M3C, M7C3 carbides in high-chromium white iron


Figure 1: Typical as-cast microstructure of a high-chromium white iron consisting of eutectic M7C3 carbides in a matrix of austenite. Scale bar: 100 µm.


Figure 2: Typical as-cast microstructure of a low-chromium white iron consisting of eutectic M3C carbides in a matrix of austenite (gamma) plus martensite (alpha'). Scale bar: 10 µm.

Carbide name: M3C, M7C3
Record No.: 1514
Carbide formula: M3C, M7C3
Carbide type: M3C, M7C3
Carbide composition in weight %: No data
Image type: SEM, LM
Steel name: High-chromium white iron
Mat.No. (Wr.Nr.) designation: No data
DIN designation: No data
AISI/SAE/ASTM designation: No data
Other designation: No data
Steel group: Alloyed white irons
Steel composition in weight %: No data
Heat treatment/condition: No data
Note: Since the continuous network of cementite promotes brittleness in white iron, it is common to alloy such materials to get better mechanical properties. A very successful element for this purpose is chromium. In amounts between 12 and 30 wt.%, chromium changes the stoichiometry of the carbide phase from the orthorhombic M3C to the hexagonal M7C3, which is less continuous. In addition, the presence of other elements such as nickel and molybdenum, which increase hardenability, promotes the presence of the austenite in the final as-cast structure. These irons are called high-chromium cast irons, and the as-cast structure consists of eutectic carbides of the type M7C3 in a matrix of austenite (Figure 1). The presence of austenite and the less interconnected carbides gives some toughness to the alloy, and the harder M7C3 carbide gives a better wear resistance to these materials.
If the amount of chromium is less than 12 wt.%, the stoichiometry of the carbide does not change and the structure consists of eutectic M3C carbides in a matrix of austenite plus martensite. These irons are called low-chromium cast irons. Figure 2 shows the typical as-cast structure of this latter iron.
Links: No data
Reference: Not shown in this demo version.

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