Influence of Ti and N contents on austenite grain control and precipitate size in structural steels

Abstract

The austenite grain size of six steels with different Ti and N contents has been determined at 1 300°C × 10 min and at 1 100°C × 10 min. The most stable grain was achieved for a Ti/N ratio close to 2. In parallel, a study of precipitate sizes was carried out using transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The results indicate that the steels with a lower N content and approximately the same Ti content show a distribution of precipitates of larger size, which increases with the Ti content in solution at the austenitization temperature applied. As the austenitization temperature increases, the double effect of precipitate dissolution and coarsening appears, and only with a hipostoichiometric Ti/N ratio and as precipitated Ti content above 0.010 (wt%) are they capable of controlling the austenite grain up to high temperatures.