砂型鋳物及び連続鋳造材を素材としたオーステンパ球状黒鉛鋳鉄の切削性

抄録

  In this study, the machinability of austempered spheroidal graphite cast iron made by different casting methods was investigated. Spheroidal graphite cast iron samples made by sand mold casting and continuous casting, respectively ADI-S and ADI-C, were used. From the results of cutting tests, the machinability of ADI-C was always excellent compared with that of ADI-S at cutting speeds from 100 to 365m/min. The feed and thrust forces of ADI-S were higher than those of ADI-C at high cutting speeds, although their cutting resistance was almost the same at low cutting speeds. In addition, the microstructure of ADI-S chips was found to be greatly deformed near the chip-tool interface for ADI-S compared with ADI-C. It has been reported that there always exists retained austenite in austempered spheroidal graphite cast iron, and that the retained austenite transforms to deformation-induced martensite on the machined surface when the austempered spheroidal graphite cast iron is machined. From the results of the comparative analysis of ADI-S and ADI-C, the average relative volume ratio of retained austenite increased with increasing cutting speed for both ADI-S and ADI-C, and was about double in the case of ADI-S at high cutting speeds such as 365m/min. From these results, it is clear that the retained austenite in both ADI-S and ADI-C does not transform to deformation-induced martensite at high cutting speeds, and that ADI-C can be machined at cutting temperatures and with cutting resistances lower than those necessary for ADI-S, suggesting that the machinability of ADI-C is better than ADI-S.