Effect of deformation parameters on the

The recrystallization behavior of three Nb-bearing high-strength low-alloy (HSLA) steels was investigated during multipass deformation under continuous cooling conditions. The niobium concentrations of these steels varied from 0.05 to 0.09 wt pct. The specimens were tested on a computerized torsion machine using a simulation schedule of 17 passes. Deformation tem-peratures of 1180 °C to 700 °C were employed, together with pass strains of 0.1 to 0.7, strain rates of 0.2 to 10 s^-1, and interpass times of 5 to 200 seconds. By means of mean flow stressvs 1000/T diagrams, the effect of the deformation conditions on the no-recrystallization tem-perature (T _nr ), the temperature at which recrystallization is no longer complete, was determined. It decreases with increasing strain and also decreases slightly with increasing strain rate. There is aT _r minimum at times of about 12∼15 seconds, and both increases and decreases from this value raise this characteristic temperature. When the interpass times are short, solute atoms control the rate of recrystallization, the extent of which decreases as the time is decreased. When the interpass times are long, precipitation takes place and retards recrystallization, so that the extent of softening decreases. Formerly Research Associate, McGill University, Department of Metallurgical Engineering.