If you know that the crack is clean, ground, and drilled, you can begin weld preparation. Cast iron like that used in cylinder heads first, gray or ductile likes to be hot. This removes moisture and relieves stress. Heating the metal to 170-200F is best. Make sure to heat long enough to allow the heat to really penetrate.
weld cast iron
A key ingredient is the selection of the correct welding electrode. A small diameter rod is best. My favorite for 25 years has been Eutectic’s Eutectrode Xuper 2240. This rod is designed for cast iron soaked in oil. He has good strengths and is forgiving. exact instructions, which may vary depending on the welding machine used, are available from a welding supply house or on Castolin.com. Basically the electrode will cool down. Most cracks can be filled in one pass.
After the root pass, mince the slag and then, with the chipping hammer, pierce the weld. Works the surface to relieve stress. If welding on an engine block, this step must be done after each pass. THIS IS THE SECRET OF CAST IRON WELDING… PEEN! Let the part cool slowly, covering with welding blankets or anything that retards the heat. This step is important to allow stress relief again. In fact, it affects the growth of the grain of the metal. Another reason the casting got overheated. With Euctectic-Castolin rod, the finished weld will be strong and after polishing the color will probably match the head. If this is your first try, practice with a scrap cylinder head first.
Make sure your rods are dry, heat them in an oven at 150 for an hour when in doubt. Use it while it’s hot. One pound of electrodes is a lot. Keep in mind that electrodes can cost up to $ 30 a pound. You are paying for a professionally designed product. There are other brands of cast iron rods. With some I have had good results, with others not. Stick with the major brands, not the repackaged rods. 1/4 pound of rebar will repair many cracks. If you think using a 7018 electrode will work, it might look good when you’re ready, but you just made a ship anchor. The weld will crack the first time it is stressed due to a small effect known as carbon migration.