Specimens were deformed to investigate the effect of strain, strain rate, and test temperature on microstructural evolution. The strain rates and temperatures investigated are 10** minus **5 to 10** minus **2 s** minus **1 and 400 degree to 540 degree C, respectively. Strain hardening occurs at lower strain rates irrespective of temperature. Strain hardening at lower strain rates and higher temperatures can be accounted for by grain growth. Strain hardening at lower temperature is caused partly by concomitant grain growth and partly by dislocation interactions. During deformation at higher strain rates, some strain softening associated with excessive cavitation is seen.