FB2转子钢低周疲劳断口分析

Analysis of the Fracture Morphology of FB2 under Low-cycle Fatigue

采用轴向等幅低循环疲劳试验方法,对用于再热温度620℃的高效超超临界机组转子钢FB2的室温和高温低周疲劳性能进行了试验研究,并用扫描电子显微镜(SEM)和透射电子显微镜(TEM)对疲劳试样的断口以及显微结构进行了分析。结果表明:低周疲劳条件下FB2表现为循环软化,高温下疲劳寿命远远低于室温下的疲劳寿命,循环应变-寿命满足Manson-Coffin关系。疲劳断口扫描分析表明:FB2的疲劳源一般起源于表面或近表面缺陷及BN夹杂,疲劳条带形貌清晰可见;断口上可见完整BN夹杂形貌。疲劳试样透射分析表明:FB2循环软化是由位错密度的降低、马氏体板条的转化、亚晶的形成和粗化造成的。

Low-cycle fatigue properties of FB2 steel under room temperature and 620 ℃ are analyzed by axialload constant-amplitude method. The fracture morphology and microstructure of the low-cycle fatigue specimen are observed by scanning electronmicroscope （SEM） and transmission electron microscope （TEM）. Results illustrate that the FB2 is cyclic softening material. Its cycliclife under high temperature is far shorter than that under room temperature. The relationship between the cyclic strain and its lifesatisfies the Manson-Coffin model. SEM analysis shows that the fatigue cracks usually initiate from the surface defects or BNinclusions. The fatigue striations as well as the intact BN inclusions can be clearly distinguished. TEM analysis shows that the cyclicsoftening of FB2 steel is the consequence of the reduced density of dislocation, the transform of martensite laths together with theform and coarsening of sub-grain.