PHASE CHEMISTRY AND PRECIPITATION REACTIONS IN MARAGING STEELS .3. MODEL ALLOYS

This article describes studies of phase transformations during aging in a variety of model maraging steels. Atom-probe field-ion microscopy (APFIM) was the main research technique employed. Thermochemical calculation was also used during the course of the work. The composition and morphology of precipitates were compared in several maraging systems aged at different temperatures for different times to investigate the aging sequence. The APFIM results are compared with studies by other workers using different experimental techniques. In Fe-Ni(-Co)-Mo model alloys, omega phase and Fe7Mo6 mu phase have been found to contribute to age hardening at different stages of aging; no evidence was found for the existence of Mo-rich clusters in the as-quenched Fe-Ni-Co-Mo alloy. In a high-Si Cr-containing steel, Ti6Si7Ni16 G phase and Ni3Ti have been found to contribute to age hardening; reverted austenite was found after aging for 5 hours at 520-degrees-C. In a Mn-containing steel, Fe2Mo Laves phase and a structurally uncertain phase with a composition of Fe45Mn32Co5Mo19 have been found to contribute to age hardening.