Phase transformation in Fe-Mo-C and Fe-W-C steels. 2: Eutectoid reaction of M{sub 23}C{sub 6} carbide decomposition during austenitization

Journal Article · Tue Jul 01 04:00:00 EDT 1997 · Acta Materialia

DOI:https://doi.org/10.1016/S1359-6454(96)00374-6· OSTI ID:524543

Shtansky, D V; Inden, G ^[1]

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1. Max-Planck Inst. fuer Eisenforschung GmbH, Duesseldorf (Germany)

The dissolution of globular M{sub 23}C{sub 6} carbide in Fe-W-C and Fe-Mo-C steels during austenitization has been studied by means of transmission electron microscopy (TEM). It was observed that the M{sub 23}C{sub 6} carbide formed at 700 C decomposes by two different eutectoid reactions. In the early stage of dissolution, before the {alpha}{yields}{gamma} transformation is completed at austenitization temperature, the M{sub 23}C{sub 6} carbide transforms into M{sub 6}C + {alpha} with the formation of spheroidal M{sub 6}C precipitates. The first reaction takes place while the carbide is still surrounded by ferrite. After the {alpha}{yields}{gamma} transformation, the M{sub 23}C{sub 6} carbide decomposes into M{sub 6}C + {gamma} in Fe-W-C steels and into Fe{sub 2}MoC + {gamma} or M{sub 6}C + {gamma} in Fe-Mo-C steels. In the latter cases a rod-like or lamellar structure was observed. It was established that phase boundary migration during M{sub 23}C{sub 6} carbide dissolution initiates the precipitation reaction at the interface. The precipitates were characterized by X-ray diffraction and by TEM-EDS. The orientation relationship between M{sub 6}C and austenite and M{sub 6}C and martensite after M{sub 2}C{sub 6} decomposition has been determined. The results obtained indicate that in both Fe-Mo-C and Fe-W-C steels, M{sub 23}C{sub 6} carbide is not stable in the temperature range of 800--1,000 C. The observed results will be discussed in terms of local equilibrium at the phase interfaces during the reactions.

• OSTI ID: 524543
• Journal Information: Acta Materialia, Journal Name: Acta Materialia Journal Issue: 7 Vol. 45; ISSN 1359-6454; ISSN ACMAFD
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
AUSTENITE
CARBIDES
CARBON ADDITIONS
CHEMICAL REACTIONS
DISSOLUTION
HEAT TREATMENTS
INTERFACES
IRON BASE ALLOYS
MARTENSITE
MOLYBDENUM ALLOYS
ORIENTATION
PHASE TRANSFORMATIONS
PRECIPITATION
TUNGSTEN ALLOYS