Influence of Ti microalloying on the formation of nanocrystalline structure in the 201L austenitic stainless steel during martensite thermomechanical treatment

The martensite thermomechanical treatment was used for the formation of nano/ultrafine grain structure in the 201L austenitic stainless steel containing 0.12 wt% Ti microalloying element. The initial microstructure was provided through homogenizing, hot rolling and solution annealing of the as-cast ingots. The specimens were then cold rolled between 5% and 90% thickness reduction and subsequently annealed at 750-900 °C for various times. The results showed a promoting effect of Ti on the formation of strain-induced martensite (SIM). A nanocrystalline austenitic structure with average grain size of 45 nm was achieved by annealing at 900 °C for 60 s through a diffusional transformation mechanism. It was found that precipitation of nanosized TiC particles during the reversion annealing could retard the reversion process and suppressed grain growth in further annealing times. The tensile testing of the thermomechanically processed specimens showed a good combination of high yield strength (~1000 MPa, six times higher than that of the initial coarse-grained steel) and excellent ductility (42% total elongation) for the Ti microalloyed 201L steel due to the SIM formation during the deformation and impressions of the nanosized Ti carbides distributed within the nano/ultrafine grain structure.