Abstract: Coating method was applied in cast-infiltration to prepare a ternary layer containing boron,chromium and carbon on the surface of 45 steel cast using ferroboron,graphite and high carbon ferrochrome as raw materials.The influence of different coating ratios on the microstructure and hardness of the cast-infiltrated layers was studied.The results show that the cast-infiltrated layer was mainly constituted by martensite,Cr23C6,Fe-Cr,Fe23(C,B)6 and Fe3C,which were responsible for increasing nearly three times of the hardness of casting surface.The best coating ratio was w(Cr)∶w(B)∶w(C)=80∶10∶10.