M6C carbides in Fe-l.3C-12.7Mo PM steel

Figure 1: Scanning electron micrograph of a Fe-l.3C-12.7Mo alloy produced by the presintering of alloyed powders. The specimen was quenched after holding for 40 mn at a temperature in the three phase gamma/M6C/liquid field. Note; 1) the very fine intergranular eutectic carbides; 2) the coarse intergranular carbides; 3) the isolated carbides within the austenite grains. Courtesy INPG, Grenoble. Scale bar: 10 µm.

Carbide name: M6C
Record No.: 1174
Carbide formula: M6C
Carbide type: M6C
Carbide composition in weight %: No data
Image type: SEM
Steel name: Fe-l.3C-12.7Mo
Mat.No. (Wr.Nr.) designation: No data
DIN designation: No data
AISI/SAE/ASTM designation: No data
Other designation: No data
Steel group: PM steels
Steel composition in weight %: No data
Heat treatment/condition: No data
Note: Coarsening in a multiphase structure: The presintered alloy described above was held for 40 mn at a temperature slightly below that for the formation of the gamma/M6C eutectic (determined by DTA). Three phases are in equilibrium, austenite, the liquid and the eutectic carbide M6C. The austenite grains are bounded by a eutectic constituent, while the carbides can be divided into different populations, varying in size and location (Fig. 1):
The eutectic constituents, with very fine carbides formed by solidification of the intergranular liquid during quenching at the end of the holding period.
Coarse intergranular carbides, situated close to the eutectic, which probably remained in contact with the liquid at high temperature. They have coarsened rapidly at a rate almost as high as if they had been completely surrounded by liquid, the only limitation being the narrowness of the liquid corridors through which diffusional transport occurred.
Intragranular carbides, originally fine eutectic carbides, that have been trapped by grain growth. Once incorporated in the solid, their growth rate is greatly reduced, so that their size is intermediate between those resulting from diffusion in the completely solid or liquid states.
Holding just above and just below the temperature at which the third phase appears shows that coarsening of the austenite grains is considerably restricted by the presence of the carbide particles.
Links: No data
Reference: Not shown in this demo version.

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