Subsurface Fatigue Crack Generation and Strain Incompatibility Near Grain Boundaries for a Nitrogen-strengthened Austenitic Steel at Cryogenic Temperatures

Abstract

Fatigue damage in nitrogen-strengthened austenitic steel that showed subsurface crack generation and intergranular cracking at cryogenic temperatures has been characterized using electron backscatter diffraction (EBSD) analysis. Strain gradients near grain boundaries and localized stress concentrations in grains were clearly detected. The strain gradient in the vicinity of a grain boundary accompanied a misorientation of a few degrees, and may result from co-planar dislocation arrays at the grain boundary. To reduce localized strain incompatibility at grain boundaries, fine-grained duplex microstructure was obtained through partial recrystallization. The treated material showed considerably improved high-cycle fatigue strength and more homogenous plastic deformation.