【摘要】 过去文献中,有的认为共晶石墨是从液态铁水中直接析出长大的。本文通过热力学分析和对共晶铁水,对以 10⁶℃/s 的高速冷却条件下制取的试样,进行X光、电子衍射等分析,得出不同于以上结论的看法。认为一方面当过热度不高时,在共晶态的液态铁水中虽已有游离态的石墨短程序存在;但另一方面在石墨结晶过程中 Fe₃C 的分解也是重要的,（即间接石墨化过程）,不容忽视。高于临界温度 T_k 时,有利于 Fe₃C 的形成,且Fe₃C 比石墨更稳定;低于 T_k 时则 Fe₃C 不稳定,有自发分解为 Fe 与C的倾向。T_K 受化学成份的影响很大。可以认为,游离的石墨短程序固然是石墨结晶的核心,但在石墨长大的过程中,由于 Fe₃C 的分解而提供的碳也起很大作用。更多还原

【Abstract】 A conclusion that eutectic graphite is directly segregated from molten iron and then grows has been made in some earlier works[2, 3, 4].This paper, differing from such a conclusion, puts forward a new idea on the subject of graphitization in cast iron through thermodynamic analysis and experiments by x-ray and electron diffractions for eutectic molten iron with a high cooling speed of about 106℃/sec. It is true that the short-sequence graphites exist in free state in eutectic molten iron at the lower superheating temperature. However, the decomposition of Fe3C also plays an important role under graphitization so that it may be considered as an indirect graphitization process, which should not be overlooked. Here the critical temperature Tk(℃) as a parameter dependent to a considerable degree on the chemical composition is introduced. It is favourable for the formation of Fe3G and also the Fe3C is more stable than the graphite in molten iron when the temperature exceeds Tk. If the temperature is below Tk, Fe3C will be in an unstable state and will tend to decompose into Fe and C spontaneously. An relatively all-sided conclusion is probably such that the short-sequence graphite in free state can nucleate graphites in cast iron; however, the carbons supplied by the decomposition of Fe3C also play a positive role for the growth of graphites.更多还原