To solve the problem of the accuracy of the numerical simulations of cold rolling, the thermomechanical responses of 40Cr under uniaxial compression loading are presented. The strain rates include quasistatic (0.004？s？1) at temperature of 293？K and dynamic loading regime (632？s？1~5160？s？1) at temperature regime (293？K~673？K). Significant strain rate and temperature sensitivity are measured. Based on these observations, the Johnson-Cook phenomenological constitutive model is proposed to predict the mechanical behavior of the 40Cr over wide ranges of strain rate and temperature. The solution process of the equation parameters is given. Correlations with this Johnson-Cook model are shown very close to the observed responses. Important material parameters are provided to the application of numerical analysis in project. 1. Introduction High-speed cold rolling is an advanced cold bulk metal forming technology. During the forming process, the workpiece is interruptedly struck by high-speed rolls, and plastic deformation of the workpiece is gradually achieved [1, 2]. 40Cr quenched and tempered steel is the main structure material used in high-speed cold rolling technology because of its good strength and ductility combination. During high-speed cold rolling forming, 40Cr quenched and tempered steel is subjected to high strain rates (about 900？s？1~4000？s？1) and large deformation. Numerical analysis is a critical tool for understanding the complex deformation mechanics that occur during cold rolling forming processes. Confidence in the numerical analysis of formability depends on the accuracy of the constitutive model describing the behavior of the material. Therefore, there is a good need to characterize 40Cr quenched and tempered steel’s dynamic responses and constitutive model when performing numerical analysis of high-speed cold rolling. A large number of researches have been carried out in understanding and modeling the mechanical behavior of metals under different strain rates and temperatures in both experimental and theoretical schemes. Thermomechanical responses of H13 hardened steel over a strain rate range from 103？s？1 to 104？s？1 and a temperature range of 293？K to 673？K was investigated by Lu and He [3]. In their study, the determination of the Johnson-Cook material parameters of H13 hardened steel was based on the experimental results. The Johnson-Cook (JC) constitutive model was shown to correlate and predict the observed responses reasonably well. The quasistatic (10？3？s？1~10？s？1) and dynamic responses (650？s？1~8500？s？1) at room temperature of
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