Effects of pre-strain, heat treatments and magnetic fields on α′ martensite formation in Fe25.5%Ni3–5%Cr alloys

Effects of heat treatment, pre-strain at ambient temperature and high magnetic fields up to 24 T on the formation of α′ martensite at 77 K were examined for Fe25.5%Ni3–5%Cr alloys and a SUS304L stainless steel. The amount of α′ martensite formed at 77 K is not affected by solution treatment temperature and cooling rate from the solution treatment temperature in the former alloys. Also, the pre-strain shows a very small effect on the amount of α′. In the case of SUS304L steel, however, the solution treatment temperature, the cooling rate from the temperature and pre-strain show clear changes in the amount of α′ martensite. The difference in the effects between these two kinds of materials is attributed to the difference in the ease of formation of stacking faults or ε martensite.