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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 10~6℃/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 Fe_3C 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 Fe_3C 的形成,且Fe_3C 比石墨更稳定;低于 T_k 时则 Fe_3C 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 Fe_3C 的分解而提供的碳也起很大作用。
In the past literature, some believe that eutectic graphite is directly precipitated and grown from liquid molten iron. In this paper, through thermodynamic analysis and eutectic hot metal, the samples prepared under high-speed cooling conditions of 10 ~ 6 ℃ / s were analyzed by X-ray and electron diffraction to get the conclusion different from the above conclusion. On the one hand, when the degree of superheat is not high, the free state of short graphite exists in the eutectic liquid molten iron; on the other hand, the decomposition of Fe_3C is also important during the crystallization of graphite (ie, the indirect graphitization ),Can not be ignored. Higher than the critical temperature T_k, is conducive to the formation of Fe_3C, and Fe_3C is more stable than graphite; below T_k Fe_3C unstable, spontaneous decomposition of Fe and C tend to. T_K is greatly affected by the chemical composition. It is believed that the free graphite short procedure is, of course, the core of graphite crystallization. However, the carbon provided by the decomposition of Fe_3C also plays a significant role in the growth of graphite.