Abstract
It has been reported that a large amount of plastic strain is produced by strain-induced martensitic transformation during deformation in metastable austenitic stainless steel (Fe-Cr-Ni alloys). However, few fundamental studies have been carried out for such a phenomenon called transformation-induced plasticity, especially in Fe-Ni alloys. In the present study, the tensile test was carried out at various temperatures using Fe-29%Ni-0.26%C (Ms=−35°C), Fe-31%Ni (Ms=−57°C) and Fe-15%Cr-13%Ni (Ms=−58°C) alloys, and the variation in tensile properties, especially elongation, with test temperature was investigated. The results obtained are as follows :
(1) Transformation-induced plasticity occurs in Fe-Ni alloys as well as in Fe-Cr-Ni alloy.
(2) Elongation has a maximum value at temperatures between Md and Ms in both Fe-Ni alloys and Fe-Cr-Ni alloy. As a condition necessary to obtain the maximum elongation, it is essential that the strain-hardening exponent should increase continuously with increase in strain. The martensites gradually induced with strain are available for elongation. On the other hand, when the martensites are formed in large quantities in the early stage of deformation near the Ms temperature the elongation is not so large.
(3) It is considered that the main causes of the large elongation (abnormal plasticity) is the suppression of necking and of the initiation and propagation of microcracks by the formation of strain-induced martensites which contribute to the relaxation of stress concentration.
(4) The temperature range for the large elongation in Fe-Cr-Ni alloy is wider than that in Fe-Ni alloys.
