The influence of roughing strain and temperature on precipitation in niobium microalloyed steels after a finishing deformation at 900°C

This work demonstrates that the technique of stress relaxation in plane strain compression can be used to investigate the effect of process variables on precipitation of micro alloy carbides in austenite. In particular it has been used to study the influence of roughing deformation on precipitation after working at 900C. It has been demonstrated that increase in roughing strain decreases the time to the onset of precipitation after a constant strain at 900C in a range of steels with different niobium and carbon levels, but that beyond a certain value of roughing strain the time for the onset of precipitation remains constant. The flow stress in the austenite at 900C is increased with increase in roughing strain and decrease in roughing temperature. The stress relaxation technique has allowed a wider range of roughing conditions to be examined as it uses only one specimen to obtian information that would have required at least six specimens with the techniques previously used for measuring the kinetics of strain induced precipitation.