Impact of annealing treatments on the softening and work hardening behaviour of Jethete M152 alloy for subsequent cold forming processes

Cold forming processes present advantages to produce components with tight tolerances to the final (net) shape, eliminating significant production costs. These processes requires forming parts in a soft condition, with high ductility and formability. Jethete M152 alloy is a cold formable 13-Cr% martensitic stainless steel used in the aerospace industry. However, the inherent high strength of this material presents challenges in terms of the high loads and contact and friction stresses developed during cold forming processes. The main purpose of this work was to explore the impact of different types of annealing treatments (subcritical, full and isothermal treatments) on the softening and work hardening behavior of this alloy. Microstructural and mechanical testing analysis were conducted. The results indicate that only subcritical annealing treatments (T < Ar1) were successful by reducing the strength and hardness levels. However no significant effect on both work hardening behavior and uniform elongation was found. Due to the high hardenability of this alloy, those softening treatments which require the austenization of the material were translated into the formation of freshly (as-quenched) martensite, resulting into an increase of strength, loss in ductility properties and a significant change in the work hardening behaviour. Despite of the large differences in strength properties and work hardening behaviour across all the softening treatments analyzed, no significant microstructural differences were found. These results indicate that such differences are associated mainly to both dislocation density and the substructure developed during tempering/annealing at high temperatures.