Failure analysis of large melt pump chamber cracking

摘要

The failure reasons of mult pump blank were exploreed by means of chemical compostion and mechanical properties test,metallurgraphic examination and fracture analysis.The experiment results reveal that cracks on the pump blank exhibit the characteristics of large stress and multiple cracking sources,coincident with the point of delayed cracking on precipitation hardening stainless steel 0Cr17Ni4Cu4Nb after solid solution treatment.Cracking results from both heat treatment,weld and structure defect.Low impact toughness and ductility,high notch sensitivity of the pump blank meterial are the primary factors of cracking,causced by the higher content of δ-ferrite with network and strip distribution,as well as other microstructure defect.Larger sizes,improper welding,forging and heat treatment are other important factors of cracking,which result in an over large internal structural stress and thermal stress.%本文通过对失效开裂熔融泵材料的化学成分、力学性能测试,以及对泵体、裂纹附近的金相组织和裂纹面的扫描电镜分析,研究了泵体开裂的主要原因.结果表明,熔融泵在精加工前出现的泵体裂纹呈现大应力、多裂纹源特点,其主要特征与0Cr17Ni4Cu4Nb沉淀硬化型不锈钢固溶处理后延迟开裂相吻合.泵体裂纹是热处理制度、焊接、材料组织缺陷等多因素共同作用的结果.其中,材料微观组织中δ铁素体含量偏高、呈带状和网状分布、以及其他组织缺陷造成材料塑性、冲击韧性显著下降、缺口敏感性增大,是造成泵体裂纹的内部原因;而泵体尺寸过大、锻造和热处理不当,使得在固溶、时效热处理过程中产生的组织应力过大,以及流道堵头焊接过程中是引入的热应力和组织缺陷是泵体裂纹的外部原因.