Microstructure and Various High Temperature Properties in a Small Amounts of Aluminum Added High Silicon Spheroidal Graphite Cast Iron

The objective of this experiment is to increase the heat resistance of high Si spheroidal graphite cast iron (3.3%C-4%Si-0.6%Mo) which is used as turbine housing. It is known that when Al was added to the spheroidal graphite cast iron melt, nodularity and fluidity decreases, but heat resistance increases. This experiment thus aimed to demonstrate the effective utilization of Al. In samples added with a small amount of Al, microstructure was observed and mechanical properties and fluidity were measured. High temperature oxidation tests and high temperature tensile tests were also carried out. The high temperature oxidation results were used as measures of heat resistance. The results of the experiment showed that good heat resistant cast iron can be fabricated without decreasing the mechanical properties and fluidity. When the added Al was less than 0.3%, the nodularity was high and elongation of mechanical property did not decrease greatly. Al was distributed across the matrix structure. When the added Al was over 0.3%, the removal of sticking slag inside the ladle posed as a significant factor to resolve the difficulty of mass production. Therefore the optimum Al addition amount was considered as 0.2%. As operations such as melting, casting, sand molding etc. are carried out at the manufacturing site at our company, the experimental results are easy to apply to both the fabrication of the prototype and the practical products.