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用包钢1号稀土硅铁合金作球化剂处理过共晶铁水获得的稀土球墨铸铁,生产中常出现黑斑和黑点断口,严重降低材料的机械性能。我们研究了黑斑和黑点的形态。黑斑和黑点都是由不同程度球化或不同形状结晶的石墨所组成,其产生主要取于稀土硅铁的加入最与原铁水含硫量的比例关系.当RE_xO_y/S_原小于10,原铁水含碳量又偏高时出现甲类黑点,大于15,含碳又偏低,出现乙类黑点.只有RE_xO_y/S原严格控制在10—15时,才能获得全球化的稀土球铁。但是,这也正是容易出现黑斑的时候。试验统计表明,原铁水含碳过高是产生黑斑的必要条件;在高碳条件下,硅能大大促进黑斑形成。因此为避免黑斑断口出现,原铁水含碳量不应超过3.85%,碳当量不超过4.5%。此外,还进一步用同位素自射线照相研究了铈和硫在黑斑断口上的分布。
Rare earth nodular cast iron obtained by treating eutectic molten iron with Baotou No. 1 rare earth ferrosilicon alloy as nodulizer can often cause the appearance of dark spots and black spots in the production, severely reducing the mechanical properties of the material. We studied the morphology of dark spots and black spots. Black spots and black spots are composed of graphite with different degrees of spheroidization or different shapes, and the production mainly comes from the ratio of the addition of rare earth ferrosilicon to the sulfur content of the original hot metal. When the original RE_xO_y / S_ is less than 10 , The original hot metal high carbon content when the Class A black spots occur, more than 15, carbon and low, there are black spots Class B. Only RE_xO_y / S the original strict control at 10-15, in order to obtain global rare earth Ductile iron. However, this is also the time when dark spots easily appear. Experimental statistics show that the original high-carbon hot metal is a necessary condition for the production of dark spots; under high carbon conditions, silicon can greatly promote the formation of dark spots. Therefore, to prevent the appearance of dark spots, the original hot metal should not exceed 3.85% carbon content, carbon equivalent does not exceed 4.5%. In addition, isotope autoradiography was further used to investigate the distribution of cerium and sulfur on the rupture of dark spots.