Blue brittleness is exhibited by some steels after being heated to an elevated temperature. Although at high temperature a given strain is associated with a lower stress level, at the temperature at which blue brittleness is observed there is a pronounced work-hardening effect. Furthermore, the temperature at which blue brittleness occurs is a function of the strain rate. Therefore, to improve the accuracy of numerical simulations of hot or warm working which utilizes the thermal softening of steels, a dynamic constitutive equation which can model the blue brittleness phenomenon is needed. In this paper we present such a constitutive equation, which has two parts : one models the ordinary constitutive relation and the other the phenomenon of blue brittleness. Unknown material constants in the equation are determined by a non-linear least-squares method from uniaxial impact and static compressive test results. The equation is then evaluated by comparing it to experiments over a wide temperature range.
