Dynamic theory of the effect of a strong magnetic field on the martensitic transformation in steels with austenite grain sizes close to a critical value

Abstract

In the dynamic theory of martensitic transformations, temperature Ms of the start of transformation corresponds to conditions that are optimal for generating waves by nonequilibrium d electrons that control the growth of a martensitic crystal. The recognition of relative damping Г'e of s electrons plays a substantial role in this case. A general analysis that has made it possible to propose, for the first time, an analytical formula for critical size DcГ'e of austenite grains is used to interpret the results for chromium–nickel steels, in which the transformation is initiated by strong magnetic fields. Under conditions of positive bulk magnetostriction, a magnetic field with intensity H lowers the chemical potential of electrons. As a result, the Dc(Г'e, H) value decreases and austenite with a grain diameter of D, which was stabilized by condition D < Dc(Г'e, 0) in the absence of a field, becomes destabilized, since inequality D > Dc(D > DcГ'e, H)) is fulfilled. The dynamic theory predicts a sharp increase in the DcГ'e, 0) value at Г'e → 1. This is evidenced by value DcГ'e≥ 1 mm for steel 67Kh2N22, which is three orders of magnitude larger than Dc(Г'e0) ≈ 1 μm for the Fe–31Ni alloy. Other peculiarities of the effect of magnetic field on the martensitic transformation are also discussed. © 2021, Pleiades Publishing, Ltd.