Cast iron weld are prone to cracking during welding. Cast iron should not be welded by design. If the casting fractures repair welding is frequently atempted. The risk of getting additional cracking is high but welders that are experienced in cast iron welding can have a good repair succes rate. Two main procces are used, arc welding with high nickel filler metal and torch brazing with copper base filler metal.
The procedure of arc welding involves preheating to about 700 F ( 300 C ) welding with minimum weld size ang peening of the deposit followed by a slow cool to room temperature and a temper at about 600 F ( 315 C ) . The pre heat and the post heat are not needed with torch brazing because by the time the part is hot enough to melt the brazing alloy, it will be adequately preheated. The secret to succes with this procces is to slowly heat the entire casting with the torch up to at least 700 F before concetrating the torch heat at the weld joint. It is also important to apply a suitable brazing flux. After brazing the part should be slow cooled, but a temper is ussualy not necessary because with slow torch heating there is little tendency to get a quench that would cause local hardening. In general welding on all cast iron shoul be avoided, but when it is unavoidable these type of procedure should be employed