对稀土镁球铁件反白口和白亮点缺陷的认识

An Understanding of Reverse Chill and Bright Spots in RE-Mg Nodular Iron Castings

铸态稀土镁球铁铸件热节或最后凝固部位有时会出现渗碳体,因而被称为“反白口”。其原因主要是化学成分偏析及结晶速度大于扩散速度所致。为避免这种缺陷,要求铸件壁厚均匀,还应控制铁液的碳、硅量及球化剂含量,以及适当提高浇注温度。有时,球铁件某些部位还会出现一些高硬度的白亮点缺陷,通常是由于铁液温度低,孕育剂未能充分熔解扩散所致,为此必须采取相应措施。

Sometimes, cementite could be found in the hot spots or the last solidifying location of the RE-Mg nodular iron castings. Therefore, this type of defect is called as “reverse chill”, which caused normally by chemical composition segregation and by that crystallization speed is faster than diffusion speed. In order to avoid this type of defect, it is necessary to reduce thickness difference of castings, control carbon, silicon, and nodularizing elements contents, as well as increase properly~ pouring temperature. Sometimes, bright spots, the another type of defect with castings, which usually are the result countermeasures must be adopted. high hardness, maybe appeared also of the inoculant being not thoroughly in some locations of nodular iron melted and diffused, so relevant