THE EFFECTS OF HEATING TEMPERATURE AND TIME, AND ALSO AGING UPON THE INTERNAL STRESSES IN A COLD WORKED MILD STEEL.
1928 Volume 31 Issue 136 Pages 366-390
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1928 Volume 31 Issue 136 Pages 366-390
The present writer has measured the change of initial stresses in a cold drawn mild steel shaft (0.25% C) under various temperatures & durations of heating, and also aging, by Heyn's method using Zeiss'optimeter (Fig. 3 & 4) ; and obtained the following results. (1) The initial stresses have gradually released by heating up to about 300℃, markedly over 300℃, and completely at about 620℃ (Fig. 11). (2) At each temperature of heating, the release of initial stresses is remarkable during the first 30 min. of heating, and assymptotic beyond this point. At 300〜600℃, especially about 400℃, however, it is progressing even in 8 hr. of heating (Fig. 9.). (3) The release by aging are remarkable during about 20 days after cold working and assymptotic beyond this point (Fig. 9.) (4) Even a 4 years old test piece had have marked initial stresses and the distribution of initial stresses had been some what changed (Fig. 10.). >From these result the followings are considered. (a) The release of initial stresses by heating under 300℃, and over 300℃, is due to the vigorous vibration of atoms, and recrystallization of strained crystals, respectively. (b) The homogeneously distributed internal stresses, as the internal stresses, as the internal stresses produced by pure tension, etc., can not be measured by any direct methods, but the effects of heating temperatures upon these kinds of internal stresses are to be considered just the same to these results. (c) Compared these results with those of the changes of bardness, tensile properties, numbers of bending, specific gravity, magnetic properties, electric resistance, and stretching ratio of the ferrite grains of cold worked mild steel & of casting stress of cast iron by heating (Fig. 11 & 12), which are obtained by various investigaters. In addition to the above mentioned experiments, the writer measured the distribution of internal stresses of a mild steel, air coold from 650℃ after normalizing.
