目的 研究闪光焊焊接接头经过不同方式焊后热处理后冲击磨损性能的改变。方法 对未经过热处理的焊接接头和分别进行余热淬火、去应力退火和正火热处理的4种焊接接头进行不同区域的微观组织和力学性能分析。然后利用冲击磨损试验机对焊接接头进行冲击磨损试验,最后探讨焊后热处理的焊接接头冲击损伤机理。分析了不同焊接接头各区域的冲击磨损与损伤性能。结果 焊后热处理细化了焊接接头微观晶粒大小,焊后热处理不同程度地提高了焊接接头硬度,其中热处理后细晶区平均硬度在450~500HV0.5,较热处理前提高了10%以上。此外通过冲击磨损形貌分析,发现焊后热处理后材料剥落和裂纹都明显减少,在软化区表现尤为明显,磨损体积减少了30%以上。结论 焊接接头片层间距和晶粒大小直接影响硬度大小,片层间距和晶粒大小越大,硬度越低,且晶粒大小与硬度的对应性更好。焊接接头的抗冲击磨损性能与硬度密切相关,硬度越高,冲击损伤和氧化损伤越轻微,同一焊接接头中,软化区的冲击磨损现象最严重。焊后热处理可以改善焊接接头微观组织和抗冲击磨损性能,使焊接接头整体力学性能更集中,余热淬火后焊接接头抗冲击磨损性能改善效果显著,其次是正火,最后是去应力退火。
Abstract
Welded joints are the vulnerable parts in railway transportation. Therefore, research on improving the performance of welded joints is of great significance. After rail welding, the mechanical properties and microstructure of welded joints can be enhanced through post weld heat treatment. The work aims to investigate the impact wear and damage behaviors of four types of welded joints in different regions: non-heat-treated, self-quenched, stress-relieving annealed, and normalized. The effect of post weld heat treatment on the impact wear resistance of rails was explored. After post weld heat treatment, the overall microstructure type remained unchanged. The fusion zone and the normalized zone exhibited lamellar pearlite, while the softened zone showed granular pearlite. Nevertheless, the microstructure was refined, with both the lamellar spacing and grain size decreasing. The hardness of each region increased. Especially in the normalized zone, the hardness reached 450-500HV0.5, representing a 12% increase compared to that before heat treatment. It was found that the lamellar spacing and grain size of welded joints directly affected the hardness. Specifically, the larger the lamellar spacing and grain size, the lower the hardness, and the correlation between grain size and hardness was more prominent. Additionally, a new microstructure, martensite, was observed in the quenched welded joints, which further increased the hardness. Impact wear experiments were carried out on different regions of the four types of welded joints with an impact wear testing machine. The measurement results indicated that post weld heat treatment improved the impact damage of each region to varying extents. The improvement in the softened zone was particularly evident, with the impact wear volume reduced by at least 30% and the impact wear depth decreased by at least 10%. The impact wear resistance of welded joints was closely associated with hardness. The higher the hardness, the milder the impact damage and oxidation damage. Among the same welded joint, the impact wear phenomenon in the softened zone was the most severe. Under the impact effect, various micro areas under different welding processes clearly showed circular concave pits on the impact surface, accompanied by crack generation and propagation, ultimately leading to material peeling and material accumulation at the edge of the impact pit. The material deformation in the normalized zone was slight, and the edge of the impact pit was slightly raised. At the fusion line and softening zone, the material protruded significantly around the impact crater. In conclusion, post weld heat treatment can optimize the microstructure and impact wear resistance of welded joints. The self-quenched welded joints show a remarkable improvement in impact wear resistance, with the least crack initiation and spalling in each region. The normalized welded joints come second, followed by the stress-relieving annealed welded joints. The phenomenon of oxidation during impact in the softened zone is also quite obvious. The oxygen content in the softened zone of each welded joint significantly increases after impact wear, and the oxygen distribution in each zone is concentrated within the impact pit without spreading outward. In the softened zone and the fusion zone, the impact wear mainly evolves from adhesive wear to fatigue wear, while the base material zone shows adhesive wear, and the normalized zone is between the two wear mechanisms.
关键词
钢轨焊接接头 /
微观组织 /
冲击损伤 /
磨损机制 /
硬度
Key words
rail welded joint /
microstructure /
impact wear /
wear mechanism /
hardness
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基金
国家自然科学基金（52575234）; 四川省博士后创新人才支持项目（BX202420）; 轨道交通运载系统全国重点实验室自主研究课题（2024RVL-T02）; 中央高校基本科研业务费专项资金（2682024CG007）
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