J. Phys. Colloques
Volume 50, Numéro C8, Novembre 198936th International Field Emission Symposium
|Page(s)||C8-407 - C8-412|
J. Phys. Colloques 50 (1989) C8-407-C8-412
A FIELD-ION MICROSCOPY AND ATOM PROBE STUDY OF AGEING BEHAVIOUR OF A Co-BEARING MARAGING STEELW. SHA, A. CEREZO et G.D.W. SMITH
Department of Metallurgy and Science of Materials, University of Oxford, Parks Road, GB-Oxford OX1 3PH, Great-Britain
This paper reports the first atom probe field-ion microscopy (APFIM) study of the ageing reactions in a Co-bearing (C-300) maraging steel (Fe-18.5%Ni-9.0%Co-4.8%Mo-0.6%Ti-0.1% Al-0.1%Si-0.03%C (wt%)), using both the conventional APFIM and the position-sensitive atom probe (POSAP). Two families of intermetallic phases (Fe7Mo6 and Ni3(Mo,Ti) types) have been found to contribute to age-hardening. The composition and morphology of these precipitates were studied for different ageing times (0.5-128 hours at 510° C) to investigate the ageing sequence. The observation of the (Fe,Ni,Co)7Mo6 µ-phase is of interest since this is contrary to most published electron diffraction work, but is supported by thermodynamic calculations. Austenite reversion has been found to start after ageing for 4 hours and the reverted austenite approaches the predicted equilibrium composition after ageing for 8 hours.