Abstract: When combined with the high-temperature reaction characteristics of carbon dioxide—that is, the weak oxidation, endothermic, or weak exothermic effect compared with oxygen and the bubble increment effect of reacting with carbon to produce twice the gas—the carbon dioxide smelting process was targeted according to the different tasks in different periods of converter smelting. Before temperature measurement, sampling, and carbon determination using the sublance system, carbon dioxide is blown into the converter from the upper oxygen gun and the bottom blowing element of the converter. By changing the ratio of carbon dioxide and oxygen in the oxygen gun, an industrial experimental study was conducted on the effect of the carbon dioxide ratio blown from the upper oxygen gun on the endpoint of the mass fraction of phosphorus and nitrogen and the carbon–oxygen concentration product. The results show that with the gradual increase of the carbon dioxide top blowing ratio from 4.84% to 9.68% in the early and middle stages of converter smelting, the mass fraction of phosphorus at the end of the converter first decreases and then basically remains unchanged. The mass fraction of nitrogen also decreases gradually, but the decreasing range becomes smaller, and the changing trend of carbon–oxygen concentration product is the same as that of TFe in slag, which first decreases and then increases. The optimal carbon dioxide top-blowing ratio varies with the index. Furthermore, the test also shows that even if all the blown carbon dioxide reacts to generate additional carbon monoxide gas and the nitrogen is removed by the additional carbon monoxide gas generated compared with the original process, the partial pressure of nitrogen in the additional gas is much higher than the partial pressure in equilibrium with the mass fraction of nitrogen in the liquid steel. This indicates that the improvement of the denitrification effect is due to the additional gas generated by the reaction of blowing in carbon dioxide; it improves the denitrification effect of the original gas, and the generation of additional gas improves the kinetic conditions of the molten pool and facilitates the mass transfer of nitrogen. The highest decreasing ratio of the endpoint mass fraction of phosphorus, nitrogen, carbon–oxygen concentration product, and TFe in the slag of the test converter was 20.4%, 34.3%, 12.92%, and 8.89%, respectively.
Abstract: “Carbon peaking” and “carbon neutralization” are macro concepts that provide a general theoretical framework and basic ideas for China’s future economic and environmental development. Based on the in-depth analysis of the “double carbon” goal, China’s iron and steel industry is in a “carbon lock” state. Only by carrying out technological and institutional changes simultaneously can the “carbon unlock” be realized. The reasonable carbon peak time and peak value are given when the current production structure of the iron and steel industry, supply of smelting raw materials, smelting energy, energy conservation, emission reduction level, and CO2 emission status are combined. In the next two or three decades, the main process of China’s iron and steel production is still the coexistence of long process and short process. Hydrogen metallurgy technology is still difficult to carry out in industrial production. The main measure to reduce carbon emissions is to increase the proportion of all scrap short process steelmaking. In the long run, it is generally accepted that the ironmaking process in the long term will gradually change from carbon reduction to hydrogen reduction. For the ironmaking process, the products will change from the original high-carbon molten iron to low-carbon molten iron or DRI. Converter steelmaking with high decarburization has no obvious advantages, and the development of the EAF steelmaking process is an inevitable choice. However, the realization of “carbon neutralization” depends on the development and application of hydrogen metallurgy, carbon capture, utilization, and storage technology, and the reform of the system. Based on an in-depth study of the theoretical research, equipment development, and practice of all scrap electric arc furnaces in recent years, aiming at the problems existing in the smelting process of all scrap electric arc furnaces, a series of key technologies have been developed to meet the current continuous casting production process rhythm and liquid steel quality control under the condition of all scrap, to provide theoretical support for the development of all scrap electric arc furnace.
Abstract: In an era of green and low-carbon development, the global steel industry has conducted low-carbon research, and various low-carbon technologies have continuously emerged. This paper summarizes the CO2 emission status of the global steel industry and international steel enterprises, such as ArcelorMittal, Nippon Steel, POSCO, and Big River Steel, and summarizes the carbon emission reduction targets and low-carbon development projects of major steel-producing countries, such as the United States and Japan. Based on this, the low-carbon strategy is analyzed in detail, noting that the low-carbon development direction of the international iron and steel industry is mainly focused on developing electric furnace processes, hydrogen metallurgy technology, carbon capture, utilization and storage (CCUS) technology, and clean energy utilization. In addition, the EU is actively building a carbon emission trading system and achieving carbon reduction using policies and regulations such as a carbon tax and carbon border tax. After analyzing the low-carbon development situation of the international steel industry, this paper focuses on the low-carbon green development of the domestic steel industry. Firstly, combined with the total output of crude steel, total CO2 emissions, CO2 emissions per ton of steel, and other data of China’s iron and steel industry, this paper analyzes the status quo of carbon emissions in China’s iron and steel industry. Secondly, it summarizes the carbon emission reduction targets of Baosteel, HBIS, and other large state-owned iron and steel enterprises. Thirdly, the countermeasures for China’s steel industry to achieve a “carbon peak and carbon neutrality” are summarized as follows: implement crude steel output control, adjust the production process structure, conduct research and development of low-carbon energy-saving technology, and build a carbon trading system; among them, reduction development and process structure adjustment are the main future directions of low-carbon development of China’s iron and steel industry, while low-carbon energy-saving technology and a carbon trading system are important guarantees for China’s iron and steel industry to achieve carbon neutrality. Finally, to make the four macro strategies proposed above more specific and visualized, a typical steel enterprise in China is selected based on its technical characteristics, geographical location, resource endowment, and development planning. Seven emission reduction paths, including iron resource optimization, process optimization and reconstruction, system energy efficiency improvement, energy consumption structure optimization, low-carbon technology transformation, industrial coordination, and carbon reduction management enhancement, are analyzed and proposed to point out the direction of green and low-carbon development for the enterprise.
Abstract: The cleanliness level and nonmetallic inclusion distribution characteristics of M50 aerospace-bearing steel are key factors affecting its quality and service life. The simultaneous addition of Ce–Mg has been proposed in this paper as an innovation to improve cleanliness dramatically. Based on the thermodynamic calculation, the underlying functional mechanism has been revealed. Additionally, the effects of Ce, Mg, and Ce–Mg simultaneous additions on oxygen content, sulfur content, and inclusion distribution characteristics have been analyzed comparatively. The vacuum induction melting process was used to prepare the M50 aerospace-bearing steel ingots. The chemical compositions of experimental steels were acquired using inductively coupled plasma-atomic spectroscopy, Leco TC500 N2/O2 analyzer, CS-3000 carbon/sulfur analyzer, and SPECTROLAB M11 stationary metal analyzer. The statistical distribution characteristics of inclusions were obtained using the image processing software based on optical microscopy images. The composition and morphology of inclusions have been characterized using scanning electron microscopy equipped with energy dispersive spectroscopy. The results indicated that Ce could significantly enhance the efficiency of deoxidation and desulfurization. Preferentially, Ce addition would lead to the formation of Ce2O2S inclusions in the steel. As the oxygen content in liquid steel decreases, Ce could also react with As to form a compound, and this could further purify the molten steel since As has generally been recognized as a harmful element. Meanwhile, Ce would also react with the magnesia–aluminum spinel refractory and cause an increase in the number density of inclusions in the steel. Thus, in comparison to the Ce-treated steel with higher Ce content, the smallest size and number of inclusions have been obtained in the steel with a total Ce mass fraction of 0.018%. In addition to deoxidation and desulfurization, Mg addition could also inhibit the reaction between Ce and magnesia–aluminum spinel refractories. The thermodynamic calculation results demonstrated that the dissolved [Ce] in the molten steel could react with the magnesia–aluminum spinel refractory material, resulting in an increase in the concentration of [O] and [Al] in the molten steel, while this reaction could significantly be inhibited by the dissolved [Mg] in the molten steel. In summary, Ce–Mg synergistic treatment could significantly decrease the number and size of inclusions in the steel. Based on this novel technology, the ultraclean M50 aerospace-bearing steel with an oxygen mass fraction of 0.00075% has successfully been obtained. This work has opened a new insight into the deoxidation mechanism of Ce–Mg synergistic treatment and provided a novel method to further improve the cleanliness of molten steel during the vacuum induction melting process.
Abstract: Nonmetallic inclusions in steel significantly influence the steel life, quality, toughness, and corrosion resistance. Pitting corrosion is the most common type of localized corrosion in stainless steel. Rare-earth elements, which are key materials in the metallurgical sector, largely influence the modification of sulfur (S) and oxygen (O) inclusions in steel. Numerous experimental studies have been conducted on the corrosion of the rare-earth metal cerium (Ce); however, studies on the microscopic-scale mechanism are few. In this study, in situ corrosion observation and the first-principle calculations based on density functional theory were applied to investigate the effects of the rare-earth element cerium on inclusions in J5 stainless steel and the inclusion-induced corrosion process. The changes in the inclusion composition and the primary types of inclusions in the steel were investigated by scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy. The results show that CeAlO3?Ce2O2S, Ce2O3?Ce2O2S, and MnS are representative inclusions. MnS and other oxide inclusions in stainless steel were treated with Ce to generate stable Ce2O3, Ce2O2S, and CeAlO3 inclusions, according to formation energy calculations. The surface energy of the Fe (100)-2 plane is measured as 2.4374 J·m?2, and the work function of this crystal plane is predicted to be 4.7352 eV. The crystal plane stability was examined according to the surface energy. The work functions and potential differences between the inclusion and the steel matrix were analyzed to compare the trend of pitting corrosion induced by different Ce-containing inclusions, and the influences of different atomic positions, atomic numbers, and different slab models on the work function were explored. Compared with the electronic work function of the Fe (100)-2 surface, the potential difference between MnS and the three modified inclusions CeS, Ce2O3, and Ce2O2S is typically less than zero, and the potential difference of CeAlO3 is about 0 eV. The average work function of the crystal plane with a large number of nonmetal atoms such as O and S is higher. Ce addition reduces the work function of the crystal plane, and the molecular mechanism of pitting corrosion according to different crystal planes and termination planes of inclusions is revealed. The five types of inclusions and the steel matrix are in the following order: CeAlO3>Fe>MnS>CeS>Ce2O2S>Ce2O3. The experimental findings on composite inclusions in stainless steel reveal that Ce2O3 has the highest chance of pitting corrosion, and CeAlO3 can significantly improve steel corrosion resistance.
Abstract: In China’s marine strategy, using oxide metallurgy technology to develop high heat input welding steel is an important guarantee for developing marine engineering equipment and high-tech ships. The theory of microalloying based on oxide metallurgy studies the mechanism of multiple factors that induce preferential competitive precipitation of ferrite in grain. This theory integrates the oxide metallurgy technology into the entire process of design, production, and welding of high heat input welding steels and considers the requirements of strength, toughness, and weldability of thick plate steel. Herein, the development of oxide metallurgy technology at home and abroad was introduced, and then the progress of microalloying theory based on oxide metallurgy was expounded. Meanwhile, the coordination and interaction of various microalloying elements, as well as the influence of the precipitation and evolution of inclusions and second-phase particles on the microstructure transformation and steel properties, were investigated. The thermodynamics and kinetics of the precipitation of beneficial inclusions during smelting and solidification were analyzed. The effects of the inclusions’ properties, size, and distribution on the nucleation of Ferrin were analyzed. The mechanisms of microstructure evolution, grain refinement, preferential precipitation of ferrite, and improvement of strength and toughness of base steel and weld heat-affected zone during hot working and welding were reviewed. The research progress and existing problems of oxide metallurgy were completely summarized. Combined with the results of the research group, the theory of microalloying based on oxide metallurgy was put forward, and microalloying based on oxide metallurgy has been proposed. Including the design theory of the microalloy system, the synergistic and interactive mechanism of microalloying elements under the condition of multi-element coexistence, and the effects of microalloying elements oxidation, carbonitriding, and sulfurization on the formation, evolution, and distribution of inclusions and second-phase particles in the whole process. The mechanism of inclusions and the properties and distribution of the second-phase particles improving the strength and toughness of coarse-grain heat-affected zone (CGHAZ) and inducing the preferential precipitation of ferrite in grain were also discussed. Microalloying based on oxide metallurgy is a further development of the oxide metallurgy technology. This research will greatly promote the development of oxide metallurgy technology. This will provide a theoretical and technical basis for developing steel materials with high strength, high toughness, and excellent weldability. It will provide an effective method for producing high-strength and high-toughness thick plate steel, section steel, and nonquenched and tempered steel by oxide metallurgy technology.
Abstract: The production of high purity steel is a major issue for iron and steel enterprises. Obtaining bubbles with controllable size and dispersed distribution in liquid steel is an important method for removing fine inclusions and producing high-quality steel. Microheterogeneous purification of molten steel technology is a carbonate decomposition reaction-based process that generates fine bubbles and slag droplets to eradicate small inclusions. On this basis, composite spheres (powders) with various metallurgical functions are designed, and industrial field tests are carried out at ANSTEEL. The results show that the microheterogeneous purification of molten steel is a low-cost, high-efficiency, simple, and easy molten steel purification technology. The carbonate composite sphere (powder) can cause dispersion, microbubbles, and slag droplets in the molten steel. Its size is 0.02–0.2 mm, and the size distribution and slag droplet composition can be controlled. Rapid dephosphorization and slag-forward movement can be achieved by feeding composite balls during converter tapping. For low phosphorus steel, the minimum phosphorus content can reach 0.002% (in mass, the same below) and the dephosphorization efficiency is >50%. The slag-forward movement process can reduce the temperature drop during molten steel transmission, promote rapid slag formation in ladle furnace (LF) refining, increase the LF heating rate by 2 °C·min–1, and shorten the refining LF treatment cycle by 3–5 min. The addition of composite spheres in the Rheinstahl–Heraeus (RH) refining process can remove fine inclusions and provide deep desulfurization. The inclusion of free molten steel in the interstitial can be effectively removed. Compared to conventional inclusion removal technology, the number of the oxide inclusions can be reduced, and the inclusion size becomes finer. The total oxygen (mass fraction) in the as-cast slab can approach 5×10?6 using this novel technology, and the steel production cost per ton can be reduced by 5–12 RMB. The sulfur content of ultralow carbon nonoriented silicon steel can be consistently controlled below 0.002%, and the desulfurization efficiency is >50%. Recently, the advancement of this process has piqued the attention of metallurgical workers, and some new technologies have emerged and matured. Based on the principle of microheterogeneous purification of molten steel process, this paper introduces the latest progress of microheterogeneous purification of molten steel technology in detail, summarizes the characteristics and mechanism of microheterogeneous removal of fine inclusions, desulfurization, dephosphorization, slag migration, and RH rapid decarbonization, and looks forward to the problems to be solved in the engineering field and the future developments.
Abstract: Thin slab continuous casting and rolling process is an important way to produce hot-rolled strips. Recently, the process has been widely used to produce Nb/V/Ti/B bearing microalloyed steel. However, during the continuous casting of the thin slabs of the microalloyed steel, there are frequent cracks on the corners of the slabs, which would cause quality defects, such as scars and cracks at the edges of the hot-rolled coils. These defects are a common technical issue in the steel industry. In this paper, the characteristics of the microstructure and carbonitride precipitation of the thin slab corner of QStE380TM low carbon niobium–titanium bearing microalloyed steel, as well as the reduction of area of the steel under different cooling and tensile rates, were detected. Moreover, the evolutions of the temperature of the solidified shell in different structure molds and secondary cooling processes, as well as the stress of the thin slab surface during liquid core reduction, were numerically simulated. The results show that there is a significant third brittle temperature zone during continuous casting of microalloyed steel thin slabs, and the greater the deformation rate of the thin slab, the more significant the third brittle temperature zone is. Under the conventional thin slab continuous casting process, the cooling rate of the thin slab corners in the upper part of the mold and the secondary cooling zone from the mold exit to the liquid core reduction segment is lower than 5 °C·s?1, which is the key factor to lead a chain of niobium–titanium carbonitrides precipitate at the grain boundaries of the corners. As a result, the plasticity of the thin slab corners is greatly reduced. During the process of liquid core reduction, the low plasticity corners of the thin slab crack because of large deformation and stress. Applying the Gaussian concave curved surface mold, which the narrow face copper plates could efficiently compensate the shell shrinkage, the narrow face-foot roll zone hard cooling process can increase the cooling rates of the thin slab corners over 10 and 20 °C·s?1 in the mold and the narrow face-foot roller cooling zone, respectively. As a result, the carbonitrides precipitate in the thin slab corners disperses, and the stress of the thin slab corners reduces since the new mold promotes the metal flow of slab narrow surface broadsiding during the liquid core reduction. Finally, the cracking rate of the thin slab corners during the microalloyed steel thin slab casting has been reduced significantly.
Abstract: The success of the continuous casting process is inseparable from the correct use of mold powders. However, fluoride volatilization and the contradiction between slag entrapment, heat transfer, and lubrication that occurs in the mold restrict the development of green and efficient continuous casting. Through the physical and chemical research of mold powders, Chongqing University found that the intermediate elements of network formation represented by aluminum in the mold powders have remarkable effects of adapting to the working environment of the mold. These effects include: (1) These elements inhibit the degree of ion exchange between the slag and the water and fix fluorine and sodium. (2) They also form a heterogeneous network structure such that the slag produces shear and thinning behaviors and realizes slag viscosity control in different positions. (3) Under the condition of low basicity, aluminum shows a unique thermal diffusion effect, which promotes the transformation of glass slag film to a crystal slag film. On this basis, the design theory of “Smart Mold Powders” for continuous casting, which is referred to as the “SMP” theory, is proposed. This theory was used to develop environmentally friendly non-Newtonian fluids and thermal diffusion effects to mold powders. Industrial application results show that this type of mold powders can achieve environmental friendliness without fluoride reduction, minimize the rejecting ratio of cold-rolled plates, and improve the surface quality of slabs for high-nitrogen stainless steel.
Abstract: In this study, the defects in the wall of petroleum casing steel pipe were investigated. The morphology and composition of inclusions in the defects of the steel pipe were analyzed using scanning electron microscopy–energy-dispersive X-ray spectroscopy. The thermodynamic calculation of the Ca?Al equilibrium phase diagram of molten steel in tundish and the changes of the ladle slag phase composition with cooling temperature was performed using FactSage8.0. The results show that the longitudinal surface of the defect is mainly composed of shallow and deep stripes. A large number of MgO·Al2O3 inclusions containing a small amount of Mn is detected at shallow stripes, and a large number of inclusions, such as Al2O3, MgO·Al2O3, and CaO·Al2O3·SiO2 are detected at deep stripes. The three main types of inclusions in the cross-section of the defect zone are CaO·Al2O3·SiO2, CaO·Al2O3·MgO, and CaO·Al2O3·MgO·SiO2. According to the analysis results of inclusions in the cross-section and the calculation results of the phase transformation of slag droplets during solidification and cooling, the formation mechanism of the defects in the wall of steel pipe can be speculated as follows: (1) At the end of pouring, the ladle slag in molten steel in the ladle enters the tundish. Further, the slag droplets adsorb the fine xAl2O3·yCaO or Al2O3 inclusions with high Al2O3 content in molten steel, increasing the Al2O3 and CaO contents in the slag droplets. (2) Ladle slag in molten steel is subjected to strong stirring in Ar gas in the vacuum degassing (VD) refining process. Moreover, the slag droplets adsorb the fine Al2O3 inclusions in molten steel, increasing the Al2O3 content in the slag droplets. During solidification and cooling, the slag droplets formed in the two aforementioned forms of inclusions are transformed into three types of inclusions: CaO·Al2O3·SiO2, CaO·Al2O3·MgO, and CaO·Al2O3·SiO2·MgO. In the process of round billet piercing deformation, under the action of longitudinal tensile stress and transverse shear stress, the large slag droplets involved extend along the longitudinal cross-section and finally form defects in the wall of the steel pipe.
Abstract: The smelting reduction of manganese ore in the converter has been reported in China since the 1990s, and some steel enterprises have successively carried out industrial tests of this technology. However, the recovery ratio of Mn in manganese ore is low and fluctuates greatly due to various reasons such as inadequate hot-metal pretreatment, the poor bottom blowing effect of the converter furnace, and unreasonable positioning of the smelting end point. The smelting reduction of manganese ore has not been successfully applied in converter steelmaking and failed to benefit steel enterprises. In this study, the thermodynamic parameters of manganese ore melting reduction were discussed to improve the recovery ratio and yield of manganese and find a way to directly use manganese ore in a converter. The industrial test was carried out in a 200 t converter at a steel mill. Results showed that the efficient and stable ‘tri-de’ (dephosphorization/desulphurization/desiliconization) hot-metal pretreatment was the basic premise for the success of manganese ore smelting reduction. The theoretical calculation revealed that when the content of MnO in slag is 5%–10% and the terminal content of [C] is 0.13%–0.36%, the end-point of [Mn] in molten steel can be controlled above 0.3%. For an improved recovery ratio of Mn in manganese, the industrial test mainly adopted the smelting operation of double-slag operation to ensure that the amount of slag and iron oxide in the slag was reduced as much as possible under low phosphorus content in molten iron in the early stage. Under the existing process control conditions, the industrial test results showed a manganese yield of more than 40% and an average value of 51.40% when the added amount of manganese ore was under 10 kg·t?1. For an excellent manganese yield, the total amount of manganese smelting reduction slag must be strictly controlled from 40 kg·t?1 to 60 kg·t?1, and the amount of lime must be 10–15 kg·t–1. This work provides an important reference for the development and direct application of manganese ore in the converter.
Abstract: The automobile industry has entered a new stage of development, with new changes in steel materials for car bodies and increasingly stringent requirements for energy conservation and emission reduction. This paper summarizes the recent research and development progress of new cold-rolled sheet steels for the car body. The technical routes, product advantages, and application of dual-phase steel with improved formability (DH steel), zinc–aluminum–magnesium (Zn–Al–Mg) coated steel, and automobile outer panels with high distinctness of image have been emphasized. In DH steel, an appropriate amount of retained austenite with high stability greatly improves the total elongation and work hardening rate, which is effective in solving stamping cracking. In addition, DH steel has a higher tensile strength under the same elongation in comparison to traditional DP steel. Thus, it is possible to make the body lightweight by applying thinner sheets. The special phase structure of Zn–Al–Mg coated steel determines its excellent corrosion resistance and formability compared with pure zinc-coated steel, which is widely used in automobile inner and outer plates. The surface waviness of parts is an important index of an automobile’s outer plate with a high distinctness degree of image. Shougang has developed the evolution mechanism and control technology of surface waviness and solved the problem of coordinated control of steel sheet surface roughness and waviness. Simultaneously, it is noted that the research and development of DH steel should focus on some production and application problems, such as continuous casting difficulties and surface defects due to high Al and Si content, mechanical property fluctuations caused by high alloy content, hydrogen embrittlement of high-strength products, and liquid metal embrittlement (LME) of the coated sheet during welding. The basic data of welding, coating, bonding, and forming of Zn–Al–Mg coated steel sheets are not perfect, and the high corrosion resistance needs to be inspected and recognized by more users. The high distinctness of automobile outer plate needs to further reduce the number and size of surface defects and decrease the longwave surface contour in the future to achieve a high degree of cleanliness and homogenization of the automobile outer panel surface. Continuously improving the performance advantages of the above materials through a combination of theoretical research, process progress, and equipment upgrading, as well as expanding their application in the automotive field, requires the joint efforts of iron and steel production enterprises, material application enterprises, and scientific research institutions.
Abstract: Molten steel temperature is a parameter in converter end-point control. Accurate prediction of molten steel temperature is crucial for converter end-point control. However, most of the previous end-point prediction models are static models, which can only predict the molten steel temperature at the end-point of converter blowing and cannot realize dynamic prediction, affording a limited role for these models. To solve this challenge, a data-driven prediction model of molten steel temperature in the second blowing stage in a converter is proposed. First, the model retrieves the similar cases in the historical case base through the process parameters in the main blowing stage of the new case, such as carbon content and temperature of TSC measurement, based on the case-based reasoning (CBR) algorithm. Second, the process parameters in the second blowing stage of the similar cases, such as oxygen flow, lance position, and argon flow, are used to train the relationship between the process parameters and the molten steel temperature based on the long short-term memory (LSTM) algorithm. Third, the trained LSTM model is used to dynamically calculate the molten steel temperature in the second blowing stage of the new case. Finally, the actual production data is divided into five sets for cross-validation, and the model prediction accuracy changes are tested when the number of reuse cases ranges from 1 to 10, and the number of neurons is 5, 10, 15, and 20. The results show that, on the one hand, the prediction accuracy of the model first increases and then decreases with an increasing number of cases, and when the number of reused cases is 4, the prediction accuracy of the model is the highest, indicating that the number of cases is increased when training the model. Improving the prediction accuracy of the model is beneficial; however, the reference value of the case decreases with the similarity of the case, reducing the prediction accuracy of the model. Conversely, when the number of neurons is 10, the prediction accuracy of the model reaches it’s the highest value. The hit rate of the prediction error in the range of [?5 ℃, 5 ℃], [?10 ℃, 10 ℃], and [?15 ℃, 15 ℃] reached 40.33%, 68.92%, and 88.33%, respectively. This paper also establishes the traditional quadratic model and cubic model as well as further proves the effectiveness of the model by comparing the three indicators of these models, namely, the RMSE, MSE, and hit rate.
Abstract: Bearing steel is subjected to complex alternating stress conditions for a long time which requires excellent service properties such as high hardness, high wear resistance, high elastic limit, and high contact fatigue strength. Therefore, during bearing steel production, it is necessary to strictly control the process and improve the purity of steel to ensure high precision, long service life, and high reliability of bearings. China has made considerable progress in the production technology of high-quality bearing steel, and some enterprises can produce world-class bearing steel. However, the stability of bearing steel still requires improvement. Currently, the aluminum deoxidation process is mainly used to produce bearing steel at home and abroad. Through aluminum deoxidation and the production of high-alkalinity slag, the oxygen content in liquid steel can be rapidly reduced. The total oxygen mass fraction in high-quality bearing steel can be controlled below 5×10?6. However, fatigue failure caused by occasional Ds-type inclusions still occurs. Concurrently, other problems such as blockage of small billet continuous casting nozzle and difficulty in stable control of ultralow total oxygen and titanium content also occur. To circumvent the aforementioned problems, this study proposed a nonaluminum deoxidation process by adding silicon–manganese alloy for pre-deoxidation during converter tapping, adding silicon deoxidizer to the ladle furnace (LF) slag surface for diffusion deoxidation, and Ruhrstahl?Heraeus (RH) vacuum deep deoxidation to ensure that the total oxygen mass fraction of the molten steel was approximately 8×10?6, to produce bearing steel. While ensuring the low aluminum and low titanium contents of liquid steel, low-alkalinity slag is used to change the type of inclusions and control the plasticity of inclusions to effectively solve the problem of liquid steel fluidity. The fatigue life of bearing steels by two kinds of processes was evaluated using the ultrasonic fatigue testing machine, the effects of different types of inclusions on fatigue performance were verified, the fatigue fracture mechanism of bearing steels by different processes was analyzed, and the critical size of inclusions causing fatigue cracks was predicted. The application of the aforementioned key technologies plays a guiding role in the large-scale production of nonaluminum deoxidized high-quality bearing steel. However, its quality still lags behind the most advanced production level of bearing steel worldwide, including the poor desulfurization effect caused by the use of low-basicity slag in the refining process, which needs to be further investigated.
Monthly, started in 1955 Supervising institution：Ministry of Education Sponsoring Institution：University of Science and Technology Beijing Editorial office：Editorial Department of Chinese Journal of Engineering Publisher：Science Press Chairperson：Ren-shu Yang Editor-in-Chief：Ai-xiang Wu ISSN 2095-9389CN 2095-9389
