Ｘ線材料強度 高マンガンオーステナイト鋳鋼の疲労き裂進展挙動とＸ線フラクトグラフィ

Abstract

Fatigue crack growth tests were carried out using a high manganese austenitic cast steel under constant amplitude loading. Average crystal grain sizes of the material are 200 micro-meters and 1000 micro-meters. For this material, threshold stress intensity factor range (ΔKth) is about 8MPa√m which is quite large as compared to the ΔKth of general structural steels. The crack growth rate is lower than the general structural steels especially in the lower ΔK region. The reasons of this behaviour are crack closure due to bridging and fretting oxide, decreasing of the stress concentration near the crack tip due to secondary crack and slip on crystal plane. X-ray fractography can be applied to the fatigue fracture surface of the material which has large grain by using oscillation of X-ray beam and in-plane oscillation on the fracture surface. The half-value breadth of the diffraction profile on the fracture surface increases with increase in the effective stress intensity factor range. The relationship between the half-value breadth and the effective stress intensity factor range was represented by a narrow band regardless of the stress ratio.Therefore, the effective stress intensity factor range can be estimated from this relation in fractured surface of actual components.