利用光学显微镜、扫描电镜以及能谱仪对超超临界机组服役8 000 h后的主蒸汽管道P92钢焊接接头焊缝金属中的微裂纹进行了观察,分析了微裂纹的形态、分布和性质.结果表明:P92钢焊接接头焊缝金属中的微裂纹呈蠕虫状断续分布,走向既有沿晶又有穿晶;在裂纹尖端区域有大量析出相;微裂纹的产生与应力和微区的组织状态有关,它起源于焊接过程中的低温区,是由微小脆化裂纹在应力场的作用下相互连接而形成的.
Some micro-cracks were found in weld metal of P92 steel welded joint in ultra supercritical unit after 8 000 h service,these micro-cracks were observed and analyzed by optical microscopy (OM),scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS).Morphology,distribution and property of these micro-cracks were analyzed.Results show that both intergranular and transgranular cracks in P92 steel welded joint were presented,and the micro-cracks showed wormy shape with discontinuous distribution.A large number of precipitates were distributed in the front area near the crack tips.The formation of micro-cracks was related with stress and structure of micro-zone,and the micro-cracks derived from low temperature region during welding procedure and formed from interconnection of micro brittle cracks under the influence of stress field.
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