Changes in Residual Stress, Domain Size and Microstrain during Fatigue of 1008 Steel.
NORTHWESTERN UNIV EVANSTON IL DEPT OF MATERIALS SCIENCE
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Changes in the positions and shapes of x-ray diffraction peaks have been examined after low-cycle and high-cycle strain-controlled fatigue of normalized and cold-worked 1008 steel. Measurements were made at and below the surface. Domain mosaic size is sometimes the major contributor to peak breadth, but sometimes it is controlled by microstrain, or by both quantities. Microstrains are larger after low-cycle fatigue than after high-cycle fatigue. The surface residual stress is altered by fatigue, and the pattern of change with cycling is similar for low or high strains, and for initially normalized or cold-worked specimens. Near failure in low-cycle fatigue of a cold-worked specimen, the domain size and microstrain approach those for a cycled annealed specimen. Dislocation densities are the order of 10 to the 13th power - 10 to the 14th power per sq m. Cycling in the initially normalized condition increases both the dislocation density and dislocation arrangements with long-range strain. However, with cold-worked 1088 steel, the density decreases and, near failure, the dislocation array is nearly random. In all cases, the peak breadth passes through a minimum vs. depth below the surface.
- Properties of Metals and Alloys