Investigating the Influence of Mid-Chilling on Microstructural Development of High-Chromium Cast Iron

Abstract

The solidification rate during the casting of high-chromium (high-Cr) cast iron determines the size and distribution of carbides in this alloy, which, in turn, influence its mechanical properties. The effects of middle-chilling processes during the casting on the microstructures of directionally solidified high-chromium (high-Cr) cast iron containing carbon equivalents of 4.17% have been investigated. The middle part of the mold was a chilled copper mold that was kept cold by circulating water, thereby enabling simultaneous directional solidification in the upper and lower zones. The resulting solidified microstructure was affected by fluid convection between these zones. When the samples were placed on a chilling block on top of a sand mold, bidirectional fluid convection occurred, and the solution mixed sufficiently and decreased the segregation ratio. The lower zone had a faster cooling rate (5.1°C/s) than the upper zone (3.8°C/s), and further, the liquidus and solidus gradients (0.09; 8.07°C/mm) were lower. The cooling effect was significant in hypoeutectic (N_eu) cast iron. Moreover, the N_eu cast iron that solidified in the chilled zone had finer average particle sizes (1.54 µm), greater hardness, and higher wear resistance. The results of this study represent a significant step toward manufacturing industrially applicable wear-resistant alloys.

Keywords:

• Carbide
• Cast
• Chilled
• Cooling
• Gradient
• Microstructure
• Segregation
• Solidification