高純度白鋳鉄の黒鉛化に及ぼす焼鈍サイクルの影響

抄録

  The first stage graphitization time of white cast iron varies with the holding temperature. The difference of the holding temperature signifies the difference in the ratio of cementite and austenite in the white iron at the temperature before annealing. Therefore, the different ratio suggests the transformation of the rate controlling step in the graphitization reaction. This step, which may be solution of cementite or diffusion of carbon, iron or silicon, is thought to affect the formation of the temper carbon. The authors have already suggested a new classification of five types of temper carbon, which are spheroidal, compact, aggregated, snow-flaky and fine by controlled solidification and graphitization of pure white cast iron. The present investigation is conducted to find the precipitation condition of various types of temper carbon with the different annealing cycle of graphitization. The concept of “the stability of an austenite shell”, which means that austenite affects the growth of graphite nucleus, is introduced to explain the various types of temper carbon and the rate controlling step of graphitization reaction.