Effects of solidification conditions on the microstructural morphologies and strengths of hypereutectic high-chromium white cast iron castings

Although studies on hypereutectic high-Cr white cast iron (HCWCI) castings have been conducted to improve the toughnesses and quantify the microstructures of these castings, to date, only few studies have been reported on the quantitative influences of solidification conditions on the microstructures and mechanical properties of these castings. Accordingly, herein, the effects of solidification conditions on microstructural morphologies and strengths of hypereutectic HCWCI castings were investigated. Microstructural observation implied positive correlations between the minimum Feret diameter of primary M7C3 and length of M7C3 calculated from a threedimensional geometric relationship under the approximation of the cylindrical shape of M7C3 and between experimental minimum Feret diameters of primary and eutectic M7C3. Additionally, the experimental minimum Feret diameter of primary M7C3 divided by the cube root of the volume fraction of M7C3 corresponded to the solidification velocity and temperature gradient obtained via solidification simulation. These results indicate that the parameters demonstrating three-dimensional morphologies of primary and eutectic M7C3 can be obtained by solidification simulation. Then, the strengths of the HCWCI castings were evaluated from the rule of mixtures considering the Stroh and Kelly-Tyson equations, where the volume fraction of M7C3 was acquired via thermodynamic calculations according to the chemical compositions of the castings and the strength of the matrix was substituted by the standard strengths of carbon steels under the same C equivalents as that of the matrix. The calculated strength exhibited almost the same magnitude and tendency as those of the experimental strength. The abovementioned findings reveal that not only the microstructural morphologies but also the strengths of the HCWCI castings can be estimated via computer-aided engineering. The results of this study can be utilized to predict the distributions of microstructural morphologies and strengths of the HCWCI castings.