Abstract
This paper presents the effect of the level of plastic deformation on the ductility of a mild steel (0.06 mass % C). The steel was cold rolled to five degrees of 2, 5, 10, 25 and 50 % in thickness reduction (R). Tensile tests for smooth and notched specimens were carried out to examine the effect of the level of plastic deformation on the change of ductile-brittle transition temperature (T_c). The specimens were tested at any desired temperatures between 293 K and 77 K and at a strain rate of 4.2 × 10^<-3> s^<-1>. The results obtained in this work are summarized as follows: (1) As-annealed smooth specimen was fractured including the ductile elongation even if the testing temperature was lowered to 90 K, but it was ruptured without any elongation at 77 K and the ductile-brittle transition temperature was determined to be 90 K. After the specimen was rolled to the reductions of 5 % to 25 % in thickness, the values of the transition temperature increased up to 113 K. In contrast with this, the transition temperature was lowered to below 77 K for the heavily hardened specimen with 50 % thickness reduction. (2) The presence of a notch causes the transition temperature to increase by 43 K to 100 K over the thickness reduction range of 0 % to 50 %.
