INFLUENCE OF CALCIUM-STRONTIUM CARBONATE AND COOLING CONDITIONS DURING SOLIDIFICATION ON STRUCTURE AND PROPERTIES OF COMPLEX-ALLOYED WHITE CAST IRONS OF Fe–C–Cr–Mn–Ni–Ti–Al–Nb SYSTEM

Abstract

Under severe operating conditions, such as aggressive abrasives, high temperatures and harmful working environments, machine and equipment parts are favoured that are made mainly of white cast irons. The structure and the amount of carbide phase in these cast irons influence their mechanical properties and their ability to resist wear at elevated temperatures. White cast irons owe their particular wear resistance to the high content of primary MC carbides and eutectic carbides such as M7C3 in the mat¬rix, which is mainly composed of austenite or austenite and ferrite. There is a wide variety of technological methods that are designed to improve the special characteristics of cast irons, centred mainly on improving the structure of the materials. The most effective methods for improving the mechanical and special properties of foundry alloys are refining and complex modification. The heat resistance of cast iron is improved as a result of removal of harmful impurities from the melt and formation of refractory inclusions such as SrO and avail-able MgO, Al2O3, SiO2 in carbonate. These inclusions serve as crystallisation centres, which leads to melt supercooling and structure refinement. The modifying effect of carbonate is due to the formation of SrO oxide, these inclusions act as modifiers of the second kind. When cast iron is heated, an oxide film of stron-tium chromate (SrCrO4) is formed on the surface of castings, which has a higher density and better adhe-sion to the metal base than spinel oxide (FeO·Cr2O3). This results in better resistance to scale formation.