STUDY ON THE PRODUCTION CONTROL AND SOLIDIFICATION PROCESS OF COMPACTED/VERMICULAR GRAPHITE CAST IRON.

摘要

This research was conducted to investigate (1) the production of compacted (vermicular) graphite cast iron for application in ingot molds, (2) structure control of rare earth treated compacted graphite cast iron, and (3) the analysis of the solidification process of compacted graphite iron.; Charge materials from various sources were used to produce compacted graphite iron in heavy section castings. Only modest modification of charge composition was conducted as would be practical and possible in a plant producing ingot molds. Variables involved to study the effects on graphite formation, matrix structure and tensile properties include silicon content, manganese content, sulfur level, treatment temperature and cooling rate.; The desirable structure can only be achieved by through control during production process. Metallographic examination of casting sections has been performed to evaluate the effects of post inoculation, iron chemistry, holding temperature and casting section size. In addition, the influence of inoculation amount and procedure, and the interaction between the fading of rare earth addition and post inoculant on the microstructure and chilling tendency were investigated over the holding period. The relationship between the cooling curve and graphite structure was also discussed.; The study of the solidification of cast iron with compacted graphite was conducted by the analysis of samples produced by rapidly quenching from successive stages during the solidification process.; It was determined that graphite precipitates in a spheroidal shape which degenerates early in the austenite-graphite eutectic transformation, and subsequently develops into compacted graphite. Detailed observation of the graphite morphology with the aid of the scanning electron microscope varified that degeneration of small graphite nodules occurs by the extension of several graphite segments out of the graphite spherical surface. These segments grow in contact with the melt and diverge further as growth proceeds, resulting in an interconnected cell. This growth sequence of compacted graphite was further confirmed by considering the relative changes in graphite nodule count and the number of compacted graphite particles upon solidification. Based on the information obtained, the role of spheroidizing agent, post inoculant, and the C.G. iron cooling curve which is characterized by a substantial undercooling and recalescence phenomenon were thereby described.