft alloy tube”(20130172110024). In this study, the nickel-base superalloy Haynes230 and the magnetically soft alloy 1J50 are chosen as research objects, the mechanical property test, the metallographic analysis and other method are taken to obtain their constitutive model and microstructure evolution. The following works were carried out:(1) The unidirectional tensile test was taken to study the mechanical property of two metals at room temperature, the constitutive model and parameters of them were obtained. The metallographic analysis were done and it shows that the grains of Haynes230 are stretched when forming, the dislocation generated in plastic forming of Haynes230 result in the work-hardening effect is obvious, which is hard to get severe plastic deformation. On the other hand, the twin austenite of 1J50 is the main reason of its poor plasticity.(2) Several methods to choose the annealing process was summaried and the appropriate annealing of two metals are obtained. For the Haynes230 with 30% deformation, fully recrystallization organization can be obtained with the insulation at 1100 ℃ for 50 min, the plastic forming property is excellent, which can be used in the middle time annealing when multi-pass forming is applied. For 1J50, fully austenitic organization can be obtained with the insulation at 700 ℃ for 1 h, the plastic forming property is excellent. The annealing process can improve the process ability and form at room temperature.(3) Based on the property of two metals and the power spinning, several temperature and strain rate are chosen to have the hot tensile test. A modified Johnson-Cook model was proposed to describe the relationship between stress and strain of Haynes230 and 1J 50 at high temperature, the fitting precision is high.(4) The microstructure of two metals in hot forming are studied and the influence on the microstructure by temperature and strain rate were obtained, on the other hand, the flow stress and plasticity were analyzed too. When the temperature are in 1100℃ and 1200℃, the dynamic recrystallization of Haynes230 is turned out and grain grows when the strain rate is low, which would decide the strength and plasticity. When the temperature are in 800℃ and 900℃, the dynamic recrystallization of 1J50 is turned out and the lower the strain rate is, the more recrystal grains are turned out.