Abstract
The age-hardening behaviours of the Fe-Ni-Mn martensitic alloys have been studied in relation to hardness, microstructure, lattice constant, electrical resistivity and magnetic properties comparing with those of the non-age-hardenable Fe-Ni and Fe-Mn martensitic alloys. The results obtained in this study are summarized as follows.
(1) In the age-hardenable Fe-Ni-Mn alloys, the matrix becomes etchable accompanying the reveal of fine particles during age-hardening. In this hardening stage, the electrical resistivity decreases and the lattice constant of matrix is maintained in almost constant while the half width of X-ray diffraction line increases. The reversion can be observed in the age-hardened Fe-Ni-Mn alloys.
(2) In the non-age-hardenable Fe-Ni alloy, austenite appears during aging and grows in lameller and the half width decreases abruptly on a short time aging.
(3) Although the age-hardening of Fe-Ni-Mn martensitic alloys cannot be ascribed to one factor, it seems likely that the strain hardening due to the formation of the coherent precipitate or zone in the matrix is a major factor. It is difficult to consider that such coherent precipitate or zone will be formed in the non age-hardenable Fe-Ni or Fe-Mn martensitic alloys.
(4) The formation of such precipitate or zone will be possible when the miscibility gap island can be assumed in the martensitic matrix of Fe-Ni-Mn alloys.
