Investigation of nickel effects on ductile cast iron and its mechanical behavior of weldments

Abstract

Ductile iron is a high carbon cast iron containing carbon above its newlinesolubility; this rich carbon solidifies as graphite in the form of spheroids with newlineferrite or pearlite as matrix. It finds large applications as structural members, newlineIC engine parts, automobile transmissions and earth moving components newlinebecause of its favorable mechanical properties. The properties of this metal are newlinereformed by alloying, heat treatment and are always compared with the newlineproperties of steel and malleable iron. But the high carbon content of this metal newlinemakes it difficult to weld and to get a desirable welded joint property. newlineThis research work emphasizes the Gas Tungsten Arc Welding (GTAW) newlineof ductile iron alloyed with nickel. Ductile iron melt is produced in an iron newlinefoundry by following the tundish cover magnesium treatment process. Standard newlineY-block castings are made with unalloyed and nickel additions of 0.5 wt%, newline1.0 wt% and 1.5 wt%. Tensile test specimens are machined and their properties newlineare studied. Specimens are also cut for the GTA welding process. Manual GTA newlinewelding is done by using AWS-E Ni Fe-CI filler rod with welding currents of newline80 to 180 amps at an interval of 20 amps. Specimens for tensile, hardness and newlineimpact tests are machined from the weld joint and conducted by following the newlineASTM standards. Austempering heat treatment includes austenitizing the newlinespecimens at 920°C for two hours and austempering at 300°C and 400°C for two newlinehours in salt bath furnaces is also done on the welded specimens. newlineThe microstructure of the base metal shows spheroidal graphite newlinesurrounded by ferrite phase. Addition of nickel suppresses the ferrite matrix and newlinepromotes the pearlite matrix structure. A smaller quantity tensile strength newlineimprovement only noticed by alloying 0.5 wt% nickel on ductile iron with the newlinespare of ductility in the as-cast condition. newline