Can you weld stainless steel to Inconel?

Can you weld stainless steel to Inconel?



 

Inconel is a family of registered high-strength austenitic nickel-chromium-iron alloys with excellent corrosion and heat resistance properties. These alloys contain high levels of nickel and can be considered super stainless steels. Inconel is used in a variety of extreme applications, including naval ship exhaust ducts, submarine propulsion motors, subsea cable jackets, heat exchanger ducting and gas turbine shrouds.

Inconel has been used in the exhaust systems of Formula One and championship racing cars for many years. Recently, several Winston Cup racing teams have used Inconel to produce ultra-lightweight, high-durability exhaust headers.

GNEE Stainless Steel recommends Inconel 625 alloy for exhaust systems due to its excellent strength, corrosion resistance and workability. The alloy also has high creep and rupture strength; excellent fatigue and thermal fatigue strength; and excellent weldability (although those who weld it may have different opinions!). Inconel 625 contains molybdenum and columbium, which hardens and strengthens nickel-chromium substrates without the need for precipitation hardening treatments. However, some hardening does occur when heated to intermediate temperatures (1200 F to 1600 F), thereby increasing room temperature strength. Additionally, the alloy retains more than 75% of its room temperature strength at 1200 F. The alloy is available in a variety of forms, including tubing, sheet, rod, plate and castings. GNEE Stainless typically stocks welded and drawn Inconel 625 tubing. Pipe specifications are SAE AMS 5581, nickel alloy, corrosion and heat resistant, seamless or welded.

Inconel 625 can be welded using conventional stainless steel TIG welding techniques. Inconel Filler Metal 625 Welding Rod is used to weld Inconel to Inconel as well as dissimilar metals including stainless steel. Inconel alloy weldments have high strength and strong resistance to corrosion and oxidation. Many welders describe Inconel welding as "dirty." In other words, the molten pool appears to lie beneath the "skin" and is not well defined. Additionally, the molten pool is somewhat "sluggish" compared to steel or stainless steel. These properties tend to cause weldments to look "rough" compared to stainless steel. Welding Inconel is not necessarily more difficult to weld than stainless steel, it's just different. Inconel 625 can be successfully welded by following the welding procedures outlined in the Head Construction Tips article.