New Concepts and Characterization of Gradient Castings Composed by low Alloyed White Cast Iron and Spheroidal Graphite Cast Iron

Abstract

This work deals with the problem of casting production regarding composed castings for rolls, also called gradient castings. The technology of production is a combination of the horizontal centrifugal casting of alloyed white cast iron (two sequences) and gravity casting of cores which occurs in third sequence. From the industrial casting, the systematic sampling for different investigation methods was done. The following examination methods were used: chemical analyses, thermodynamic calculation of equilibrium phases by TCW and Computerm programs, dilatometry in the solid state, calculation of density for extracted microstructural components by program TAPP 2.2, linear hardness measurements, determination of mechanical properties at room temperature and higher temperatures, optical and electron microscopy, FEM calculation of casting processes for all three sequences of casting. The working layer of the roll is made from chromium alloyed white cast iron. The core is made of spheroidal graphite cast iron (SGI). The main focus was on the intermediate layer, which is made from flake graphite cast iron. Microstructural constituents were determined quantitatively and qualitatively. Centrifugal casting is a highly complex process. With the help of the mentioned programs, the calculation of density was done for each microstructural constituent. It was discovered that austenite and M7C3 types of carbides have a difference in densities of approximately 0.3kg/dm3 which influences the distribution of microstructural constituents in the roll cross-section due to centrifugal forces. The internal stresses in the casting were also calculated and measured. The explanations of the influences of inhomogeneous carbide distribution in the first and second layers, and the influence of core made by SGI on the mechanical properties of the casting were also made, together with internal stress.