Prediction of Aluminum Nitride Embrittlement in Heavy Section Steel Castings

Abstract

Aluminum Nitride (AlN) embrittlement is a problem in heavier section (>4″) steel castings. AlN precipitates at higher residual aluminum and nitrogen levels and slow cooling rates. In load critical components, the formation of AlN will embrittle the casting, reducing the impact strength and ductility of the steel. The precipitation diagram for AlN from Hannerz is reviewed and his more accurate equation plotted. In addition, this information is matched to simulated cooling curves in slab castings to plot maximum aluminum content against section size to avoid embrittlement. However, these rules of thumb can be misleading in analyzing geometries without final rigging or production information like the sand properties. The most important information in predicting AlN is the cooling rates in the production setting. Therefore, the equations are incorporated into casting simulation software to use the simulated cooling curves to locate embrittled volumes. Two example castings serve to show the use of the AlN embrittlement indicator. This prediction will help to avoid AlN embrittlement in the design of heavy section steel castings and rigging.