Investigation on Tensile Properties of Austempered SAE52100 Steel
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INTRODUCTION
SAE52100 (AISI52100/GCr15/En31/SUJ2/ 100C6/100Cr6/I915) is a high carbon ferrous alloy which is frequently used in bearing applications.[1–4] The traditional heat treatment process applied on SAE52100 steel is quench-tempering, which has been widely used in many industries because of its low cost and high efficiency in production. The quench-tempering process consists of an austenitizing step followed by a rapid quenching step to achieve the formation of martensite. Then, as-quenched steels are subjected to an additional tempering step to reduce the brittleness and release internal stress. The final mechanical properties are strongly dependent on the tempering temperature and time.[5–8] In tempering, martensite is transformed into tempered martensite containing carbide particles or islands in a ferrite substrate.[9–11] Martensitic SAE52100 steel has good strength, high hardness, and excellent fatigue resistance which are vital to satisfy lifetime requirements for bearings.[12–14] YUMING PAN and GARY C. BARBER are with the Automotive Tribology Center, Department of Mechanical Engineering, School of Engineering and Computer Science, Oakland University, Rochester, Michigan, 48309. BINGXU WANG is with the Faculty of Mechanical Engineering and Automation, Zhejiang Sci-Tech University, Xiasha High Education District No.2 Street, #928, Hangzhou, Zhejiang, 310018, P.R. China. Contact e-mail: [email protected] Manuscript submitted August 10, 2019.
METALLURGICAL AND MATERIALS TRANSACTIONS A
In the last two decades, austempered SAE52100 steel with its unique bainitic microstructure has attracted considerable attention since it is expected to have better properties than conventional SAE52100 steel. The isothermal heat treatment used to produce the bainitic microstructure has two separately controlled steps: austenitizing step and austempering step. The austenitizing step is used to convert the as-received microstructure into unstable austenite above the Acm temperature. In the austempering process, fully austenitized steel is quenched to a low temperature which is above the formation temperature of martensite and maintained for a specific duration. During this process, the austenite is transformed into bainite. The intermediate quenching should be as rapid as possible to avoid the formation of pearlite which would result in the degradation of mechanical properties. The performance of austempered SAE52100 steel has been studied by varying the heat treatment parameters, chemical compositions and test apparatus and methodologies. Krishna et al.[15] found that austempered SAE52100 specimens with an austempering temperature of 350 °C had higher impact strength than martempered specimens, and improvements became remarkable with the extension of holding time. Chakraborty et al.[16] proposed to develop SAE52100 steels with a duplex microstructure containing bainite and martensite instead of full bainite. The test results showed that the duplex matrix could significantly enhance the hardness, tensile strength, and impact
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