Corrosion Fatigue Crack Initiation of Type 316N Weldment Under the Influence of Cyclic Stress Amplitude

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Corrosion Fatigue Crack Initiation of Type 316N Weldment Under the Influence of Cyclic Stress Amplitude A. Poonguzhali1,2 · S. Ningshen1,2   · G. Amarendra1,2 Received: 13 March 2019 / Accepted: 28 July 2019 © The Korean Institute of Metals and Materials 2019

Abstract Corrosion fatigue behavior of type 316N stainless steel (SS) weldments on the damage characteristics is studied. The S–N curve of the fatigue life versus stress amplitude showed a specific two slope Basquin relationship. At low stress amplitude, the deformation microstructure consists mainly of planar slip dislocation structure and at high-stress amplitudes, planar multiple slip dislocations govern the cyclic behavior. A correlation between microstructural changes and the corresponding susceptibility of 316N SS weldment in as-welded condition towards environmental cracking in boiling acidified aqueous solution has been presented. The objective of the present study is to investigate the environmental effects on the corrosion fatigue crack initiation of type 316N weldmetal under the influence of cyclic stress amplitude. The difference in deformation micro mechanisms with stress amplitude in a corrosive environment is believed to be the major reason for the occurrence of a specific bilinear Basquin relationship in the S–N curve. Keywords  Stainless steel · Nitrogen · Corrosion fatigue · Deformation damage · Dislocation

1 Introduction Cyclic loading on engineering structures occurs due to transients in pressure, temperature, moment and force of system that are subjected to in-service. Environmentally assisted fatigue, known as corrosion fatigue, occurs due to the combined effect of stress, material and corrosive environment [1]. Type 316LN stainless steel (SS) has been chosen as a structural material for many primary heat transfer components in the Indian Prototype Fast Breeder Reactor (PFBR) for its superior creep strength as well as excellent corrosion resistance. Nitrogen added SS also improves resistance to pitting and crevice corrosion, sensitization and stress corrosion cracking. During welding of SS, hot cracking of the weld metal is one the most common problems other than sensitization. To achieve better creep strength and to avoid * S. Ningshen [email protected] 1



Corrosion Science and Technology Division, Metallurgy and Materials Group, Indira Gandhi Centre for Atomic Research, Kalpakkam 603 102, India



Homi Baba National Institute, Metallurgy and Materials Group, Indira Gandhi Centre for Atomic Research, Kalpakkam 603 102, India

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hot cracking in as-weld condition, some amount of high temperature delta ferrite is retained in the weld deposit [2]. Ferrite content between 3 and 7 FN, along with primary ferritic solidification mode is rendered to avoid hot cracking during welding process [3]. High heat input during welding also affects sensitization as well as hot cracking behavior [4]. These micro-chemical heterogeneities in the weldmetal result in preferential corrosion attacks at the δ/γ boundaries. Presence of δ-ferrite decreases th

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