Introduction
Hardfacing alloys are used under the conditions of extreme erosion and abrasive wear. The exceptional abrasive and erosive wear resistance characteristics of hardfacing alloys results primarily from their high volume fraction of hard carbides, although the toughness of the matrix also contrib- utes to the wear resistance. Observations of Fe-Cr-C alloys of Fe-Cr-C alloy micro- structures have shown that these types of materials contain hypoeutectic, eutectic and hypereutectic structures.1) M7C3 primary carbides are formed in large amounts at higher carbon concentrations. These types of microstructures have good wear resistance properties.2,3) Fe-1235Cr-C white cast irons are used as hardfacing alloys; these alloys have a high hardness value due to their high M7C3 content.4–7) M7C3 is surrounded by austenite, which is relatively soft in comparison to the extremely hard M7C3. Consequently, cracks propagate along the interface between austenite and M7C3. This causes a serious problem for hardfacing materials. Fe-28Cr-C hardfacing alloys are also used commercially for components that are subject to harsh abrasive conditions. The large amounts of carbides present in their microstruc- tures consist of M23C6. They can be described as composites with large and extremely hard carbides in a softer body- centered-cubic (bcc) Cr-Fe alloy matrix. Hardfacing alloys obtained using high-energy density sources such as electron beam welding, plasma arc and lasers have been widely applied in the industry to enhance the wear and corrosion resistance of the surfaces of underlying materials.8–10) The criteria used for selecting the welding surface for wear and hardness applications depends on the features of its microstructure. In this investigation, the gas tungsten arc welding (GTAW) process is employed to form a Fe-Cr-C hard surface with high
chromium content over the ASME A36 steel with chromium and graphite alloy fillers. The changes in the microstructures and the wear characteristics of the coated surfaces were studied in detail by using an optical microscope (OM), a field emission scanning electron microscope (FE-SEM), an elec- tron probe micro analyzer (EPMA), an X-ray diffractometer (XRD) and a dry sand rubber wheel abrasion tester.