Is Inconel easy to weld?
Inconel welds are prone to cracking, which makes welding quite tricky. Therefore, some Inconel alloys are specifically designed for welding. For example, Inconel 625 is very easy to weld compared to other Inconel alloys. Inconel 718 is another alloy that is particularly weldable. Its high iron content makes it less expensive per kilogram than other materials of the same type, and it is precipitation hardened, reducing the likelihood of cracking.
Electron beam welding is generally considered the preferred welding process for high-temperature alloys such as Inconel. Electron beam welding has the high power required to melt materials quickly, ensuring a very narrow fusion zone (FZ) and a minimized heat-affected zone (HAZ), thereby reducing distortion and residual stresses. Electron beam welding is performed in a vacuum, which reduces material contamination and produces clean welds at any depth of penetration.
As always, it is critical to thoroughly clean all joint areas before EB welding. First, any machining oil and chips should be removed from the part using a standard alkaline cleaning process. Then, passivation should be performed to maintain the corrosion resistance of the material. This process will first remove any free iron from the interface with the machine tool or other surfaces that come into accidental contact. It should be noted that the alloyed iron in Inconel does not need to be removed. The passivation solution then converts "free" chromium into chromium oxide to maximize the material's corrosion resistance.
There are two main methods for passivating Inconel, and the method is very similar to that of 300 series stainless steel. One option is to immerse Inconel parts in a 25-50% nitric acid solution at room temperature to about 140°F (60°C) for about 20-30 minutes. A similar soaking process can be performed using a 10% citric acid solution at a similar temperature range and time.
