Annealing effects on precipitation and high-temperature properties of a Cu-containing alumina-forming austenitic steel

• The AFA alloy annealed at 1230 °C yields better properties at 700 °C than alloy A1080.
• Dislocations can cut L12-ordered precipitates and be pinned by MC precipitates.
• Nanoscale precipitates formed during creep testing are crucial to creep/rupture life.

A novel Cu-containing alumina-forming austenitic (AFA) stainless steel was annealed at 1080 °C and 1230 °C following the same treatments. Annealing at different temperatures renders different microstructure and properties of the AFA steels. In comparison to alloy A1080, the grain size of alloy A1230 after annealing is larger and the high temperature properties of A1230 is better, i.e. higher strain hardening ability and longer creep/rupture life at 700 °C. Coherent L12-ordered precipitates of 10–20 nm appear in both alloys and the amount of nanoscale MC precipitates is obviously higher in alloy A1230. Evidence of L12-ordered precipitates cut by dislocation and dislocation pinned by MC precipitates is clearly shown. The precipitation behavior of MC carbides agrees with the calculated Time-Temperature-Transformation (TTT) curves. The results show that nanoscale MC precipitates formed during creep testing contribute to the longer creep/rupture life of alloy A1230.