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对近年来国内1 000 MW超超临界塔式炉中频发的水冷壁T23接头短期失效案例进行了分析,观察了裂纹的宏观和微观形态,通过OM、SEM和TEM分析了裂纹附近的的显微组织,并测试了接头的力学性能。通过有限元软件模拟了附加应力对裂纹形成的影响。最后在上述此基础上判断裂纹的性质,阐明其形成机理,并提出预防措施。结果表明,裂纹为蠕变沿晶裂纹,沿焊缝横向分布在管子的6点钟或12点钟位置。焊态焊缝形成了较多高硬度的马氏体,其在运行后的室温冲击韧性很低。这种焊缝在水冷壁工作温度下具有蠕变脆性,在结构附加应力和疲劳载荷的作用下易于发生蠕变沿晶开裂。选择低强度等级焊材、进行焊后热处理、细化晶粒和减小水平方向的结构应力有助于抑制裂纹。
The short-term failures of the T23 connector in water wall of 1 000 MW ultra-supercritical tower furnace in recent years were analyzed. The macroscopic and microscopic morphologies of the cracks were observed. The results of OM, SEM and TEM were analyzed. Micro-organization, and tested the mechanical properties of joints. The influence of additional stress on crack formation is simulated by finite element software. Finally, on the basis of the above, we judge the nature of the crack, clarify its formation mechanism and propose preventive measures. The results show that the crack is creep along the crystal crack, along the weld transverse distribution in the tube 6 o’clock or 12 o’clock position. Weld weld seam formed more high-hardness martensite, its impact toughness at room temperature is very low. The weld has creep and brittleness at the working temperature of the water wall, and is prone to creep and intergranular cracking under the additional stress and fatigue load of the structure. The choice of low-strength grade consumables, post-weld heat treatment, grain refinement and reduction of structural stresses in the horizontal direction can help suppress cracking.