X-Ray Measurement of Stress in Shot-Peened Spring Steel

Abstract

The correlations between the change of stress ΔσX measured by CrKα radiation and the nominal stress ΔσN were investigated on shot-peened spring steel specimens in various surface conditions.Tests were made under uniform bending. Besides, the residual stress distributions in shot-peened decarburized or non-decarburized specimens were examined.In case of shot-peened decarburized specimens, the ratio ΔσX/ΔσN was 0.59, and the residual compressive stress measured by X-rays showed steep ascent in the surface adjacent layer up to 30μ depth. The peak of the residual stress distribution appeared at about 100μ depth from the surface, and gradually decreased thereover. When the surface layers of shot-peened decarburized specimens were electrolytically polished to 100μ, the ratio ΔσX/ΔσN attained to 0.86∼0.88. When the residual stress of shot-peened decarburized specimens were relieved by annealing, the ratio ΔσX/ΔσN became 0.73∼0.82.In case of shot-peened non-decarburized specimens, the ratio ΔσX/ΔσN was 0.84∼0.93, and residual compressive stress measured by X-rays remained almost constant in the surface adjacent layer.It has been confirmed that the stress of shot-peened specimen measured by X-rays is much affected by steep residual stress distribution in the surface adjacent layer, but scarcely affected by the surface roughness.