A. Shekhter et al., Effect of temper embrittlement and specimen size on Charpy impact testing of a Cr-Mo-V rotor steel, MATER SCI T, 17(2), 2001, pp. 141-147
Full and sub-size Charpy V notch specimens from several locations of a high
pressure-intermediate pressure Cr-Mo-V turbine rotor were tested. A compar
ison between full and sub-size impact energy data showed that the smaller s
pecimens exhibited qualitatively similar behaviour, with a systematic reduc
tion in fracture appearance transition temperatures (FATTs). The full and s
ub-size impact energy data were normalised against the specimen area and vo
lume. The latter normalisation produced the closest match and the offset be
tween the two data sets was described by a simple linear equation. The sens
itivity 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 sub-size specimens for embrittled samp
les was at least double that of de-embrittled samples. It is proposed that
the observed specimen size/impact energy/FATT variations with degree of emb
rittlement arise from sensitivity of intergranular fracture to lineal speci
men thickness, since fracture occurs predominantly through a two-dimensiona
l network of grain boundaries.