The Reserach Of Hot Deformation Constitutive Model And Deformation Coordination Of Duplex Stainless Steel

Duplex stainless steels(DSS) which consists of austenite and ferrite exhibit a good combination of strength, ductility and corrosion resistance, i.e. weld ability of austenite and the high resistance to stress corrosion of ferrite. It is a genuinely high performance structural material. At present, it is being used more and more in the petrochemical, paper and petroleum industries. However, there are great differences in the constitutive characteristics and the deformation mechanism of the two phases, the distribution of stress and strain in the two phases during deformation is very uneven, which can lead to void nucleation and crack, lead to the final fracture and failure of the material. Which become a bottleneck of the dual phase stainless steel manufacturing. Therefore, clear the constitutive properties of each phase and obtain the rules of stress and strain distribution under different condition, it is very contribute to break through the technical bottleneck of the duplex stainless steel, which is sensitive to deformation, has important engineering significance.In this paper, the tensile properties and hot deformation behavior of 2 205 duplex stainless steel continuous casting slabs in different regions were studied by room temperature tensile test, optical microscope(OM), electron back scattering diffraction(EBSD), thermal simulation test, etc. And the most easily cracked columnar crystal zone was selected for further study. The prediction model of the macro flow curve of the experimental steel and the constitutive equation of each constituent phase were obtained, and then based on the finite element analysis, the relationship between the two phase stress and strain distribution in the deformation process of DSS were simulated and the deformation and cracking mechanism of the DSS were analyzed and discussed. The main results were as follows:(1) The mechanical properties of the different regions of the experimental steel were different, and the columnar zone have the worst mechanical properties and were most prone to crack.(2)The flow stress was positively correlated with the strain rate, and negatively correlated with the temperature. The deformation mechanism of the two phases is different, the ferrite is mainly dynamic recovery, and the austenite is dynamic recrystallization. The nucleation of crack in the phase boundary and extends along the phase boundary or in the ferrite phase.(3) By considering the influence of the friction and the plastic heat on the flow stress during the deformation process, flow curves of the experimental steel were modified, On the basis of this, a flow curve prediction model considering temperature, rate and strain was established. And by comparing with the experimental results, the correctness of the prediction model was verified.(4) By using the JMatPro software, the flow curves of the different phases of the DSS were obtained. Based on the corrected flow curves of the DSS and rule of mixtures, the constitutive equations of the two phase stainless steel under different heat compression conditions were obtained. Finally, the distribution law of stress and strain in the deformation process of duplex stainless steel was defined.(5) Some 2-D microstructure models with different austenite microstructure were established based on the EBSD map of the material. The 2-D and 3-D multi crystal models of the experimental steel were established based on the Voronoi diagram.(6) The finite element simulation was carried out by embedding the constitutive equation of each phase of DSS under different conditions into the established model. The stress and strain distribution and deformation coordination and cracking(failure) of DSS in the process of deformation were studied, and the simulation results were compared with the experimental. It was found that the two were in good agreement, which indicates that the constitutive equation and the finite element model were correct.