Abstract
It is known that the notch strength and the notch toughness are considered to be the important characteristics for constructional alloy steels possessing higher level of strength.
From the results of former investigations, one of the authors found out that low tempering temperature embrittlement of hardened alloy steels which occurred at tempering temperatures of 300-350°C markedly reduced the notch strength of the steels under various testing conditions, such as repeating impact, tensile and fatigue tests performed to see the properties of notched bar.
This report was intended to state the studies made on the effect of testing temperatures, varying from -70 to +200°C on Charpy impact values with two heats of Ni-Cr steels which were oilhardened and then tempered at various temperatures ranging from 100 to 450°C. From the results it was noted that the transition temperature, observed from impact value, was apparently a function of the tempering temperature, and that the tempering within the range of embrittlement caused a higher transition temperature, whereas the tempering at approx. 200°C resulted in the lowest transition temperature. Refering this result to the results of studies made by other investigators, on the influencing factor on low-tempering-temperature embrittlement together with the factors generally affected on the transition temperature of steels, the authors suggested the possible reduction of the embrittlement by improving steel-making process, especially by means of the careful operation in the practice of deoxidation, dephosphorization, nitrogenfixation and grain-size controlling.
