Hot Deformation Behavior and Microstructural Evolution of SA508-IV Steel

The hot deformation behavior and microstructural evolution of SA508-CYRILLIC CAPITAL LETTER BYELORUSSIAN-UKRAINIAN IV steel are studied through hot compressive tests in the temperature range of 950-1250 degrees C, and in the strain rate range of 0.001-1 s(-1). The hot deformation activation energy and the stress exponent are calculated to be 328.73 KJ mol(-1) and 3.29 by the regression analysis of sine hyperbolic function. On this basis, the constitutive Equations are developed. Moreover, the relationship between work hardening and dynamic softening is explained, and a two-stage constitutive model is established to predict the flow stress of SA508-CYRILLIC CAPITAL LETTER BYELORUSSIAN-UKRAINIAN IV steel. The predicted and experimental values show a good consistency. Based on the conventional dynamic recrystallization kinetics model, the volume fraction of the dynamic recrystallization is also estimated, and the results show that the maximum fraction is close to 100% under the higher temperature and lower strain rate. Furthermore, the microstructural evolutions at different deformation conditions are also analyzed, and the DRX grain size has an exponential increase with increasing deformation temperature and decreasing strain rate.