n order to study the morphology q[ strain-induced martensite and the plasticity induced by the martensitic transformation, tellsile tests at various temperatures were carried out using Fc-31% N i, Fe-29%N i-O.26%C and Fe-15% Cr-13%N i alloys whose Ms temperatures u:ere below room temjlerature and the microstructures were observed.The results obtained are summarized as fo llows.In Fe-Ni and Fe-Ni-C alloys, a characteristic martensite whose morphology is entirely different fiom that of thermalfv transformed martensite is formed ~y tensile deformation mainly at the temperatures between Md and M s.This characteristic martensile is forme d continuously little by Little with increasing strain and contributes to the transformation-induced jJlasticity.The difference of morphology between thermally transformed martensite and stra in-induced martellsite must be caused by the change of transformation mechanism .In the case of Fe-Cr-N i alloy, however, the morjJ!wlogy of strain-induced martensite is not dijJerent from that of thermally transformed martensite.Transform ation-induced plasticity occurs in Fe-N i alLqys and the Fe-Cr-N i alloy.The elongation has a maximum value at a temperature between M d and M s.I n the test in which the maximum elongation is obtained, the strain-hardening exjJonent increases continuously with increase in strain.The main prerequisite for maximum elongation is that the martensite is constantly .f~m7CdLittle by little du ring deformation up to fracture.The difference between the F c-Ni alloys and the Fe-Cr-N i alloy is that the temperature range showing large elollgation is wider in the Fe-Cr-Ni alloy than in Fe-N i alloys.This is caused by the dijJerence in transformation behavior of martensite.
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Tamura et al. (1970) studied this question.