Abstract
The temperature-impact value curves determined by the Charpy impact tests have been obtained for low carbon steel (SM41) subjected to prestrain tension of 0.15. The effects of prestrain on the ductile-brittle transition temperature, the maximum impact value and the slope in the transition region of the curve were studied.
It was found that (1) the transition temperature rose in the range of 0 to 0.10 prestrain but fell in that of 0.12 to 0.15, and (2) the minimum value of the slope and the maximum impact value were both at approximately 0.10 prestrain.
The dependence of the transition temperature upon prestrain was discussed by means of Stroh's theory, which is based on the probability of the dislocation source to break away from Cottrell's environment. The experimental results show that the dependence of the transition temperature upon prestrain can not be explained by the prestrain dependence of the activation energy for the dislocation source to break away from Cottrell's environment; rather the dependence can be qualitatively explained by the length of the dislocation source estimated from the dislocation distribution in the prestrained steel as observed by transmission electron microscopy. The dependence of the slope upon prestrain can be also qualitatively explained by the dislocation distribution.
