Si3N4-SiC composite ceramics are attractive for high-temperature applications in hydrogen metallurgy due to their mechanical strength and oxidation resistance. This work investigates the microstructural evolution and kinetic mechanisms under pure CO and 50 vol% H2-50 vol% CO atmospheres between 600 and 1300 degrees C. Under pure CO atmosphere, oxidation followed gas-phase diffusion-controlled parabolic kinetics, where the rate was governed by CO diffusion through the porous SiO2-rich product layer, with an activation energy of 26388.211 J/ mol. Under H2-CO mixed atmospheres, the corrosion involved coupled oxidation-reduction reactions. Below 1000 degrees C, kinetics were dominated by gas-phase diffusion of CO through the product layer coupled with interfacial surface reactions, with an activation energy of 61017.652 J/mol. Above 1000 degrees C, hydrogen reduced SiO2 to volatile SiO, and the overall kinetics were controlled by coupled gas-phase diffusion and reduction-driven volatilization processes, leading to porous product layers and an activation energy of 99533.554 J/mol. The results clarified the competing roles of CO oxidation and H2 reduction in Si3N4-SiC composite ceramics degradation and provide kinetic models for predicting performance in reducing atmospheres. These findings provide theoretical guidance for the design and optimization of Si3N4-SiC ceramics for service in hydrogen-based steelmaking and other reducing environments.

Tap hole clay requires binders that provide sufficient plasticity, mechanical reliability across broad temperatures, and resistance to physical impact during blast furnace operation. Coal tar offers favorable thermoplasticity but raises environmental concerns, whereas phenolic resin provides high residual carbon yield but inadequate workability. This study examines the complementary functions of coal tar-phenolic resin composite binders and their influence on the performance and microstructure of tap hole clay. The composite system exhibits a more balanced property profile than single-binder formulations and reduces coal tar usage by approximately 20%-25% compared with traditional coal-tar-only binders. When resistance to physical impact is the primary requirement, a 3:1 coal tar-thermosetting resin ratio achieves the highest strength, with a Marshall value of 1.650 MPa, dried Cold crushing strength of 24.65 MPa, and sintered Cold crushing strength of 13.91 MPa. Microstructural analysis shows that improved pore refinement is closely associated with enhanced mechanical properties. Additionally, carbonized structures observed after heat treatment suggest the possible coexistence of lamellar carbon from coal tar and amorphous carbon domains from phenolic resin. These findings provide guidance for designing high-performance composite binders for tap hole clay.

The multiphase reaction behavior of chlorine in blast furnace (BF) directly affects the stable operation and the degradation and cracking of refractory materials in the hearth. The morphology, composition, and distribution of chlorine-containing phases were investigated through the hearth dissection to obtain samples including residual iron and refractory materials based on a 3200 m3 BF in this paper. Various thermodynamic behaviors of chlorides and HCl were calculated by FactSage 8.3. The results indicated that the predominant chloride in the residual ceramic cup of the sidewall and the carbon bricks at the bottom was KCl, accompanied by phases such as KAlSi3O8, K2S and NaCl. KCl was observed to be enriched in clusters of cubic crystal particles within the refractory materials pores, which led to the corrosion of Al2O3 particles and the carbon matrix, resulting in the accelerated cracking and pulverization. Thermodynamic calculations revealed that KCl could not be directly formed under the high-temperature conditions prevailing in the hearth but rather the reaction of HCl gas with potassium-bearing burdens in the upper part of BF. KCl was enriched and subsequently transported downward to hearth after undergoing a "vaporization-condensation-revaporization" cycle. KCl condensed and deposited in the medium-to-low temperature zones of the refractory materials driven by the temperature gradient and the difference in saturated vapor pressure, which ultimately led to volume expansion and accelerated embrittlement or cracking of the hearth refractory materials. The detrimental effects of chlorine on BF operations and proposes corresponding control strategies were summarized at the end, which intended to enhance the service life of the hearth refractory materials, promote stable and smooth BF operation.

Al2O3–SiC–C (ASC) castables are widely applied in critical metallurgical equipment such as blast furnace hearths; however, their fracture and failure mechanisms under complex service environments remain unclear. In this paper, based purely on laboratory multi-scale thermal shock simulation experiments, the multi-scale crack evolution behavior and coupled failure mechanisms of ASC castables are systematically revealed. Two-dimensional analysis of SEM images and three-dimensional non-destructive reconstruction via industrial CT were employed to quantitatively extract crack characteristics under varying thermal shock conditions. The results indicate that as the thermal shock temperature increases, the material’s failure mode transitions from localized macroscopic spalling (600 °C) to an interconnected, penetrating macro-micro 3D crack network (1200 °C). Quantitative analysis of physical and mechanical properties reveals distinct thermal fatigue sensitivities: compared to 600 °C, the enhanced formation and crystallization of mullite at 1200 °C effectively enhances the physical properties of the castable matrix. This matrix can deflect cracks by forming a branch crack network, thereby absorbing the thermal stress induced by thermal shock cycling and retarding the propagation of the main crack. Guided by crystallographic theory, idealized crystallographic calculations indicated that the individual reactions may involve substantial local solid-volume changes. However, their bulk contributions depend strongly on the actual reacted phase fractions, particularly for anorthite because of the limited CaO content. Based on thermoelastic theory, the critical short-term maximum allowable temperature difference for crack propagation in the castables was calculated to be 204 °C to 398 °C, systematically elucidating the thermo-mechanical and thermo-chemical coupled failure mechanism of crack initiation and propagation under the present laboratory thermal-shock conditions.

Unexpected cracking of carbon bricks in blast furnace hearths remains a critical challenge for campaign safety and long service life, while deterministic criteria based solely on stress magnitude are insufficient to describe the stochastic fracture behavior of porous brittle materials. In this study, a three‐dimensional thermomechanical finite element model with explicit brick‐joint geometry is established, and a Weibull‐based probabilistic criterion is introduced to relate stress state to crack initiation risk. Joint width, hot‐face temperature, and the thermal conductivity of the ramming mix are systematically analyzed. The results show that joint width governs a transition in stress mode and thereby changes the calculated cracking‐risk index: at 0.1 mm, strong constraint causes radial tensile‐stress concentration near the hot face, with a local cracking‐risk index of 19.1%, whereas at 0.5 mm, weakened constraint promotes the simultaneous increase of radial and circumferential tensile stresses, raising the index to 24.4%; by comparison, a joint width of about 0.3 mm gives the lowest cracking‐risk index of 17.8%. Hot‐face temperature is identified as the dominant variable. The local cracking‐risk index reaches 36.81% at 1450 °C and increases sharply thereafter. The proposed framework provides guidance for joint design and thermal management of blast furnace hearth carbon bricks.

The blast furnace remains the most efficient, energy-saving, and environmentally friendly core equipment for ironmaking. The formation of a stable protective layer in the hearth is essential to ensure the safe and long-term operation of blast furnace smelting. In this study, the phase composition and microstructure of the hearth protective layer were systematically investigated to elucidate its formation mechanism based on the nucleation and growth processes. The protective layer samples were analyzed using X-ray fluorescence (XRF), high-frequency infrared carbon/sulfur analyzer (HFC/S), X-ray diffraction (XRD), and scanning electron microscopy with energy-dispersive spectroscopy (SEM-EDS). The results reveal that the protective layer consists of an interwoven mixture of iron and graphite phases, with a phase ratio maintained between 4.0 and 10.3. Graphite is distributed within the iron matrix in branched or strip-like morphologies, accompanied by cracks within and along graphite boundaries. When the molten iron is cooled to 1304 °C or below 1150 °C, the ordered graphite and iron will transform into a nucleus when they reach the critical size under a certain degree of undercooling. Graphite grows anisotropically along both planar and axial directions, facilitated by rotational twinning and screw dislocations. Iron forms equiaxed crystals through dendrite growth, and then evolves into columnar crystals due to growth constraints. The mutual growth and integration of graphite and iron ultimately lead to the formation of a dense graphite–iron composite protective layer. The corrosion resistance, stability, uniformity, and rapid formation of the protective layer can be regulated by promoting the formation of the protective layer network structure, the precipitation of heterogeneous nucleation cores, and the increase of artificial nucleation sites.

This paper investigates erosion behaviors of Al2O3-SiC-SiO2-C (ASSC) castable refractory in a 2650 m3 blast furnace hearth. Post-service residual thickness measurements, conducted via 3D laser scanning and manual gauging across multiple hearth orientations with radial sampling at 8.7 m and 6.7 m elevations, revealed critical erosion zones at the "elephant foot" region (1.5-2 m below taphole centerline) and furnace bottom. Minimum residual thicknesses were recorded at 300 mm (sidewall) and 160 mm (bottom), with erosion rates reaching 81.99 % (314.6 mm/yr) and 84.00 % (168.0 mm/yr), respectively. The 3D erosion profile exhibited a distinctive "shallow pot-bottom" morphology, where measured thicknesses exceeded theoretical predictions by approximately 50 mm. Scanning Electron Microscopy-Energy Dispersive Spectroscopy (SEM-EDS) analysis elucidated erosion mechanisms: The taphole area exhibited tri-layered degradation from molten iron, slag, and harmful elemental penetration, while the elephant foot region showed predominant iron and elemental infiltration. Design recommendations include increasing ASSC layer thickness in taphole and elephant foot zones, along with thermocouple integration for realtime monitoring. Operational strategies to prolong refractory lifespan involve maintaining saturated carbon/silicon content in hot metal, controlling charge impurities, and implementing regular alkali removal protocols. These findings provide mechanistic insights for optimizing hearth design and operational practices in large-scale blast furnaces.

In this paper, the distribution characteristics and heat transfer performance of the protective layer of a large blast furnace hearth in China are studied in detail. The phase composition, chemical composition and microstructure of the protective layer were characterized by X-ray diffractometer, X-ray fluorescence spectrometer, highfrequency infrared carbon-sulfur analyzer, and scanning electron microscopy-energy dispersive spectroscopy. The results show that the thickness of the protective layer of the blast furnace hearth increases with the decrease in the height, and the thickness is bigger at the junction of the hearth and the bottom of the blast furnace, which is about 400-500 mm. The protective layer of blast furnace is mainly composed of graphite and iron. The proportion of graphite and iron is about 22.7 %-25 %. There are many cracks and holes at the boundary of graphite and iron. The heat transfer performance within and between graphite layers may be mainly affected by phonon velocity and mean free path. Based on the semi-coherent interface model, graphite and iron crystals are easy to nucleate effectively, but there are vacancies at the two-phase interface, and the thermal expansion coefficients of the two are quite different, resulting in the heat transfer performance of the graphite-iron protective layer is weakened. The low heat transfer performance of the protective layer will reduce the heat transfer between the molten iron and the carbon brick, reduce the temperature of the hot surface of the carbon brick, and then protect the carbon brick structure.

The macro and micro morphology, phase, and chemical composition of carbon bricks in a large blast furnace (BF) hearth after service were analyzed. The results show that the blast furnace hearth presents “elephant foot” erosion as a whole, the ceramic pad at the bottom of the BF is completely eroded, and the erosion in the taphole area is the most serious. The erosion of carbon bricks above the taphole is mainly affected by the harmful element zinc. The erosion at the taphole is mainly caused by zinc erosion, potassium erosion, and slag-iron alternating erosion. The “elephant foot” erosion morphology is mainly caused by the circumferential flow of molten iron. The erosion morphology of the BF bottom is mainly affected by the gas blowby, resulting in the uplift of the foundation of BF and the crushing of the ceramic pad. The serious erosion of the hearth taphole area of the BF is mainly affected by the flow of molten iron. The essence of carbon brick erosion by molten iron is that carbon atoms are separated from the carbon brick, enter the interstitial position of iron atoms, and may form a solid solution.

This work was aimed at systematically investigating the high-temperature/pressure corrosion behaviour of Si3N4-SiC composites in H2-CO mixed atmospheres, simulating hydrogen-enriched blast furnace conditions. Controlled experiments were performed at 700-1100 degrees C and 0.1-0.5 MPa, combined with thermodynamic analysis, microstructural characterization, and mechanical testing. CO-driven oxidation led to the formation of a SiO2 layer that provided temporary protection. As the temperature increased, the dominant mechanism shifted to SiO volatilization and re-oxidation, producing porous and non-protective oxide scales. Elevated pressures promoted gas penetration and grain-boundary attack, resulting in the expansion of nanocracks. Hydrogen synergistically interacted with CO by reducing the protective SiO2 layers, resulting in a 17.5 % loss in compressive strength at 1100 degrees C/0.5 MPa. A distinctive cauliflower-like morphology was observed, attributable to coupled SiO volatilization, re-condensation, and hydrogen-induced destabilization of the oxide layer. Overall, these findings clarify the combined effects of temperature and pressure on corrosion evolution, providing valuable insights for the design of refractory materials in hydrogen metallurgy.

An autopsy of a 2650 m(3) Al2O3-SiC-SiO2-C type castable blast furnace was conducted in this study, where castable samples from various heights after service were obtained through manual sampling. The phase composition and micromorphology of the post-service castable samples were analyzed using X-ray diffraction (XRD) and scanning electron microscopy with energy-dispersive spectroscopy (SEM-EDS). The research revealed that the erosion of the castable in the region above the taphole centerline on the side wall of the hearth exhibited characteristics of hot-face slag erosion and cold-face harmful element erosion. Below the taphole centerline, the castable demonstrated a combination of hot-face slag-iron erosion and cold-face harmful element erosion. In the region above the taphole centerline, high-melting-point slag phases such as magnesium aluminum spinel, anorthite, and calcium aluminosilicate formed and adhered to the hot face of the castable, preventing further erosion by molten iron and harmful elements. In the region below the taphole centerline, the castable reacted with high-temperature molten iron, causing the reaction products to dissolve into the molten iron, which led to structural damage of the castable. Harmful elements such as K, Na, and Zn diffused into the cold end in the form of vapor along the damaged areas, condensed, and then reacted with the castable to form potassium-sodium feldspar, garnet, as well as zinc oxide and zinc sulfide. The volume expansion resulting from these reactions caused damage to the cold face of the castable.

Analyzing the wetting behavior between carbon brick and molten iron in a blast furnace is crucial for understanding prolonging the furnace's lifespan. This study investigates the wetting behavior between microporous carbon brick and molten iron. The contact angle between the carbon brick and molten iron is measured at various temperatures and carbon saturation conditions, while the microscopic morphology of the reacted interface is examined. Furthermore, the wetting mechanism of molten iron on the carbon brick surface is elucidated. The findings reveal that both the microporous carbon brick and molten iron remain in a never‐wetting state within the furnace. As the temperature rises from 1150 to 1450 °C, the contact angle decreases from 138° to 128°, whereas the initial carbon content in the molten iron increases from 2.6 wt% to 4.1 wt%. Additionally, the initial contact angles gradually increase from 128.3° to 133.6°, with final equilibrium contact angles of 119.2° to 127.0°, indicating a nonwetting state. The carbon dissolution reaction occurs within the carbon matrix region of the microporous carbon brick prior to carbon saturation in the molten iron. Conversely, the presence of a ceramic phase in the ceramic area hampers both chemical erosion and physical penetration of the molten iron.

In this study, through thermodynamic calculation, the possible reactions of carbon composite bricksCarbon composite bricks in a high-temperature water vapor environment were analyzed. The morphology of carbon composite bricks after water vapor erosionErosion was investigated through a water vapor oxidation experiment. In addition, a damage investigation was carried out on a blast furnaceFurnace using hydrogen-rich gas smelting. During the period, a green-white phase with a thickness of 150 mm–200 mm was found inside the carbon composite brick in the taphole area. The carbon bricks in this area were sampled, and XRD, chemical analysisAnalysis, and SEM–EDS detection were carried out. The test results show that there is blast furnace slag erosionErosion and harmful element Zn erosion in carbon composite bricksCarbon composite bricks. The erosion of harmful elements caused the expansion and ring crackingRing crack expansion of carbon composite bricks, resulting in further slag erosion, which eventually led to the macroscopic slag phase erosionSlag phase erosion in the taphole area. The service life of carbon composite bricks can be effectively improved by optimizing the structure of carbon composite bricksCarbon composite bricks, reducing the number of pores, optimizing the pore structure, and promoting the formation of a slag-rich protective layer on the hot surface of carbon composite bricks by improving the structure of blast furnace slag system.

The carbon bricks eroded by harmful elements after dissection investigation in a Chinese 4000m3 blast furnace hearth is studied in detail. The occurrence state of harmful elements is characterized by chemical analysis, X-ray diffraction and scanning electron microscopy-energy dispersive spectroscopy. The results show that the content of K and Zn in the carbon brick at the tuyere of blast furnace is the highest. ZnO is the main reason for the formation of macro cracks and brittle layer of carbon brick., and K2O and KCl generated by liquid K and blast furnace gas may be the inducements for the formation of brittle layers. The nucleation and growth of ZnO in carbon bricks will undergo three processes: the heterogeneous nucleation of ZnO cell on the surface of C, the heterogeneous nucleation of ZnO cell on the surface of ZnO, and the continuous collision and growth of ZnO cell.

Hydrogen metallurgy technology is essential for reducing CO2 emissions. Hydrogen (H2) serves as an ideal energy carrier to replace carbon-based fuels, producing only water as a byproduct. Al2O3-SiO2 refractories are commonly used in hydrogen metallurgy technology, including in technologies like HyCROF(Hydrogen-enriched Carbonic oxide Recycling Oxygenate Furnace) and gas heating furnaces. It is important to systematically study their corrosion in high-temperature reducing gas environments. The results indicated that the Al2O3-SiO2 refractory remained stable in pure H2 atmosphere at temperatures below 1200 degrees C. However, SiO2 and mullite were reduced by H2 when the temperature was increased above 1200 degrees C. Carbon precipitation was observed in both pure CO atmosphere and H2-CO mixed atmosphere, resulting in an increase weight of the sample. Additionally, the sample developed mullite whiskers after heating treatment at 1200 degrees C in H2-CO mixed atmosphere. This study aims to clarify the corrosion mechanism of Al2O3-SiO2 refractory in reducing atmosphere and to provide a theoretical basis for the selecting and optimizing refractories for hydrogen metallurgy technology.

The presence of cinder in the tuyere bird's nest region poses a significant obstacle to the energy-saving production of blast furnaces by impeding the penetration of high-temperature gas into the charge column. This paper provides a comprehensive review of the multiphase occurrence state, formation mechanism, and modification methods of cinder. Firstly, the phase composition and high-temperature performance of cinder are investigated from various perspectives, including tuyere coke, tuyere slag, coal ash slag, and the interaction between residual carbon and coal ash slag. These aspects shed light on the characterization of cinder and its behavior at elevated temperatures. Secondly, the formation mechanism of cinder is explored, aiming to unravel the factors contributing to its generation. Understanding the underlying mechanisms is crucial for devising effective strategies to mitigate or modify its formation. Thirdly, the paper examines the modification methods of cinder from three aspects: tuyere flux injection technology, tuyere hydrogen-rich injection technology, and tuyere sequence impulse injection technology. These approaches offer potential means to alter the characteristics and behavior of cinder. Finally, future research on cinder can focus on the characterization and performance analysis, depth analysis of formation mechanisms, and exploration of the modification mechanisms.

Investigating the presence of a Ti(C,N) protective layer in molten iron is of great significance for achieving low carbon and safe production in blast furnaces. This study focuses on analyzing the high temperature dissolution experiment of TiC0.3N0.7 in molten iron to elucidate the kinetics and mechanisms involved, as well as strategies for regulating its dissolution. The results reveal that the dissolution reaction of TiC0.3N0.7 is predominantly influenced by the temperature and flow speed of the molten iron. The dissolution process can be categorized into two stages: dissolution reaction and physical penetration. Diffusion mass transfer is the dominant factor controlling the dissolution of TiC0.3N0.7, with an apparent activation energy of 60.15 kJ/mol. Upon contact with molten iron, dendritic penetration of TiC0.3N0.7 particles occurs, starting from the edges. To enhance the stable presence of TiC0.3N0.7, recommendations include reinforcing furnace cylinder cooling, reducing the heat transfer coefficient of the blast furnace hearth's resistant material, increasing the carbon content of the molten iron, and decreasing the sulfur content of the molten iron.

Hydrogen metallurgy technology reduces the energy consumption and CO2 2 emissions of the ironmaking systems. With the development and promotion of hydrogen metallurgy technology, the reducing gases have affected the refractory materials of metallurgical equipment, placing new demands on the refractories. Si3N4-SiC 3 N 4 - SiC ceramic is a type of refractory material with a wide range of applications in blast furnace linings, aluminium reduction cell linings and ceramic kiln furniture, etc. In this study, Si3N4-SiC 3 N 4 - SiC ceramic samples were used to conduct gas corrosion experiments for 6 h at different reducing atmospheres (H2, 2 , CO and 50 vol%H2-50 2-50 vol%CO) and temperatures (600, 800, 1000 and 1200 degrees C). The corrosion mechanism was mainly assessed via thermodynamic calculations and analyses of the change in mass, changes in the phase composition and micro-morphological evolution. The results indicated that the reducing gas penetrated the interior of the material and underwent a series of chemical reactions with the sample. Solid products accumulated on the surface of the sample and the gaseous products were released from the surface of the sample. The Si3N4-SiC 3 N 4 - SiC ceramic was stable in pure H2 2 atmosphere, and a solid product film was generated on the surface in pure CO atmosphere. However, under the mixed H2-CO 2 - CO atmosphere, the reduction of the solid product, SiO2, 2 , by H2 2 formed gaseous products, which were released from the sample and degraded the solid film, increasing sample corrosion. This study aims to provide a basis for the selection of refractories for different hydrogen metallurgy technologies and to improve the lifetime and operational efficiency of high-temperature equipment for hydrogen metallurgy.