Regularities of Martensitic Transformations of Fe–Ni Alloys Rapidly Quenched from Melt

Abstract

The regularities of formation of the grain structure of metastable iron–nickel alloys formed in conditions of high temperature gradients during the melt hardening (spinning) and its effect on the characteristics of martensitic transformations (MT) in local areas of thin ribbons are reviewed and studied. A comparison of the texture of the austenitic and martensitic phases on different sides of thin ribbons is carried out. The consequences of influence of relaxation processes in hardening of thin ribbons on regularities of formation of the grain structure are investigated. The proposed x-ray method of measuring the amount of martensite allows solving the problem of measuring the amount of martensite in the local areas of textured alloys. As established, the completeness of MT is different for the contact and free sides of the ribbon. The main factors, which determine the heterogeneous distribution of the martensitic phase in the local areas of the ribbon, are analysed. The size effects at MP, residual stresses, and changes in the chemical composition of the austenitic phase on the distribution of the martensitic phase in local sections of the ribbon are analysed. The influence of size effect on the direct γ–α- and reverse α–γ-MT in thin ribbons is studied. The role of ultradispersed component of austenitic grains in the stabilization of austenite of rapidly quenched alloys with cyclic γ–α–γ MT is revealed.

Keywords

• martensitic transformations
• fe–ni alloys
• melt spinning
• ribbon
• grain structure
• texture
• stresses