Precipitate Evolution in 22Cr25NiWCuCo(Nb) Austenitic Heat-Resistant Stainless Steel during Heat Treatment at 1200 °C

In this study, 22Cr25NiWCuCo(Nb) heat-resistant steel specimens with high Cr and Ni contents were adopted to investigate the effect of Nb content on thermal and precipitation behavior. Differential scanning calorimetry profiles revealed that the melting point of the 22Cr25NiWCuCo(Nb) steel specimens decreased slightly with the Nb content. After heat treatment at 1200 degrees C for 2 h, the precipitates dissolved in a Nb-free steel matrix. In addition, the Z phase (CrNb(C, N)) and MX (Nb(C, N), (Cr, Fe)(C, N), and NbC) could be observed in the Nb-containing steel specimens. The amount and volume fraction of the precipitates increased with the Nb content, and the precipitates were distributed heterogeneously along the grain boundary and inside the grain. Even when the heat treatment duration was extended to 6 h, the austenitic grain size and precipitates became coarser; the volume fraction of the precipitates also increased at 1200 degrees C. The Z phase, rather than the MX phase, became the dominant precipitates at this temperature.

Automated summary

The study investigated the effect of Nb content on thermal and precipitation behavior in 22Cr25NiWCuCo(Nb) heat-resistant steel. Increasing Nb content led to an increase in the amount and volume fraction of precipitates, which were heterogeneously distributed along grain boundaries and inside grains. The Z phase became the dominant precipitates at 1200 degrees C, even after extended heat treatment duration.