Inconel is a registered trademark that refers to nickel-chromium superalloys with common characteristics. As austenitic nickel alloys, the Inconel family is also at times referred to as Chronin, Altemp, Haynes, Nickelvac and Nicrofer. While Inconel alloys can differ widely in terms of composition, all feature nickel as the highest percentage element used, with chromium as the second highest percentage.
Some common characteristics of Inconel alloys include corrosion-resistance, oxidation-resistance, the ability to work well in extreme environments and to retain strength at high temperatures. As a result, Inconel alloys including 600, 601, 625, 690, 718, 751, 903 and 939 are often used for high temperature applications in industries such as: nuclear, in which Inconel 718 is often used in nuclear reactors, rocket motors and spacecraft; chemical, Inconel 600, 625, 690, 718 and 601 are often used for processing equipment; industrial manufacturing, for all Inconel alloys for use in heat treating equipment such as furnaces and various machines and components such as gas turbines; marine, for salt corrosion-resistant piping, springs and fasteners; and aerospace, where Inconel alloys 625 and 718 are used for piping, safety wire, shims and other structural metal on aircrafts.
Each Inconel alloy has its own unique composition. As examples, the composition of the three most commonly used Inconel alloys are: Inconel 600, 72% nickel, 14-17% chromium, 6-10% iron, 1% manganese, and trace amounts of copper, silicone, sulphur and carbon; Inconel 625, 58% nickel, 20-23% chromium, 5% iron, 8-10% molybdenum, 3.15-4.15% niobium, 1% cobalt and trace amounts of manganese, aluminum, titanium, silicone, carbon, sulphur and phosphorus; Inconel 718, 50-55% nickel, 19% chromium, 17% iron, 3% molybdenum, 5% niobium, 1% cobalt, 1% aluminum and trace amounts of manganese, copper, titanium, silicone, carbon, sulphur, phosphorus and boron.
Since Inconel alloys rapidly harden under machining, they can be difficult to shape. Often, the Inconel alloy must be in a solutionized form for machining to occur. However, machining must be done aggressively and using hard tools, such as in welding or brazing stainless steel threaded inserts are commonly used.
In addition, the most common welding technique that is used on Inconel alloys is gas tungsten arc welding (GTAW), which is more generally known as tungsten inert gas (TIG) welding. However, recent developments in pulsed micro laser welding are becoming an increasing popular technique for welding Inconel alloys as well.