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P92 steel (9Cr-0.5Mo-1.8W) was subjected to a heat treatment of 1050°C/30 min/air cooling/780°C/ 120 min/air cooling followed by 1080°C/30 min/air cooling/740°C/60 min/air cooling to obtain tempered martensite microstructure, for better creep strength. Stress rupture tests carried at 600°C in the range of 250-350 MPa resulted in rupture times in the range of 200-3000 h. Straight line plot of stress rupture curve indicated no major change in deformation mechanism. Coarsening of precipitates and substructure development were the main reasons for microstructure degradation, consequently leading to reduced hardness of the sample. Gauge and grip portions of the same sample were sectioned to comparatively evaluate the effects of stress and aging. Gauge portion of 3000 h sample showed considerable change in the microstructure in terms of boundary migration, while that of grip portion hardly evolved. The ruptured samples exhibited predominantly ductile fracture with elongated cavities at higher rupture times.

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