Abstract: A cyclic quenching treatment (CQT) succeeded in turning a 2.3 GPa maraging steel with a Charpy impact energy of 9 J into a new grade with the same strength but a Charpy impact energy of 20 J upon 4 cyclic treatments. The improvement of mechanical properties is attributed to the refinement and increased chemical heterogeneity of the martensitic substructure, rather than the refinement of prior austenite grain (PAG), as well as the Transformation-Induced Plasticity (TRIP) effect facilitated by small austenite grains. The role of local segregation of Ni during CQT in the formation of Ni-rich austenite grains, Ni-rich martensite laths and Ni-poor martensite laths, was investigated and verified by DICTRA simulations. This study highlights the important influence of Ni partitioning behavior during CQT, providing insights into microstructural evolution and mechanical properties.

Key words: Maraging steel, Cyclic quenching treatment, Ni partitioning, Ultrafine lath, Austenite, Toughness