CM 939 Weldable® Alloy

IN 939 alloy, developed by the International Nickel Co. in the late 1960s, is a unique 22% Cr hot corrosion resistant γ′ strengthened, cast nickel-base superalloy. It is widely used in industrial gas turbines for equiaxed vanes, vane segments and burner nozzles and is of interest to the aero turbine industry for LP and PT integral nozzles (vane rings) and high temperature turbine casings. However, IN 939 is considered difficult to weld repair without parent metal microcracking and can exhibit marginal ductility in heavy section castings. Cannon-Muskegon has developed a proprietary chemistry modified version of IN 939 alloy designated CM 939 Weldable®. Emphasis has been directed on optimizing aim chemistry and ultra high purity manufacture using CM-developed single crystal superalloy melting and raw material technology and subsequently on obtaining superior casting microstructure for improved weldability and mechanical properties. Alloy purity and heat cleanliness will be discussed, along with a simplified two-step heat treatment cycle, resulting in attractive microstructure, mechanical properties and repair weldability. Significant market interest has resulted in extensive vacuum casting experience throughout the gas turbine industry. Excellent results in terms of fluidity, casting cleanliness and minimal microporosity have been obtained without any hot tearing or hot cracking problems.