A general perception is that welding iron is highly difficult as it has presence of carbon content at high levels. The carbon has a tendency to penetrate either into the weld metal, the heat-affected area adjacent to the weld metal, or both. When this happens, the end result is hardness or brittleness. This also leads to cracking after the weld. Hence, welders define weldability of cast iron as low.
Well, cast iron welding is challenging indeed, but not impossible subject to some conditions.
Types of Cast Iron Welding Rod
The casting welding rod choice depends on one welder to another. However, the most commonly used ones are 99% nickel rods, 55% nickel rods and steel rods. The casting welding rod specification varies according to welding current, wire chemistry and other parameters if applicable.
Steps to Cast Iron Welding
There are four essential steps to do weld cast iron:
Determine which allow needs to be used – grey cast iron, white cast iron, ductile/nodular, malleable iron.
Clean the casting meticulously – remove all surface materials such as paint, grease, oil, etc.
Choose a pre-heat temperature – preheating before welding is done to avoid cracks.
Choose the right welding technique – it depends on the suitability of the cast iron alloy that is being welded.
As far as welding techniques of cast iron are concerned, it can be done through Metal Inert Gas (MIG), Tungsten Inert Gas (TIG), Oxy Acetylene and braze welding. However, these techniques involve many challenges and require precautions. Hence, experts believe that Manual Metal Arc (MMA) which is also known as stick welding or shielded metal arc welding might be a better and safe welding testing method initially.
Some experts also recommend a radiographic test for welding cast iron. It is a non-destructive testing technique that helps to detect discontinuities in the welded structures before destroying them.
Bead welding is another method preferred by welders. In this method, small beads of 1” are used at a lower heat to avoid cracking. The welders peen the bead while it is hot with the help of a round-nosed peen hammer.
Heat Vs No Heat
Preheating is recommended for cast iron welding. However, some welders also keep it cool. Here, cool means low temperature without being too cold. It is advisable to stick to only one way – either preheating or cooling. If it is changed in the middle of the process, then welding will not yield desired results.
Cast iron welding requires practice, patience and experience. Keep the above guidelines in mind to get it right.