The oxidation of heat-resistant castings during operation mainly refers to the oxidation caused by oxidizing gas along the graphite edge and crack infiltration into the cast iron and the volume expansion of castings caused by graphitization due to the decomposition of Fe3C. Adding Al, Si and Cr into cast iron, a dense oxide film such as SiO2,Al2O3,CrO3 can be formed on the surface of cast iron, which can obviously improve the oxidation resistance of cast iron at high temperature, and at the same time, it can make the matrix of cast iron become single-phase ferrite.
The silicon and aluminum of heat-resistant castings can increase the phase transition point, so that the solid phase transition does not occur at the working temperature, which can reduce the volume change and microcracks. Chromium can form stable carbides and improve the thermal stability of cast iron. Commonly used heat resistant cast iron are medium silicon cast iron, high chromium cast iron, nickel chromium silicon cast iron and so on, mainly used in the manufacture of furnace accessories, such as furnace bottom plate, chain feeding components, heat exchanger and so on.
The sheet graphite in heat-resistant castings is serious in splitting the matrix, which easily causes stress concentration at the tip of graphite. The tensile strength, ductility and toughness of gray cast iron are much lower than that of steel, but the compressive strength of gray cast iron is equal to that of steel. It is also the worst cast iron with mechanical properties in common cast iron parts. The mechanical properties of heat-resistant castings are related to the microstructure of matrix and the morphology of graphite. Strict technical requirements, with advanced automatic inspection equipment, a good guarantee of product quality.www.wuxiorient.com