Abstract
In a previous report, the present author observed the growing behaviour of austenite grains, and clarified thereby the relation between the grain growth and the dissolving state of fine aluminium nitride particles into the matrix, and that the fineness of grain size is obtained when aluminium nitride is contained in a more than a certain critical quantity at the soaking temperature. In this report, the author observed the grain growth whithin γ-range of variously heated Al-Killed fine grained steel by using high temperature oxidation coloring method and an emission type electron-microscope, and explained its characteristics and the effect of maintenance temperature, maintenance time, heat treatment and chemical composition upon the incubation period up to coarsening and the progress of coarsening and got the following results:-(1) The more of aluminium nitride is contained in the specimen, the more strongly is impeded the grain growth at higher temperature. (2) This obstruction tendency changes according to the change of heat treatment, and when the aluminium nitride particles are reduced in size and they are equally distributed by means of heat treatment, the obstruction effect is more conspicuous. (3) The influence of heat treatment is the more conspicuous if the specimen contains the more aluminium nitride.
