Significant research has been conducted over the past decade concerning austempered high Silicon Steels. These steels can be regarded as advanced steels, as they reach very high strength and toughness, comparable to maraging steels. In addition, they are relatively inexpensive, as both the alloying elements used and its processing have low cost. The excellent properties rely on a careful design of the chemical composition and heat treatment cycle that leads to a microstructure after austempering composed by a very fine mixture of ferrite and high Carbon retained austenite. Most published research about this material has been carried out on rolled or forged steels. Little attention has been given to cast steels. Nevertheless, a steel of these mechanical properties and low cost can be potentially attractive for the construction of a number of cast parts. As cast steels parts will inherit a number of potentially detrimental characteristics such as microsegregation, coarse grain structure, microshrinkage, etc, there is a reasonable doubt concerning the possibility of reaching the excellent properties found on rolled steels when cast parts are produced and heat-treated. In earlier investigations, the authors studied the solidification macrostructure, microsegregation and austempering kinetics of seven experimental high Si steels including different concentrations of Si, C and other alloying elements. The studies concluded that, in spite of the very coarse solidification structure and the chemical inhomogeneity of the cast products, reasonably short austempering cycles could be designed to obtain nearly homogeneous carbide free bainitic microstructures. These results encourage the study of the resulting mechanical properties.
The present study describes the main aspects concerning the solidification and heat treatment of the high Si steels investigated and reports the mechanical properties obtained after austempering heat treatment. Test results confirmed the high mechanical properties of this type of steel and its potential applicability for the fabrication of high strength cast parts. The ratio between tensile strength and elongation satisfies the more demanding category of ASTM A148 for structural cast steels.