基于失效分析的给水泵泵轴显微组织和力学性能对比研究

Comparative study of microstructure and mechanical properties of feed water pump shaft based on failure analysis

以9F燃机余热锅炉给水泵断裂泵轴和供货态17-4PH不锈钢为研究对象,分析了泵轴的失效机理,并通过化学成分分析、能谱分析、光学显微镜、扫描电镜、高分辨率透射电镜和力学性能试验对两种试样在合金元素含量、微观组织和力学性能上的差别进行了分析研究。断口扫描电镜分析表明,失效泵轴断面多处呈现起伏较大的扇形台阶分布,表明给水泵泵轴属典型的扭转应力所致的多源疲劳断裂;化学成分分析表明泵轴材质错用,合金元素Cu含量偏低4%、Ni含量偏低3%,不能有效析出各种合金强化相,造成宏观力学性能降低,是泵轴失效的主要原因。拉伸试验和布氏硬度对比分析结果表明,失效泵轴较供货态17-4PH试样抗拉强度、布氏硬度较分别低500MPa和150HBW左右。相比于失效泵轴,供货态合金组织中细小均匀的柱状马氏体结构和弥散分布的第二相是17-4PH合金沉淀强化的主要来源。

Based on the failed feed water pump shaft in HRSG(heat recovery steam generator)of 9F gas turbine and normal 17-4PH stainless steel,the fracture reasons were analyzed and the difference of alloying element content,microstructure and mechanical property between the failed pump shaft and normal 17-4PH steel were researched using chemical composition analysis,optical microscope,energy dispersive spectrometer(EDS),scanning electron microscopy(SEM),high resolution transmission electron microscope(HRTEM)and mechanical property test.SEM analysis of fracture showed that large fluctuation was observed in two fracture surfaces with clearly fan-shaped steps,which present the obvious characteristic of multiple-sources of fatigue and fracture.The chemical composition analysis reflected an extremely low content of alloying element of Cu(lower 3%)and Ni(lower 4%)for the failed pump shaft,which caused the lower mechanical properties caused by the less alloy strengthening phase result from the misapplication of material.The contrastive analysis of tensile test and hardness test show that the failed feed water pump shaft shows lower tensile strength(Rm)and brinell hardness(HBW)than those of normal 17-4PH steel(500MPa and 150HB,respectively),which are attributed to the finer and homogeneous columnar martensite construction,and the second phase dispersed uniformly in the matrix of normal 17-4PH steel.