Experimental Research of Mechanical Behavior and Constitutive Model for Mould Steel NAK80

The experiment of mechanical behaviors test of plastic mould steel NAK80 is carried out at a wide temperature range (25°C~500°C) and high strain rates (700s^-1~5000s^-1) with the INSTRON-5887 electronic material test machine, GLEEBLE-3500 thermal simulator and Split Hopkins on Pressure Bar (SHPB). The stress-strain curves of NAK80 under temperature and strain rate actions are obtained. On the basis, the mechanism of effect of temperature and strain rate on the plastic flow stress of material is discussed. The results show that the plastic flow behavior of NAK80 is less sensitive to strain rate. And the flow stress decreases with temperature increasing at the same strain rate (10-2s^-1) as well as yield strength. Under the condition of high temperature, its thermal softening effect is obvious, leading to stress decreasing with strain increasing after yielding. The Johnson-Cook constitutive model, fitted by the stress-strain curves that are obtained from the experiments, can provide satisfactory prediction and description of the plastic flow behavior of mould steel NAK80.