Search

As a protective layer for the copper stave in the blast furnace, the characteristics of the slag crust have a non‐negligible influence on the heat transfer of the copper stave. Combined with the characteristics of slag crust thermal conductivity, flowing temperature, and thickness, the influence of slag crust on heat transfer from copper stave under different operating conditions is investigated, and the potential of slag crust thickness regulation to reduce carbon consumption in blast furnaces is assessed. It is found that the slag crust thicknesses calculated by the model are consistent with the range of thicknesses of the actual slag crust samples, validating the correctness of the model. To ensure the operational safety of the copper stave, in the actual production process of the blast furnace, the slag crust thickness should be controlled between 30 and 60 mm, and the corresponding thermocouple temperatures, water velocities, and heat flux intervals are calculated. In addition, when the slag crust thickness is increased from 10 to 30 mm, the 2650 m3 blast furnace can reduce the coke ratio by a maximum of about 14 kg t−1. [ABSTRACT FROM AUTHOR]

The blast furnace is the dominant high-temperature reactor in the modern ironmaking industry. Iron oxide in iron ores can be converted to metallic iron through blast furnace smelting, and this high-temperature melting can be used to separate the molten iron from the gangue components. The formation and thickness of the hot-surface slag crust on the copper stave in the high-temperature area of the middle and lower parts of the blast furnace are crucial for the safe operation and long campaign of the blast furnace. To enhance the precision of determining the thickness of the slag crust in this specific region, samples were extracted from the hot surface of the copper cooler situated in the high-temperature area. This extraction was carried out during the maintenance procedure of the blast furnace stockline. Subsequently, the thermal conductivity and melting performance of the slag crust were measured. The slag crust thicknesses corresponding to the various temperature measurement sites of the stave were determined by developing a mathematical model for the heat transfer of the copper stave. The actual slag crust thickness measurement data were acquired while the blast furnace stockline was in operation, and the data were then utilized to corroborate the model’s predictions. A blast furnace with an effective volume of 3200 m3 was used to test the model. The average thickness of the hot-surface slag crust was computed for cases that occurred between 2020 and 2022. The data’s correlations with the blast furnace’s technical and economic indices during the same time period were examined. The findings indicated that the blast furnace’s operation indices improved with a thinner slag crust, but there was also a higher chance of damage to the copper stave’s internal cooling water pipes. Taking into account the technical and economic indices as well as a long campaign of the blast furnace, 150–200 mm is recommended as the appropriate average slag crust thickness on the surface of the copper stave in the high-temperature section.

Understanding the heat transfer properties of the slag crust is critical to the safe operation of copper staves. The distribution of metallic iron and bubbles in the slag crust is detected by X‐ray computed tomography. The thermal conductivity of the slag crust is modified based on an effective thermal conductivity model and laser thermal conductivity measurements to predict the effect of metallic iron and bubbles on the heat transfer in the slag crust. The results show that the average volume fractions of metallic iron and air bubbles in the slag crust are 3% and 4.5%, respectively. The measured value is consistent with the trend of the effective thermal conductivity calculation model, and the calculation result of the Maxwell–Eucken effective thermal conductivity model is very accurate. Variations in the volume fraction of metallic iron in the slag crust have a greater effect on the thickness of the slag crust, while variations in the volume fraction of bubbles have a smaller effect on the thickness of the slag crust. It is recommended to keep it between 10 and 30 mm in blast furnace production to help improve the operational life of the copper stave. [ABSTRACT FROM AUTHOR]

The relevance of using slag crust separation methods, which are characterized by easy separation and are based on thermodeformation processes in the sample, is shown in the development of new welding materials. The developed method of assessing slag separation based on the theoretical calculation of thermo-deformation processes in the base metal has passed the stages of experimental research The experimental approbation of the proposed methodology for assessing the separation of the slag coating from the surface of welded joints under experimental fluxes based on the TiO2-MnO-SiO2–MgO–CaO-FeO-Al2O3 slag system was carried out for different welding regimes. The evaluation criterion for the high-temperature separation of the slag coating takes into account: the ratio of the geometric parameters of the test sample, the amount of heat input during the surfacing process, and the factor of the presence of spinelforming components at the slag-metal interface. The selected parameters for evaluating the separation of the slag crust in points, where the guaranteed separation of the slag coating is counted for the arbitrary separation of the slag during its destruction or the arbitrary separation of the slag by a monolithic layer. The practical value of the proposed method lies in the possibility of quantitative assessment of the probability of high-temperature separation of the slag coating for a wide range of fluxes for surfacing. The results of the conducted experiments show the efficiency of the developed methodology for evaluating the high-temperature separation of the slag coating from the surface of the weld metal. [ABSTRACT FROM AUTHOR]

The blast furnace is the dominant high-temperature reactor in the modern ironmaking industry. Iron oxide in iron ores can be converted to metallic iron through blast furnace smelting, and this high-temperature melting can be used to separate the molten iron from the gangue components. The formation and thickness of the hot-surface slag crust on the copper stave in the high-temperature area of the middle and lower parts of the blast furnace are crucial for the safe operation and long campaign of the blast furnace. To enhance the precision of determining the thickness of the slag crust in this specific region, samples were extracted from the hot surface of the copper cooler situated in the high-temperature area. This extraction was carried out during the maintenance procedure of the blast furnace stockline. Subsequently, the thermal conductivity and melting performance of the slag crust were measured. The slag crust thicknesses corresponding to the various temperature measurement sites of the stave were determined by developing a mathematical model for the heat transfer of the copper stave. The actual slag crust thickness measurement data were acquired while the blast furnace stockline was in operation, and the data were then utilized to corroborate the model's predictions. A blast furnace with an effective volume of 3200 m3 was used to test the model. The average thickness of the hot-surface slag crust was computed for cases that occurred between 2020 and 2022. The data's correlations with the blast furnace's technical and economic indices during the same time period were examined. The findings indicated that the blast furnace's operation indices improved with a thinner slag crust, but there was also a higher chance of damage to the copper stave's internal cooling water pipes. Taking into account the technical and economic indices as well as a long campaign of the blast furnace, 150–200 mm is recommended as the appropriate average slag crust thickness on the surface of the copper stave in the high-temperature section. [ABSTRACT FROM AUTHOR]

The peculiarities of the process of forming complex compounds, namely, spinels, in flux-cored arc welding for the slag TiO2-MnO-SiO2-MgO-CaO-FeO-Al2O3 system are studied. An experimental investigation of the mechanism of spinel formation in conditions of electrode arc welding and cladding under flux is carried out. Based on the analysis of microimages of the slag surface obtained using scanning electron microscopy, the mechanism of spinel formation, namely, the growth of microcomplex compounds into macrospinels, is presented. The main stages and mechanism of formation of the complex compounds, namely, spinels, are described. As shown, the structure of spinels is determined by the temperature conditions of the crystallization of the slag melt. The study reveals that one of the determining factors of high-temperature separation of the slag crust during multilayer cladding with overlap of the previous layer is the formation of spinels at the interphase boundary between the slag and the metal. Based on modern ideas about the structure of slag melts, a mechanism for the formation of complex compounds at the interphase boundary between slag and metal is proposed. The main factor determining the process of high-temperature separation of the slag coating for the TiO2-MnO-SiO2-MgO-CaO-FeO-Al2O3 system is the formation of complex compounds based on spinel-forming elements and slag oxides at the interphase boundary between the slag and the metal. [ABSTRACT FROM AUTHOR]

The operating conditions influence the stability and consumption of a blast furnace. Recognizing these conditions makes changing the burden distribution parameters more efficient. The cooling stave temperature (CST) is a crucial state parameter that indicates the conditions of the process. Owing to the high data volume of the CST and the lack of methods for recognizing the stability of the slag crust, it is difficult for operators to recognize the conditions accurately according to the CST during the ironmaking process. Thus, in this study, a condition recognition method with information granulation for burden distribution in a blast furnace was presented. First, information granulation was employed to reduce the volume of the CST data and present it in a granular form. Then, considering the lack of a method for calculating the similarity of CST information granules, a novel fuzzy similarity calculation method was devised to calculate the membership grades of information granules belonging to different standard granules. Finally, the conditions were recognized according to the membership values. Experimental results based on industrial data demonstrated that the proposed method can be used to recognizes the conditions in the blast furnace. [ABSTRACT FROM AUTHOR]

The use of wastes of fused and agglomerated fluxes is an urgent task. But as-applied to agglomerated fluxes the data on the effective use of slag crust are absent in the literature. In this work the analysis of possibility of using a slag crust of agglomerated fluxes for production of fluxes, providing the quality formation and high mechanical properties of weld metal at high-speed multi-arc welding of cold-resistant low-alloy steels was carried out. The comparative investigation of welding and technological properties of original flux OK 10.74 and experimental fluxes based on the crushed slag crust in single- and four-arc welding was carried out. Using the method of spectral analysis the chemical composition of weld metal was studied. The method of optical metallography was used to investigate the distribution of nonmetallic inclusions in them and characteristics of microstructure. The impact toughness of weld metal was determined by tests on impact bending. It was established that the flux, produced by the method of agglomeration with addition of 5 wt.% of metallic manganese into the composition of charge, was close to original flux OK 10.74 according to all the investigated indicators, and as to the level of impact toughness met the requirements for welded joints of cold-resistant gas-pipeline steel up to strength category X80 inclusive. The results represent interest to the consumers of flux from the point of view of improving the efficiency of its use in multi-arc welding of large-diameter pipes. 10 Ref., 4 Tables, 3 Figures. [ABSTRACT FROM AUTHOR]

The blast furnace tuyere is a crucial component for blast furnace production. The frequent damage of the copper tuyere impedes the smooth operation of the blast furnace. Welding a wear‐resistant layer on the tuyere can extend its service life, but it still falls short of the expectation in a large blast furnace. In this article, it is aimed to elucidate the erosion mechanism of the wear‐resistant layer. A scanning electron microscope, an energy dispersive spectrometer, and an optical microscope are employed to examine the morphology, composition, and metallographic structure of the samples obtained from a 5800 m3 blast furnace tuyere in China, as well as to calculate the frequency of daily slag crust shedding from cooling staves. The results indicate that the main cause of the erosion of the wear‐resistant layer is the shedding of slag crust due to the temperature fluctuation of the cooling staves. Finally, the erosion mechanism of the wear‐resistant layer is proposed. It is suggested that the formation and propagation of cracks caused by erosion of slag and hot metal are the primary failure mode of the wear‐resistant layer. [ABSTRACT FROM AUTHOR]

Copper staves have been widely applied in large blast furnaces especially those whose inner volumes exceed 2000 m3 due to high cooling capacity. In the past decade, copper staves suffered severe damages in some blast furnaces, which not only shortened their campaign lives, but also caused huge economic losses. In order to make out this phenomenon, the damage mechanism of copper staves was investigated via analyzing the chemical composition, thermal conductivity, metallographic aspects and microstructure in this paper. As a result, the working state was more likely to damage copper staves instead of their materials. At the beginning, the poor quality of the coke and the large bosh angle promoted the development of edge airflow, which intensified the erosion of refractory materials, resulting in the fall-off of slag crusts and damage of cooling water pipes. After repair, the cooling capacity of copper staves still declined, causing the temperature to rise easily; consequently, hydrogen attack happened when the temperature reached 370 °C, which degraded the performance of copper staves. Therefore, copper staves were worn too quickly to form slag crusts, which finally failed under the hydrogen attack and the scouring of the edge airflow at high temperatures.

Proper burden distribution is an important way to improve conditions of a blast furnace, which indicate the stability and energy consumption. However, it is difficult for operators to recognize the stability and energy consumption at the same time and adjust them through burden distribution, due to complex iron-making mechanism. Therefore, this article presents a two-stage decision-making method for the burden distribution parameters based on recognizing the conditions. First, the stability and energy consumption are recognized, respectively, according to the classification of stability of slag crust (SSC) and the gas utilization rate (GUR). And then, two prediction models are presented for the SSC and GUR to predict the conditions. Finally, the burden distribution parameters are determined in two stages, where edge parameters of the burden distribution are determined at first according to the SSC, and then, center parameters are determined according to the GUR. Experimental results based on industrial data show that the proposed method provides an effective decision-making way for improving the conditions. [ABSTRACT FROM AUTHOR]

It was shown as a result of analysis of mechanisms of slag crust removal from the weld metal surface that the spinels at slag-metal interface and their intergrowth have the main influence on this process. It was found on the basis of analysis of structure of spinels and slag melt that to prevent the formation of spinels at the interface and intergrowth of metal and slag, it is necessary to provide the presence in the slag melt of a structural element with configuration of a linked structure, differed from tetra- and octahedral structures, and not capable to formation of spinels. It was established that prevention of formation of spinels in providing necessary welding-technological properties of flux of SiO2-Al2O3-MgO-CaF2 system can be attained at adding of zirconium oxide in the amount of 3.5-5.5 % into flux composition. The flux has been developed, which provides a spontaneous removal of slag coating at high temperatures. 13 Ref., 6 Figures. [ABSTRACT FROM AUTHOR]

The effects of two cokes with different reactivity on the lump ore's metallurgical properties and coke's solution loss are investigated under the high‐temperature load reduction. The work used an improved test device for softening‐melting and dropping characteristics of iron ores in both CO2 and CO2H2O atmospheres. The deterioration behavior of highly reactive cokes is expounded under hydrogen‐rich conditions. High‐reactivity cokes under hydrogen‐rich conditions are more favorable for enhancing the breathability of charge and the penetration of the coke layer. However, it increased the thickness of the softening zone. High‐reactivity cokes had obvious internal and external reaction gradients. The solution loss reaction mostly occurred on the surface, with selectivity. The longitudinal stacking height, layer number, and order degree in the carbon structure decreases after the reaction. The carbon‐structure difference weakens between the shell and core. The enhancement of coke's reactivity, however, results in the significant loss of coke powders on its surface. Unreduced FeO and refractory Fe2SiO4 are more likely to appear in the droplets, which is not conducive to the reduction of Fe and the generation of slag crust in the furnace. The difficulty in separating lump ores and cokes is aggravated, and more iron‐containing charge remain in the furnace. [ABSTRACT FROM AUTHOR]

The work is aimed at studying the effect of additions of oxides K2O, Na2O, MgO, Al2O3 on slag density and viscosity, as well as the separability and covering capacity of slag of the CaO–MnO–SiO2 system obtained by melting the fused flux during automatic arc welding of low-carbon steels. The subject of research is physicochemical and technological properties of slags, mechanical properties of welded joints obtained as a result of the process of automatic submerged arc welding. It is shown that with an increase in K2O and Na2O content slag density and viscosity, as well as the separability of the slag crust, decrease, and an increase in MgO and Al2O3 content increases slag density and viscosity. Based on results of the work, a composition of the slag base of fused flux is developed on the basis of oremineral raw materials of the Republic of Uzbekistan, selected on the basis of the CaO–MnO–SiO2 ternary system melting diagram. The results obtained make it possible to increase welded joint strength properties by 10–12%. [ABSTRACT FROM AUTHOR]

This work investigates the influence exerted by the combined thermal effects of aluminothermic welding and arc welding with solid wire on the residual stress in the plate material. A mathematical model is constructed based on the Prandtl-Reuss model, where Hooke's law is substituted with the Duhamel- Neumann law. It is considered that the deformations are low. Irreversible deformations develop when the von Mises yield criterion is satisfied, which includes the Johnson-Cook strain hardening function. In order to determine the parameters of this function, a number of tensile tests are carried out on parent metal samples and welding material obtained by electric arc welding with solid section wire or by a combined method of aluminothermic welding. The thermal effects are modeled by a double comet- shaped ellipsoid proposed by Goldak. For the combined welding method, the additional thermal effects from the exothermic reaction of the aluminothermic filler material and the lower heat dissipation due to the formation of a slag crust are considered. By analyzing the residual stresses, it is concluded that the use of flux-cored wire with aluminothermic filler in automatic electric arc welding results in lower levels of residual stresses, thereby positively affecting the subsequent operation of the welded structure. [ABSTRACT FROM AUTHOR]

This study experimentally assessed the effect of microadditives of the Ti–TiC system modifier on the functional properties of the deposited metal of 25Kh5FMS semi-heat-resistant tool steel. The used Ti–TiC system modifier powders were obtained by high-voltage electric discharge treatment of Tipowder, which resulted in changes in its structural, chemical, and phase composition. It was determined that modification of the deposited metal with titanium carbides in an amount of ≈ 0.01% did not impair the quality of the formation of welded rollers and slag crust detachment. It was experimentally determined that introducing titanium carbide micro-additives in the amount of 0.01% to the deposited metal increased its heat resistance and wear resistance at elevated temperatures by 15–50%, depending on the modifier additive used. The obtained results can be useful in selecting materials for welding parts operated under abrasive wear and cyclic thermomechanical loads. [ABSTRACT FROM AUTHOR]

Mechanized multilayer MIG/MAG welding by high-alloy wires is associated with the feasibility of formation of lacks of fusion and slag pieces in weld metal. Therefore, the improvement of technology, in particular the selection of shielding gas composition, is urgent. Feasibility of application of mixtures CO2 + 3 % N2 and CO2 + 3 % N2 + 0.5 % O2 as a shielding gas in mechanized arc welding of dissimilar steels is shown. It is shown that the metal oxidation occurs mainly in the inter-dendrite regions, intensity of which is increased with increase in amount of nickel in the welding wire. Weld metal alloying with nitrogen does not change the intensity of metal oxidation process and almost has no influence on slag crust removal from the deposited metal surface. 17 Ref., 2 Tables, 3 Figures. [ABSTRACT FROM AUTHOR]

The optimized blast furnace design is the prerequisite for low-carbon smelting. The salamander depth and bosh angle are the key parameters, which determine the blast furnace longevity. In this paper, the physical and mathematical force model of deadman and cooling stave was established. The relationship between operating parameters and the salamander depth, as well as bosh angle, was analysed, and the gas flow scouring curve was proposed. The following results were obtained: first, the reasonable salamander depth/hearth diameter ratio and bosh angle should be 23∼25% and 73°∼75° in China, respectively. Second, the key factors that influence the floatation of deadman and wear of the cooling stave are the deadman voidage and the slag crust thickness, respectively. Lastly, it is necessary to adjust some measures such as coke ratio, blow velocity and tuyere length. This paper is meant for optimizing the design of blast furnace. [ABSTRACT FROM AUTHOR]

The problems of Russian welding materials for welding highly alloyed austenitic steels that are not inclined to intergranular corrosion are considered. A new agglomerated flux for welding with austenitic welding materials is developed. Slag composition is selected that ensures a stable welding process, good separation of the slag crust and the formation of a seam. The possibility of introducing ferroalloys and metal powders through the flux ensures the necessary level of mechanical characteristics of the weld metal, and increases also the resistance of the weld metal to hot cracks and pore formation. [ABSTRACT FROM AUTHOR]