Haynes Hastelloy X description: HASTELLOY X RTW fi ller metal is used for the gas metal arc and gas tungsten arc welding of X alloy. The deposited weld metal has an exceptional combination of oxidation resistance, fabricability and high-temperature strength. It has also been found to be exceptionally resistant to stress-corrosion cracking in petrochemical applications. X alloy exhibits good ductility after prolonged exposure at temperatures of 1200, 1400, 1600F (650, 760 and 870C) for 16,000 hours.