The Aging and Tempering of Iron-Nickel-Carbon-Martensites.
Abstract
The aging and tempering of freshly quenched (M(s)> RT) and virgin (M(s)< RT) martensites with lath and plate morphologies in Fe-Ni-C alloys have been studied to obtain kinetic and structural information. At subambient temperature, the first change is attributed to isothemal conversion of a small amount of retained austenite or to slight relaxations in the martensite, but this is not a significant part of the martensite aging process. Aging above -40 C to about 70 C is accompanied by the diffusion-controlled clustering of carbon atoms, resulting in an increase in electrical resistivity proportional to the carbon content but independent of the martensitic morphology. This regime is followed above 100 C by the precipitation of epsilon-carbide (i.e., the conventional first stage of tempering), which may emerge directly from the carbon-rich clusters. At still higher temperatures, cementite forms separately (i.e., the conventional third stage of tempering) in competition with the epsilon-carbide. These two precipitation processes overlap, and their kinetics appear to be controlled by iron-atom diffusion away from the growing carbide particles along dislocation paths. No evidence was found in this investigation for a regime reflecting carbon migration to dislocations or other defects, but this possibility is not ruled out by the experimental methods employed. (Author)
Document Details
- Document Type
- Technical Report
- Publication Date
- Dec 31, 1981
- Accession Number
- ADA110657
Entities
People
- A. Sherman
- G. T. Eldis
- Morris B Cohen
Organizations
- Massachusetts Institute of Technology