The physical and microstructural properties of peened austenitic stainless steel

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Abstract

Surface treatments used to improve the life of a material known as peening are already extensively used in industry. The main aim of peening is to introduce compressive resiudal stress to the surface and subsurface of a metallic material, however literature also includes a number of microstructural and mechanical effects that peening introduces to a material when the compressive residual stress is established.The aim of this dissertation is compare and contrast the mechanical and microstructural effects of a current industrial peening method called shot peening, with three new increasingly competitive surface treatments. These are laser shock peening, ultrasonic impact treatment and water jet cavitation peening. The surface finish, and changes in microstructure, hardness depth profile, residual stress depth profile and plastic work depth profile of the four surface treatments are analysed. The effect of the peening parameters on the material is also determined, such as length of time of treatment, shot size, step size, direction of treatment, and irradiance per centimetre squared.The effect of peening on the residual stress depth profile of a gas tungsten eight pass grooved weld is also determined. Welding is a known region of early failure of material, with one of the factors affecting this being the introduction of tensile residual stress to the surface and near surface of the weld. An analysis to determine if peening the welded region alters the residual stress was carried out.In all experiments in this dissertation, the material that was used was austenitic stainless steel, as this material is highly used, especially within the nuclear industry.The results of this dissertation show that different peening types and peenign parameters produce a variety of surface, microstructural and mechanical effects to austenitic stainless steel. Peening of an aaustenitic stainless steel welded region results in teh near surface tensile residual stress to alter to ccompressive residual stress.

Keyword(s)

peening, austenitic stainless steel, shot peening, laser shock peening, ultrasonic impact treatment, water jet cavitation peening ; residual stress, surface finish, hardness, plastic work, microstructure, welds

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