Thermo-Mechanical Processing-Induced Microstructure Refinement of Co-۲۸Cr-۶Mo-۰.۳۳C Alloy and Its Impact on Wear Behavior

Grain refinement in Co-۲۸Cr-۶Mo-۰.۳۳C alloy was achieved through minimal plastic deformation and a two-step heat treatment. The solution-treated specimens were furnace-cooled, resulting in a pearlitic structure at grain boundaries. These were then compressed and aged at ۸۵۰°C, leading to the decomposition of the austenite phase into a lamellar eutectoid structure (α+M۲۳C۶). Reverse treatment at temperatures stabilizing austenite facilitated nucleation of a fine-grained austenitic structure with an average grain size of ۴۸.۲۳ μm, about one-tenth of the original size. The hot compression behavior was examined between ۱۱۰۰-۱۲۰۰°C and strain rates of ۰.۰۰۱-۱ s-۱. The activation energy was calculated as ۷۴۴.۶ kJ/mol. Microstructural analysis showed competition between dynamic recrystallization (DRX) and precipitation, especially at low strain rates (۰.۰۰۱ s-۱). Precipitates at grain boundaries hindered DRX, while prolonged coarsening of precipitates promoted DRX. This competition caused serrated grain boundaries and oscillations in the flow curves. Wear behavior, assessed by pin-on-disk tests, indicated that carbide shape, distribution, and size significantly affected wear resistance. Large and lamellar carbides resulted in lower wear resistance compared to fine globular carbides in solution-treated and quenched specimens. ε-Martensite formation during sliding reduced wear rate due to fewer slip systems in the hexagonal structure.

کلیدواژه ها:

Co-Cr-Mo-C alloys ، Material characterization ، Microstructural refinement ، Precipitate formation ، Microstructural improvement ، Tribological behavior.