Metallurgical and Materials Transactions B最新文献

For the control of the wear amount of work rolls and replacement moment in finishing rolling, most of the traditional models are unable to accurately predict the optimal finishing wear amount and replacement moment of work roll in advance, which may lead to the disruption of the production rhythm, and even cause product quality defects. This research describes a Lévy's improved arithmetic optimization algorithm twin support vector regression (LAOA-TSVR) prediction model for wear amount of work roll and replacement moment in a finishing mill. Firstly, the research group initially employed real production data from a hot strip finishing mill to identify influential factors of wear amount of work roll through correlation analysis using SPSS. Subsequently, to validate its predictive performance, the model was compared against three classical algorithms: Back Propagation (BP), Radial Basis Function (RBF), and Support Vector Machine (SVM), confirming LAOA-TSVR's superior accuracy. Finally, the model underwent practical production testing with a dataset totaling 200 sets. The findings reveal that the model attains a 95.2 pct hit rate for predicting wear amount of work roll within ± 0.5 pct. Likewise, it achieves a 98.3 pct hit rate for predicting the replacement moment of work roll for finishing mill.

The influence of magnesium treatment on cleanliness and microstructure characteristics of as-cast high-nitrogen stainless bearing steel (HNSBS) was systematically investigated. Results manifested that as the magnesium content increased from 0.0003 to 0.0054 wt pct, the oxygen and sulfur contents in steel, along with the number density and average size of inclusions significantly decreased due to the strong thermodynamic affinity and the removal of inclusions. Meanwhile, the inclusion evolution processes were Al₂O₃ → MgO·Al₂O₃ → MgO and MnS → MgS + Mg₃N₂, and the magnesium content in HNSBS should not exceed 0.0047 wt pct to prevent the formation of deleterious Mg₃N₂ inclusion. Additionally, the secondary dendrite spacing and the area fraction of precipitates (M₂₃(C, N)₆ and M₂(C, N)) at the 1/2 radius of ingots decreased form 83 ± 25 μm and 17 pct to 63 ± 16 μm and 12 pct, respectively. The dendrite structure was refined owing to the increase in effective nucleation sites for γ-Fe provided by MgO·Al₂O₃ and MgS inclusions, as well as the enrichment of magnesium in the liquid phase at solidifying front. The area fraction and size of precipitates were reduced due to the decrease of chromium activity. The finer and more dispersed precipitates was attributed to the reduction of growth space and increase in effective nucleation sites. This work provides theoretical guidance for preventing the formation of deleterious inclusions (especially for nitrides) in high-nitrogen alloy systems and refining the microstructure of alloy systems containing M₂₃(C, N)₆ and M₂(C, N) precipitates.

Thin slab casting and rolling (TSCR) is a near-net-shape manufacturing process and a key development technology in China's iron and steel industry. This study uses cross-scale calculations to analyze the complete process of thin slab casting. The focus is on simulating and predicting the final solidification structure by adjusting process parameters. The aim is to enable further investigation into material performance and establish a foundation for researching deformation and phase transformation. To achieve this, a coupled model has been developed to simulate the entire thin slab casting process, using hot stamping steel as the research subject. The model encompasses fluid flow, heat transfer, and solidification. The study identifies the optimal combination for flow field, temperature distribution, and equiaxed grain ratio within the specified parameter range at a casting speed of 4.0 m/min and a superheat of 40 °C. The aim of the study is to establish an integrated computational materials engineering (ICME) research system for near-net-shape automotive steel casting processes.

Graphical Abstract

In the current study, the quantity, size, and spatial distribution of non-metallic inclusions along the thickness direction of an ultralow carbon IF steel were detected employing an automatic SEM-EDS scanning system. And the distribution of the slab subsurface inclusions was mainly analyzed. In addition, the total oxygen content in the steel and the solidification structure of the slab were analyzed. Upon the application of M-EMS, the solidification front was flushed due to the stirring effect generated by the electromagnetic force, promoting the floating removal of inclusions, thereby improving the overall cleanliness of the slab. However, the probability of the collision and agglomeration of inclusions was increased by applying M-EMS, resulting in an increase in the size of inclusions. The influence of M-EMS on inclusions was primarily on the slab subsurface. Following the application of M-EMS, the inclusions in the slab subsurface were experienced a reduction in number density from 9.99 to 6.11 #/mm², and the area fraction was decreased from 69.51 × 10⁻⁶ to 57.31 × 10⁻⁶. However, the average size of inclusions was increased from 2.45 to 2.87 μm. With the application of M-EMS, the total oxygen content in the subsurface of the slab was reduced by 1–3 ppm, and the total oxygen content in the center of the slab was reduced by 0–1 ppm. These results indicated that the adoption of M-EMS contributed positively to the reduction of inclusions from the slab subsurface, thereby enhancing the surface quality of the slabs. Furthermore, the analysis revealed that the equiaxed crystal area comprised 12.06 pct of the total area without the consideration of M-EMS, while with the application of M-EMS, this proportion increased to 20.99 pct.

The stirring energy of bottom blowing is one of the most important factors affecting the steel scrap melting in converter. In this paper, a three-dimensional turbulent-multiphase-solidification/melting-solute transport coupling mathematical model is developed to investigate the molten metal flow and scrap melting behaviors in a steelmaking converter under asymmetric bottom blowing conditions. The mathematical model is verified by hot-state experiments. The results show that the dead zone volume fraction and mixing time can be reduced by 3 pct and 30 second by asymmetric bottom blowing, which can provide greater stirring kinetic energy for the molten bath, especially at the bottom of the molten bath, thereby accelerating the melting rate of the steel scrap. In Scheme A1, the time required for the complete melting of the steel scrap is 434 second, which is reduced by 96 second compared with the scheme of symmetrical blowing. Asymmetric bottom blowing can promote the heat exchange between low-temperature molten metal around steel scrap and high-temperature melt in other regions, so that the temperature field around steel scrap is stable at about 1710 K. Meanwhile, it can effectively promote the diffusion of carbon in steel scrap and then promote the rapid melting of scrap.

This study investigated the impact of BaO/Al₂O₃ molar ratio on the electrical conductivity and Al coordination state of CaO–MgO–SiO₂–Al₂O₃–BaO slag using four-electrode technique and ²⁷Al MAS-NMR spectroscopy, respectively. With an increasing BaO/Al₂O₃ molar ratio from 0.14 to 0.36, BaO preferentially participated in charge compensation of Al³⁺, which facilitated the transition from AlO₅ and AlO₆ structures to AlO₄ structure and increased the stability of AlO₄ tetrahedra, thus enhancing the slag’s polymerization and reducing its electrical conductivity. However, once the compensation achieved equilibrium, remaining BaO was involved in depolymerizing the tetrahedral structure and promoting the formation of AlO₅ and AlO₆ structures. Consequently, the decreased degree of polymerization and increased concentration of free ions together led to an increase in electrical conductivity. However, the increased migration resistance due to the large radius of Ba²⁺ ion is responsible for the electrical conductivity minimum near the molar ratio of 0.43.

Hot tearing, a severe casting defect in magnesium ingots, necessitates the development of constitutive relations to accurately predict the susceptibility of magnesium alloys. In this study, we propose an elastic–viscoplastic (E–V) model for forecasting the hot tearing propensity of Mg–Zn–Cu alloys. Our findings demonstrate that the E–V model yields a hot tearing indicator (HTI) that closely aligns with experimental results compared to the elastic–plastic (E–P) model. Moreover, the E–V model successfully synchronizes with experimental data regarding the initiation temperature for hot tearing. Notably, considering viscoplastic strain leads to higher strain values in the E–V model than those observed in the E–P model. Furthermore, our research highlights that employing an E–V approach is more suitable for predicting hot tearing in magnesium alloys and provides valuable insights into evaluating casting defects within this material system.

The coating fluxes used in SMAW electrodes for nuclear power plants have been specially developed. The study investigates various characteristics such as floatation coefficient, work of adhesion, spread area, and contact angle at a high temperature of 1323 K. The flux compositions, comprising Na₃AlF₆–CaO–Al₂O₃–SiO₂, are developed using the extreme vertices design approach, resulting in 26 different compositions. Furthermore, the surface tension of these fluxes was calculated as part of the investigation. Regression analysis was employed to predict the influence of individual constituents and their interactions on the wettability properties of the flux coatings. Additionally, artificial neural network (ANN) models were developed and compared to regression analysis to assess prediction accuracy. The fluxes underwent further characterization through X-ray diffraction (XRD) and Fourier transform infrared (FTIR) analysis to identify the phases present. The structural analysis of the molten slag was conducted by examining the powdered samples obtained through quenching. The FTIR results indicate the presence of [SiO₄]⁴⁻ tetrahedral units and [AlO₄]⁵⁻ tetrahedral units, suggesting the formation of a network structure. Additionally, it is observed that CaO acts as a network breaker, causing the release of non-bridging oxygen (O⁻) at the expense of bridging oxygen (O⁰). The individual components CaO, Na₃AlF₆, Al₂O₃, and SiO₂ were found to cause a decreased effect, while the binary interaction of the coating constituents shows a significant effect on the contact angle and floatation Coefficient. Individual interactions, CaO, SiO₂, Al₂O₃, and Na₃AlF₆ exhibit a positive impact, while the binary interactions of Na₃AlF₆·SiO₂, Na₃AlF₆·Al₂O₃, CaO·Na₃AlF₆, Al₂O₃·SiO₂, CaO·SiO₂, and CaO·Al₂O₃ have been found to have a decreasing effect on the spread area and work of adhesion.

A computational fluid dynamics-population balance model-boundary transfer model (CFD-PBM-BTM) coupled model was developed to predict the dynamic change behaviors of inclusions in molten steel. Brownian collision, turbulent collision, and Stokes collision were used to describe the collision–coalescence of inclusions in molten steel. Moreover, three boundary transfer models, namely ideal removal model, Stokes removal model, and Fan-Ahmadi removal model, were adopted to calculate the removal rate of inclusions at the steel/slag interface. The results show that inclusion size and number density distribution predicted by the developed model, with the Flint-Howarth coalescence probability sub-model, Fan-Ahmadi removal sub-model, were in good agreement with the industrial measurements. The deviation of model predictions with 21 inclusion size groups was only around 9 pct from industrial measurements. Turbulent collision was found to significantly affect the collision–coalescence rate of small size inclusions. For inclusions larger than around 10 μm, Stokes collision becomes critical and the Stokes collision rate can reach 1×10^-13 m³/s for the collision between 24.3 and 42.5 μm inclusions. In addition, the inclusion removal ratio in the pouring region was about 50 pct of that in the casting region. This is due to the impinging steel flow effect on inclusion moving. As inclusion diameter increased from 1.1 to 42.2 μm, the removal rate increased from 1.4×10^-4 to 7.7×10⁻⁴ m/s. Furthermore, the inclusion removal rate increased with an increased steel/slag interface roughness. Specifically, the total removal ratio of 1.1, 10.6, 24.3, and 42.2 μm inclusions was 0.1, 3, 14, and 42 pct for the roughness value of 0 mm, respectively. The ratio increased to 7, 10, 21, and 50 pct, respectively, when the roughness value was 1 mm.

Graphical Abstract

The type and morphology of inclusions have an important influence on the properties of high strength oil casing steel. In this paper, laboratory experiments were carried out to investigate the effect of cerium (Ce) alloying and holding time on inclusion modification of oil casing steel. The results show that with the increase of Ce content and the holding time, inclusions gradually changed from irregular shape to ellipsoidal shape. During the modification process, inclusions underwent the following transformations: Ca–Al–O + Al₂O₃ + Al–Mn–Si–O → Ca–Ce–Al–O + Ce (Mn, Si)–Al–O → CeAlO₃ → CaO-Ce₂O₃ + Ce₂O₃. When the holding time was 5 minutes, the average size of inclusions decreased from 1.26 to 1.14 μm with Ce content increased from 0 to 77 ppm. Nevertheless, when the holding time was over 20 minutes, the average size of inclusions firstly exhibited a decrease trend while it then showed an increase trend with an increased Ce addition. In addition, the number density of inclusions in molten steel was gradually reduced with Ce content increased from 0 to 77 ppm. For the ingot samples cooled down to room temperature within the furnace, the transformation of inclusions evolved the following characteristics with an increased Ce content in steel: Al₂O₃ + xCaO·yAl₂O₃ → Ca–Ce–Al–O → CeAlO₃ + CeAl₁₁O₁₈→CeAlO₃ → CeAlO₃ + Ce₂O₃. In this study, the optimum modification time and Ce content in Rare Earth Metal (REM) modified high-strength oil casing steel of inclusions was 20 minutes and above 60 ppm, respectively.