Hardness Change of Ferrous Martensite by Deformation

A series of Fe-Ni-C martensites having transformation twins and an Fe-Cr-Ni-C martensite not having transformation twins but dislocations were rolled at 200°C, room temperature and liquid nitrogen temperature. The hardness change and the deformation mode of the martensite were examined. The twinned martensites were deformed by slip, when the carbon content of the martensite was low or the deformation temperature was high. In this case, the hardness change with reduction of deformation showed usual strain-hardening. However, when the carbon content was high or the deformation temperature was low, the martensite was deformed by twinning. In this case, the martensite showed strain-softening at a small percent of reduction, and then it was strain-hardened rapidly beyond the minimum hardness with increase in reduction. The untwinned martensite was deformed by slip, and the hardness change with reduction showed a usual strain-hardening curve