Abstract The research focuses on the modification of the microstructure in high-pressure diesel engines through improvements in the austempering process. Unstable conditions during the austempering treatment led to the formation of undesirable microstructural features, including non-uniform subsurface decarburization, excessive carbide precipitation, and regions of pearlitic phases due to inadequate cooling. These defects contributed to surface peeling and fatigue cracking under high cyclic pressure, leading to fuel leakage. A comprehensive root cause analysis was performed to examine the heat treatment and post-processing methods. The study highlights modifications to the austempering quenching process to achieve a more consistent lower bainitic microstructure, which enhances fatigue strength and wear resistance. Studies were performed on precise salt bath control, optimized racking configurations, and refined heat treatment parameters to ensure uniform quenching conditions and promote complete bainitic transformation. Post-processing shot peening treatment was also introduced to mitigate the effects of hot corrosion, further enhancing component durability in cyclic high-pressure environments.
Sun et al. (2026) studied this question.