K438高温合金补焊接头热处理裂纹研究

Study on Crack of K438 Superalloy Repair Welding Joint after Heat Treatment

对K438高温合金补焊件热处理裂纹进行了研究,观察了裂纹的分布特征,分析了不同裂纹的形成机理。结果表明,热处理后热影响区出现两类裂纹:不连续的液化裂纹和起始于熔合区,向母材扩展的应变时效裂纹。应变时效裂纹取决于焊缝的残余应力和敏感组织,M_(23)C_6和M_6C的存在增加了晶界脆性,增大了裂纹开裂的倾向性。当应力超过合金的强度极限即发生开裂。液化裂纹是由于晶界的低熔点(γ+γ′)共晶相在热处理时被重新熔化,削弱了晶粒间的内聚力,导致裂纹的产生。

The crack of K438 superalloy repair welding casting after heat treatment was studied, the distribution characteristics of the cracks were observed, and the formation mechanism of different cracks was analyzed. The results show that there are two types of cracks in the heat affected zone after heat treatment. One is discontinuous liquation crack, the other is strain aging crack which initiates in fusion zone, and extends to base material. The occurrence of strain aging crack depends on the residual stress of weld and sensitive tissues. M23C6 and M6C increase grain boundary brittleness and the tendency of crack, when the stress exceeds the tensile strength of the alloy, the cracks occur. The liquation crack is due to the liquefaction of γ＋γ＇ eutectic phase with low melting point at the grain boundary during heat treatment, which weakens the cohesive force between grains and leads to crack.