The effects of strain, strain rate and temperature on grain refinement and hot workability of type 305 stainless steel

Abstract

Both falling-temperature and isothermal hot compressive deformation schedules were performed on type 305 stainless steel in order to study the effects of strain, strain rate and temperature on grain refinement and to assess the effect of grain refinement on hot workability. In these refinement sequences, which simulate the hot rolling of as-cast ingots (grain size of 1300 μm) down to the final product (grain size of 9 μm), temperature plays the dominant role in controlling the limit of grain refinement. The final grain size was found to depend only on the finishing temperature and to be independent of additional deformation and recrystallization steps at the finishing temperature. For a given range of hot-working temperatures (start to finish) and for a fixed total shape change (ingot to final product), total grain refinement was found to be independent of the chosen combination of strain and number of steps, for incremental strains between 10% and 25%. Changing the strain rate from 10 to 0.01 s−1 barely reduced the refinement at individual steps in a sequence and had only a slight effect on the total refinement. For the temperature range from 1149 down to 927°C (from 1422 down to 1200 K), there was no measurable difference between the flow stress of as-cast metal and the flow stress of metal undergoing a hot-working schedule (recrystallization and refinement at at each step). Ductility increased as the grain size decreased.