The investigation of mechanical properties of 45Mn5 steel after surface modification processes

ABSTRACT Masters Thesis THE INVESTIGATION OF MECHANICAL PROPERTIES OF 45Mn5 STEEL AFTER SURFACE MODIFICATION PROCESSES Serkan ISLAK Firat University Graduate School of Natural and Applied Sciences Department of Metallurgy Education 2005, Page: 105 In this study, on the surface of a 45Mn5 steel a silicon carbid (SiC) powder layer was coated with use of GTA method. As first the specimen thickness was fixed and subsequently the different powder quantities (in gram) were used. Besides, process parameters such as heat input, coating speed and welding current were varied and the effect of these parameters on microstructural chancing, microhardness, macrohardness and abrasive wear resistance of modified materials were investigated. The microstructure of the coating layer was characterized by optical microscope (OM), scanning electron microscope (SEM), X-ray diffraction (XRD), energy dispersive spectrometer (EDS) and spectral analysis. While the hardness of the modified layer was measured by microhardness tester, abrasive wear properties were evaluated under pin-on-disc abrasive wear test conditions. After wear tests, wear rates were calculated via the mass losses of the specimens which were measured. While the 45Mn5 steel was used as the substrate material, coating powder (SiC) was alloyed at 0.5, 1, 1.5, 2 and 2.5 gr. quantities on to surface of these steel. Effect on the properties of the coating materials amount of SiC was investigated experimentally. The hypoeutectic and hypereutectic microstructures were observed in coated specimens. Because of rapid solidification, dendritic phases were formed. Because of high cooling rate, dendrites become finer from interface zone to top of coating and their directions were getting differently. Besides, microstructures containing Fe7C3, Fe2C, FeSi2 and Feo.4Mn3.0C carbid and intermetallic complex phases having different shape and Xcomposition were formed. The forms of these phases were depended on the coating speed, the energy input and the powder quantity. Coating surface macrohardness importantly increased because hard phases such as FeSİ2 and carbides (Fe7C3, Fe2C) exist in microstructure. The hardnesses values measured between 510-1250 HV3. As the microhardness measurements, the hardness decreased along a line from coating toward to substrate material. This can be explained with phase transformations which the coating speed, the cooling rate and solidification conditions occured. Wear rates were calculated using mass losses obtained in the result of the abrasive wear test. In surface alloying process used SiC as coating powder, the maximum mass loss was found by high coating speed, low energy input and low powder quantity conditions. The minimum mass loss also was found by low coating speed, high energy input and high powder quantity conditions. Key words: GTA process, surface alloying, heat input, abrasive wear, silicon carbid (SiC) XI