Abstract
Continuous improvement in the quality of castings is especially important since a cast without defects is a more competitive product due to its longer lifecycle and cheaper operation. Producing quality castings requires comprehensive knowledge of their production, crystallization process, and chemical composition. The crystallization of alloyed ductile iron (without the addition of magnesium) with oxide bifilm inclusions is discussed. These inclusions reduce the quality of the castings, but they are a catalyst for the growth of spheroidal graphite that crystallizes in their vicinity. The research was carried out for cast iron with a highly hyper-eutectic composition. Scanning electron microscopy and EDS analysis were used in the research. A detailed analysis of the chemical composition was also carried out based on the spectrometric method, weight method, etc. Based on the obtained results, a model of spheroidal graphite crystallization near bifilm inclusions was proposed. The surface of the analyzed graphite particles was smooth, which suggests a primary crystallization process. The phenomenon of simple graphite and bifilm segregation towards the heat center of the castings was also documented.
Highlights
Foundry engineering processes are prone to many issues during casting manufacturing that may influence the final casting quality
Gyarmati et al [2] explained that the bifilm content in the melt is much more important than the dissolved gas content such as hydrogen, which has always been considered to be the major source of defects. They proved that with proper degassing, bifilm inclusions can be eliminated from the melt, and regardless of the hydrogen content, aluminium castings without defects can be manufactured
This hypothesis was indirectly supported by a large number of spheroidal graphite precipitates in the presence of bifilms
Summary
Foundry engineering processes are prone to many issues during casting manufacturing that may influence the final casting quality. As one of the researchers explains [5], according to this theory, turbulence during the pouring generates defects inside the alloy as air bubbles and oxide films form on the surface of the liquid metal. They proved that with proper degassing, bifilm inclusions can be eliminated from the melt, and regardless of the hydrogen content, aluminium castings without defects can be manufactured.
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