Containerless solidification of low alloyed commercial grey cast iron in two different cooling media (N2 and He) using a 6.5 m high vacuum drop-tube have been investigated. Both the conventionally cooled, as-cast alloy and the rapidly cooled drop-tube samples were characterized using SEM, XRD and Vickers microhardness apparatus. The estimated range of cooling rates are 200 K s−1 to 16,000 K s−1 for N2 cooled droplets and 700 K s−1 to 80,000 K s−1 for He cooled droplets (in each case for 850 μm and 38 μm diameter droplets respectively). Microstructural analysis reveals that the as-received bulk sample displayed a graphitic structure while the rapidly cooled samples display decreasing amounts of α-Fe as the cooling rate increases. At moderate cooling rates α is replaced with γ and Fe3C, while at higher cooling rates with α′. Microhardness increase with cooling rate but cannot be mapped uniquely onto cooling rate, suggesting undercooling also influences the mechanical properties.
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机译：已经研究了使用6.5 m高真空下降管在两种不同的冷却介质（N2和He）中对低合金灰铸铁进行无容器凝固的方法。使用SEM，XRD和维氏显微硬度仪对常规冷却的铸态合金和快速冷却的滴管样品进行了表征。对于N2冷却的液滴，冷却速率的估计范围为200 K s-1至16,000 K s-1，对于He冷却的液滴，冷却速率的估计范围为700 K s-1至80,000 K s-1（在每种情况下，直径为850μm和38μm的液滴分别）。显微组织分析表明，随着冷却速度的增加，刚接收的大块样品显示出石墨结构，而快速冷却的样品显示出减少的α-Fe含量。在中等冷却速率下，用γ和Fe3C代替α，而在较高冷却速率下，用α'代替。显微硬度随冷却速率的增加而增加，但不能唯一地映射到冷却速率上，这表明过冷也会影响机械性能。
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