STRUCTURE PECULIARITIES OF MARTENSITE, FORMED BY THE EFFECT OF MAGNETIC FIELD

Structural changes in alpha-martensite forming by the action of a magnetic field have been investigated for high-nickel steel which remains in an austenitic state even when subjected to very low temperatures. It is shown that the thin plate martensite produced by exposure to a pulsed magnetic field becomes lenticular in the course of subsequent isothermal soaking without application of a magnetic field. Electron microscope studies of the structure of martensite plates at different stages of their formation are also presented

Effect of a dc magnetic field on the isothermal martensitic transformation in the Fe-24%Ni-4%Mn alloy

Effects of a dc magnetic field on the isothermal martensitc transformation in the region of the kinetic maximum of the Fe-24%Ni-4%Mn alloy and on the martemsitic transformation at a liquid-helium temperature were studied. It was shown that a dc magnetic field markedly affects the isothermal martensitic transformation. In particular, it shifts the temperature range of the martensitic transformation and the kinetic maximum toward higher temperatures and initiates the nucleation of isothermal martensite crystals and their subsequent growth upon isothermal holding. A dc magnetic field of a sufficiently high strength causes the intense formation of athermal martensite at the liquid-helium temperature, at which no transformation develops without a magnetic field. A comparison of the effects of the pulse and dc magnetic fields on the martensitic transformation in the alloys with martensite transformation isothermal kinetics was carried out

The Observation of the Martensite-Like Shear Diffusionless α→γ Transformation in Carbon Steels with Pearlitic Structure

The structure of eutectoid carbon steel with the initially pearlitic structure was studied by transmission electron microscopy and electron diffraction after laser heating. It is shown that, under ultrarapid laser heating, the α-γ phase transformation can proceed by a shear-type diffusionless mechanism that results in the deformation of cementite platelets. The crystallographic characteristics of shear planes involved in the α-γ transformation are determined. Austenite formation was found to occur through the diffusionless shear mechanism, with orientation relationships close to those of Kurdjumov-Sachs

A kinetic model of lath martensite formation

A kinetic theory of martensite formation is developed for the case when isothermal transformation does not complete, which is conventionally explained in terms of the change in the state of $\gamma$ phase. The closest agreement with experiment is obtained when the Kaufman-Cohen theory modifie by Borgenstam and Hillert is used for the nucleation rate