Precipitation behavior of α-solid solutions of the Fe-Sn system

Abstract

The solubility limit for tin in a-iron was established from lattice parameters determined by X-ray measurements. The precipitation processes in α-Fe-Sn solid solutions are of both continuous and discontinuous types. The discontinuous precipitation cells form at grain boundaries, subgrain boundaries, and in the matrix. They contain no lamellae, but rather either crystallographically oriented, ordered, needle-shaped particles or a mass of irregular precipitated particles. The linear growth law and the results of X-ray diffraction studies confirm the discontinuous character. The activation energy of the process lies in the range of that for volume diffusion of substitutional elements in a-iron. The application of the Zener equation yields effective diffusion coefficients which lie in the range of the bulk diffusion coefficients. A dislocation mechanism is evidently responsible for the autocatalytic growth of the discontinuous precipitation in α-Fe-Sn alloys. At high annealing temperatures a continuous precipitation process sets in at grain and subgrain boundaries and in the grains themselves.