Studies on the magnetic properties of martensitic phase in an Fe-Cr-C alloy

摘要

It has been well established that there is a strong correlation between the magnetic behaviour of Fe based alloys and their austenite to martensite phase transformation. Despite the paramagnetic nature of the austenitic parent phase in these alloys, martensi-tic product phase exhibits a distinctive ferromagnetic character [1-4]. On the other hand, applied magnetic fields alter the austenite to martensite transformation kinetics by creating a free-energy difference between the two phases [1]. Tamarat et cil. [2] examined the magnetic transitions during the austenite to e martensite transformation in an Fe-Mn-Si alloy by measuring the magnetic susceptibility variation, and observed a sharp change between different magnetic states at the trans-formation temperature (Ms). Yang et cd. [3] also observed that similar changes occurred after the formation of ￡ martensite in some Fe-Mn based alloys, and discussed the influence of austenite deformation on the magnetic properties of parent and product structures. In addition, they examined the influence of magnetic transition upon the transformation characteristics at various temperatures and described the strong dependence of the ther-mally induced martensite formation on the magni-tude of this transition. However, in Fe based alloys, besides the thermal activation of martensitic trans-formation, martensite formation can, in general, also be induced by the plastic deformation of the matrix austenite [5]. Although the formation mechanism of thermally-induced martensite is different from that of the strain-induced type, there are still several similarities in their physical properties [6—8]. Despite the previous reports on the ferromagnetic transition occurring during the martensite formation and the effect of deformation upon the magnetic characteristics of the austenite and martensite phases, there has not yet been any study to examine the magnetic changes that accompany strain-induced martensite formation and to compare the magnetic behaviours of thermally- and strain-induced marten-sites. Therefore, the present study aimed to investi-gate the magnetic properties of these two martensitic products formed in an Fe-Cr-C alloy, by using magnetic susceptibility measurements.