CrMoW转子钢高温超长寿命疲劳行为

Fatigue behavior of CrMoW rotor steel at elevated temperature in very high cycle regime

利用旋转弯曲疲劳试验机,研究了CrMoW转子钢在常温与600℃条件下的超高周疲劳特性。对试验数据采用了三参数模型拟合,利用扫描电子显微镜(SEM)对疲劳断口进行分析。研究结果发现,600℃下的S-N曲线呈现连续下降的趋势,不存在传统意义上的疲劳极限。高温会加速试样的氧化,促进裂纹的萌生与扩展,降低材料的疲劳寿命。疲劳加载后材料的微观结构没有发生明显的变化,微观组织中有少量淬火加热时未溶解的残余MX相。断口分析表明,疲劳裂纹主要萌生于试样表面。在600℃下,裂纹萌生区发现夹杂物,该处裂纹的萌生是表面裂纹起源和亚表面夹杂物相藕合的结果。

Rotating beam fatigue tests were performed to evaluate the very high cycle fatigue properties of CrMoW rotor steel at room temperature and 600 ℃. The experimental data were fitted by three parameter model, and the fracture morphology was observed by SEM. The results show that the S-N curve presents a continuously descending shape at 600 ℃ , and a conventional fatigue limit is not obtained. The oxidation of sample is accelerated at elevated temperature. Accordingly, the crack initiation and crack propagation are also promoted at elevated temperature so that fatigue life is decreased. The microstructure of specimen has no obvious changes after the fatigue loading. Small amount of undissovled MX-type particles during the quenching heat treatment are found in the microstructure. From the result of fractography, the fatigue crack is mainly initiated at the surface of specimen. The inclusions are observed in the crack initiation area at 600 ℃ and the fatigue crack initiation results from crack initiating at surface and inclusion at subsurface.