J. Phys. Colloques
Volume 47, Numéro C2, Mars 198632 nd International Field Emission Symposium / 32ème Symposium International d'Emission de Champ
|Page(s)||C2-265 - C2-275|
J. Phys. Colloques 47 (1986) C2-265-C2-275
AGEING AND TEMPERING OF FERROUS MARTENSITESLI CHANG1, G.D.W. SMITH1 et G.B. OLSON2
1 Department of Metallurgy and Science of Materials, University of Oxford, Parks Road. GB-Oxford OX1 3PH, Great Britain
2 Department of Materials Science and Engineering, M.I.T., Cambridge, M. 02139, U.S.A.
The low temperature ageing of a Fe-15wt%Ni-1wt%C martensite (Ms temperature -35 C) has been investigated using field - ion microscopy and atom probe microanalytical techniques. It is demonstrated that both the amplitude and the wavelength of the carbon composition fluctuations observed during room-temperature ageing increase with time, indicating that the alloy decomposes by a spinodal process. The carbon-rich regions approach a limiting composition of Fe8C during this reaction. The tempering behaviour of a high-cobalt-nickel secondary hardening steel, AF 1410, was also studied. The composition of the fine M2C carbides formed during the standard tempering treatment at 510 C was determined, and coarser particles of M2C and MC formed during overaging at 593 C were also analyzed. Some evidence of atomic ordering was observed in the Fe-Ni-Co-rich matrix ; such an effect would help to explain the high resistance to dislocation recovery which is observed in this class of steels.