The morphology of martensite in Fe-C,Fe-Ni-C and Fe-Cr-C alloys

The morphology of martensite in widely varying series of Fe-C, Fe-Ni-C and Fe-Cr-C alloys was investigated using optical microscopy. The effects of formation temperature and alloying elements on the martensite morphology were studied in detail. It was found that in Fe-C alloys, lath martensite forms in alloys with less than 0.8wt% carbon, butterfly martensite forms in alloys with between 0.98 and 1.42wt% carbon and lenticular martensite forms in alloys with more than 1.56wt% carbon. In Fe-Ni-C alloys, four different martensite morphologies form depending upon the formation temperature and composition, and for alloys of a fixed carbon content the martensite morphology changes from lath to butterfly to lenticular to thin plate as the formation temperature is decreased. In Fe-Cr-C alloys, lath martensite forms at high temperature, and below the lath formation temperature mainly {2 2 5}_f plate martensite is formed. Based on the results obtained, the importance of the strength of austenite, and the austenite stacking fault energy to the martensite morphology was discussed.