提高大吨位厚大断面球墨铸铁球化率的探索

Exploration on improving the spheroidization rate of large-tonnage thick and large section ductile iron

球墨铸铁中石墨绝大多数呈球团状,但随着球墨铸铁壁厚增加,凝固时间的延长,球化孕育的衰退,反球化微量元素的富集,石墨会出现:蠕虫状、开花状、碎块状、水草状等形态,铸件表层到心部石墨形态由球团状,逐渐变为团絮状、蠕虫状、开花状,碎块状等三明治现象。石墨的分布也会出现一些特殊规律,如:列队石墨球,偏聚石墨球,石墨球漂浮等。这些现象已严重影响了球墨铸铁厚大部位的球化率。我们采用合适的碳当量、铁水中加入0.005%的Sb,采用低稀土球化剂,使用高效、长效孕育等工艺方法,成功将500mm×500mm×500mm的试块心部球化率提高至Ⅵ+Ⅴ≥80%。

The majority of graphite in ductile iron is pelletized, but with the increase of wall thickness of ductile iron, the prolongation of solidification time, the decline of spheroidization, and the enrichment of anti-spheroidized trace elements, graphite will appear: worm-like, flowering, broken pieces, and water grass, etc. The shape of the graphite from the surface layer of the casting to the core has been gradually changed into a flocculent shape, a wormlike shape, a flowering shape, and broken pieces. There are some special rules for the distribution of graphite, such as: lined up graphite balls, segregated graphite balls, and graphite balls floating, etc. These phenomena have seriously affected the spheroidization rate of the thick parts of ductile iron. By use of a suitable carbon equivalent, adding 0.005% Sb in molten iron, and a low rare earth spheroidizing agent with high-efficiency & long-lasting gestation methods, the core spheroidization rate of 500mm×500mm×500mm sample and 200mm wall thickness castings has been increased from VI+V=30% to 50% to VI+V≥85%.