Abstract
Full and subsize Charpy V notch specimens from several locations of a high pressure–intermediate pressure Cr–Mo–V turbine rotor were tested. A comparison between full and subsize impact energy data showed that the smaller specimens exhibited qualitatively similar behaviour, with a systematic reduction in fracture appearance transition temperatures (FATTs). The full and subsize impact energy data were normalised against the specimen area and volume. The latter normalisation produced the closest match and the offset between the two data sets was described by a simple linear equation. The sensitivity of impact energy and FATT to specimen size was examined in samples possessing different degrees of temper embrittlement. It was found that the difference in FATT between full and subsize specimens for embrittled samples was at least double that of deembrittled samples. It is proposed that the observed specimen size/impact energy/FATT variations with degree of embrittlement arise from sensitivity of intergranular fracture to lineal specimen thickness, since fracture occurs predominantly through a twodimensional network of grain boundaries.
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