静置时间对蠕墨铸铁凝固参数与石墨衰退的影响

Effect of Holding Time on the Solidification Parameters and Graphite Degeneration of Compacted Graphite Cast Iron

研究了铁液静置时间(0～12 min)对蠕墨铸铁凝固曲线特征温度和蠕墨衰退的影响。结果表明:随着静置时间的延长,凝固曲线上初晶温度Tal和共晶最低点温度Teu逐渐升高,而共晶最高温度Ter变化不明显。静置0～2 min时,凝固出现明显的再辉现象,但静置6～12 min时,再辉现象不明显。随着静置时间的延长,铁液中的残留镁当量与硫元素之比MgE/S值将降低,石墨逐渐由蠕虫状转变为蠕虫状+片状石墨。当该比值在1.4～1.6的范围时,蠕化率能够达到80%以上,蠕墨衰退程度较小,当MgE/S值低于1.12时,蠕墨衰退显著。蠕墨衰退需要的成分条件一是石墨微区铁液中氧原子的富集,二是氧富集区域蠕化元素含量较少。

The solidification parameters and microstructure of compacted graphite cast iron, the melt of which was held for different time(0-12 min), were studied. The results show that with increasing the holding time,the initial crystallization temperature Tal on the solidification curve and the lowest eutectic temperature Teu gradually increase, and the maximum eutectic temperature Ter does not change notably. As the holding time is in the range of 0-2 min, the recalescence is obviously observed during the eutectic solidification of the cast iron, but it is unconspicuous when the holding time is in the range of 6-12 min. As the holding time is increased, the ratio of residual magnesium equivalent and sulfur element in the molten iron(MgE/S) will be reduced, the compacted graphite is gradually transformed to flake-shape graphite. When the value of MgE/S is within the range of 1.4-1.6, the compacted graphite reaches more than 80%; while the value of Mg E/S is lower than 1.12,the degeneration of compacted graphite will occurr. The graphite degeneration will appear in two conditions:one is oxygen atom enrichment near the graphite, and the other is a small amount of RE element concentration in the oxygen-enriched regions.