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ＭＣ碳化物、氧化物夹杂和显微疏松在单晶合金中是蠕变、疲劳裂纹的起源和扩展通道。为了减少ＭＣ碳化物、氧化物夹杂和显微疏松的危害，ＤＤ３合金规定：Ｃ≤０．０１０ｗｔ％，最好＜０．００６ｗｔ％，［Ｏ］≤０．００１０ｗｔ％，［Ｎ］≤０．００１２ｗｔ％。合金中脱碳、氧、氮、硫都是通过真空下的Ｃ－Ｏ沸腾反应来完成的。本文采用严格控制碳量和工艺技术的改进等措施，找到了获得Ｃ达６０ｐｐｍ，Ｓ达１０ｐｐｍ，Ｎ＿２达３ｐｐｍ，Ｏ＿２达５ｐｐｍ的ＤＤ３合金的真空感应熔炼的冶金原则。
MC carbides, oxide inclusions and microscopic looseness are the origins and expansion channels of creep, fatigue cracks in single crystal alloys. In order to reduce the hazards of MC carbides, oxide inclusions and microscopic looseness, the DD3 alloy states: C ≦ 0.010 wt%, preferably <0.006 wt%, [O] ≦ 0.0010 wt%, [N] ≦ 0. 0012wt%. Decarburization in the alloy, oxygen, nitrogen, sulfur are accomplished by the C-O boiling reaction under vacuum. In this paper, the metallurgical principles of vacuum induction melting of DD3 alloy with 60ppm of C, 10ppm of S, 3ppm of N2, and 5ppm of O_2 were found through the measures of strict control of carbon quantity and improvement of technology.