轮船锚机球墨铸铁柱塞套开裂原因分析

摘要

The physical and chemical testing and failure reason analysis were done to the fractured ductile iron sleeve of a ship anchor machine.The results show that both the coarse grain of the casting because of the high casting temperature of the liquid iron and the long sealing time,and the more porosity and pore defects because of the liquid iron not feeding in time when solidification,significantly reduced the strength and increased the brittleness of the casting.The strong impact of shot peening treatment make micro cracks produce on the workpiece surface, which brought great cracking possibility to the workpiece.The brittleness of the ferrite at subsurface layer of the workpiece was high due to the high silicon content,which further increased the cracking tendency of the workpiece. Under the high pressure of inner cavity of the sleeve,the multiple step crack sources were generated at the weak positions of the upper cover edge,and the crack continued to expand to the whole upper cover.%对某开裂失效的轮船锚机球墨铸铁柱塞套进行了理化检验和失效原因分析。结果表明：由于铁液的浇铸温度偏高，封箱时间过长，导致铸件晶粒粗大，同时铁液凝固时补缩不及时，造成较多的疏松和孔洞缺陷，因而显著降低了铸件的强度，增加了脆性；喷丸处理时极强的冲击力使工件表层留下较多的微裂纹，给工件使用开裂带来极大的隐患；工件次表层的铁素体层，因硅含量高脆性大，进一步增加了工件脆性开裂的倾向。在柱塞套内腔的高压作用下，首先沿上盖边缘强度较为薄弱的部位产生多台阶裂纹源，裂纹不断扩展直至整个上盖掀起开裂。