Effects of a Destabilization Heat Treatment on the Microstructure and Abrasive Wear Behavior of High-Chromium White Cast
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INTRODUCTION
HIGH-CHROMIUM white cast irons are widely used in industrial applications, such as cement manufacturing, mining, and mineral processing, due to their excellent abrasion wear resistance and low production costs.[1–4] Their excellent abrasion resistance resulted primarily from the morphology, distribution, amount, and type of the hard eutectic carbides and also the microstructure of the matrix.[1,5–10] Many works in the literature report that the wear resistance increases with an increase in the amount of eutectic carbide. Although the hypereutectic white cast irons have a higher amount of carbides than the hypoeutectic white cast iron, the hypoeutectic alloys are commonly used as cast components in wear applications because they have the proper combination of toughness and hardness.[7,8,11–13] The as-cast microstructure of the hypoeutectic white cast iron consists of a primary phase (i.e., austenite) with eutectic phases (austenite and M7C3 carbides).[14–16] Prior to service, the microstructure of high-chromium white cast iron is changed by applying heat treatments such as destabilization and subcritical treatments. The matrix HAKAN GASAN, Assistant Professor, and FATIH ERTURK, Graduate Student, are with the Institute of Metallurgy, Eskisehir Osmangazi University, 26480 Eskisehir, Turkey. Contact e-mail: [email protected] Manuscript submitted January 29, 2013. METALLURGICAL AND MATERIALS TRANSACTIONS A
structure transforms to martensite, while the eutectic carbides essentially remain unchanged by heat treatment. Additionally, in many alloys, some retained austenite and precipitated secondary carbides exist in the structure.[17–24] There are many studies in the literature that investigate the effect of structure on the abrasion resistance of high-chromium white cast irons. These studies have primarily focused on clarifying the structural phases resulting from different heat treatment techniques[2–8,10,14,17–28] and alloying elements.[7,9,18,29,30] From the results of these studies, it has been concluded that there is a strong correlation between the microstructural parameters and abrasion resistance. Therefore, it has been recognized that the determination of the heat treatment parameters and the optimum alloy composition for improving the wear resistance of white cast iron depends on a detailed investigation of structural parameters using various characterization techniques. There are some studies in the literature that are mainly focused on providing a quite detailed investigation of M7C3 carbides, secondary carbides, and retained austenite phases using advanced characterization methods. Volume fractions of phases (especially retained austenite) in the white cast iron have been determined using the X-ray method,[31] the Rietveld method,[32] an X-ray texture goniometer,[33] Conversion electron Mo¨ssbauer spectroscopy, and Eddy currents.[34] The formation, shape, size, morphology, and distribution of secondary carbides have been observed using a scanning
electron microscope (SEM) and transmission electro
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