Quantitative Change of Nitrogen States in Melting Process for Permanent Mold Casting of Spheroidal Graphite Iron

In former studied, authors have already succeeded to get chill-free spheroidal graphite iron castings of φ35 × t5.4 mm indicator sample and automobile knuckle, using permanent mold in as-cast condition. The process of melting, molten treatment and pouring were theoretically designed considering both the reduction and increase of free nitrogen (NF), but it was not analytically proved by actual data yet. In this study, the amount of NF was analyzed using chill samples, which were taken at critical points like melting and molten treatment. As the results, the processes which reduce and increase NF were made clear. The increasing NF was occurred on the process during heating up, carbon addition and temperature slightly increased at near the TEC. The decreasing NF was occurred the process of alloy addition, during super-heating and temperature decreased at under the TEC. Furthermore, as the amount of molten metal decarburization increased, the variation of NF changed from adsorption to denitrification.