An opproisal of the energy crdck zero (ECo) test in the evaluation of tempered martensite embrittlement (TME)

Tempered martensite embrittlement (TME) was investigated in an electroslag remelted (ESR) aeronautical grade SAE 4340 steel. The Charpy - V impact, plane strarn fracture toughness (K1") and energy crack zero (ECo) tests were employed to evaluate the reduced toughness of 300"C as compared with 200"C-tempered specimens after fracture in the temperature range from - 70'C to + 150"C. The ECo and Charpy - V results were comparable. The K1. test, however, failed to detect TME, even though a fatigue precracked specimen was used as in the ECo test. This discrepancy between the two tests is attributed to the different rnfluence of a microtough zone a few pm thick at the crack tip. Caution is therefore advised in the conversion of ECo values to their K6 equivalents.