Microstructural analysis of phase precipitation during high temperature creep in AISI 310 stainless steel

Stainless steels subjected to constant load at high temperature, such as under creep conditions, are known to develop microstructural changes including precipitation of distinct phases. The present work investigated the quantitative precipitation process in an AISI 310 stainless steel creep-tested at 650, 675 and 700 degrees C under a constant load corresponding to a stress of 100 MPa. The microstructural evolution was evaluated by transmission electron and scanning electron microscopies as well as X-ray diffraction and microhardness. Even after a short time of 2 h at 675 degrees C, Cr23C6 precipitates were nucleated inside grains. After 140 h of creep test at 700 degrees C, both Cr23C6 and sigma phase were found in the grain boundaries. A quantitative analysis revealed that sigma phase emerged with 2.4 vol.% at 675 degrees C after 22 h to an increasing volume of 15.0 vol.% at 650 degrees C. A microhardness increase was associated with the presence of Cr23C6 and sigma phase. After 1231 h at 650 degrees C a microhardness decrease was attributed to coalescence and growth of Cr23C6 precipitates. (c) 2023 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Automated summary

This study investigated the quantitative precipitation process in stainless steels subjected to constant load at high temperature. The evolution of microstructure was evaluated and the presence of precipitates was analyzed using various techniques. The results showed that Cr23C6 precipitates were nucleated after a short period of time, and both Cr23C6 and sigma phase were found after a longer creep test. The volume of sigma phase increased with decreasing temperature, and the presence of precipitates led to an increase in microhardness.