Effects of In-Mold Additions of Al, Ca, Ce, Sr, or Ti on Austenite Grain Morphology and Eutectic Cell Size of a Hypoeutectic Gray Cast Iron

Effects of different in-mold additions on the morphology of austenite and the eutectic cell structure in gray iron were investigated using a hypoeutectic gray iron. Direct austempering after solidification (DAAS) heat treatment was adopted to retain the grain boundaries of austenite at room temperature in a gray iron alloyed with Ni, Mo, and Cu. The additions studied included Al, Ca, Ce (added as mischmetal), Sr, and Ti. In a single heat, each addition was added into individual mold cavities prior to pouring of the gray iron at 0.05%. The austenite grain boundaries and the eutectic cell structures were revealed with chemical etching. The results indicated that the Sr was most effective on refining austenite at the tested addition rate. Meanwhile, Al had the least refined structure with the largest grains and the fewest grains. Additionally, it was found that larger equiaxed zones had larger eutectic cells.