１ＣｒＭｏＶ鋼切欠き材のクリープ疲労寿命と内部損傷

Abstract

Creep-fatigue rupture life and its elastic stress concentration dependence for circumferentially notched 1CrMoV steel bars have been investigated. The elastic stress concentration Kt dependence of creep-fatigue life under 30 minutes tensile hold cyclic loading at 550°C for the long term used material was different from the unused material. The notch strengthening behavior was observed on the both materials as in the case of creep loading conditions. The maximum rupture life was observed at Kt=1.9 for the unused material, while it was at Kt=2.6 for the long term used material.The distribution of hardness across the minimum notch section corresponded to the distribution of cavity density. Many cavities were observed at the softening part. The hardness of the long term used material was lower than the unused one.The fracture strain of the notched specimen under creep-fatigue loading had an inversely proportional relationship with the rupture life. The high triaxial stress state specimen of the unused material (Kt=2.6 or 3.5) exhibited low fracture strain in the intermediate stress range, about a half of the strain of others. The fracture strain of the long term used material was higher than the unused one. In the lower stress range, the fracture strain of the notched specimen was relatively low for both of the materials. Bridgman effective stress which considers the stress triaxiality seemed useful to well evaluate the rupture life of circumferentially notched specimen under creep-fatigue conditions for both the long term used and unused materials.