Abstract
In the present study, grade 92 steel blanks were subjected to normalizing (1080 °C / 1 hr.) and tempering (780 °C / 1 hr.) followed by air cooling. Stress rupture tests were performed using start testing systems’ uni-axial creep testing machines. The specimens used were circumferential 60° V-notch specimens with notch depth of 0.5, 1.0 and 2.0 mm. The test temperature was 650 °C and net applied stress level was 195 MPa. Notch strengthening effect was observed in grade 92 steel due to generation of tri-axial state of stress at the notch root. Post-creep characterization included scanning electron micrography of creep fractured samples which showed mixed mode of fracture. The fracture at area near the notch root was dominated by brittle fracture whereas the one near the center of the specimen was dominated by ductile fracture. Brittle mode of fracture was attributed to the mechanical constraint at the notch root and ductile fracture developed following creep cavitations and micro-void coalescence.
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