Metallurgical and Materials Transactions B最新文献

Enameled steel is widely used owing to its superior fatigue and strength properties. However, the presence of inclusions formed during the steelmaking process significantly affects these properties. Therefore, this study investigated a factory-enameled steel slab to elucidate its behavior. Additionally, the study analyzed the distribution of inclusions across the slab thickness, and characterized the variation in oxygen, nitrogen, carbon, manganese and sulfur contents. Moreover, the type, number density, size, and morphology of inclusions were examined across the slab thickness. The findings revealed that the center of the slab exhibited the lowest sulfur and manganese contents, which gradually increased toward the edges. Conversely, nitrogen content reached the maximum at the slab center and decreased toward the edges. The oxide inclusions mainly comprised Al₂O₃–MgO cores. Furthermore, the oxide inclusions in the slab mainly exhibited ellipsoidal morphology, with sizes concentrated between 1 and 5 μm. Moreover, the slab contained MnS and TiN inclusions, which exhibited symmetric variations in number density and average size from the edge to the center of the slab. The number density of MnS first decreased and then increased from the inner arc to the outer arc, while TiN exhibited the opposite trend. Additionally, MnS had a smaller average size than TiN, despite its higher number of inclusions. Furthermore, Ti₄C₂S₂ inclusions were mainly distributed between 1 and 3 μm and clustered in the slab. Additionally, theoretical calculations revealed that the elemental segregation trend followed the order of S > Ti > N > Mn. The sequence of precipitation formation was Ti₄C₂S₂ > TiN > MnS. This indicated a negative correlation between the cooling rate and inclusion size. Particularly, MnS exhibited the smallest size, while TiN featured the largest size at the center of the slab.

The aim of this study was to control large TiN inclusions in 45Cr9Si3 martensitic valve steel in ESR. For this purpose, the effects of different SiO₂ contents in CaF₂-Al₂O₃-CaO-SiO₂- MgO-TiO₂-type slags on Ti removal and TiN inclusions in steel have been investigated through laboratory-scale experiments, thermodynamic analysis, and industrial tests. The results showed that SiO₂ in slag is a good de-Ti agent. The increase of SiO₂ content in slag reduces the ratio of TiO₂ activity to SiO₂ activity, a high SiO₂ content (15.21 pct) can significantly reduce the Ti content in steel, and at the same time, the Al content also decreases correspondingly, and the O content in steel changes little, which makes the number and size of TiN and MgAl₂O₄ decrease sharply. The optimum content of SiO₂ in slag is 15.0 pct, which has good effect of removing Ti from steel and controlling Al and O contents. Combined with industrial optimization test, it is found that smelting with 20 pct SiO₂ in ESR can control the size of TiN within 5 μm, and the amount of MgAl₂O₄ is greatly reduced.

Numerical models were built and validated to analyze the flow and heat transfer in three submerged entry nozzles (SEN) and a large round billet mold. A comparative investigation of a single-port SEN and two types of four-port SEN was conducted using numerical simulation and industrial experiments, considering the effect of mold electromagnetic stirring (M-EMS). The findings indicate that the upper part of the mold exhibits increased surface activity using upward and downward four-port SENs. Single-port SEN demonstrates significantly lower velocity at the free surface (0.001 m/s) compared to four-port SENs (0.087 m/s for upward and 0.065 m/s for downward). The introduction of M-EMS activates the horizontal flow inside the mold. Additionally, the four-port SENs achieve a higher free surface temperature and demonstrate a significantly higher inclusion escape percentage than the single-port SEN. The shell thickness uniformity under four-port SENs is lower due to the convection of the steel jet. Industrial tests reveal no significant difference in corrosion among the three SENs. Moreover, the advantage of increasing the proportion of equiaxed crystals and reducing inclusion number density is observed using the four-port SENs in plant trials.

This study investigates the delubrication, reduction, and decarburization processes of powder metallurgical steel alloys (CrM, CrL, AHC, Mo85, SintD 35) and an unalloyed steel during sintering in a pure hydrogen atmosphere. Utilizing in-situ FTIR gas phase analysis, components with ethylenebisstearamide (EBS) as a lubricant are analyzed. EBS decomposition in steel components yields CO, CO₂, H₂O, and CH₄, with dominant CH groups observed in the 230 °C to 480 °C range. In the temperature range between 750 °C and 850 °C, where CO formation is expected due to the reduction of surface iron oxides, CH₄ is present instead, indicating that an “internal getter effect” also occurs in pre-alloyed powders. In addition, with high carbon activity, the reduction of internal iron oxides and the reduction of chromium oxides also trigger an internal getter effect. Depending on the carbon potential, these processes cause a considerable reduction in the carbon content of the powder metallurgical components. The study therefore shows that the decarburization of powder metallurgical components during the heat treatment phases prior to sintering in a 100 pct hydrogen atmosphere is less due to the mechanism of delubrication, but rather to mechanisms of carbothermal reduction.

To avoid coarse crystallization of CaO–SiO₂–Al₂O₃ inclusions during the solidification stage of continuous casting process, the effect of MgO on crystallization behavior of these inclusions is investigated. The single hot thermocouple technology experiment results show that the low melting point CaO–SiO₂–Al₂O₃ inclusions do not easily crystallize during the solidification stage. However, with increasing the MgO content from 4.5 to 15.7 wt pct, the initial crystallization temperature of inclusions increases from 1376 K to 1431 K (1103 °C to 1158 °C) and the crystallization ratio increases from 35.45 to 100 pct. The crystallization ability of the inclusions can be predicted by the initial crystallization potential and the viscosity at the melting point. With increasing the MgO content from 0 to 15.7 wt pct, the initial crystallization potential of the inclusions increases from 0.28 to 0.87 and the viscosity of the inclusions at the melting point decreases from 4.47 to 0.56 Pa s. The higher the initial crystallization potential and the lower the viscosity near the melting point, the easier the crystallization of the inclusions occurs. Al₂O₃ mainly acts as the network former and participates in the construction of the network structure. With the increase of MgO content, the crystallization ability of inclusions increases gradually, which is mainly related to the increase of melt structure depolymerization.

Solidification end reduction is an effective approach to control the central porosity during continuous casting of round bloom, although it is not widely reported. In the present work, a three-dimensional finite element model has been developed with coupling heat transfer and mechanical deformation for a φ690 mm continuously cast round bloom, and verified by the surface temperature, shrinkage zone width, reduction crack location, and deformed contour shape. It is found that the contact width between roller and the bloom increases with the increase of reduction amount and approximately in a parabolic relationship. To cover the whole range of the shrinkage zone, the total reduction amount should not be smaller than 25 mm as the width of the shrinkage zone is about 120 mm. The bulge width along the horizontal direction during reduction increases as the total reduction amount increases, and the relationship can be fitted by a parabolic equation. The reduction thickness in the shrinkage zone is larger when the reduction amount is higher, and it also follows parabolic relationship. The deformation in the shrinkage zone is more obvious when the reduction is conducted before crater end. The reduction efficiency for φ690 mm round bloom before solidification is between 20 and 30 pct, while after solidification is roughly between 12 and 20 pct. It increases with the increase of apparent reduction amount, mainly related to the increase of the strain rate. The deformation of the shrinkage zone in φ690 mm round bloom with 30 mm apparent reduction in continuous casting and hot rolling has been compared. The equivalent strain in the shrinkage zone of the round bloom in continuous casting is about 0.047 to 0.052, while that in hot rolling is about 0.031 to 0.036, indicating the reduction efficiency of the former is about 1.5 times higher than the latter.

The effects of pure silicon deoxidation (Si group) and ferrosilicon deoxidation (FeSi group) on the evolution of oxide inclusions in 55SiCr spring steel are methodically examined using OTSInca, SEM-EDS, and FactSage 8.0. Compared with the Si group, the FeSi group is more favorable for controlling the total oxygen content in steel, and the total oxygen content in ingots is only 0.0012 pct. The average equivalent diameter of inclusions in the Si group continuously lessens with the melting process, while it is exactly the opposite in the FeSi group, and the average equivalent diameter of the inclusions in the ingots reaches 3.64 μm. The evolution of inclusions in the Si group is essentially provided by SiO₂ → SiO₂–MnO–Al₂O₃ → SiO₂–MnO–Al₂O₃–MgO, whereas the evolution process of inclusions in the FeSi group is mainly characterized by Al₂O₃–CaO → Al₂O₃–CaO–SiO₂ → Al₂O₃–CaO–SiO₂–MgO. However, MgO–Al₂O₃ and MgO–SiO₂ inclusions are precipitated in the inclusions because of the uneven distribution of inclusions in the ingot. In continuing, the Gibbs free energy of chemical reaction is utilized to explain the evolution of inclusions. FactSage calculation results reveal that the main inclusions in the Si group under equilibrium solidification conditions are 2Al₂O₃·2MgO·5SiO₂, 5Al₂O₃·4MgO·2SiO₂, and Al₂O₃·SiO₂. Additionally, the inclusions in the FeSi group are obtained as CaO·2MgO·8Al₂O₃, MgO·Al₂O₃, and 2CaO·MgO·2SiO₂. The deformability of inclusions in the FeSi group is not as good as in the Si group. The calculated results of the complete melting temperature and Young’s modulus of inclusions indicate that reducing the proportion of Al₂O₃ and MgO in inclusions leads to the improvement of the deformability of inclusions. This study is aimed to provide a fairly solid reference for controlling and removing inclusions in spring steel.

Grain refinement is the key to developing high-quality cast aluminum alloys. Based on the solute conservation theory and dendritic growth kinetics model, this paper developed a cellular automaton (CA) numerical model and fully considered the complex evolutionary processes, such as nucleation particle characteristics, nucleation-growth process, dynamic solute diffusion, and latent heat release during the solidification process of aluminum alloys. The CA model was used to quantify the role of solidification latent heat and solute diffusion in the grain nucleation process. The influence of solute suppressed nucleation (SSN) and solidification latent heat on the grain refinement effect of aluminum alloys are systematically studied. The results showed that when only considering the SSN effect, with the increase of nucleation density, the refinement efficiency decreases from 81.2 to 45.98 pct, and the decrease gradually decreases. This was mainly due to the increase of number of particles in the solute diffusion layer. The grain separation distance (GSD) became smaller than the size of the invisible nucleus region, reducing in the nucleation efficiency of the particles there. When the model further considered the effect of latent heat, the refinement efficiency was sharply dropped to 7 pct. The re-glow phenomenon caused by latent heat release limited the possibility of nucleation of small-sized particles and particles located in the SSN zone. Therefore, latent heat was fond to be the main factor restricting grain refinement.

In this work, a data-driven model for endpoint prediction of basic oxygen furnace (BOF) steelmaking based on both tabular features (information about hot metal, scrap, additives, blowing practices) and time series (curves of off-gas profiles, sonar slagging, and blowing practices) was developed and implemented. The model was designed with the following distinctive artificial intelligence (AI) characteristics: convolutional neural networks, patching embedding, wavelet decomposition, a parallel structure, a self-attention mechanism, a collaborative attention mechanism, and so on. The model presented in this work is named the self-attention-based convolutional parallel network (SabCP) and was applied to high-carbon steelmaking scenarios. SabCP predicts the endpoint of molten steel temperature (Temp) and chemistry (contents of carbon (C), phosphorus (P), and sulfur (S)). For training, validation, and testing, historical data from 13,656 heats were collected. The testing results show that the mean absolute errors (MAEs) of SabCP for temperature and the contents of carbon, phosphorus, and sulfur are 6.374 °C, 7.192 × 10⁻³, 2.390 × 10⁻³, and 2.224 × 10⁻³ pct, respectively, while the mean square errors (MSEs) are 67.345, 1.132 × 10⁻⁴, 1.306 × 10⁻⁵, and 1.298 × 10⁻⁵, respectively, which are lower than those of other published models with same dataset. Relevant importance analyses for tabular features, time series time steps, and channels are also performed. SabCP has been implemented in a prediction module, and the practical results show its strong robustness and generalizability. This model provides significant feasibility for fully eliminating the conventional physical temperature, sampling, and oxygen test (TSO test), which may greatly decrease the cost of BOF steelmaking.

Wüstite (FeO) has been extensively studied within the context of ironmaking metallurgy and the recycling of industrial waste, owing to its crucial role in high-temperature systems that exhibit softening and melting behaviors. Understanding these behaviors is vital for advancing multi-phase transport and chemical reactions in metallurgical processes. In this work, the Tammann temperature of FeO was identified to be approximately 826 K, a finding confirmed by molecular dynamics simulations and experimental validation. Below this threshold, the atoms' thermal vibration led to a volumetric expansion of the material. Conversely, surpassing 826 K triggered solid-state sintering, resulting in a noticeable shrinkage of FeO granules and the compaction of packed beds under mechanical stress. During softening, the reorganization of FeO grains was observed, with bonding commencing at contact points and the formation of sintering necks as surface atoms migrated and diffused. As temperatures rose further, this mass transfer and atomic diffusion intensified, facilitating the outward migration across grain boundaries, and culminating in the coalescence of smaller grains into larger formations.