Effect of Cu on Solidification Microstructure and Solidification Process in High Carbon High Speed Steel Type Cast Alloy

Effect of copper on solidification microstructure and solidification process were investigated for high carbon high speed steel type alloys (Fe-2.0%C-5%Cr-5%Mo-5%V-0 similar to 7.5%Cu in mass%). The microstructure of all as-cast specimens with different copper content is dendrite consisting mainly of primary gamma, MC-gamma eutectic and M2C-gamma eutectic. In the copper-free specimen, the shape of dendrite is granular (or equiaxed), while in the copper added specimens, it is columnar, and the columnarization trend become more pronounced with increasing the amount of copper content. Furthermore, the secondary dendrite arm spacing decreased with increasing amount of copper content. The volume fraction of primary gamma dendrite gradually decrease and MC-gamma eutectic gradually increase with increasing of the amount of copper content. While the volume fraction of M2C-gamma eutectic is approximately constant regardless of the amount of copper content. The concentrations of chromium, molybdenum and vanadium within microstructure were approximately constant regardless of the amount of copper content in any microstructures. While the concentration of copper within microstructure was higher in order of dendrite, MC-gamma eutectic and M2C-gamma eutectic compared with any copper content, and its order corresponds to the solidification prosses. These results suggest that copper tends to remain in the solid phase (that is dendrite) rather than redistribute to the liquid phase during solidification.