Improvement of Mechanical Properties of Mn Containing Spheroidal Graphite Cast Iron by Molten Metal Treatment

Recently, automobile manufacturers adopt high tensile steel for car body production to reduce weight and enhance safety. The manganese (Mn) content in steel scrap however increases as more high tensile steel plates are used. Mn is known as a graphite inhibitor in cast iron, an element that especially decreases the elongation of spheroidal graphite cast iron. Therefore, either diluting the Mn percentage or removing the Mn in the steel sheet scrap is required for using high Mn steel sheet scraps in spheroidal graphite cast iron. In this study, for the purpose of increasing high Mn steel scrap recycling efficiency, the method of manufacturing spheroidal graphite cast iron without removing Mn from high Mn steel scrap was examined. It was found that the elongation of the spheroidal graphite cast iron can be increased by adding rare earth element before spheroidizing treatment and adding Fe-Si-Ca-Ba alloy together with spheroidizing treatment. These results show that spheroidal graphite cast iron with no more than 1.0%Mn complying with JIS (FCD450-10) standards by adding the rare earth element or Fe-Si-Ca-Ba alloy can be produced. It was also clarified that high Mn steel scrap can be recycled.