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

Abstract

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

The microstructure and high-temperature tribology behavior of high boron HSS under different heat treatments

“…When the hardness of the matrix is high, the matrix can play a good supporting to the oxide layers formed on the surface, and the oxide layer on the surface isn’t easy to peel, which reduces the amount of wear. When the hardness of the matrix is low, the matrix have obvious plastic deformation, resulting in the peeling of the oxide layer and the matrix, which leads to the increase of the amount of wear (Xu et al , 2012). The influence of the quenching temperature on the hardness of high boron HSS samples [Figure 6(a)] shows that the maximum hardness of high boron HSS is 63.1 HRC after quenching treatment at 1,050°C, and the wear amount is the lowest at this temperature.…”