Study on the Austenite Grain Size and it’s Coarsening Behavior of Aluminium Killed Steel

Abstract

On aluminium killed Ni-Cr-Mo case hardening steel, the austenite grain size and it’s coarsening behavior were studied in relation to the aluminium nitride precipitate observed by electron microscopy. The main results are as follows: (1) If the original structure before the austenization is same, the initial austenite grain size becomes smaller as the aluminium nitride precipitate becomes finer, in accordance with Zener’s experession. (2) When the size of the aluminium nitride precipitate is smaller than a certain degree, the discontinuous coarsening of austenite grains occurs at the temperature at which the precipitate dissolves in the matrix or aggregates to a larger size, but when larger than that, the apparently continuous or discontinuous coasening occur depending on the prior heat treatment at much lower temperatures.