Optimization Of Microstructure And Performance Of Refractories For Blast Furnace Hearth

The longevity of blast furnace is an important guarantee for high-efficiency andlow-consumption of iron and steel-making process. With the development of iron-makingtechnology, refractories used in the hearth and bottom of blast furnace are suffering fromincreasingly harsh application situation. Once damaged they are hardly repaired in timeowing to the fact the hearth and bottom are directly contacting with hot metal all the timeduring running operation. That is to say, the blast furnace campaign mainly depends on theservice life of the hearth and bottom, which is associated with the performance of therefractories. So, it is much of great significance to analyze the corrosion mechanism andthen take the appropriate measures to improve the performance of refractories with theaim to achieving the longevity of blast furnace.The research works are focusing on:(1). The temperature field distribution of typicalmasonry structure of the hearth and bottom was simulated to understand the formation ofthe so-called “soft melting layer” of hot metal on them.(2). The processing parameters ofanthracite based carbon block was optimized to improve the thermal conductivity bymeans of Support Vector Machine (SVM).(3). Ceramics bonded carbon (CBC)technology was adopted to prepare the good hot metal corrosion resistance of artificialgraphite containing refractories.(4). A new type of corundum based refractory has beendeveloped and influence on performances by change the amount of artificial graphite hasbeen systematically studied in order to optimize the thermal conductivity andmicro-porous structure on the premise of high corrosion resistance.The main results are given as follows:1. Multi-layered masonry structure was recommended for the designing of hearth andbottom of blast furnace where the refractories are adopted with increase in thermalconductivity from the inside to outside (from10W/(m·K) to40W/(m·K)). In this case,the so-called soft melting layer of hot metal will form at the bottom, whereas the layerdoesn’t form at hearth area. However, the masonry structure based on high thermal conductivity solution leads to excessive heat dissipation while it endures high thermalstress for masonry structure with insulation solution.2. The thermal conductivity of anthracite based carbon block increased against theaddition of artificial graphite content while the hot metal corrosion resistance decrease. Itreveals that thermal conductivity is strongly dependent of the addition of artificial graphitebased on Support Vector Machine (SVM) analysis.3. The ceramic-bond carbon (CBC) technology could be used to construct carbonblocks by adjusting the particle size of artificial graphite and introducing particle packing.In that case artificial graphite aggregates were covered/bonded with alumina and siliconcarbide whiskers and carbon block was characterized by micro-porous structure and hotmetal corrosion resistance.4. The decomposition and mullitization of kyanite, andalusite and sillimanite could takeplace in matrix of carbon blocks during the coking process. Meanwhile, much more SiCwhiskers formed and their aspect ratio became larger. It revealed that kyanite mineral hasthe lowest mullitization temperature.5. As titania was added into specimen, Ti(C,N) phase in-situ formed together with muchmore SiC whiskers in matrix of specimens coked at1400oC. The results showed thatspecimens containing6%TiO2had92.3%pore volume of <1μm pore size and mean poresize of less than100nm with its thermal conductivity of53.43W/(m·K). After the hotmetal corrosion test it revealed that a high viscosity layer with mixture of hot metal andTi(C,N) formed at the surface of specimens, similar to the protective layer of Ti(C,N)deposited at the wearing area by “titanium-bearing” technique.6. New Al2O3-C refractory was prepared by partly substituting corundum aggregatewith artificial graphite aggregates (less than1mm). The results showed that themicroporous structure and thermal conductivity was optimized by introducing artificialgraphite, micro silica and pitch powder in comparison with traditional ceramic cuprefractories. Such kind of Al2O3-C refractory was expecting to use as new ceramic cup forblast furnace, where it had not only good hot metal penetration and erosion resistance, but also it was favorable for the formation of so-called “iron soft melting layer” at the bottomof blast furnace.