X-ray diVraction (XRD) studies were carried out on 2•25Cr-1Mo steel boiler tubes from a thermal power station with an objective of developing a faster method of health assessment of this steel at elevated temperatures on a routine basis. Carbide phase transformations in virgin and service exposed boiler tubes (up to ~100 000 h) were determined for plate specimens using high power X-rays. Iron and chromium rich carbides were detected by XRD at various stages of transformation towards final equilibrium. Compositional variations of equilibrium precipitate M 23 C 6 with service life or overheating in the specimens studied were monitored by a shift in the lattice parameter. T he XRD results were validated by optical and electron microscopy, hardness measurements, and particle size measurements.MST /4296

Carbide phase transformation and alloying element partitioning in service exposed (about 45 000 -160 000 h) 2 . 25Cr -1Mo boiler tubes from a thermal power station were studied using X-ray diffraction and X-ray uorescence techniques on electrochemically extracted carbide precipitates. The objective of the present investigation was to develop a faster method of health assessment of this steel at elevated temperatures on a routine basis. Various carbide phases were detected with different lengths of service. The molybdenum content in extracted carbide specimens showed a systematic decrease with aging. Replenishment of molybdenum in the matrix may be a useful indicator in life assessment of this steel. When the dissolved molybdenum content in the matrix was less thañ 0 . 8 wt-%, the hardness of service exposed specimens was found to decrease. However, carbide precipitates extracted from new specimens subjected to accelerated heat treatment at 600 and 700°C showed an increase in molybdenum content with increase in temperature. The X-ray data were supplemented by microscopy, EDAX and hardness measurements.MST/5687

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