Abstract
A unified constitutive model considering dynamic strain aging effect was developed in order to describe inelastic deformation behavior of modified 9Cr-1Mo steel precisely. The inelastic behavior of the material was summarized as follows. A rate-dependent deformation was observed above 500°C, and there was no rate-dependency under 400°C. However, stress relaxation behavior under constant strain was observed even at rate independent temperature region. Further, the stress after relaxation depended on prior loading strain-rate, and it showed a higher value as the strain-rate was decreased. A feature of the proposed constitutive model was that an applied stress consisted of three components:a back stress, an overstress and an aging stress which corresponded to dynamic strain aging effect and showed a negative strain-rate-dependency. The aging stress was measured by stepwise strain-rate change tests, and it showed a larger value at smaller strain-rate and lower temperature. The back stress and the overstress were measured by strain dip tests. The back stress was approximately rate-independent below 400°C, however it showed rate-dependency above 500°C. The overstress showed a larger value as the strain-rate or the temperature was increased. Material constants involved in the constitutive model were determined systematically based on the measured values of these stress components. In order to evaluate the validity of the constitutive model, numerical simulations were conducted for various inelastic deformation behavior of modified 9Cr-1Mo steel. The simulations agreed with experimental results very well in all cases.
