Can I Weld Cast Iron to Steel?
Yes, cast iron can be welded to steel. However, there are a few things you want to remember when welding cast iron to steel.
First, usually you are doing a repair job or a retrofit if you are asking about welding cast iron to steel, so be sure to check the parts thoroughly to ensure there are no stress cracks or other signs of damage. If you see damage, you may be better fabricating a replacement for the casting than using the casting now to cut it off and replace it later.
Second, ask yourself, “Am I 100% certain this is cast iron?” Cast iron, cast carbon steel, and types of iron castings can look similar, but the metallurgy will be different. Not all cast iron is the same either. Gray iron and ductile iron will act differently. Regardless, you should be able to weld any of these together with steel, but you don’t want a weak weld because you thought you had cast iron when you really have something with a higher melting temperature.
Third, remember cast iron has a slightly lower melting temperature than steel. With the lower melting temperature, you want to ensure you not only adjust the settings on your welder appropriately, but you also want to be careful with thinner pieces of cast iron. We all know from experience the pain of fixing a part after you blew a hole in the component when you misjudged the wall thickness or you were running too hot.
Fourth, if the casting is small enough, preheating the casting helps avoid cracks forming near the weld. You can heat the casting anywhere in the range of 500-1200 degrees before welding (don’t go beyond 1200 degrees Fahrenheit). If you can’t preheat the whole part, try to at least warm the weld area up to 100 degrees.
If you preheated the part, wrap the whole component up after welding to slow down cooling. A fast cool can create very small cracks to form. On a side note, you can also use sealing compound if you need a watertight seal.
Fifth, you want to only weld only about 1” at a time to help eliminate cracking. You can stitch weld your component and then go back to fill in the gaps.
Those are the basics. Lincoln Electric has some helpful information on electrode selection for welding cast iron. Have fun welding!