Tribological Behavior of Optimized Heat-Treated Dual-Phase Bainitic and Martensitic Modified 9Cr-1Mo Steel
摘要
This study examines the tribological behavior of dual-phase bainitic–martensitic microstructures developed in modified 9Cr–1Mo steel through optimized heat treatments. Group-I specimens included Set-I and Set-II, both austempered at 460 °C for 60 and 120 min, followed by water quenching or air cooling, respectively. Group-II specimens comprised Set-III (austempered at 460 °C for 6 h) and Set-IV (austempered at 480 °C for 6 h), both of which were subsequently tempered at 760 °C for 0–30 min. Tribological testing revealed that Group-II specimens, which underwent tempering after austempering, exhibited markedly improved wear resistance compared with both the as-received and Group-I materials. The lowest wear volume, 2.88 mm3 at 30 N, was obtained for Set-III, which was tempered for 5 min, representing an 82.6% reduction relative to Set-I (16.58 mm3). The corresponding specific wear rate decreased from 4.9 × 10−4 to 8.5 × 10−5 mm3/N·m. Group-I specimens generally exhibited inferior wear performance, with wear volumes reaching up to 16.49 mm3 at 30 N. Several Group-II specimens displayed a decreasing specific wear rate with increasing load, indicating load-induced work hardening. Stable tribo-oxide films contributed to reduced friction, with Set-IV attaining a minimum coefficient of friction of 0.112 at 50 N, compared with 0.346 for the as-received material. A quantitative correlation between wear behavior and fractal dimension of wear scars offers predictive insights into wear progression. These results demonstrate a significant tribological enhancement through the combined use of austempering and tempering in modified 9Cr-1Mo steel.