论文部分内容阅读
用光学显微镜及电子扫描显微镜观察了叶轮本体与扰流板焊缝的微观组织以及焊缝处微裂纹的形貌。结果表明,应力腐蚀开裂萌生并扩展于熔合线附近的焊接热影响区,与母材相比,处于熔合线附近的叶轮本体显微组织发生了明显变化。焊接热循环直接导致熔合线附近的热影响区产生了Cr_2N,从而使其周边形成贫Cr区。贫Cr区的形成是焊缝组织耐蚀性劣化的根源,也是叶轮早期应力腐蚀开裂的主要原因。在不能进行焊后热处理的情况下,经现场验证取消叶轮近心部区域的四个扰流板不明显减弱扰流效果,同时可避免应力腐蚀开裂。
The microstructure of the weld between the impeller body and the spoiler and the morphology of the micro-cracks in the weld were observed by optical microscope and scanning electron microscope. The results show that stress corrosion cracking initiates and propagates in the weld heat affected zone near the weld line. Compared with the base metal, the microstructure of the impeller body near the weld line changes obviously. The welding thermal cycle directly leads to the formation of Cr 2 N in the heat affected zone near the weld line, thus forming a Cr-depleted zone around it. The formation of lean Cr region is the root cause of the corrosion resistance of the weld microstructure and also the main reason for the early stress corrosion cracking of the impeller. In the absence of postweld heat treatment, the four spoilers removed in the vicinity of the impeller area on site verification did not significantly attenuate the turbulent flow and avoid stress corrosion cracking.