Hot deformation and optimization of process parameters of an as-cast 6Mo superaustenitic stainless steel: A study with processing map

• Hot compression tests of as-cast S31254 SASS were preformed in a wide range of working conditions.
• The PMs at strains of 0.4 and 0.9 were constructed on the basis of DMM and Prasad instability criterion.
• The microstructure evolution during the hot deformation was analyzed.
• The optimal working condition had been proposed for the present steel.

The deformation characteristics of as-cast S31254 superaustenitic stainless steel (SASS) have been investigated by the isothermal compression testing at temperature of 1173–1473 K and strain rate of 0.01–10 s−1 on a Gleeble-1500D thermo-mechanical simulator. The approach of processing map (PM) was used to reveal the hot workability affected by the process parameters (such as ε̇, T and ε) and microstructural evolution during the hot deformation. It is found that the process parameters have obvious effects on the power dissipation efficiency, instability factor and softening characteristic. The safe deformation domain can be identified from the PM, and the variation of peak efficiency with strain is obtained in the safe domain. The optimal hot working condition at large strains (⩾0.7) corresponds to the temperature range of 1376–1473 K and the intermediate strain rate range of 0.07–1.38 s−1, with a peak efficiency of 35% at ∼1473 K and 0.4 s−1. In this field, the original coarse grains can be substituted by the fine recrystallized grains, indicating that the high power is dissipated by the dynamic recrystallization. Meanwhile, three instable regions, which should be avoided in hot processing, are detected from the PM and the related instability mechanisms are also discussed.