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本文用模拟实验与生产性实验相结合的方法研究了轻、重烯土对大断面球墨铸铁中碎块形石墨形成的影响规律。结果表明:当稀土超过某临界量后,促使碎块形石墨产生,且稀土含量越高越严重。在实验条件下,轻稀土的临界含量约为0.006％左右,重稀土约为0.018％左右。用模拟试样液淬方法观察到碎块形石墨是在共晶凝固的中、后期从残余铁水中长出的,是一种晶间型共晶石墨。微区成份分析表明:稀土易在凝固前沿界面上富集,促使碎块形石墨产生。最后,文中提出了碎块形石墨的生长过程模型。
In this paper, the influence of light and heavy earth on the formation of broken graphite in large section ductile iron has been studied by a combination of simulation experiments and productive experiments. The results show that when the rare earth exceeds a certain critical amount, the crumb-shaped graphite is produced, and the higher the content of rare earth is, the more serious it is. Under the experimental conditions, the critical content of light rare earth is about 0.006%, about 0.018% heavy rare earth. The liquid quenching method with simulated samples was observed that the lump-shaped graphite is eutectic graphite grown in the residual molten iron in the middle and later stages of eutectic solidification. The analysis of the micro-zone composition shows that the rare earth is easily enriched on the interface of the solidification, leading to the generation of broken graphite. Finally, the model of the growth of chunk-shaped graphite is proposed.