Abstract: The tungsten-inert-gas arc welding of YG30/cermat and 45 steel was carried with pure Ni and Ni-Fe alloy welding wires.The scanning electronic microscope and wavelength dispersion analysis of X-ray were used to analyze the morphologies,distributions,and chemical composition of η phase in welded joints.The results showed that η phases appeared,accumulated,and grown at the zones near the boundaries of YG30/and weld metal.When the iron content was about to 40% at in YG30/cermat,the tungsten carbides would decompose into the η phases in M₆C type of carbides with high concentration of tungsten and iron,in which iron content was about 23at%.