Effect of K / Na on Primary Boride of Hypereutectic High-Boron Alloy

High-alloy materials such as high chromium cast iron and high speed steel have excellent wear resistance under extreme wear conditions. But they consume much expensive chromium, molybdenum, tungsten and other alloying elements too. The hypereutectic high boron alloy has good wear resistance because it contains many high hardness primary borides. But the dimension of primary borides is big. In this paper, the hypereutectic high boron alloy was prepared using sand casting method, and the primary borides were modified by different amount of K / Na modificator. The results show that the primary boride of hypereutectic high boron alloy is Fe2B. K/Na modificator has a significant influence on primary Fe2B. The best grain refinement effect of primary Fe2B is obtained when the amount of K/Na modificator is 0.3%. The refining mechanism of primary Fe2B is that K/Na modificators can not only increase the supercooling degree to improve nucleation rate but attach to the crystal face of fastest growth direction to prevent grain from growing