Diffusion crushing of graphite in integrated cast iron processing

Abstract

Purpose. It is necessary to investigate the possibility of crushing graphite inclusions in cast irons. The aim of the work was to study structural changes in graphite under explosive action followed by thermal cycling treatment of gray cast iron. Methods. Gray cast irons were subjected to explosive action (pressure is 90 GPa, the deformation rate is 100 s^-1, the time is 10^-6...10^-7 s). Then the cast irons were subjected to thermal cycling: 950 °C, holding for 20 min, cooling with a furnace; 5 cycles. Metalographic ("Neophot-21"), micro-X-ray spectral
("Nanolab-7"), X-ray diffraction (DRON-2.0) research methods were used. Results. The features of diffusion crushing of graphite in cast irons with different types of metal matrix (ferritic, austenitic) and graphite shape (lamellar, spherical) have been studied. The features of structural changes in the cast iron matrix under explosive action, which determine the conditions for the transformation of graphite during subsequent thermal cycling, are discussed. It is shown that this process of diffusional crushing of graphite can be accompanied by local melting, which leads to the formation of regularly distributed dispersed particles of graphite. Scientific novelty. From the point of view of physical mesomechanics of plastic deformation, the processes of structural changes in the metal matrix of cast irons are considered. It is shown that nonequilibrium defect substructures of the cast iron matrix obtained during the explosion determine the features of diffusion crushing of graphite inclusions during subsequent thermal cycling. The conditions for diffusion crushing of graphite with reflow and in the solid-phase state have been established. Practical significance.  It has been established that the complex processing of “explosive loading + thermal cycling” promotes crushing of coarse graphite inclusions, which is favorable for the mechanical and operational properties of cast irons. The use of the results obtained will make it possible to develop technologies for complex processing with regulated parameters of graphite inclusions, which will lead to an expansion of the field of application of gray cast irons.

Keywords: cast iron; shock wave treatment; graphite; thermal cycling; stress relaxation