The effect of magnetic fields on martensitic transformations in Fe-8.0Mn-4.5-5.3C(at%) alloys, which exhibit a paramagnetic to antiferromagnetic transition in the austenitic state, has been examined by means of differential scanning calorimetry, magnetic field susceptibility and magnetization measurements and optical microscopy, applying a pulsed ultra high magnetic field. As a result, it was found that the martensitic transformation was not thermally induced in all the alloys even at liquid helium temperature, but it occurred under magnetic fields higher than a critical one only in the alloy with 4.5 at%C. The critical magnetic field vs temperature relation in the 4.5 at%C alloy showed a C-curve, being largely different from that for all the ferrous alloys previously examined. Irrespective of the formation temperature, the amount of magnetic field-induced martensites was dependent on the strength of magnetic field near the critical one, but was independent on a little higher magnetic fields. Morphology of the magnetic field-induced martensites was the same irrespective of the formation temperature. Thermodynamic analysis suggested that an antiferromagnetic short range order which exists in the paramagnetic austenite suppressed the martensitic transformation.
(Received April 14, 1988)
Keywords: martensitic transformation, magnetic field inducement, paramagnetic austenite, antiferromagnetic austenite, magnetic transition, antiferromagnetic short range order, iron-manganese-carbon alloy, critical magnetic field, martensite amount, martensite morphology.
* A part of this paper was originally presented at the Annual Autumn Meeting of the Japan Institute of Metals, Kumamoto, (1987).
** The Institute of Scientific and Industrial Research, Osaka University, 8-1, Mihoga-oka, Ibaraki, Osaka 567, Japan.
*** Graduate Student, Osaka University at Suita-Ibaraki Campus. Present address: Sumitomo Special Metals Co. Ltd., 2-15-17, Edogawa, Shimamoto-cho, Mishima-gun, Osaka 618, Japan.
**** Physics Department, Faculty of Science, Osaka University, 1-1, Machikaneyama-cho, Toyonaka, Osaka 560, Japan.
***** Graduate Student, Osaka University at Toyonaka Campus. Present address: Mitsubishi Electric Corporation, 8-1-1, Tsukaguchi-honmachi,