INFLUENCE OF THE CHEMICAL COMPOSITION OF HIGH-CHROMIUM CAST IRON ON THE CONTENT OF CHROMIUM IN NEAR-CARBIDE ZONES AFTER ANNEALING AT 720 °С

Abstract

Purpose. Increasing the corrosion resistance of wear-resistant high-chromium materials operating in a liquid abrasive environment makes it possible to increase the service life of products made from these materials, which is an important task in materials science. One of the main reasons for the occurrence of damage during corrosion processes is the uneven distribution of chromium in the metal base, which leads to the formation of microgalvanic pairs on the surfaces of parts in an electrolytic environment. The creation alloys of wear-resistant high-chromium, in the metal base of which microgalvanic vapors are not formed, is a promising direction for increasing the corrosion resistance of such materials. Investigation of chromium distribution processes after heat treatment parts of high-chromium cast iron, namely the formation of metal base zones near carbides.
 Research methods. Analytical review of publications. Metallographic, microstructural and local X-ray microanalysis. Mathematical modeling of processes.
 Results. It was revealed that during the heat treatment in high-chromium cast irons, structures with significant segregation of chromium are formed. It has been established that after annealing of castings at 720 °C, the minimum chromium content in the metal base is observed in the zones near carbides, and the maximum in the central zones of the graids. The presence zones with a chromium content of more than 12 % (positive potential) and less than 12 % (negative potential) leads to the formation of microgalvanic couples, which is the main reason for the acceleration of corrosion damage in the metal base. The dependence of the chromium content in the zones near the carbides after annealing at 720 °C on the chemical composition of cast iron has been determined.
 Scientific novelty. The mathematical model is proposed for determining the chromium content in the zones near carbides after annealing at 720 °C with an exposure of 9 hours from the chemical composition of cast iron in the Fe-C-Cr-Mn-Ni system. This makes it possible to predict the chromium content in the zones near the carbides and prevent the formation of microgalvanic pairs.
 Practical value. The dependence (mathematical model) obtained can be used in the development of compositions of high-chromium wear-resistant cast irons with increased corrosion resistance and machinability.