Production of ADI by hot shake out - microstructure and mechanical properties

The present study investigates the production of ADI by direct austempering after hot shake out. The aims of the study are to find a procedure to obta in carbide free ductile iron in a permanent mold, to austemper the samples during the post solidification cooling stage, and to characterize the micro structure and mechanical properties of the resulting ADI, The requirements to obtain carbide free microstructures for the present exp erimental conditions were identified. The austempering thermal cycles were carried out after hot shake out by transferring the casting to a molten sal t bath. The influence of the use of an intermediate temperature homogenizat ion stage was also investigated. The microstructure and mechanical properti es of hot shake out specimens, were compared to those corresponding to samp les of the same heat, solidified and heat treated conventionally. The resul ts show that coarser acicular structures are obtained after austempering du ring post solidification cooling, as a result of the differences in the str ucture of the prior austenite, Nevertheless, measured mechanical properties are satisfactory, and surpass the specification of ASTM 897-90, These resu lts encourage the continuation of research and development in this subject, A novel procedure to reveal the solidification macrostructure of ductile i ron has been identified.