As a commonly used engineering machinery material, 65Mn steel is widely used in manufacturing critical components, such as springs, gears, and cutting tools due to its excellent mechanical properties and cost-effectiveness. However, under actual working conditions, these components often experience serious failure due to complex loading and harsh environments involving high-speed operations. To extend the service life and meet practical engineering requirements, the work aims to employ plasma surface strengthening technology to perform surface quenching on 65Mn steel with varying overlap ratios, so as to enhance its wear resistance, hardness, and quenching efficiency. First of all, based on a self-developed experimental platform for laminar plasma surface hardening, and in conjunction with defined single-path hardening process parameters for 65Mn steel, experiments were conducted with overlap ratios of 0%, 20%, 40%, and 60% between adjacent hardening tracks during multi-paths hardening. Then, the microstructural evolution, hardness distribution, and wear resistance of the hardened specimens were characterized and analyzed through metallographic microscope, scanning electron microscopy, Vickers hardness testing, ultra-depth 3D microscopy, and white light interferometry, to explore the effect of the overlap ratio on the surface microstructure and mechanical properties of the 65Mn steel. The results indicated that after multi-paths quenching treatment, the specimen was divided into three cross-sections: quenching zone (comprising the first and second quenching paths, both exhibiting crescent-shaped profiles), the overlap zone and the substrate, and with the increasing overlap ratio, the quenching depth at the center of both hardened zones demonstrated an approximately linear growth trend. In addition, with the increase of the overlap ratio, the hardness of the first quenching zone and the second quenching zone gradually decreased, while the hardness of the overlap zone showed a trend of first increasing and then slightly decreasing. At the same time, the wear resistance of the overlap zone exhibited a consistent trend with its hardness variation, and when the overlap ratio was 40%, the hardness increased from 220HV0.2 to 340.44HV0.2, which was 55% higher than that of the substrate. The corresponding wear volume decreased from 2.59×10-3 mm3 to 1.64×10-3 mm3, which decreased by 37% compared with the substrate. The corresponding volume wear rate decreased from 5.39×10-6 mm3/(N·m) to 3.42×10-6 mm3/(N·m). Under dry friction conditions, the wear mechanism of the substrate was mainly abrasive wear, and the wear mechanism of the overlap zone was the joint action of abrasive wear and adhesive wear. With the increase of the quenching overlap ratio, the wear marks of the specimen surface first became shallow and then slightly deeper, and the wear morphology quality first improved and then slightly deteriorated. These results showed that the surface quenching quality and comprehensive mechanical properties were the best when the overlap ratio was 40%. The overlap ratio in laminar plasma surface hardening significantly affects the microstructure characteristics and surface wear resistance of the hardened zone, and an appropriate overlap ratio can contribute to the enhancement of the surface performance of 65Mn steel.
Key words
65Mn steel /
overlap ratio /
wear resistance /
microstructure /
laminar plasma surface hardening
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Funding
Luzhou City Science and Technology Plan Project (2024JYJ004); Scientific Research and Innovation Team Program of Sichuan University of Science and Technology (SUSE652A004); Panzhihua Key Laboratory of Advanced Manufacturing Technology Open Fund Project (2022XJZD01)
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