Characterization and formation mechanism of graphite-rich iron protective layer in blast furnace hearth. (15th December 2021)

• Record Type: Journal Article
• Authors: Jiao, Kexin; Feng, Guangxiang; Zhang, Jianliang; Ma, Hengbao; Guo, Ziyu
• Is Part Of: Fuel. Volume 306(2021)
• Publication Date: 2021-12-15
• Subjects: Blast furnace -- Hearth -- Protective layer -- Formation mechanism -- Graphite crystals; Fuel -- Periodicals; Coal -- Periodicals; Coal; Fuel; Periodicals; 662.6
• DOI: 10.1016/j.fuel.2021.121665
• Languages: English
• ISSNs: 0016-2361

Abstract

Highlights: Protective layer is fully characterized based on systematic field drill-core sampling. Morphology of graphite in the protective layer is screw spire-like and flaky. Structural order of protective layer increased from the top to bottom of hearth. Formation mechanism of graphite-rich iron protective layer is proposed. Screw spire-like graphite helps protective layer to adhere stably to carbon bricks. 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.