Microstructure and Mechanical Properties of an Austenitic Heat-Resistant Steel after Service at 570 °C and 25.4 MPa for 18 Years

Abstract

Microstructure and mechanical properties of an austenitic heat-resistant steel (12Cr18Ni12Ti) serviced in a supercritical power plant at 570 °C/25.4 MPa for 160,000 h were investigated. The results show that the hardness and the tensile strength did not decrease; however, the impact toughness was remarkably reduced. The TiC precipitate shows excellent thermostability; for example, it hardly grew up, and no big M23C6 carbides were found. However, large Fe, Cr-rich σ-phase was doomed to precipitate along grain boundary, which should be responsible for the reduced toughness. The growth of σ-phase was observed to have an interaction with the preexisted carbides.