Non-metallic inclusions in steel are a significant challenge, affecting material properties and leading to issues such as stress concentration, cracking, and accelerated corrosion. Current methods for removing inclusions, including bubble, electromagnetic stirring, filtration separation, fluid flow, and sedimentation, often struggle with the removal of fine inclusions. Apart from these known methods, pulsed electric current (PEC), as an emerging technology, has demonstrated immense potential and environmental advantages. PEC offers adjustable current parameters and simple equipment, making it an attractive alternative to traditional methods. Its green energy-saving features and excellent results in regulating inclusion morphology and migration, as well as inhibiting submerged entry nozzle (SEN) clogging, make it a promising technology. In comparison to continuous current technology, PEC has shown significant advantages in regulating inclusions, not only improving purification efficiency but also demonstrating outstanding performance in flow stability and energy consumption. The ability of PEC to efficiently reduce inclusion numbers enhances the purity and quality of molten steel, improving its mechanical properties. Currently, the theoretical basis for controlling the movement of inclusions by current is mainly composed of three major theories: the double electric layer theory, electromagnetic force reverse separation theory, and electric free energy drive theory. These theories together form an important framework for researchers to understand and optimize the behavior of impurity movement controlled by electric current. Looking ahead, PEC is expected to pave the way for new solutions in directional regulation of inclusion migration, efficient inclusion removal, SEN clogging prevention, and the purification of molten steel.
The effect of (CaO+SiO2) mass ratio on high-Ti vanadium titanomagnetite sintering was systematically studied at the fixed basicity (CaO/SiO2) of 2.0. The results show that sinter matrix strength is improved with (CaO + SiO2) mass ratio while the total iron content is reduced. Thermodynamic analysis indicates that the increase in (CaO + SiO2) mass ratio from 15.0 to 22.5 wt.% contributes to the formation of liquid phase, especially silico-ferrite of calcium and aluminum (SFCA). In addition, the formation of perovskite is inhibited and liquid phase fluidity is improved. The porosity of sinter matrix is reduced by 34.5% and SFCA amount is increased by 47.2% when (CaO + SiO2) mass ratio is increased from 15.0 to 18.0 wt.%. With the further increase in (CaO + SiO2) mass ratio, the structure of sinter matrix is too dense and the improved extent of SFCA amount is increasingly low. The appropriate (CaO + SiO2) mass ratio should be 18.0 wt.% overall. Under this condition, sinter matrix strength is greatly improved by over 13.5% compared with the base case and the total iron content can be maintained at about 49 wt.%.
The permeability of the sintering process can be significantly improved by the pellet sintering, but the excessive permeability will impact the heat accumulation of the sinter bed. Thus, it is very essential to clarify the influence of the pellet particle size on the heat transfer process of sintering. Therefore, pilot-scale sinter pot tests of pellet sintering with manganese ore fines of different particle sizes were conducted, and traditional sintering was compared to reveal the heat transfer process of sintering and its impact on the microstructure of sintered ore. The results indicate that under suitable pellet sizes (8-12 mm), the heat transfer efficiency and the heat accumulation effect between the layers of sinter bed are strengthened by the pellet sintering, as well as the highest temperature in the combustion zone and the duration of hightemperature zone. This also leads to the further growth of ferrotephroite or hausmannite in liquid phase and its more reasonable crystal distribution. Ultimately, compared with the traditional sintering process, the total solid fuel consumption can be reduced by 20%-30%, and the productivity can be increased by 11.71%-16.21%.
Against the background of ‘‘carbon peak and carbon neutrality,’’ it is of great practical significance to develop non-blast furnace ironmaking technology for the sustainable development of steel industry. Carbon-bearing iron ore pellet is an innovative burden of direct reduction ironmaking due to its excellent self-reducing property, and the thermal strength of pellet is a crucial metallurgical property that affects its wide application. The carbon-bearing iron ore pellet without binders (CIPWB) was prepared using iron concentrate and anthracite, and the effects of reducing agent addition amount, size of pellet, reduction temperature and time on the thermal compressive strength of CIPWB during the reduction process were studied. Simultaneously, the mechanism of the thermal strength evolution of CIPWB was revealed. The results showed that during the
Pursuing green, low-carbon ironmaking technology primarily aims to reduce fuel ratios, especially coke ratios. Simultaneously, the reduction in coke ratios causes the coke layer in the blast furnace (BF) to become thinner, deteriorating the gas and liquid permeability of the burden column. This exacerbates coke degradation, significantly impacting the smelting process and increasing the demand for high-quality coke. To investigate the existence state of coke in the hearth, a 2500 m3 BF in China was taken as the research object, and three sets of samples at different heights of the hearth were obtained during planned outage. The results indicate that coke undergoes a significant degradation upon reaching the hearth. The proportion of coke particles smaller than 50 mm ranges from 81.22% to 89.50%. The proportion of coke particles larger than 20 mm decreases as the distance from the centerline of the tuyere increases, while the proportion of particles smaller than 10 mm increases with this distance. Additionally, the closer the bottom of the furnace is, the smaller the coke particle size becomes. The composition of slag filling the coke pores is similar to that of the final slag in the blast furnace, and the graphitization of coke is comparable to that of the final slag. The graphitization of coke starts from the surface of coke and leads to the formation of coke fines, and the graphitization degree of - 74 lm coke fines is the highest. The temperature has an effect on the reaction rate of coke solution loss, and the higher the temperature is, the faster the reaction rate is. Keywords: Blast furnace; Hearth; Coke; Graphitization; Dissolution reaction
The top-bottom combined blowing converter mainly adopts the blowing method of top-blowing oxygen and bottomblowing nitrogen. In the production process, there are some disadvantages, such as a significant temperature difference between the top and bottom of the molten pool, inadequate gas permeability of bottom blowing, and low decarburization efficiency. Therefore, we propose a novel bottom-blowing gas doped oxygen process to enhance the smelting conditions in the converter. The 500 kg medium frequency induction furnace with top and bottom-blowing function was used to explore the influence of the proportion of bottom-blowing gas doped oxygen on the smelting effect in different smelting cycles. Subsequently, industrial experimental verification was carried out on a 60 t converter. The results of intermediate frequency furnace experiments demonstrate that the bottom-blowing gas doped oxygen process exhibits a superior heating rate and decarburization efficiency during the initial and final stages of blowing compared to pure N2 used for bottomblowing. Simultaneously, the dephosphorization efficiency exhibited an initial increase followed by a subsequent decrease as the bottom-blowing oxygen content increased. The industrial test of 60 t converter validates the findings above. Moreover, when the oxygen content in bottom-blowing gas is 5%, the average blowing time reduces by 54 s, and the minimum endpoint carbon-oxygen equilibrium reaches 0.00219 under this condition. The results demonstrate that the appropriate amount of oxygen doped in bottom-blowing gas can effectively enhance the metallurgical conditions of the converter and improve production efficiency.
The production of ferroalloys is a resource-intensive and energy-consuming process. To mitigate its adverse environmental effects, steel companies should implement a range of measures aiming at enhancing the utilization rate of ferroalloys. Therefore, a comprehensive ferroalloy model was proposed, incorporating a prediction model for alloying element yield based on case-based reasoning and support vector machine (CBR-SVM), along with a ferroalloy batching model employing an integral linear programming algorithm. In simulation calculations, the prediction model exhibited exceptional predictive performance, with a hit rate of 96.05% within 5%. The linear programming ingredient model proved effective in reducing costs by 20.7%, which was achieved through accurate adjustments to the types and quantities of ferroalloys. The proposed method and system were successfully implemented in the actual production environment of a specific steel plant, operating seamlessly for six months. This implementation has notably increased the product quality of the enterprise, with the control rate of high-quality products increasing from 46% to 79%, effectively diminishing the consumption and expenses associated with ferroalloys. The reduced usage of ferroalloys simultaneously reduces energy consumption and mitigates the adverse environmental impact of the steel industry.
The continuous growth behavior of austenite grain in 20Cr peritectic steel was analyzed by experiment and theoretical modeling. The peculiar casting experiment with different cooling rates was achieved by multigradient operation scheme, and different morphologies in austenite grain were observed at the target location. The increase in austenite grain size with increasing cooling rate was firstly revealed in steels. The anomalous grain growth theoretically results from the mechanism of peritectic transformation transiting from the diffusional to massive type, and the additional energy storage stimulates the grain boundary migration. A new kinetic model to predict the growth behavior of austenite grain during continuous cooling process was developed, and the energy storage induced by massive type peritectic transformation was novelly taken into account. The parameters in the model were fitted by multiphase field modeling and experimental results. The kinetic model was finally verified by austenite grain size in laboratory test as well as the trial data at different locations in continuously cast bloom. The coarsening behavior of austenite grain during continuous casting was predicted based on the simulated temperature history. It is found that the grain coarsening occurs generally in the mold zone at high temperature for 20Cr steel and then almost levels off in the following process. The austenite finish transformation temperature Tγ and primary cooling intensity show great influence on the grain coarsening. As Tγ decreases by 1 ℃, the austenite grain size decreases by 4 μm linearly. However, the variation of Tγ against heat flux is in a nonlinear relationship, suggesting that low cooling rate is much more harmful for austenite grain coarsening in continuous casting.
The electromagnetic swirling flow in nozzle (EMSFN) technique is designed to mitigate the adverse effects of unstable and uneven flow within the submerged entry nozzle in continuous casting. Utilizing electromagnetic forces, EMSFN stabilizes the flow within the nozzle, leading to a more controlled flow in the mold. Numerical simulations were used to quantitatively analyze the magnetic and flow fields in a slab continuous casting system under EMSFN. Results indicate that EMSFN significantly stabilizes the outflow from the nozzle, with stability increasing with higher current intensity. At 10,000 Ampere-turns (At) of the coil, meniscus fluctuations were unstable. They stabilized at 13,000 At, with minimal changes observed beyond this point. The optimal current intensity for stable mold flow, at a casting speed of 1.56 m/min, is 13,000 At. These findings confirm the effectiveness of EMSFN in stabilizing the internal flow field of the slab mold and determining optimal operational current intensity.
An opposite combined vertical linear electromagnetic stirring (CV-LEMS) was proposed, which is applied in the final solidification zone of bloom continuous casting. The melt flow, heat transfer, and solidification under CV-LEMS were investigated by establishing a three-dimensional numerical simulation model and a pilot continuous casting simulation experiment and compared with the conventional rotary electromagnetic stirring (REMS). The results show that a longitudinally symmetric linear magnetic field is formed in the liquid core of the bloom by applying CV-LEMS, which induces a strong longitudinal circulation flow both on the inner arc side and the outer arc side in the liquid core of the bloom. The height of the melt longitudinal effective mixing range under CV-LEMS reaches 0.9 m, which is greater than that of the REMS and makes up for the deficiency of REMS sensitivity to the position of the final solidification zone. CV-LEMS strongly promotes the mixing of upper melt with high temperature and the lower part melt with low temperature in the liquid core, improves the uniformity of melt temperature distribution and significantly increases the melt temperature near the solidification front, and the width of the liquid core increases by 4.2 mm at maximum. This shows that the appliction of CV-LEMS is more helpful to strengthen the feeding effect of the upper melt to the solidification shrinkage of the lower melt than the conventional REMS and inhibits the formation of porosity, shrinkage cavity and crack defects in the center of the bloom.
The variations in the mechanical and magnetic properties of cold-rolled 20Mn23AlV non-magnetic structural steel after annealing at different temperatures were investigated. The microstructure and precipitation changes during annealing were studied by optical microscopy, scanning electron microscopy, and transmission electron microscopy. The results show that recrystallization completed after annealing at 620 ℃, resulting in grain sizes of approximately 800 nm and the best combination of strength and plasticity. The yield-to-tensile ratio of the non-magnetic structural steel after cold rolling continuously decreases from low to high temperatures after annealing, with the highest value being 0.89 and the lowest value being 0.43, indicating a wide range of yield-to-tensile ratio adjustment. The introduction of numerous dislocations during cold rolling provided favorable nucleation sites for precipitation, leading to abundant precipitation of the fine second-phase V(C, N). The phase composition of the samples remained unchanged as single-phase austenite after annealing, and the relative permeability values were calculated to be less than 1.002, meeting the requirements for nonmagnetic steel in terms of magnetic properties.
Non-metallic inclusions are a significant factor causing fractures during the manufacturing process of tire cord steel, and dissolution in the steel profoundly affects them.Howthe basicity andAl2O3 content in SiO2-CaO-Al2O3-MgO refining slag affect non-metallic inclusions in tire cord steel at 1873 K was investigated. A quantitative relationship has been established between the slag basicity and the dissolved oxygen content in steel. The results demonstrate that non-metallic inclusions in steel transform along SiO2-MnO-Al2O3→SiO2-MnO system of inclusions. When the basicity is controlled within the range of 0.8-1.0, the corresponding dissolved oxygen content should be between 4×10-6 and 10×10-6.When Al2O3 content in the refining slag is maintained at 5%, and the slag basicity is controlled between 0.8 and 1.0, or if the slag basicity is precisely 1.0 with Al2O3 content kept below 11%, control over the plasticization of SiO2-MnO-Al2O3 system within the inclusions can be effectively achieved. Combined with thermodynamic calculation andmeasurement of the dissolved oxygen ([O]) activity in the steel, controlling SiO2- MnO-Al2O3-like inclusions in the plastic region range can be achieved by adjusting the refining slag composition.
304H austenitic stainless steel wire was investigated, emphasizing microstructural deformation, martensite phase transformation, and residual magnetic properties during drawing. Utilizing several microstructural observation techniques, the volume fraction of martensite, modes of grain deformation in distinct regions, and the phase relationship between austenite and martensite were comprehensively characterized. In addition, a finite element simulation with representative volume elements specific to different zones also offers insights into strain responses during the drawing process. Results from the first-pass drawing reveal that there exists a higher volume fraction of martensite in the central region of 304H austenitic stainless steel wire compared to edge areas. This discrepancy is attributed to a concentrated presence of shear slip system {111}<110>γ crystallographic orientation, primarily accumulating in the central region obeying the Kurdjumov-Sachs path. Subsequent to the second drawing pass, the cumulative shear deformation within distinct regions of the steel wire became more pronounced. This resulted in a progressive augmentation of the volume fraction of martensite in both the central and peripheral regions of the steel wire. Concurrently, this led to a discernible elevation in the overall residual magnetism of the steel wire.
The effects of niobium on the high-temperature oxidation resistance of austenitic stainless steel were systematically investigated. Two austenitic stainless steels with different Nb contents were prepared and exposed to air at 850 ℃ for 200 h. Results show that Nb positively affects the high-temperature oxidation resistance of austenitic stainless steels. The matrix organization of austenitic stainless steels with added niobium does not change, while the austenitic grain size is significantly refined, and it also promoted the release of internal stresses in the oxide film, which in turn improved the integrity of the oxide film and adhesion to the substrate. In addition, with the addition of Nb element, a large number of Nb(C, N) particles are diffusely distributed in the matrix. Nb(C, N) phase distributed in the matrix and the niobium-rich layer formed by the diffusion of niobium into the interface between the metal matrix and the oxide film during the hightemperature oxidation process effectively prevents the diffusion of iron into the outer layer and enhances the oxidation resistance at high temperatures.
A prediction model leveraging machine learning was developed to forecast the tensile strength of wear-resistant steels, focusing on the relationship between composition, hot rolling process parameters and resulting properties. Multiple machine learning algorithms were compared, with the deep neural network (DNN) model outperforming others including random forests, gradient boosting regression, support vector regression, extreme gradient boosting, ridge regression, multilayer perceptron, linear regression and decision tree. The DNN model was meticulously optimized, achieving a training set mean squared error (MSE) of 14.177 with a coefficient of determination (R2) of 0.973 and a test set MSE of 21.573 with an R2 of 0.960, reflecting its strong predictive capabilities and generalization to unseen data. In order to further confirm the predictive ability of the model, an experimental validation was carried out, involving the preparation of five different steel samples. The tensile strength of each sample was predicted and then compared to actual measurements, with the error of the results consistently below 5%.
Machine learning is employed to comprehensively analyze and predict the hardenability of 20CrMo steel. The hardenability dataset includes J9 and J15 hardenability values, chemical composition, and heat treatment parameters. Various machine learning models, including linear regression (LR), k-nearest neighbors (KNN), random forest (RF), and extreme Gradient Boosting (XGBoost), are employed to develop predictive models for the hardenability of 20CrMo steel. Among these models, the XGBoost model achieves the best performance, with coefficients of determination (R2) of 0.941 and 0.946 for predicting J9 and J15 values, respectively. The predictions fall with a ± 2 HRC bandwidth for 98% of J9 cases and 99% of J15 cases. Additionally, SHapley Additive exPlanations (SHAP) analysis is used to identify the key elements that significantly influence the hardenability of the 20CrMo steel. The analysis revealed that alloying elements such as Si, Cr, C, N and Mo play significant roles in hardenability. The strengths and weaknesses of various machine learning models in predicting hardenability are also discussed.
The effect of rare-earth cerium on impurity P-induced embrittlement for an advanced SA508Gr.4N reactor pressure vessels steel is investigated by virtue of microstructural characterization, Auger electron spectroscopy (AES), and spin-polarized density functional theory (DFT) calculations. The ductile-to-brittle transition temperatures (DBTTs) are evaluated by Charpy impact testing, and grain boundary segregation (GBS) of P is quantified by AES. Trace addition of Ce can effectively reduce GBS level of P, thereby substantially decreasing the embrittlement induced by P. A linear correlation between DBTT (℃) and GBS level of P (Cp, at.%) is observed for both undoped and Ce-doped samples, being expressed as DBTT=13.13Cp-335.70 (undoped) and DBTT=12.67Cp-350.78 (Ce-doped). In the absence of GBS of P, the incorporation of Ce appears to play a pivotal role in augmenting the intrinsic toughness. These results imply that the impact of Ce on impurity P-induced embrittlement may be attributed to a combination of increasing the intrinsic toughness and lowering GBS of P. DFT calculations indicate that there is a negligible interaction between Ce and P in the ternary alloy, and thus GBS of P and Ce is mainly site-competitive.
A novel Al-alloyed press-hardening steel (PHS) was developed, which exhibits excellent tensile, bending and antioxidation properties. Al is a ferrite-forming element that can hinder the formation of cementite and enhance the stability of austenite. The incorporation of Al not only induces the formation of ferrite within martensitic matrix but also enhances the stability of retained austenite (RA). The microstructure of novel steel consists of martensite, ferrite, and RA after press hardening. Investigations into the role of Al in RA development were supported by thermo-kinetic calculations. The simultaneous introduction of ferrite and RA into the martensitic matrix via tailored chemical compositions significantly enhances the elongation and bending toughness of the novel PHS. Additionally, Al can form a dense Al oxide at the bottom of oxide layer, resulting in the improved antioxidant properties. Compared to 22MnB5 steel, it is an exciting discovery as there is a significant improvement in total elongation and bending toughness of novel PHS without compromising strength. The novel PHS, with its exceptional balance of strength and ductility, will play a crucial role in reducing weight when it replaces the existing class 22MnB5 PHS in different structural components of vehicle bodies.
The micro-area characterization experiments like scanning Kelvin probe force microscope (SKPFM) and Kernel average misorientation have the defects of complex sample preparation and occasional errors in test results, which makes it impossible to accurately and quickly analyze the pitting behavior induced by inclusions in some cases, prompting attempts to turn to simulation calculation research. The method of calculating band structure and work function can be used to replace current-sensing atomic force microscopy and SKPFM to detect the potential and conductivity of the sample. The band structure results show that Al2O3 inclusion is an insulator and non-conductive, and it will not form galvanic corrosion with the matrix. Al2O3 inclusion does not dissolve because its work function is higher than that of the matrix. Moreover, the stress concentration of the matrix around the inclusion can be characterized by first-principles calculation coupled with finite element simulation. The results show that the stress concentration degree of the matrix around Al2O3 inclusion is serious, and the galvanic corrosion is formed between the high and the low stress concentration areas, which can be used to explain the reason of the pitting induced by Al2O3 inclusions.
To enhance the corrosion resistance and electrical conductivity, the surface of 316L stainless steel was modified by the ion implantation of Mo. By investigating various accelerating voltages and implantation doses, it was found that the corrosion resistance of stainless steel was enhanced by 50%-80% and the surface conductivity by 15%-28% at most. The minimum stabilized current density is 0.72 lA/cm2. This is due to the formation of a Cr and Mo riched modified layer on the surface of the stainless steel. Mo oxides synergize with Cr oxides in the form of a solid solution to enhance the corrosion resistance of passivation films on the stainless steel surface. The optimum parameters were Cr in the proportion of 6%-8% and Mo in the proportion of 4%-5%.
Pinless friction stir spot welding (P-FSSW) was performed to manufacture Mg/steel lap joints. Orthogonal tests for P-FSSW of Mg/steel were investigated, and the main factors affecting the properties of Mg/steel lap joints were derived. The shear force of the Mg/steel lap joints gradually increased and then decreased as the welding time increased. Maximum shear force was 5.3 kN. Fe-Al intermetallic compound (IMC) was formed at the Mg/steel interface near the steel side, and Mg-Al IMCs were formed at the Mg/steel interface near the Mg alloy side. Mg/steel lap joint was transformed from an initial solid-state welding to fusion-brazing welding as the welding time increased. No hole defects were formed in Mg/steel solid-state welding joints, whereas hole defects appeared in Mg/steel fusion-brazing welding joints. The temperature field of Mg/steel lap joints was simulated to analyze hole defects generated during the welding process. Hole defects can be eliminated by changing the spindle deflection angle, and the shear force decreased. Excessive spindle deflection can also lead to failure to form a stable joint. Hole defects were removed because the spindle deflection angle reduced the interfacial reaction temperature, and a solid-state welding joint was formed, which resulted in an absence of fusion-brazing welding hole formation.
0.05 wt.% Y was incorporated into IN718 alloy powders, and specimens were fabricated using selective laser melting (SLM) technology. High-temperature tensile tests were then performed at 650 ℃ on both the as-built and heat-treated specimens. The results revealed that both the as-built and heat-treated 0.05Y-IN718 specimens exhibit a slight increase in tensile strength compared to 0Y-IN718 specimen, attributed to the formation of Y-O and Y-Al-O nano-oxides. Notably, the ductility of 0.05Y-IN718 alloy was largely improved in as-built state, but only marginally improved in heat-treated state. Previous research suggests that the improved ductility can be ascribed to Y effect on grain boundary purification and alterations in the morphology of carbides and d phase. However, an in-depth analysis was conducted based on the scanning/transmission electron microscope and density functional theory results and demonstrated that it is Y segregation in the Laves/c matrix interface that actually plays the vital role for enhancing interfacial bonding. Hence, the extremely fast cooling rate during SLM processing facilitates mass accumulation of Y in the interdendritic region or cellular wall, achieving a large improvement in the ductility.
The electrochemical performance and corrosion properties of Fe40Mn20Cr20Ni20 high-entropy alloys (HEAs) in a 3.5% NaCl solution with various pH values were thoroughly investigated. The results revealed a close correlation between the corrosion properties of HEAs and the pH value. On the one hand, the pH value can affect the semiconducting properties of the passive film on the alloy surfaces, thereby further influencing the protective capacity of the passive film. On the other hand, an excess of H+ or OH- promotes the growth of localized corrosion, facilitating the formation of a larger number of larger-sized localized corrosion pits. Ultimately, the corrosion of HEAs is most severe in acidic solutions.
