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 200-500 degrees C. To determine the tempered martensite embr
ittlement the Charpy-V test at the temperature -50 degrees C was perfo
rmed. The methods of light mickroscopy transmission electron microscop
y (TEM) scanning electron microscopy (SEM) and hardness testing (HRC)
were applied. In failure energy temperature dependence the minimum at
350 degrees C was found to exist. The mechanism of transgranular cleav
age corresponding to a transgranular mode of the tempered martensite e
mbrittlement was found put during the failure. In the microstructure o
f the quenched states the retained austenite around the martensitic la
ths as well as the fine carbide particles inside the laths were observ
ed. This can be considered as a cause of the transgranular mode of the
tempered martensite embrittlement. The difference in grain size (0.1-
0.8 mm) affects the tempered martensite embrittlement of steel only we
akly.