Influence of charging raw materials on spheroidal graphite cast iron properties

摘要

The influence of different charging raw materials on strength and plastic properties of spheroidal graphite cast iron in the thermally untreated state was studied. Charging raw materials (pig irons, sorelmetal, an steel scrap) were chosen with the aim of achieving the Mn and Cr content in the made cast iron as low as possible. The Mn and Cr content depended on the charge composition. The highest Mn contents were found out in melts made from steel scrap. The Mn and Cr content influenced especially the plastic properties of ferritic cast irons. The determined dependence between plastic and strength characteristics was statistically impact. With regard to this dependence in could be stated that the charge composition under the studied conditions had no influence on the studied cast iron properties. The size of graphite and of eutectic cells was influenced by the double step inoculation. As expected the decrease of eutectic cells has led to the reduction of the ferrite content in structure. For pearlitic cast irons the charge composition remained the same and the pearlitic structure was achieved with Cu and Sn addition. No influence of the charge composition on the studied properties was also found out in pearlitic cast irons. Fatigue properties in the thermally untreated state for chosen melts were studied and they were compared with results of fatigue tests in the thermally treated state. In the second part of the contribution the model of kinetics of spheroidal graphite growth up to temperature at which the ferrite becomes to separate around graphite is used. The model was used for explaining the influence of chemical composition and inoculation on segregation of chosen elements. The segregation of carbide forming elements towards the cell periphery leads to the pearlite formation in the ferritic matrix.