Physical and Technical Institute of the National Academy of Sciences of Belarus, Minsk, Republic of Belarus:

A. I. Pokrovsky, Cand. Eng., Associate Professor, Head of the Laboratory of High Pressures and Special Alloys, e-mail: arturu@tut.by

It is shown that nucleation and growth of a spherical graphite inclusion during solidification of a cast iron is a rather complex and multistage process, and it can be described by several simultaneously acting mechanisms. In this paper, the mechanism of nucleation on oxide inclusions and the adsorption mechanism are considered to be preferable. Metallographic evidences of the polycrystalline structure of a spherical graphite inclusion, which consists of prisms with a base close to a hexagon, and of the layer-by-layer growth of flakes in the radial direction are presented. Mathematical modeling has revealed a number of important technological parameters, including the dependence of the diffusion growth rate of a spherical graphite inclusion in ductile cast iron on the crystallization time. A hypothesis has been put forward that graphite inclusions in the cast iron undergo plastic deformation during hot forming without any traces of destruction into segments or turning into powder. The hypothesis is experimentally confirmed by electrolytic etching of the metal matrix and studying the "bare" surface of inclusions, both in the as-cast and in deformed iron. A mechanism of plastic deformation of spherical graphite inclusions in a metal matrix is proposed. It consists in sliding of prismatic sectors (blocks) of the graphite relative to each other and wedging out of the central ones. The deformation process is very short, it lasts about 1 second. After completion of the deformation, interatomic bonds are recovered along the shortest interatomic distances.
The work was carried out at the Physical and Technical Institute of the National Academy of Sciences of Belarus (Minsk) within the framework of the State Scientific Research Institute "Electromagnetic Technologies", task No. 3.3.3.

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