Abstract In this study, the effects of ultrasonic nanocrystal surface modification (UNSM) treatment on the surface integrity, microstructures and wear resistance of 300M ultra-high strength steel (300M steel) were investigated. The results showed that surface roughness of 300M steels after UNSM processing was significantly decreased with a lower scanning speed even though the surface roughness values were higher than that of mechanically polished control samples. In addition, the surface hardness of 300M steel was significantly enhanced as the static load increased. It was found that using a static load of 50 N and a scanning speed of 250 mm/min in the UNSM process can significantly improve surface hardness (797 HV) while slightly increasing the surface roughness. With these parameters, the resulting microstructure of UNSM-processed samples have three layers: the layer of severe plastic deformation, the layer with gradual plastic deformation, and the unaffected layer. Due to the plastic deformation, greater and deeper compressive residual stresses were induced in the UNSM-processed samples. In addition, the wear resistance of UNSM-processed samples was significantly improved, which was attributed to the refined martensite laths, work hardening and compressive residual stress.

中文翻译：

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超声纳米晶表面改性对300M马氏体超高强钢表面完整性、显微组织和耐磨性的影响

摘要 本研究研究了超声纳米晶表面改性(UNSM)处理对300M超高强度钢(300M钢)表面完整性、显微组织和耐磨性的影响。结果表明，UNSM 处理后 300M 钢的表面粗糙度在较低的扫描速度下显着降低，即使表面粗糙度值高于机械抛光对照样品的表面粗糙度值。此外，300M钢的表面硬度随着静载荷的增加而显着提高。发现在UNSM工艺中使用50 N的静载荷和250 mm/min的扫描速度可以显着提高表面硬度（797 HV），同时略微增加表面粗糙度。有了这些参数，UNSM 处理后样品的微观结构分为三层：严重塑性变形层、逐渐塑性变形层和未受影响层。由于塑性变形，UNSM 处理的样品中产生了更大和更深的压缩残余应力。此外，UNSM 处理后试样的耐磨性显着提高，这归因于细化的马氏体板条、加工硬化和压缩残余应力。