Wear and Phase Transformation of Medium-Carbon Nanostructured Bainitic Steel Under Dry Sliding for Automotive and Rail Applications
摘要
In this study, the dry-sliding wear behavior of medium-carbon nanostructured bainitic steel was investigated. The increasing demand for strong, tough, and wear-resistant materials in automotive and rail applications has made bainitic steel with retained austenite a promising option. X-ray diffraction (XRD) confirmed the presence and quantified the volume fraction of retained austenite, while optical, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analyses revealed a fine bainitic matrix with dispersed retained austenite films. Wear behavior was investigated under varying normal loads (15 to 60 N) and sliding distances from 1500 to 4500 m, revealing an increase in specific wear rate from 2.45 × 10−6 to 3.11 × 10−6 mm3/N m. The wear mechanisms evolved with increasing load and sliding distance, transitioning from grooves and localized detachment at lower loads to delamination and oxidative wear at higher loads. Quantitative hardness measurements showed an increase from 610 ± 7 to 665 ± 6 HV (D70 sample) and from 627 ± 6 to 690 ± 8 HV (D80 sample) after wear, indicating significant work hardening. Importantly, phase transformation was detected early during wear, with retained austenite content decreasing due to wear-assisted strain-induced martensitic transformation. Electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM) analyses of worn surfaces provided direct evidence of this transformation, revealing the formation of martensitic phases and microstructural refinement at the wear interface. This transformation intensified with increasing load and sliding distance, culminating in the near-complete disappearance of retained austenite at the highest test conditions, thereby enhancing surface hardness and wear resistance.