球铁铸件断口灰斑分析

QT700铸态球铁凸轮轴断口出现灰斑,扫描电镜观察发现灰斑区石墨球数量和w(C)量明显高于银色区,但金相组织观察显示,黑斑区球化情况良好,无组织缺陷。断口扫描电镜确定灰斑区断口为韧性断裂,银色区断口为解理或准解理脆性断裂。断口灰斑再现试验证明,球铁铸件断口上的灰斑说明该区域是韧性断裂区域,并非组织异常,也并非是铸造缺陷。

Analysis of Gray Spot in Fracture of Nodular Iron Casting

There was gray spot appearing in the fracture of QT 700-2 grade as-cast nodular iron camshaft and SEM observation revealed that the nodule count and w（C ） in the gray spot area was obviously higher than the silver area. However, the metallographical observation showed that the nodnlarity of the gray area was all fight and no structure defect was found. Based on the SEM analysis inspection, it was considered that the fracture of the gray area was of the tough fracture, and the fracture of the silver area was of the cleavage or quasi-cleavage fracture. By the gray spot reappearing test, it was testified that gray spot appearing in the fracture of the nodular iron casting only indicated that the area is of the tough fracture area, but not the abnormal structure area, and also not casting defects.