Alloy 718(GH 4169) is an nickel-iron alloy precipitation-hardened from γ'' and γ". ed as high-strength alloy and corrosion resisting alloy since it has outstanding fatigue-resistivity, radioresistance, inoxidability, corrosion resistance and excellent machining performance, weldability and structure stability. It could be manufatured into various forms of components which wildly used in aviation, nuclear industry and petrochemical industry.