Abstract: The formation mechanism of the viscous layer in the blast furnace hearth was studied through chemical analysis， XRD， SEMEDS analysis and the carbon composite brick property test. The results showed that the carbon composite brick has excellent anticorrosion properties to the iron and slag because of its dense microstructure. Furthermore， it has selfprotection function by formation the multiphase system consisted of the graphiteC layer， high alumina slag layer and the graphite layer. The thermodynamic condition of the graphite precipitation on the sidewall of the hearth was calculated. Under a certain flow condition of the molten iron， there was a dissolution and precipitation equilibrium between the graphite precipitation and the molten iron. Thereby， the graphite separated the direct contact of the molten iron from the brick. Then the erosion of the brick slowed down and the long service life of the blast furnace was achieved.

Key words: blast furnace, hearth, carbon composite brick, viscous layer, graphite