EFFECT OF GRAPHITE FLAKES ON THE MICROSTRUCTURE OF MELTED, TRANSITION AND HEAT AFFECTED ZONES IN GREY CAST IRON REMELTED BY TIG

In this study the effect ofgraphite flakes present in a pearlitic grey cast iron on the microstructure of melted, transition and heat affected zones formed during surface remelting (in order to improve wear resistance) with tig process has been investigated. relationship between various tig parameters and thickness of remelted and heat affected zones revealed that a high concentrated heat energy is imposed by tig process which makes it a proper option for focused surface treatment. based on microstructural examinations five areas with different microstructure and microhardness were identified within the surface area. graphite flakes were totally dissolved within the first area leading to the transformation of denderitic austenite to plate martensite and the formation of ledeburite within interdenderites. the main feature of the second area, resulted from the presence of graphite flakes, was the local melting with a gap in the vicinity of graphite flakes and that of third area was the formation of finer and denser martensite plates closer to the graphite flakes compared with those formed at a further distance. in the fourth layer there is a mixture of martensitic and pearlitic matrix while the matrix of fifth layer has no change of microstructure.