Long-term aging at 475°C: Effects on the microstructure and properties of custom 465® alloy

• Investigates long-term aging effects at 475 °C on Custom 465® alloy. • Precipitation of η-Ni₃Ti and α′-Cr-rich phases observed during aging. • Increase in reverted austenite helps maintain elongation and impact energy. • Mechanical strength decreases slightly, but ductility is preserved. • Insights into optimizing thermal stability for demanding engineering uses. This study examines the effects of long-term aging at 475 °C on the microstructure and mechanical properties of the precipitation-hardened stainless-steel alloy, Custom 465®. The research combines theoretical insights with experimental analyses to investigate key transformations occurring during extended thermal exposure. Advanced characterization techniques, including TEM and XRD, showed that quality heat treatment facilitates the precipitation of η-Ni₃Ti particles and the development of a minor portion of RA within tempered lath martensite. Prolonged aging for 1000 and 2000 hours enhances the precipitation of η-Ni₃Ti particles and the α′-Cr-rich phase through the spinodal decomposition of the α-solid solution, accompanied by an increase in the amount of reverted austenite. The mechanical properties of the alloy were found to evolve with aging time. While strength values decreased slightly, elongation and impact energy remained stable, highlighting the critical role of reverted austenite in mitigating the embrittlement caused by the α′-Cr-rich phase. These findings underscore the complex interplay between phase transformations and mechanical behavior, suggesting that controlled heat treatment can optimize the balance between strength and ductility. This research provides valuable insights into the thermal stability of Custom 465® alloy, with implications for its application in demanding engineering environments.