超超临界锅炉水冷壁T23/12Cr1MoV异种钢焊接接头焊后热处理裂纹分析

Crack analysis of T23/12Cr1MoV dissimilar steel welded joints during PWHT in the water-wall of USC boiler

分析了T23/12Cr1MoV异种钢焊接接头焊后热处理裂纹的宏观和微观特征、断口形貌及接头的显微组织,测试了接头的硬度分布,在此基础上讨论了裂纹的性质及形成原因,并提出了防止裂纹的措施。结果表明,裂纹启裂于T23钢侧焊趾部位,沿粗晶粒热影响区(CGHAZ)晶界扩展,为典型的再热裂纹。焊后热处理明显降低了异种钢焊接接头两侧热影响区的硬度,T23钢侧CGHAZ产生再热裂纹与其在焊后热处理过程中晶界析出碳化物有关,其析出促进了孔洞的形成。在焊后热处理前,对异种钢焊接接头进行一次550℃×1 h的中间热处理有利于抑制再热裂纹的产生。

Macro and micro morphologies of cracks occurring in T23/12Cr1MoV dissimilar steel welded joint(DSWJ)during PWHT were analyzed,the microstructure and fracture morphology of the DSWJ were observed,and the hardness distribution across the DSWJ was tested.Based on the experimental results,the types and causes of cracks were discussed,and the measures to prevent cracks were proposed.The results show that the crack initiates at the weld toe of T23 steel side,then propagates along the grain boundaries of its coarse grain heataffected zone(CGHAZ),which exhibit the characteristics of reheat crack.After PWHT,the hardness of HAZs on both sides of the WM in DSWJ obviously decreases.The formation of reheat crack is related to the precipitation of carbides at grain boundary which promotes the formation of pores in the CGHAZ of T23 steel side during tempering.Before PWHT an intermediate heat treatment performed at 550℃for 1 h is beneficial to suppress reheat crack.