Abstract
In the previous paper the author reported that the toughness of high tensile steel through the standard V-notch Charpy test is recovered by the tensile prestrains at room temperature which are at the slight necking point (the 1st recovery point) and the maximum load-point (the 2nd recovery point). In one part of this study the 1st recovery of toughness is interpreted from the stress-strain relation of a torsional test. And another part gives the examples of the recovery of the toughness by prestrain of the practical cold-worked steels though it is difficult to judge whether it is the 1st or the 2nd recovery. The results obtained are summerized as follows:
1. The 1st recovery at the slight necking point is correlated to the increasing steepness of the transition curve.
2. The slight necking point almost coincides with the decreasing point of the rate of strain hardening.
3. The increasing steepness is caused by the decreasing of the rate of strain hardening. Therefore the 1st recovery can be interpreted by the decreasing of the rate of strain hardening.
4. The cold-bent semi-killed steel in pipe type and the cold-drawn killed steel, also, show the recovery of the toughness by prestrain through the notch impact test.
