汽轮机高压导汽管插管P91/P22异种钢焊接接头裂纹原因分析

Analysis of cracking reason for P91/P22 dissimilar steel welded joint of high-pressure plug-in pipe in turbine

通过宏观观察、显微硬度分析、显微组织分析等对P91/P22异种钢焊接接头P91钢侧热影响区裂纹进行研究,以分析裂纹的形成机理。结果表明,裂纹位于焊接接头热影响区相变区,并表现为沿晶和穿晶混合型裂纹,裂纹处热影响区硬度值偏高,焊接接头硬度偏高处存在较大残余应力。裂纹产生原因为焊接热处理温度选用不当,造成材料性能出现异常,在残余应力与管道应力共同作用下,出现疲劳裂纹。P91/P22异种钢在使用R407焊条焊接时正确的焊后热处理工温度至少为750℃。

Macroscopic observation,microhardness and microstructure analysis were carried out on the crack in the heat affected zone （HAZ） of P91 steel side in the P91/P22 dissimilar steel welded joint to find the formation mechanism of the crack. The results show that the intergranular and transgranular cracks are located in the phase transformation area of heat affected zone and meantime,higher residual stress exists there together with higher hardness value. The incorrect post-weld heat treatment temperature leads to the abnormal microstructure and performance and therefore,the fatigue crack initiates under the co-action of residual stress and structural stress. The correct post weld heat treatment temperature of the P91/P22 dissimilar steel should be at least 750 ℃ when the R407 electrodes rod is used.