Changes of Residual Stresses in Austempered Spheroidal Graphite Cast Irons due to Cyclic Stress.

概要

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The austempering treatment for spheroidal graphite cast iron is to produce a residual compressive stress at the surface of specimen and some retained austenite corresponding to the austempering temperature. This study was carried out to investigate the effect of the residual stress and the retained austenite on the fatigue behavior. The degree of the residual stress relaxation due to cyclic load which varies with the applied stress ratio (σmax/σB, σmax=cyclic max. stress, σB=tensile strength): at the higher stress ratio the change of the residual stress is dominated at the first loading. At the lower one the extent of the relaxation of residual stress depends on the magnitude of cyclic load and the number of cycles. While the amount of the retained austenite decreases progressively during fatigue process regardless of the applied stress ratio.These results suggest that a measurement of the residual stress and/or the retained austenite is available to predict the degree of the fatigue damage for spheroidal graphite cast iron.
The Iron and Steel Institute of Japanの論文