Dissolution of nanosized NbC precipitates in austenite matrix during elastic deformation - Deleterious effect of high number density

An austenitic stainless steel with large number density of nanosized NbC precipitates distributed in matrix was developed with the addition of small amount of Mn and application of proper thermo-mechanical process. Micro-pillar compression tests were performed to evaluate the strengthening effect of nanosized NbC. Despite much higher number density of NbC precipitates in the Mn-added alloy, the strengthening effect was measured to be significantly less than expected. Then, the compressed micro-pillars were then subjected to post-mortem microstructure analyses focusing on the dynamic evolution of NbC precipitates and austenite matrix. Extensive dissolution and re-precipitation of NbC precipitates were observed in the elastically and plastically deformed micro-pillars. In addition, stacking faults and deformation twin were also observed near the precipitates. From the relationship between the number density of the NbC precipitates, microstructure evolution, and dissolution of NbC, it was found that higher number density of nanosized NbC precipitates associated with dislocations in austenitic stainless steel enhanced dissolution of them by nano-scale yielding during elastic deformation, which limited the strengthening effect of nanosized NbC precipitates.