Abstract
Despite the many investigations on the effects of various elements on the formation of spheroidal graphite in cast iron there are only a few studies that report when and how these elements have harmful influences on the spheroidal graphite formation. In order to clarify these problems, experiments were conducted to study the inhibitory effects of tin on the formation of spheroidal graphite.
The base material, composed of electrolytic iron and electrode graphite, was melted in a high frequency induction furance and cast into iron mold. Fifty gram of this alloy with a carbon content of 4.35% was placed in a fused silica crucible and melted in a resistance furnace. Graduated levels of tin, up to 3.0%, were added to the melt. At 1,350°C the melt was treated with Fe-Si-Mg (21.4%) alloy and cooled while the cooling curve was plotted. At various predetermined temperature the specimen was quenched in ice water to interrupt the solidification process and the graphite nodule number and the amount of solidified part in eutectic were observed microscopically. Electron probe microanalysis and X-ray micro-diffraction were also carried out to determine the distribution of tin.
By the addition of tin, quasi-spheroidal graphite formed at the middle stage of eutectic solidification and thread-like graphite at the final stage. There is an enrichment of tin in the liquid ahead of austenite-lipuid interface during solidification and, therefore, a tin-rich phase results at the austenite boundary at the end of eutectic solidification. The tin-rich phase was determined as FeSn2 by means of X-ray micro-diffraction. According to the previously reported classification of the inhibitory behavior of the elements in the spheroidization of graphite, i.e. sulpher type, titanium type and lead type, tin will be classified with the titanium type.
