Identification of M{sub 5}C{sub 2} carbides in ex-service 1Cr-0.5Mo steels
Journal Article
·
· Metallurgical Transactions, A
OSTI ID:31958
- Monash Univ., Clayton, Victoria (Australia). Dept. of Materials Engineering
Rod-shaped precipitates up to 6{mu}m long and 0.25 {mu}m wide, observed as a common feature within proeutectoid ferrite grains of ex-service 1Cr-0.5Mo steels, have been characterized using electron microdiffraction, energy-dispersive X-ray spectroscopy, and electron energy loss spectroscopy. The majority of the rods have been identified as M{sub 5}C{sub 2} carbides, although some were M{sub 3}C. The M{sub 5}C{sub 2} carbide, also known as the Haegg or {chi}-carbide, is a monoclinic phase that is not known to have been identified previously in creep-resistant Cr-Mo steels. The M{sub 5}C{sub 2} rods appeared to nucleate heterogeneously on M{sub 2}C carbides and persisting ferrite regions from which the needlelike M{sub 2}C carbides had disappeared. This suggests that the M{sub 5}C{sub 2} carbide is more stable thermodynamically than M{sub 2}C in 1Cr-0.5Mo steels under typical service conditions. The metallic element compositions of the rodlike carbides varied, but the average compositions were in the range 48 to 56 at. pct Fe, 32 to 42 at. pct Cr, 8 to 12 at. pct Mn, and about 1 at. pct Mo. The Mn content of the rods varied systematically with exposure temperature and thus might be applied to the estimation of the effective service temperature of 1Cr-0.5Mo steel components.
- OSTI ID:
- 31958
- Journal Information:
- Metallurgical Transactions, A, Journal Name: Metallurgical Transactions, A Journal Issue: 3 Vol. 26; ISSN 0360-2133; ISSN MTTABN
- Country of Publication:
- United States
- Language:
- English
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