Erosive wear behavior of a high-chromium cast iron: effect of different destabilization heat treatments

High-chromium cast irons are typically used in high demanding applications, where low production costs and wear performance are key factors. The excellent resistance of these alloys to both abrasion and erosion results from the overall microstructural features, i.e. type, morphology and distribution of hard primary and secondary carbides, along with the matrix constituents. More specifically, it has been suggested that erosive wear resistance is strongly affected by the behavior of the matrix. Hence, according to the specific chemical composition, the microstructure can be tuned, e.g. by increasing its hardness and toughness, to enhance the lifetime of such wear- resistant materials. Heat treatments performed to destabilize the austenite promote its transformation into martensite, the coalescence and thickening of secondary carbides thus increasing the overall hardness of the material. The present study investigates the effects of different destabilization heat treatments performed on a hypereutectic white cast iron, with 21 % Cr and 4 % Nb, applied as an hardface coating to a low carbon steel substrate to improve its erosive wear resistance. The hardfacing plate was made by the open-arc welding of a flux- cored wire: high-chromium cast iron electrodes were deposited onto the substrate. The as-received and the heat- treated material was analyzed through optical and scanning electron microscopy, X-Ray diffraction and hardness tests to determine the relationship between microstructural variations and heat-treatment parameters. The erosive resistance was evaluated per the ASTM G76 standard in a purpose-built air blast test rig: experiments were performed with clinker powder (with a d90 of 9.73 μm) as erodent particles at an impingement angle of 90°. The tribological performance was assessed through weight loss measurements and analyses of the worn surfaces. The results suggest that erosion is dependent on carbide volume fraction and hardness along with the matrix microstructure: the hardest martensitic matrix gave the greatest erosion resistance.