超超临界锅炉T23钢水冷壁管开裂分析

以超超临界锅炉SA213?T23钢水冷壁失效管为试验对象，通过宏观检查、化学成分分析、金相检验和硬度试验，分析失效原因。结果表明:该水冷壁管化学成分正常，材质性能未发生明显劣化；水冷壁失效原因为鳍片焊缝开裂，该裂纹为沿晶界扩展的再热裂纹，起源于焊缝熔合线附近的热影响区粗晶区域，先沿热影响区横向扩展，然后扩展至母材区域，最终导致管壁泄漏失效；热影响区粗晶区域显微组织为粗大的马氏体和贝氏体组织，硬度明显偏高于焊缝熔合线另一侧的焊缝区域，脆性增大。两者在显微组织和硬度上的明显差别，使焊缝熔合线附近的热影响区粗晶区域容易产生应力集中，在高温运行中发生晶间开裂。

Cracking Analysis of Water-cooled Wall Pipe of T23 Steel for Ultra-supercritical Boiler

In the present work, the cracking of a SA213?T23 steel water-cooling wall pipe in a power plant boiler was analyzed by macroscopic examination, chemical composition analysis, metallographic examination and hardness test. The results show that the chemical composition of the pipe was normal, and its property didn’t obviously deteriorate. The failure of the pipe was caused by the crack of weld of water-wall fin. The crack was intergranular reheat crack, which initiated at the coarse-grained heat-affected zone(CGHAZ) near the weld fusion line, propagated along heat-affected zone, and then extended to the base metal, eventually resulting in the leakage of the pipe. The microstructure of the coarse-grained heat-affected zone was coarse martensite and bainite with obvious fragility, and the hardness of CGHAZ was obviously larger than that of weld zone. There is obvious the difference in microstructure and hardness between CGHAZ and weld zone, so stress concentration easily occurred at CGHAZ near the fusion line. As a result, intergranular cracking took place during high temperature operation.