An investigation into the mechanism of tempered martensite embrittlement (TME) has been made in AISI 4340 steel.
The toughness of AISI 4340 steel, austenitized at high (1200℃) and low (870℃) temperature prior to tempering up to 400℃, had been evaluated by Charpy V-notch (CVN) impact test.
The CVN energy of the low temperature austenitized steel was higher than that of the high temperature austenitized steel, but both the high and low temperature austenitized steel showed the characteristic TME through at 300℃.
Interlath retained austenite was detected in as-quenched steel. At 300℃, cementite existed and fracture was intergranular.
The results indicated that TME in AISI 4340 steel was associated with the combined effects of the precipitated cementite by the decomposition of retained austenite and the impurity segregation during the austenitizing treatment.
