Effect of manganese on the transformation of austenite in white chromium cast irons

Conclusions

• 1. When the manganese content is raised from 0.22 to 5.2% in chromium cast iron (12–14% Cr), the rate of the isothermal transformation decreases both in the pearlitic and intermediate ranges, the transformation temperature range becoming narrower, while the temperature where the stability of austenite is lowest decreases.

  The temperature at the start of the martensitic transformation also decreases and the amount of retained austenite in the structure increases.

• 2. The characteristic feature of the isothermal transformation of austenite in chromium-manganese cast irons is its incompletion.

• 3. The effect of manganese on the transformation of austenite in the pearlitic range is evident in the lesser extent of the transformation; the incubation period hardly changes as the manganese content is reduced.

• 4. The intensity of the effect of manganese on the transformation of austenite increases considerably with decreasing amounts of carbon in cast irons, which is due to redistribution of the alloying elements between carbides and the base metal.

• 5. The larger amount of retained austenite and its greater stability as the result of alloying lead to a reduction of the wear resistance in wear tests under conditions of microshaving.

For machine parts operating under such conditions the optimal structure of the matrix of white cast irons is martensite or martensite with metastable austenite.