Atomic structure of the Cu precipitates in two stages hardening in maraging steel

Fine precipitates in 15-5 PH Maraging steel in two stages hardening were analyzed by transmission electron microscopy. HREM observation reveals the formation of the fine precipitates (4-12 nm) with a 9R structure, after aging at 480 °C for 2 h. A second type of copper precipitate with a f.c.c. structure, spherical in shape, was observed on aging at 650 °C. The spherical copper precipitates are thought to grow by the mechanism of moving steps.