The paper deals with the tempered martensite embrittlement phenomenon
in the low-carbon low alloy 3Cr-Mo-V steel tempered in the temperature
range of 523-773 K. To determine the tempered martensite embrittlemen
t the Charpy-V test at the temperature 223 K was performed. The method
s of light microscopy, transmission electron microscopy (TEM) scanning
electron microscopy (SEM) and hardness testing (HRC) were applied. In
temperature dependance of CVN the minimum at 623 K was found to exist
. The mechanism of transgranular cleavage corresponding to a transgran
ular mode of the tempered martensite embrittlement was found out durin
g the failure. In the microstructure of the quenched states the retain
ed austenite around the martensitic laths as well as the fine carbide
particles inside the laths were observed. This can be considered as a
cause of the transgranular mode of the tempered martensite embrittleme
nt. The difference in grain size (0.1-0.8 mm) affects the tempered mar
tensite embrittlement of steel only weakly.