A Journey With Prasad's Processing Maps

Abstract

The constitutive flow behavior of austenitic stainless steel types AISI 304L, 316L, and 304 in the temperature range of 873 K (600 °C) to 1473 K (1200 °C) and strain-rate range of 0.001 s−1–100 s−1 has been evaluated with a view to establishing processing-microstructure-property relationships during hot working. The technique adopted for the study of constitutive behavior is through establishing processing maps and instability maps, and interpreting them on the basis of dynamic materials model (DMM). The processing maps for 304L have revealed a domain of dynamic recrystallization (DRX) occurring at 1423 K (1150 °C) at 0.1 s−1, which is the optimum condition for hot working of this material. The processing maps of 304 predict DRX domain at 1373 K (1100 °C) and 0.1 s−1. Stainless steel type 316L undergoes DRX at 1523 K (1250 °C) and 0.05 s−1. At 1173 K (900 °C) and 0.001 s−1 this material undergoes dynamic recovery (DRY). In the temperature and strain rate regimes other than DRX and DRY domains, austenitic stainless steels exhibit flow localization. Large-scale experiments using rolling, forging, and extrusion processes were conducted with a view to validating the conclusions arrived at from the processing maps. The “safe” processing regime predicted by processing maps has been further refined using the values of apparent activation energy during deformation. The validity and the merit of this refining procedure have been demonstrated with an example of press forging trials on stainless steel 316L. The usefulness of this approach for manufacturing stainless steel tubes and hot rolled plates has been demonstrated.