Correlation of Cooling Rate, Microstructure and Hardness of S34MnV Steel
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INTRODUCTION
THE crankshaft is a critical component of large marine engines. Because of its complicated running condition, very strict quality requirements are needed for the crankshaft.[1] A semi-built method is used to manufacture the large marine crankshaft. The crankthrows and the main journals are formed separately, then assembled together using a shrink fitting process. The crankthrow is the key part of the whole crankshaft, and it is generally formed by a bending process. Owing to its complex shape and ease of introducing defects at the heating and heat treatment stages, as well as during the forging stage, the mechanical and material performance requirements are always difficult to achieve. Originally, researchers only focused on studying the forging process. Sun et al.[2] established an empirical model to simulate the grain size distribution and evolution during a large crankthrow heating and forging process. To optimize and control the whole manufacturing process of large crankshafts more reasonably, phase transformations should also be taken into account. Milenin et al.[3] developed a mathematical
ZHIYING CHEN is with the School of Mechanical and Automotive Engineering, Shanghai University of Engineering Science, 333 Long Teng Road, Shanghai 201620, P.R. China Contact e-mails: [email protected], [email protected] PHILIP NASH is with the Thermal Processing Technology Center, Illinois Institute of Technology, 10 West 32nd Street, REC-243, Chicago, IL 60616-3793. YING ZHANG is with the School of Materials Engineering, Shanghai University of Engineering Science, 333 Long Teng Road, Shanghai 201620, P.R. China. Manuscript submitted December 10, 2018. Article published online June 10, 2019. 1718—VOLUME 50B, AUGUST 2019
model of crankshaft deformation during heat treatment, considering both the elastic–plastic deformation and phase transformations. For a particular steel composition, most properties depend on microstructure. Processing methods, such as forging and heat treatment provide efficient ways to control the microstructure and manipulate the properties of the metal. The Jominy end-quench test is one of the most reliable and common methods used for the characterization of the hardening and microstructures of steels. C¸akir and O¨zsoy[4] examined the hardenability of the AISI 1050 steel using the Jominy test for three different quenching media. Franco et al.[5] studied the relation between magnetic Barkhausen noise and hardness for Jominy quench tests in SAE-4140 and SAE-6150 steels. Hadi et al.[6] carried out hardenability experiment of EMS-45 tool steel using Jominy ASTM A255 test method. Using the Jominy test, Fernandino et al.[7] concluded that the microstructure is largely influenced by the cooling rate for a partially austenitized ductile iron, Dobuzhskaya et al.[8] established the relationship between hardness and microstructure of K76F rail steel corresponding to specific cooling rates, Zheng et al.[9]studied dissolution and precipitation behaviors of boron-bearing phase and their effects on hardenabi
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