Characterization and formation mechanism of graphite-rich iron protective layer in blast furnace hearth

Abstract

Though blast furnace ironmaking is a well-established industrial process, the formation and control of a durable protective layer that is essential for extending the campaign life of blast furnace are poorly understood. Based on a field sampling of the hearth protective layer with graphite-rich phase, the study applied multiple methods to characterize its morphology and structure, and further revealed the formation mechanism of the graphite-rich iron protective layer. More coarse graphite was formed in the protective layer of hearth upper part, and its surface morphology was a screw spire-like shape by graphite layers highly stacked. The bottom was mainly flaky. Raman spectrum and X-ray diffraction showed that the graphitization degree and structural order of the graphite-rich iron protective layer increased from the upper to the bottom of the hearth. This strengthened its ability to resist scouring by hot metal. Graphite monocrystal grew after its formation using defects in screw dislocation and rotation boundary. The formation of a screw spire-like graphite will contribute to the stable adhesion of protective layer on carbon bricks. Compact flake graphite provided better protection against the dissolution of carbon bricks by hot metal.