Phase instability of manganese-iron carbides

The stability of carbon saturated manganese-iron alloys was studied by means of simulated decrepitation tests, and it was found that the product must contain a minimum of about 5 wt pct iron to be stable during storage. By means of several experimental techniques it was shown that the structure of the carbide phase present in carbon saturated ferromanganese determines whether the alloy is stable. Below the critical iron content of about 5 wt pct, the carbide phase is Hāgg carbide (MnFe)5C2, whereas above about 5 wt pct iron the carbide phase is cementite (MnFe)3C. The role of iron is to stabilize the cementite phase. Experiments with the synthetic manganese carbides, Mn5C2 and Mn3C, showed that the former reacts readily with water whereas the latter is stable.