Co-strengthening of dislocations and precipitates in alumina-forming austenitic steel with cold rolling followed by aging

The microstructural evolutions of the alumina-forming austenitic (AFA) steel subjected to different cold-rolled reductions and then aging at 700 °C were investigated by multiple characterization methods, and the mechanical properties were also examined. The results show that the increased dislocations (especially, edge dislocations) after cold rolling can effectively enhance the volume fraction and refine the particle size of precipitates during initial aging and subsequently accelerate the coarsening rate of precipitates in the AFA steel, resulting in a high coarsening exponent. The coarsening rate of B2–NiAl phase is higher than that of Laves phase. Excellent mechanical properties with a combination of yield strength (1152 ± 32 MPa) and elongation (44.8 ± 4.1%) of cold rolled AFA steel after aging for 2 h can be obtained due to co-strengthening contribution derived from dislocations and precipitates. With the duration of aging, the dislocation strengthening constantly decreases, the effect of precipitation strengthening is contrarily larger than that of dislocations.