Browsing by Author "Han, Jingtao"

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    Ex situ analysis of high-strength quenched and micro-alloyed steel during austenitising bending process: numerical simulation and experimental investigation
    (Springer, 2022-05-11) Lu, Yao; Xie, Haibo; Wang, Jun; Jia, Fanghui; Lin, Fei; Zhou, Cunlong; Xu, Jianzhong; Han, Jingtao; Jiang, Zhengyi
    This paper compares the microstructure and mechanical evolution in a high-strength quenched and micro-alloyed steel during the austenitising bending process. Simulation results indicated a new finding that the stress neutral layer (SNL) tends to move to the tension zone during straining. The hardness gradient detected from the centre to compression/tension zones was resulted from comprehensive factors: First of all, the location of SNL revealed a prominent impact on strength. Second, the dislocation accumulation would be responsible for the hardness gradient on the surfaces. In addition, the overall strength decrease during straining was mainly ascribed to integrated effects of dynamic recovery (DRV) and dynamic recrystallisation (DRX). Apart from that, overall smaller martensite packet size and coarser prior austenite grains resulted in the increased hardness value at a lower bending degree. Also, the high consistency between experimental and simulation results is instructive for the practical forming process of railway spring fasteners.
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    Forming rate dependence of novel austenitising bending process for a high-strength quenched micro-alloyed steel: experiments and simulation
    (MDPI, 2025-02-06) Lu, Yao; Wang, Jun; Li, Zhou; Lin, Fei; Pan, Di; Jia, Fanghui; Han, Jingtao; Jiang, Zhengyi
    This austenitising bending investigation was carried out in a vacuum environment with the forming rates of 1, 10, and 100 mm/min under a certain bending temperature of 900 °C by a thermomechanical simulator. The enhanced strength at the accelerated forming rate and on the compression/tension zones throughout the thickness of the bent plates was discussed in detail in terms of dislocation pile-up, smaller prior austenite grain size, dynamic recrystallisation, smaller martensite packet, and stress-neutral layer. Since the simulation results were validated to match the experimental trend, this investigation could be applied as a valuable reference to simulate the practical manufacturing process of railway fasteners.
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    Optimising two-stage vacuum heat treatment for a high-strength micro-alloyed steel in railway spring clip application: impact on microstructure and mechanical performance
    (MDPI, 2023-07-10) Lu, Yao; Wang, Jun; Pan, Di; Han, Jian; Zhu, Lisong; Diao, Chenglei; Han, Jingtao; Jiang, Zhengyi
    The heat treatment process is a vital step for manufacturing high-speed railway spring fasteners. In this study, orthogonal experiments were carried out to obtain reliable optimised heat treatment parameters through a streamlined number of experiments. Results revealed that a better comprehensive mechanical performance could be obtained under the following combination of heat treatment parameters: quenching temperature of 850 °C, holding time of 35 min, medium of 12% polyalkylene glycol (PAG) aqueous solution, tempering temperature of 460 °C, and holding time of 60 min. As one of the most important testing criteria, fatigue performance would be improved with increasing strength. Additionally, a high ratio of martensite to ferrite is proven to improve the fatigue limit more significantly. After this heat treatment process, the metallographic microstructure and mechanical properties satisfy the technical requirements for the high-speed railway practical operation. These findings provide a valuable reference for the practical forming process of spring fasteners.