Ferromagnetically ordered clusters in austenite as the areas of martensite formation

Abstract

In this research, the peculiarities of the magnetic state of austenite of carbon steels were studied. The effect of an external magnetic field on the process of martensitic transformation is discussed. It is shown that there are nanoscale regions with ferromagnetic order in austenite. These regions are possible locations for the nucleation of martensite. In the case of magnetic field influence, the ferromagnetic clusters are able to perceive the energy of the external magnetic field by magnetostrictive stresses (which reduce the energy of martensite formation). Ferromagnetically ordered clusters have a certain critical size, below which the single-domain region becomes unstable. The dependence of the critical size of the ferromagnetic cluster on the intensity of the magnetic field was observed. This dependence shows that the higher the intensity of the field, the smaller the size of the clusters that can remain stable. Thus, a strong magnetic field increases the amount of ferromagnetic nanoclusters (consequently, the number of the nucleation centers of martensite increases). The results of the research allow estimating more accurately the effect of a magnetic field on decreasing the formation energy of a nucleation center.