P. M. Singh, H. Garmestani, Georgia Institute of Technology, Atlanta, GA; B. Nguyen, Moog, Torrance, CA; T. R. McNelley, Naval Postgraduate School, Monterey, CA
Custom 465 (S46500) is an age-hardenable martensitic stainless steel designed for applications requiring combinations of high strength and toughness. However, custom 465 in the solution annealed and cold treated condition is relatively low in strength and strain-hardening rate due to the low carbon concentration in the martensite. Aging of fully martensitic precipitation hardening in S46500 stainless steel results in strengthening due to the formation of precipitate like γ-phase (Ni3Ti). Cold working prior to aging enhances the precipitation and resulting aging response. For example, the yield strength is increased from about 240 ksi for unreformed material to approximately 295 ksi in material given a 70% cold reduction prior to aging at 482°C (H900). Deformation-induced defect structures may affect precipitation kinetics and precipitate morphology. This behavior of steel was exploited to develop a surface layer with high strength and high hardness on the annealed Custom 465 samples by surface straining the samples by shot peening treatment prior to final aging. This allows for the surface hardness to be increased without significantly reducing the bulk toughness. Corrosion properties of surface treated samples were compared with the non-treated annealed Custom 465 samples. Improvements in the surface hardness with shot peened and aged samples will be discussed.
