한국주조공학회

In this study, the influenced of graphite shape on the boriding of cast iron and boride structure was investigated. Gray cast iron, ferritic and pearlitic ductile cast iron were borided at 750,850,900 and 950℃ for 1,3 and 5 hours by powder pack method with the mixture of B_4C_9 Na_2B_4O_7, KBF_4 and Shc. The boride layer was consisted of FeB(little), Fe_2B (main) and graphite. Some possibility of the existence of unknown Fe-B-C compound in the boride layer was suggested. And precipitates in the diffusion zone was Fe_3(B,C). The concentration of Si and precipitation of Fe_3(B,C) in the α layer raised the hardness of this Zone. The depth and hardness of boride layer increased with the increase of treating temperature and tim. But high temperature (over 950℃)caused pore at graphite position and long treating time (5hrs) sometimes caused formation of graphite layer beneath the boride layer. So, for the practical application of borided cast iron, treating in short time and at low temperature was recommended. And for ductile cast iron, ferritizing or pearlitizing heat treatment was seemmed to be possible at the same time with boriding. The graphite in the boride layer was deeply concerned with the qualitx and characteristics of the boride layer. And it greatly influenced on the shape of the boride phase, structure of the boride layer. Generally speaking, the existance of graphite restrained the growth of the boride phase. But the boundary between the gsaphite and the matrix acted as the shortcut of boron diffusion. So, for gray cast iron, the graphite layed length-wise led the formation of boride layer.