WEAR AND CRYSTALLIZATION BEHAVIOR OF A GRAY CAST IRON SURFACE TREATMENT BY SULPHUR ADDITIONS IN THE MOULDING SAND

The aim of this paper is to study the surface treatments of grey cast iron by sulphur additions into a face moulding sand on the microstructure, hardness and wear resistance of the skin layer of casting. To evaluate the wear behavior a Pin-onDisk wear test machine was used. Pins which were prepared from the samples with the skin layer treatment by different sulphur additions of 0, 1, 2,4, 6, 8, 10 wt.% on the face moulding sand were worn on a steel counterface having a hardness of  63HRC under applied load of 80 N at a constant sliding velocity of 1200 rpm.  Results showed that sulphur lead to white iron skin layer formation and the thickness of which is depended either on both sulphur content and casting wall thickness (cooling rate). An increase of casting thickness ranging from 10 up to 40 mm increased the thickness of white cast iron as well. These both factors mentioned above influenced the microstructure of white iron layer, which changed from hypoeutectic to hypereutectic in mode.  The wear and hardness results indicate that the surface treatment grey cast iron exhibits superior wear properties and  have high hardness to as cast gray cast iron under the similar conditions. Therefore, this hard layer caused by the formation of a microstructure martensite and cementite phases resulted in a better wear resistance in comparison to the as cast samples. Higher sulphur content result in greater pearlite and cementite (ledeburite) contents and hardness. Both sulfur and casting thicknesses increase the amount of ledeburite formed in skin layer casting throw the transformation range. For casting of thickness 40 mm and sulphur content 10 wt.%, was characterized with coarse lath of primary Fe3C precipitate in ledeburitic matrix. The grey iron casting surface treatment with 6% sulphur added into the face molding sand exhibits the best wear resistance, hardness and clear white iron microstructure in the skin layer.