Abstract
In some kinds of cold worked metals and alloys sometimes an extraordinary hardening occurs by the annealing at the lower temperature than their recrystallization one. The cause of hardening is attributed to the precipitation, or precipitation process is caused by the decrease of the solubility limit after cold work. We examined the low temperature phenomena of the cold worked purest Ni, Cu, Ag, Fe (C%: <0.01%) prepared chemically, by observing whether the hardening had occured or not from the hardness-time curves measured at each constant temperature from room temperature to 600°C. The conclusions of the experiments performed with the pure metals are as follows: (1) Generally, it is concluded that the hardening phenomenon is seen even in the pure metals in low temperature annealing after cold rolling. In this case, there is a linear relation between the time of reaching maximum hardness and that of the reciprocal of the absolute temperature. (2) Variously treated pure Ni showed the same hardening phenomenon (same hardness) in the low temperature annealing except in the case in which the time of reaching maximum value of the purest one was slower than the other. (3) In the case of the pure Fe the hardness obtained in the low temperature annealing after cold work was greater than the value obtained by water quenching the specimen from high temperature in α-range and subsequently aging at the same temperature. From the above mentioned phenomenon, we found that the hardening produced by the low temperature annealing can not be solved only by the precipitation theory or as the process of precipitation even in precipitating alloys.
