Strain-induced grain evolution in an austenitic stainless steel under warm multiple forging

The dynamic processes of ultrafine grain evolution in an S304H austenitic stainless were studied in multiple forging tests at temperatures ranging from 500 °C to 700 °C. The multiple forging was accompanied by the development of dynamic recrystallisation (DRX), which resulted in the formation of ultrafine grained structures. The size of the DRX grains decreases from 0.3 μm to 0.1 μm with a decrease in the temperature from 700 °C to 500 °C. The continuous DRX makes the main contributions to the overall recrystallisation process, although the discontinuous DRX plays an important role in the new grain development at moderate to large strains at 700 °C. The variation in the DRX mechanisms results in a change in the DRX kinetics. The fraction of high-angle boundaries can be expressed as FHAB∼0.2 ε in the range of 0<ε<2 for processing at 500–600 °C, whereas FHAB∼0.45 ε was obtained in the range of 1.2<ε<2 at 700 °C.