球铁件皮下气孔形成机理的研究

摘要

The subcutaneous blowhole is one of defects in nodular cast iron, and its formation mechanism has no final conclusion in the area of foundry technology. Because non-metallic inclusion always transfers in metal liquid together with bubbles, we believe that determinations of magnesium in different inner parts of a casting will be helpful in analyzing the motion paths of bubbles migration. The testing results have shown that the magnesium content gradually increases from the surface to the center of the casting, and the oxide film has shown enrichment of magnesium and sulfur. Our study shows that the oxide films hinder the bubbles to transfer outward and those stranded bubbles form subcutaneous blowholes. Increasing of carbon equivalent will raise the graphitization expansion property, and in the meanwhile accelerate the bubbles transfer, so, the subcutaneous blowholes will be avoided.%皮下气孔是球铁件常见的铸造缺陷之一，其形成机理至今说法不一．既然非金属夹杂物伴随气泡一并迁移，那么，检测铸件各部位的镁含量势必能够追踪到气泡的迁移路径，从而能够对其运动过程作出分析．检测结果表明，铸件内部的镁含量由外而内呈梯度增加，铸件表面的氧化皮中富含镁元素．研究表明，皮下气孔由不能外逸的气泡形成，其外逸阻力来自于已经凝固的氧化膜，提高碳当量有助于增强石墨化膨胀能力，从而存氧化结膜前将气泡尽快挤出金属液，避免皮下气孔的产生．