Strengthening and fracture mechanisms of Fe–20Ni–14Cr–2Cu alumina-forming austenitic steel during creeping

The strengthening and fracture mechanisms of Fe–20Ni–14Cr–2Cu alumina-forming austenitic (AFA) steel during creeping at 973 K/130 MPa were systematically investigated. Microstructural observations show that during creep after priorly aged at 973 K for different times, three main types of precipitates, i.e., Laves, B2-NiAl, and σ phases, are found in Fe–20Ni–14Cr–2Cu AFA steel. Laves and B2-NiAl phases dispersed in austenitic matrix contribute to the creep properties of AFA steel due to their small particle sizes, while the coarsening of hard-brittle σ phase in δ-ferrite region seems to be the main reason for creep failure. The Fe–20Ni–14Cr–2Cu AFA steel priorly aged for 1000 h possesses excellent creep property at 973 K with the minimum steady-state creep rate of 7.64 × 10–6 s−1 and the longest creep life of 329.5 h. The contribution of Laves and B2-NiAl phases to creep strength of AFA steel at 973 K/130 MPa after priorly aged for 1000 h is 261.2 MPa.