Hot-workability of super-304H exhibiting continuous to discontinuous dynamic recrystallization transition

Abstract

The hot workability, deformation behavior and microstructure evolution of a Cu alloyed super-304H stainless steel is studied over a wide range of temperatures (1173–1423 K) and strain rates (0.001–10 s−1). The processing map and activation energy map are developed for delineating the stable and unstable domains of processing. Microstructural analysis have revealed that continuous dynamic recrystallization (cDRX) is the primary restoration mechanism at lower strain rates (< 0.5 s−1). The occurrence of cDRX is confirmed by the evidence of progressive conversion of low angle boundaries (LABs) to high angle boundaries in where few LABs exhibit a typical value of strain-induced boundary misorientation. However, a sharp transition from cDRX to discontinuous dynamic recrystallization (dDRX) is observed following deformation at higher strain rates (0.5–10 s−1) and temperatures (1350–1423 K). The dDRX domain is identified as optimum for processing due to its higher efficiency levels (30–35%), lower activation energy (450–550 kJ mol−1) and evolution of defect-free fine and equiaxed grains. Unstable regions are observed in 1173–1300 K and 0.03–1 s−1 which is characterized by higher activation energy for deformation (650–950 kJ mol−1) and presence of micro-cracks in the product microstructure.