抄録
The high purity cast irons containing 4.3% of carbon and some arsenic were quenched into water to interrupt the solidification process at various predetermined temperatures in the solidification interval, and the graphite nodule number and the fraction of solid in eutectic were determined microscopically. Electron probe microanalysis and X-ray microdiffraction were carried out to determine the distribution of arsenic.
By the addition of arsenic, aggregated graphite formed at the first stage, quasi-spheroidal and vermicular graphite at the middle stage and thread-like graphite at the final stage of eutectic solidification. There was an enrichment of arsenic in the liquid in front of the austenite-liquid interface during solidification, which resulted in the formation of various types of degenerated graphite. By increasing arsenic, the arsenic-rich phase with high contents of iron and arsenic formed and α-Fe, Fe3C, Fe2As were observed in this phase, and then it was considered that this phase resulting from the arsenic segregation was the ternary eutectic α-Fe, Fe3C and Fe2As which solidified at about 800°C after binary eutectic solidification. In terms of the previously reported classification of the inhibitory behavior of the harmful elements in the spheroidization of graphite, i. e., Mg-consuming type, boundary concentrating type and mixed type, arsenic should be classified into the boundary concentrating type.
