The static recrystallization kinetics of hot deformed austenite were characterised by a combination of in-situ laser-ultrasonics and stress relaxation measurements. Samples were deformed in compression at temperatures of 850°C and 900°C. The applied strain was varied between 0.2 and 0.5, whilst the strain rates used were 0.1 s⁻¹ and 0.5 s⁻¹. At various points during annealing samples were quenched and analysed by optical microscopy.
During recovery prior to recrystallization the ultrasonic velocity change and attenuation were almost constant. During recrystallization, the velocity change and attenuation decreased for the conditions imposed. The decrease in velocity change was mostly due to a change in the overall texture. The decrease in attenuation could be explained by a change in grain size. Unfortunately, the additional effect of dislocation damping on attenuation could not be quantified.
Comparison of the stress relaxation kinetics with the observed decrease in ultrasonic velocity change and attenuation generally showed good agreement.
From the attenuation measurements the grain sizes in the recrystallised structure for various applied strains were calculated. Comparison with grain sizes determined from optical microscopy showed reasonable agreement considering the accuracy of the attenuation measurements and the assumptions made.