Study on Hot Cracking Susceptibility in Multipass Weld Metal of Ni-Base Super-Alloys

为弄清镍基高温合金多道焊金属微裂纹产生的机理，开展了试验研究。对微裂纹断口进行金相和断口分析。此外，还研究了P、Si和S对70%Ni-Cr-Fe三元合金二次加热焊缝金属热裂纹敏感性的影响，以明确这些杂质元素对镍基焊条多道焊焊缝金属热裂纹敏感性的影响。主要研究结果如下：(1)详细的断口分析表明，多道焊金属中的微裂纹是熔化裂纹或再热焊缝金属出现的塑性-凹陷裂纹。(2)70%Ni-Cr-Fe三元合金再加热焊缝金属的熔化开裂敏感性太低，且随杂质元素含量的增加而增加。含S的材料比含P和Si的材料具有更高的塑性-裂纹敏感性。尤其是含0.007%S的0%铬和20%铬合金的裂纹敏感性高于5%铬和10%铬合金。(3)S。

This paper was carried out in order to make clear the cracking mechanism of microfissure in multipass weld metal of Ni-base super-alloys. Metallographic and fractographic examinations were performed to the fracture surface of microfissure. Moreover, the effects of P, Si and S on hot cracking susceptibilities in reheated weld metal of 70%Ni-Cr-Fe ternary alloys were evaluated in order to make clear the effects of these impurity elements on hot cracking susceptibilities in multipass weld metal of Ni-base welding rods. Main results obtained are as follows.(1) A detail fractographic examination has made clear that microfissure in multipass weld metal was liquation crack or ductility-dip crack occurring at reheated weld metal.(2) The liquation cracking susceptibilities in reheated weld metal of 70%Ni-Cr-Fe ternary alloys were too low and they increased with an increase in impurity elements. Ductility-dip cracking susceptibilities of materials containing S were much higher than those containing P and Si. Especially cracking susceptibilities of 0%Cr and 20%Cr alloys containing 0.007%S were higher than those of 5%Cr and 10%Cr alloys.(3) There was the suitable Cr content for reducing the ductility-dip cracking susceptibility because of contrary effects due to grain boundary carbide, hardness and grain boundary segregation of S.