What is easier to weld carbon steel or cast iron?

Answer 1

any steel or alloy of iron and carbon having a carbon percentage of above 0.3% is difficult to weld. carbon steel can have maximum carbon percentage of about 2% and cast iron with carbon percentage between 2% to 4%. the welding of any iron alloy with carbon percentage above 0.3% becomes difficult because of the formation of the martensite in the welding areas, heat affected zone etc., the fusion welding process which is usually employed to weld carbon steel and cast iron takes the metal or alloy to their respective melting point (in this case about 1650 C) which is above the austenizing temperature of most steel and cast iron. when the weld is finished it undergoes a process similar to hardening. the nearby non heated parts of the welded material acts as the cold bath resulting in the hardening process which involves sudden cooling for the formation of martensite which is very brittle, any pressure applied will crack the weld immediately. hence before welding the nearby parts of the material to be welded is preheated so that they wont act as any cold bath. but any way cast irons are very difficult to weld than the steels. this is because of the fact that the martensite formed is as a result of trapped carbon atoms in the iron crystal making a distorted body centered tetragonal crystal structure(martensite). higher the percentage of carbon the martensite formation is even better. hence cast irons are especially difficult to weld. design engineers never suggest a welding process for cast iron. cast irons are welded only when there is no other choice but to weld it.