Abstract
It is well known that almost all the b. c. c. metals show brittleness at low temperature. This property means that viscosity falls with decrease in temperature. It is expected from this that there is a change of ultrasonic attenuation in the metal at the transition region from ductile to brittle property. In our previous investigation, attenuation in carbon steels at low temperature decreased suddenly in a way similar to the notched-bar impact value under similar condition.
In the present paper is reported the change of transition temperature of the ultrasonic attenuation in S20C carbon steel with the number of repeated stress cycles within the range of -20°C to room temperature. The relation is explained by Orowan's theory.
The results are summarized as follows:
(1) The transition temperature rises with increase in the number of repeated stress cycles, and the rising rate depends on the amplitude of repeated stress.
(2) The transition region becomes small with increase in the number of repeated stress cycles.
(3) The model which had been conceived previously for the relation between attenuation and fatigue of carbon steel, has been adapted to the fatigued S20C carbon steel at the region from ductile to brittle property.
