Solidification and microstructural characterisation of iron-chromium based hardfaced coatings deposited by SMAW and electric arc spraying

The microstructure and solidification of shielded metal arc welding (SMAW) hardfaced Fe-Cr-C deposits used in the sugar industry as well as electric arc-sprayed Fe-Cr-B coating have been determined using a combination of optical microscopy, image analysis, SEM and XRD. The aim of this study was to examine the morphology, microstructure and chemical composition of the coating. The weld microstructures consisted primarily of (Fe,Cr,Mn)7C3 carbides, austenite (γ) and ferrite (α), while the arc-sprayed coating was composed of two metallic phases, α (Fe,Cr) and Fe1.1Cr0.9B0.9, which were intermingled with oxides of iron and chromium. The highest average hardness (850 kgf/mm2) occurred in weld coating A80, compared to the 730 kgf/mm2 measured in the arc-sprayed coating. The results of the study also showed that different welding electrodes as well as weld procedure variation produced significant differences in the morphology of the carbides, structure of the deposit and microhardness. Although the microhardness of the welded deposits was higher than the arc-sprayed coating, the arc-sprayed coating exhibited a more consistent hardness value. Porosity and oxide inclusions were more evident in the arc-sprayed coating: 1% and 3% in the weld coatings S80 and A80, respectively, and 6.5% in the arc-sprayed coating. The implications of the result with respect to solidification and microstructure are discussed.