Microstructure, Mechanical and Abrasive Wear Behavior of 8.0 wt pct Cr White Iron Subjected to Continuous and Cyclic Ann
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HIGH-CHROMIUM white irons extensively used in mining and mineral processing[1–3] usually belong to hypoeutectic type containing 10 to 30 wt pct Cr and 2 to 3.5 wt pct C. The as-cast microstructure consists of hard eutectic carbides in a matrix of austenite which may transform to pearlite along with some martensite if the post-solidification cooling is not fast enough.[4–9] The high-chromium white irons containing 30 to 40 wt pct Cr and 1.5 to 2.5 wt pct C show ferrite matrix, normally undesirable in wear environment,[10] but suitable for corrosion resistance and heat resistance.[11] In cast hypoeutectic iron, the hard eutectic network of M7C3 carbides is crucial to the wear resistance, while the matrix microstructure makes a large contribution to the overall toughness.[6–9] In spite of higher eutectic carbide contents in hypereutectic white iron, the hypoeutectic alloys are preferred in wear applications because they provide better hardness in association with toughness as a major property requirement for mining implements experiencing a degree of impact during service. Further, researchers[9,12–14] have thought of alloy addition choosing elements like Ti, V, Nb,
SIDDHARTHA SANKAR MANDAL, K.S. GHOSH, and DIPAK KUMAR MONDAL are with the Department of Metallurgical and Materials Engineering, National Institute of Technology (NIT), Durgapur, 713209, India. Contact e-mail: dk_mondal2003@ yahoo.co.in Manuscript submitted November 4, 2016. METALLURGICAL AND MATERIALS TRANSACTIONS A
Mo, and W with a view to enhance the wear resistance through introduction of harder carbides and also to improve the hardenability of the alloy. Prior to service, high-chromium white irons are subjected to destabilization treatment[2,4,7,15–21] at low temperatures causing no modification to the as-cast eutectic carbides, but allowing precipitation of the secondary carbides from the austenite phase which later transforms to martensite on post-destabilization air cooling. In contrast, high-temperature destabilization favors spheroidization of the eutectic carbides and provides greater solubility of carbon and chromium in the austenite, thereby reducing precipitation of the secondary carbides. The carbon-enriched austenite experiences lowering of Ms-temperature and its retention in the air-cooled structure.[22] However, use of sub-critical treatment[23] followed by cryogenic treatment[24,25] has been suggested to reduce the retained austenite content in a martensite matrix. The types of secondary carbide formed during destabilization treatment depend on the composition and temperature of destabilization. Usually M7C3 and M6C carbides occur in 15 to 20 wt pct Cr white irons,[15,26–28] while the stable form of M23C6 carbides appear in white irons containing 25 to 30 wt pct Cr.[2,15,29] Relatively large volume fraction of carbides including both eutectic and secondary nature and their type, morphology, and distribution used to influence the wear resistance of chromium white irons. On the other hand, the matrix microstructure developed throug
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