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本文主要针对汽轮机高压调速汽门螺栓断裂问题进行了分析研究。利用扫描电子显微镜、光学显微镜对断裂的20CrlMolVTiB钢螺栓的断口宏观形貌、微观形貌以及金相组织进行了观察,利用硬度计对硬度进行了测试。实验结果发现,螺栓断面平直,无明显塑性变形,断口形貌呈冰糖状,并伴有河流状花样,有蠕变孔洞存在。由于碳化物的析出,致使硬度和脆性增加,韧性下降。实验结果分析表明,断裂的主要原因是在长期的高温运行过程中蠕变损伤所致。另外,螺栓在承受较大的预紧力、热应力和蒸汽工作应力的同时,还可能由于偏心装配引起的附加弯曲应力的作用,使得螺栓两侧受力不均。在使用中发生沿晶和穿晶混合的脆性断裂。
This paper mainly analyzes the problem of steam turbine bolt breaking at high speed governor. The fracture morphology, microstructure and microstructure of 20CrlMolVTiB steel bolt were observed by scanning electron microscope and optical microscope. The hardness was tested by using a durometer. The experimental results show that the section of the bolt is flat and has no obvious plastic deformation, the shape of the fracture is rock candy, accompanied by a river-like pattern with creep holes. Due to the precipitation of carbides, resulting in increased hardness and brittleness, toughness decreased. Experimental results show that the main reason for fracture is caused by creep damage during long-term high temperature operation. In addition, the bolts can withstand the preload, thermal stress and steam work stress, but also may be due to eccentric bending caused by the additional assembly of the role of stress on both sides of the bolt so uneven. Brittle fracture that occurs during the intergranular and transcrystalline mixing occurs during use.