Hot Deformation Behavior and Dynamic Recrystallization of Medium Carbon LZ50 Steel
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THE understanding of the hot deformation behavior together with the constitutive relations describing material flow is a prerequisite for large-scale production in the industry. The constitutive modeling of flow stress is thus important in forming processes because any feasible mathematical simulation needs accurate flow description.[1–3] In the past several decades, a number of research groups have paid attention to hot deformation behaviors of microalloyed steels,[4–6] carbon manganese steels,[7,8] and stainless steels.[9–11] During hot working, dynamic recovery (DRV) and dynamic recrystallization (DRX) are the restoration phenomena that significantly affect the flow behavior. DRX is an important mechanism for the microstructure control during hot deformation. DRX plays a major role in reducing the flow stress and is a powerful tool for controlling mechanical properties during processing. In the previous research, DRX behavior during hot deformation of metallic materials has been widely investigated. Mirzadeh investigated the constitutive relationships and DRX characteristics of a medium carbon V-Ti microalloyed steel.[12] Lv et al. investigated the DRX behavior of Mg-2.0Zn-0.3Zr alloy by hot SHIWEN DU is with the School of Materials Science and Technology, Taiyuan University of Science and Technology, Taiyuan, 030024 , Shanxi, China, and also with the Shanxi Key Laboratory of Metal Forming Theory and Technology, Taiyuan, Shanxi, China Contact e-mail: [email protected], [email protected] SHUANGMEI CHEN, JIANJUN SONG, and YONGTANG LI are with the School of Materials Science and Technology, Taiyuan University of Science and Technology. Manuscript submitted December 11, 2015. Article published online January 9, 2017 1310—VOLUME 48A, MARCH 2017
compression experiments.[13] Wang et al. evaluated the DRX behavior and microstructural evolution of V-Ti microalloyed forged steel.[14] However, limited research has focused on the hot deformation characteristics of medium carbon steels, which are widely used in forging due to their superior properties such as high strength and plasticity. The medium carbon steel LZ50 tested in this study is widely used in railway axles. In order to improve the mechanical performance of the products, microstructural evolution of LZ50 steel during hot deformation process should be controlled precisely. However, up to now, microstructural modeling and simulation for LZ50 steel during hot deformation have not been reported. In this paper, the effects of deformation temperature and strain rate on the flow stress and microstructure are experimentally determined, which is followed by a description of the flow behavior under conditions hot compression. Two-stage flow stress model is used to predict its flow stress behavior. Finally, the evolution of DRX microstructure, as well as DRX models of the volume fraction and average grain size is proposed.
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EXPERIMENTAL PROCEDURE
The isothermal compression was conducted using a Gleeble-3500 thermo-mechanical simulator. The cylindrical compression samples, with a
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