Abstract
There are ever so many representation methods of austenite grains, but they have, in general, some limitation when applied to practical use in some or other cases of chemical compositions of steel. Moreover, there was no trustworthy and versatile method of invesitgating the behavior of grains at high temperature where their actions are very remarkable. The method described here is, however, versatile enough to be used in this field of science. When the specimen is kept in inert atmosphere of high temperature, corrosion by evaporation will be noticed most conspicuously at the grain boundaries, and owing to the evaporation and rearrangement of grain surface atoms, surfaces characteristic of and inherent to crystal will be exposed. Each surface has a fixed resistance to the oxidation according to its orientation, respectively, so that when oxydized by a small quantity of oxygen the surfaces take various colors of their own. By using this method we have the advantage of observing austenite grains treated at an arbitrary temperature and duration. The present authors studied the behavior of the growth of low carbon steel grains by means of this method and noticed the pronounced correlation between the coarsening of fine grains of Al-killed steel and the solubility of AlN into γ-iron.
