The Mechanical Threshold Stress model for various tempers of AISI 4340   steel
  Numerical simulations of high-strain-rate and high-temperature deformation of pure metals and alloys require realistic plastic constitutive models. Empirical models include the widely used Johnson-Cook model and the semi-empirical Steinberg-Cochran-Guinan-Lund model. Physically based models such as the Zerilli-Armstrong model, the Mechanical Threshold Stress model, and the Preston-Tonks-Wallace model are also coming into wide use. In this paper, we determine the Mechanical Threshold Stress model parameters for various tempers of AISI 4340 steel using experimental data from the open literature. We also compare stress-strain curves and Taylor impact test profiles predicted by the Mechanical Threshold Stress model with those from the Johnson-Cook model for 4340 steel. Relevant temperature- and pressure-dependent shear modulus models, melting temperature models, a specific heat model, and an equation of state for 4340 steel are discussed and their parameters are presented. 
Biswajit Banerjee