Study of martensite of isothermic and athermic reactions by nuclear gamma resonance method

It is found that the isothermal and athermic martensite transformations are irrespective processes, each one having peculiarities of its own. A Moessbauer study was made of the martensite obtained in isothermal and athermic reactions of the Fe - 23.9 at.% Ni - 3.1 at.% Mo alloy. The isothermal martensite build-up was performed at 90 deg C (a hold-up for 1 hr), and the athermal reaction was conducted by a sharp cooling down to -196 deg C with a subsequent rapid heating in warm water to prevent the isothermal transformation. In both cases about 70% of martensites have been accumulated. For the Fe - 23.9 at.% Ni - 3.1 at.% Mo alloy the isothermal martensite differs from the athermic one by the distribution of molybdenum atoms. The isothermal martensite is characterized by the molybdenum atom distribution close to a statistical one, whereas the athermic martensite contains less molybdenum atoms in the vicinity of the iron atoms. We suppose that the discovered peculiarities of fine atomic martensite structure in the Fe - 23.9% Ni -3.1% Mo alloy are the sequence of a difference in the alpha-crystal formation mechanism during the athermic and isothermal martensite transformations