Heat treatment of investment cast PH 13-8 Mo stainless steel; Part 2: Isothermal aging kinetics
- Sandia National Labs., Albuquerque, NM (United States). Physical and Joining Metallurgy Dept.
- Colorado School of Mines, Golden, CO (United States). Dept. of Metallurgical and Materials Engineering
The hardening response of investment cast PH 13-8 Mo stainless steel has been evaluated by hardness measurements following aging in the temperature range normally specified for this alloy (510 C to 593 C). A new relationship between fraction transformed and hardness was developed, and analysis of the data in terms of the kinetics of precipitation, in a manner similar to that frequently applied to other precipitation-hardenable martensitic steels, yielded low time exponents and a low value for the apparent activation energy. The values of the time exponents were 0.49, 0.37, 0.56, and 0.53 at 510 C, 538 C, 566 C, and 593 C, respectively, and that for the apparent activation energy was 139 kJ/mole. As has been proposed for other maraging type steels, these estimates suggest that [beta]-NiAl precipitates along or near dislocations and that growth of the precipitates is dominated by dislocation pipe diffusion. However, these predictions were neither supported nor refuted by transmission electron microscopy (TEM) because of difficulties in imaging the [beta]-NiAl precipitates at the aging times and temperatures used. Further, analysis of the data using the formalism of Wert and Zener for the growth of precipitates with interfering diffusion fields indicated that the estimates of fraction transformed from hardness data are not fully appropriate for maraging type steels. Consideration of the nature of the Avrami analysis and the electron microscopy results suggests that other phenomena, including dislocation recovery and reversion of martensite to austenite, occur at rates sufficient to convolute the Avrami analysis. It is further suggested that these results cast doubt on the fundamental implications of previous analyses of precipitation kinetics in age-hardening martensitic steels.
- DOE Contract Number:
- AC04-94AL85000
- OSTI ID:
- 7087251
- Journal Information:
- Metallurgical Transactions, A (Physical Metallurgy and Materials Science); (United States), Vol. 25:4; ISSN 0360-2133
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
STAINLESS STEELS
AGE HARDENING
HARDNESS
CRYSTAL-PHASE TRANSFORMATIONS
HEAT TREATMENTS
PRECIPITATION HARDENING
ALLOYS
HARDENING
HIGH ALLOY STEELS
IRON ALLOYS
IRON BASE ALLOYS
MECHANICAL PROPERTIES
PHASE TRANSFORMATIONS
STEELS
360101* - Metals & Alloys- Preparation & Fabrication
360103 - Metals & Alloys- Mechanical Properties