In situ investigation of the martensitic transformation in Fe-12 wt.%Ni-0.6 wt.%C steel at subzero temperatures

Martensitic transformation in a Fe-12 wt.%Ni-0.6 wt.%C alloy was investigated with magnetometry and in situ (synchrotron) X-ray diffraction at sub-zero Celsius temperature. In situ X-ray diffraction at the HZB-BESSY II synchrotron facility was applied to quantitatively determine the fractions of retained austenite and martensite formed during: (i) isochronal transformation, while cooling at a rate of 3 K/min from room temperature to 138 K, and (ii) isothermal transformation, while holding at 138 K. X-ray diffraction analysis was also used for a qualitative evaluation of the stress evolution in austenite during the transformation. Magnetometry was applied to monitor the overall kinetics for the same isochronal and isothermal transformations. The results are discussed in the light of the current theories on martensitic transformations. (C) 2012 Elsevier B.V. All rights reserved.