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

Abstract

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 °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 °C, Cr23C6 precipitates were nucleated inside grains. After 140 h of creep test at 700 °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 °C after 22 h to an increasing volume of 15.0 vol.% at 650 °C. A microhardness increase was associated with the presence of Cr23C6 and sigma phase. After 1231 h at 650 °C a microhardness decrease was attributed to coalescence and growth of Cr23C6 precipitates.

Keywords

• Austenitic steels
• Aging by creep
• Cr23C6
• Sigma phase