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

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. A schematic of corrosion fatigue crack initiation involving the emergence of a slip step and dissolution of the step on the surface: (a): before cyclic loading (b): fatigue crack initiation and (stage I and II) crack propagation during cyclic loading.