Erosion behavior of carbon bricks in a blast furnace hearth: differential effects of Na, K, and Zn

To investigate the influence and mechanism of harmful elements on the erosion of carbon bricks in a blast furnace hearth, this study simulates the actual working conditions of the blast furnace hearth, formulates a slag-iron system containing Na, K, and Zn, and tests the erosion of ultramicroporous carbon bricks. XRD, SEM‒EDS, and other methods were used to characterize the eroded carbon bricks, and an erosion index (EI) model was constructed by combining the weight loss rate, the change in the diameter of the erosion layer and other parameters. The results revealed that the weight loss rate of the Na erosion group was the highest, at 17.8%, and the diameter of the brick samples in the slag erosion layer decreased from 23.4 mm before the test to 17.1 mm, followed by that of the K erosion group. The weight loss rate of the Zn erosion group was only slightly higher than that of the control group. Microscopic analysis revealed that Na and K reacted with carbon brick components to generate low-melting point compounds, which accelerated interfacial melting loss and carbon loss, whereas Zn existed in the form of simple substances or oxides, which led mainly to the expansion of carbon bricks through physical penetration. The erosion index model proposed on the basis of experimental data quantitatively reveals the erosion intensity of each element on carbon bricks (EI_Na>EI_K>EI_Zn>EI_{Blast Furnace Slag}), which provides a theoretical basis for the selection of refractory materials for blast furnaces and the control of harmful elements. This study suggests optimizing the pore structure of carbon bricks to block the infiltration of harmful elements and strictly controlling the Na and K contents in the raw materials entering the furnace to prolong the life of the furnace hearth.