Constitutive equation and dynamic recrystallization behavior of as-cast 254SMO super-austenitic stainless steel

摘要

The deformation behavior and microstructural evolution of as-cast 254SMO super-austenitic stainless steel (SASS) were studied by hot compressive tests in the temperature range 900-1200 ℃, and in the strain rate range 0.01-10 s~(-1). The results show that the single peak characteristic appears on almost all the obtained flow curves, indicating that DRX is the primary softening mechanism. Either increasing deformation temperature or decreasing strain rate makes the flow stress level reduce remarkably. The hot deformation activation energy and the stress exponent are calculated to be 577.845 kJ/mol and 4.62 by the regression analysis of sine hyperbolic function, respectively. From the deformed microstruc-tures, it is found that the DRX nucleates mainly through grain boundary bulging but occasional through subgrain evolution only occurred at high strain rates and high temperatures. The critical stress and corresponding strain for DRX can be expressed through the dimensionless parameter, Z/A The critical ratios of σ_c/σ_p and ε_c/ε_p are also identified, which are 0.98 and 0.72, respectively. Moreover, the DRX kinetics for as-cast 254SMO SASS can be represented in the form of Avrami equation, and the predicted volume fraction of new grains based on the developed model agrees well with the experimental results.