M6C carbides in Fe-W-C alloy

Figure 1: Scanning electron micrographs on vertical sections of DTA specimens quenched during solidification. W13) Fe-12.6W-3.96C alloy cooled at 5 C/h. W20) Fe-19.8 W-3.1C alloy cooled at 2 C/h. gamma=austenite, c = cementite, eta = M6C, g=graphite. Courtesy INPG, Grenoble. Scale bars: 100 µm.

Carbide name: M6C
Record No.: 1186
Carbide formula: M6C
Carbide type: M6C
Carbide composition in weight %: No data
Image type: SEM
Steel name: Fe-W-C alloy
Mat.No. (Wr.Nr.) designation: No data
DIN designation: No data
AISI/SAE/ASTM designation: No data
Other designation: No data
Steel group: Steels
Steel composition in weight %: No data
Heat treatment/condition: No data
Note: Settling and flotation effects: The Fe-W-C system can be quite puzzling, and the experimental determination of liquid/solid equilibria encounters several difficulties. The most readily visible effect is the tendency for tungsten carbide WC to settle out at the bottom of the crucible. Similar gravitation-driven segregation of tungsten in the liquid is less easy to detect. Another major problem is the formation of highly stable intermetallic compounds which solidify with a high degree of supercooling. The solidification paths are therefore extremely difficult to interpret. Several phases can show primary solidification morphologies, due to the fact that their growth has not been stopped by that of another phase. Figure 1 shows the microstructures of two slowly solidified specimens. In the micrograph W13, the austenite appears in the form of primary dendrites. The same is true for the large graphite flakes and for the white tungsten carbides (WC) that have settled to the bottom of the crucible in the form of coarse facetted particles. Three phases can be distinguished in the interdendritic regions; austenite (gamma), fine graphite filaments and white M6C carbides. Austenite and M6C appear to be combined in a eutectic. A ternary eutectic, gamma/M6C/graphite also appears to exist. The microstructure resembles that of a grey cast iron in which segregation has caused the formation of local regions of white cast iron.
The structure is even more complicated in micrograph W20, where at least four phases can be identified, gamma, Fe3C, WC and M6C. Several of them have primary solidification morphologies (the austenite dendrites, the settled-out WC carbides and the large cementite needles). The gamma/Fe3C/M6C ternary eutectic is present in large amounts in the upper part of the specimen, while the ternary eutectic gamma/Fe3C/WC can also be seen in a band about a millimetre wide, above the settled-out WC carbides.
Links: No data
Reference: Not shown in this demo version.

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