Exposure-History-Dependent Hydrogen Retention and Release in 100Cr6 Steel and Their Implications for Bearing Design

This study examines operational hydrogen memory in hardened 100Cr6 bearing steel using an analytical model constrained by published room-temperature effusion and FE8 accumulation measurements. The primary single-exponential retention model has an apparent room-temperature half-life of 63.4 h; an added fast decay was poorly identifiable. An effective input inferred from the 30 h FE8 measurement reproduced the 50 h increment within 0.3% as a conditional source-scale check. For 10 h of input at 0.005 ppm per hour followed by a 40 h interruption, the first interruption removed 35.4% of the releasable hydrogen. The post-interruption residual increased from 0.0306 ppm after the first cycle to 0.0725 ppm after 12 cycles, approaching a periodic value of 0.0726 ppm. When cumulative input and interruption times were both fixed at 120 h, replacing one long input–interruption pair with 24 shorter pairs increased the final releasable hydrogen content from 0.0899 to 0.2062 ppm. The exposure sequence thus determines the residual state alongside cumulative durations. This ordering persisted in conditional bootstrap and leave-one-out calculations and the exploratory two-exponential comparison. The results support comparing both peak content and the residual before renewed loading, using measured uptake and release responses to screen effective entry and sustained low-input interruptions for candidate bearing designs.