## 1 Introduction
The MTS [11] constitutive model can accurately reflect the change in the flow stress of the material at a high strain rate and can well express the plastic deformation coupling mechanism of the two-phase material. The only drawback is that the model lacks the viscous effect. If the model is modified, and the viscous effect is taken into account, the cutting process of the dual-phase material will be better simulated. There are two main methods to obtain constitutive parameters: the finite element method and the Hopkinson pressure bar experiment. [PERSON] et al. [12] proposed a hybrid strategy to determine the constitutive parameters for thin-walled tubes based on experimental responses from hydraulic bulge tests. The method integrates analytical models, finite element analysis, and gradient-based optimization algorithms. [PERSON] et al. [13] proposed a finite element identification method for parameters based on the Levenberg-Marquardt search algorithm. Although this method can be used to develop the constitutive equation for the material, it requires a lot of calculation and is time-consuming. The Hopkinson pressure bar experiment is the most direct method to obtain the parameters. Several studies have developed constitutive equations for different materials using the Hopkinson pressure bar experiment [14]. [PERSON] et al. [15] determined the parameters of the 11 MnNiMo constitutive model by adopting the Hopkinson pressure bar experiment. However, this method can only be used to study the behavior of the metal at a strain rate of 10\({}^{3}\)-10\({}^{4}\) s\({}^{-1}\). The existing parameter acquisition methods are difficult to apply in identifying the viscous behavior of materials under high strain rate conditions in the cutting process. It is also difficult to ensure the reliability of test data and the adaptability of test conditions. Therefore, in view of the above problems, we analyze the viscous effect of duplex stainless steel under high strain rate conditions and establish the MTS constitutive equation for S32760 duplex stainless steel based on the viscous effect of the two phases and the mixing rule. A reverse identification method for parameters based on a cutting theory suitable for high strain rate conditions is also proposed. Based on the characteristics of the ferrite and austenite phases of S32760, the theoretical range of the undetermined parameters of the S32760 two-phase constitutive model is determined, and a model of equal shear zones in orthogonal cutting is established. Based on the results of the metal cutting trials, the constitutive parameters of S32760 duplex stainless steel are modified, and the viscous behavior of duplex stainless steel under a high strain rate is analyzed. In this paper, the equal shear zone model of orthogonal cutting is established based on [PERSON]'s theory, and then the improved MTS constitutive model is established. Based on the principle of the least-square method and genetic algorithm, the constitutive parameters are preliminarily identified. The constitutive equation is used in the shear zone model to extract parameters such as strain and strain rate. Combined with the cutting force determined in the orthogonal cutting experiment, the constitutive parameters are inversely identified and corrected. The modified constitutive equation is then used in the shear zone model to predict the cutting force, and the results are compared with the cutting experimental data to verify the accuracy of the model. The constitutive model proposed in this manuscript can lay a theoretical foundation for the study of grain size and microhardness of machined surfaces and provide a theoretical basis for the optimization of cutting process parameters in the production of duplex stainless steel.