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 iron and steel industry, standing as a quintessential manufacture example with high consumption, pollution and emissions, faces significant environmental and sustainable development challenges. Electric arc furnace (EAF) steelmaking process mainly uses scrap as raw material and is characterized by environmentally friendly and recyclable process. However, the further development of EAF route in China is limited by the reserve, supply, availability and quality of scrap resource. Direct reduced iron (DRI) is one of typical low-carbon and clean charges, which can effectively make up for the adverse effects caused by the lack of scrap. The physical and chemical properties, classifications, and production technologies of DRI are firstly reviewed. In particular, the reducing gas types, reduction temperature, and reduction mechanism of the DRI production with gas-based shaft furnace (SF) technology are detailed. Considering the crucial role played by DRI application in EAF, the influences of DRI addition on EAF smelting rules and operations including the blending and charging process, heat transfer and melting in molten bath, slag formation operation, refractory corrosion, and slag system evolution are then further discussed. Finally, the comparative analysis and assessment of the consumption level of material and energy as well as the cleaner production both covering the clean chemical composition of molten steel and the clean environment impact in EAF steelmaking with DRI charged are conducted. From perspectives of metallurgical process engineering, a suitable route of hydrogen generation and application (from coke oven gas, methanol, and clean energy power), CO₂ capture and utilization integrated with SF-EAF process is proposed. In view of the difficulties in large-scale DRI application in EAF, the follow-up work should focus on the investigation of DRI charging and melting, slag system evolution and molten pool reaction rules, as well as the developments of the DRI standardized use technology and intelligent batching and control models.

Refill friction stir spot welding (RFSSW) provides a novel method to join similar and/or dissimilar metallic materials without a key-hole in the center of the joint. Having the key-hole free characterization, the similar/dissimilar RFSSW joint exhibits remarkable and endurable characteristics, including high shear strength, long fatigue life, and strong corrosion resistance. In the meanwhile, as the key-hole free joint has different microstructures compared with conventional friction stir spot welding, thus the RFSSW joint shall possess different shear and fatigue fracture mechanisms, which needs further investigation. To explore the underlying failure mechanism, the similar/dissimilar metallic material joining parameters and pre-treatment, mechanical properties, as well as fracture mechanisms under this novel technology will be discussed. In details, the welding tool design, welding parameters setting, and the influence of processing on the lap shear and fatigue properties, as well as the corrosion resistance will be mainly discussed. Moreover, the roadmap of RFFSW is also discussed.

Precipitation of carbides, nitrides, and carbonitrides is an important factor influencing the formation of surface transverse cracks in the continuous casting of microalloyed steel, affecting the quality and yield of the final product. Based on previous investigation, the precipitation sequence and temperature, position and mode, as well as the size, morphology, and number of different types of precipitates were reviewed. The effects of C, N, Nb, Ti, and V on the precipitation behavior and surface transverse cracks in continuous casting slabs were summarized, with a particular emphasis on the new achievements concerning Ti addition. The critical amounts of different elements to avoid serious surface cracks during continuous casting were proposed. The control mechanisms and industrial effects of composition optimization, cooling design, and chamfered mold configuration to improve surface transverse cracks in continuous casting slabs were also illustrated, and the recent application of surface microstructure control technology was emphasized. The characteristics, advantages, and shortcomings of existing theoretical and experimental methods in investigating continuous casting surface cracks regarding precipitation are finally discussed, and a new setup with advanced functions is introduced.

To improve the practical application of carbon steel, developing a superhydrophobic coating with outstanding mechanical properties is essential for effective corrosion resistance protection. Here, we obtained a robust superhy-drophobic anti-corrosion coating with a cauliflower structure by co-depositing the lauric acid with Ni ions and Mn ions onto a carbon steel through electrodeposition method. As demonstrated by the results, superhydrophobic Ni/Mn alloy (SNMAmit) displays a multi-hierarchical micro/nano cauliflower structure under the synergy of optimal parameters, exhibiting superb superhydrophobicity with contact angle of 161.9° and sliding angle of 6.2°. Surprisingly, the Tafel polarization curves in 3.5% NaCl showed that the corrosion potential of SNMAmit coating was 476 mV, and the corrosion current density was reduced from 1.39 9 10^-5 to 5.89 9 10^-7 A/cm². The reduced corrosion current density of superhydrophobic Ni/Mn alloy (SNMA) indicates that SNMA coating can significantly enhance the anti-corrosion properties of carbon steel. In addition, after being subjected to various damages such as blade scraping, tape cyclic peeling, acid and alkalis, sandpaper cyclic abrasion, high temperatures, ultrasound, and graphite contaminant, SNMA showed good mechanical stability, interference resistance, heat resistance, and self-cleaning properties, which made it suitable for hostile conditions.

Accumulative roll bonding (ARB) is a severe plastic deformation method to prepare the metallic composite material by physical method at room to elevate temperature, without the generation of additional waste solid or gas. With the physical characteristicsmulti-material and hybrid structure, the mechanical and function properties of the ARB composite material, like Al/steel, Al/Mg, Al/Cu, etc., shall have the “1+1>2” effect on the mechanical and functional properties, including the remarkable properties that include lightweight, high strength, thermal/electrical conductivity, electromagnetic shielding, and other functions. To deeply investigate the preparation method and microstructural evolution of various metal laminates by ARB, as well as the mechanical and functional properties of the laminate, an overview of the history of ARB technique, the breakthrough of ARB sheet properties, as well as the relative products in industries is provided. Additionally, the future development of ARB technology and the utilization of composite materials in different areas will be discussed.

High-temperature confocal laser scanning microscopy (HT-CLSM) is considered as a powerful tool for in situ observation of the phase transformation of steels at elevated temperatures. It breaks the limitation that conventional approaches on this aspect can only post-mortem the microstructure at room temperature. The working principle and major functions of HTCLSM in initial are introduced and the utilization in details with HT-CLSM is summarized, including the behaviors of melting-solidifying, austenite reversion, as well as the austenite decomposition (formation of Widmanstätten, pearlite, acicular ferrite, bainite and martensite) in steels. Moreover, a serie of HT-CLSM images are used to explore the growth kinetic of phase at elevated temperatures with additional theoretical calculation models. Finally, the in situ HT-CLSM observations of phase transformation, combined with post-mortem electron backscatter diffraction analysis, is also summarized to elucidate the crystallographic evolution.

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.%.

Based on a thermodynamic study of 5 wt.% Si high-silicon austenitic stainless steel (SS-5Si) smelting using CaF₂–CaO– Al₂O₃–MgO–SiO₂ slag to obtain a low oxygen content of less than 10 ×10^-4 wt.%, a kinetic mass transfer model for deep deoxidation was established through laboratory studies, and the effects of slag components and temperature on deoxidation during the slag–steel reaction process of SS-5Si were systematically studied. The experimental data verified the accuracy of the model predictions. The results showed that the final oxygen content in the steel at 1873 K was mainly controlled by the oxygen content derived from the activity of SiO₂ regulated by the [Si]–[O] equilibrium reaction in the slag system; in particular, when the slag basicity R (R = w(CaO)/w(SiO₂), where w(CaO) and w(SiO₂) are the contents of CaO and SiO₂ in the slag, respectively) is 3, the Al₂O₃ content in the slag needs to be less than 2.7%. The mass transfer rate equation for the kinetics of the deoxidation reaction revealed that the mass transfer of oxygen in the liquid metal is the rate-controlling step under different slag conditions at 1873 K, and the oxygen transfer coefficient k_O,m increases with increasing the slag basicity from 4.0 × 10^-6 m s^-1 (R = 1) to 4.3 × 10^-5 m s^-1 (R = 3). kO,m values at R = 2 and R = 3 are almost the same, indicating that high slag basicity has little effect. The integral of the mass transfer rate equation for the deoxidation reaction of SS-5Si under different slag conditions is obtained. The total oxygen content of the molten steel decreases with increasing basicity from an initial content of 22 × 10^-4 to 3.2 × 10^-4 wt.% (R = 3), consistent with the change in k_O,m with slag basicity. At R = 2, the slag–steel reaction takes 15 min to reach equilibrium (w[O] = 5.5 × 10^-4 wt.%), whereas at R = 3, the slag–steel reaction takes 30 min to reach equilibrium (w[O] = 3.2 × 10^-4 wt.%). Considering the depth of deoxidation and reaction time of SS-5Si smelting, it is recommended the slag basicity be controlled at approximately 2. Similarly, the effect of temperature on the deep deoxidation of SS-5Si was studied.

Enhancing the ductility and toughness of advanced high-strength steels is essential for the wide range of promising applications. The retained austenite (RA) is a key phase due to the austenite-to-martensite transformation and its transformation-induced plasticity effect. It is commonly accepted that slow RA-to-martensite transformation is beneficial to ductility; therefore, the RA fraction and stability should be carefully controlled. The RA stability is related to its morphology, size, carbon content, neighboring phase and orientation. Importantly, these factors are cross-influenced. It is noteworthy that the influence of RA on ductility and fracture toughness is not consistent because of their difference in stress state. There is no clear relationship between fracture toughness and tensile properties. Thus, it is important to understand the role of RA in toughness. The toughness is enhanced during the RA-to-martensite transformation, while the fracture toughness is decreased due to the formation of fresh and brittle martensite. As a result, the findings regarding to the effect of RA on fracture toughness are conflicting. Further investigations should be conducted in order to fully understand the effects of RA on ductility and fracture toughness, which can optimize the combination of ductility and toughness in AHSSs.

The dissimilar brazing of Nb521 niobium alloy to GH99 superalloy was achieved successfully using Ti-35Ni brazing filler under vacuum. The effects of brazing temperature and holding time were systematically analyzed on the interfacial microstructure evolution and mechanical properties of joints. The joints brazed at 1120 °C for 10 min exhibited a typical interfacial structure composed of Nb521/b-(Nb, Ti)+TiNi/TiNi+Ti₂Ni/TiNi+TiNi₃/Cr-rich TiNi/Ti-rich (Ni, Cr)_ss/ (Ni, Cr)_ss/GH99. The findings indicated that as the brazing temperature or holding time increased, the presence of brittle Ti₂Ni compounds decreased while the formation of TiNi₃ gradually increased and tended to coarsen. The shear strength of joints exhibited variations corresponding to changes in interfacial brittle compound, and reached the highest value of 121 MPa at 1120 °C for 10 min. In the context of shear testing, all joints displayed clear brittle fracture patterns, with fractures predominantly occurring at the brittle compounds, namely, Ti₂Ni and TiNi₃ phases.

The iron oxide (FeO) content had a significant impact on both the metallurgical properties of sintered ores and the economic indicators of the sintering process. Precisely predicting FeO content possessed substantial potential for enhancing the quality of sintered ore and optimizing the sintering process. A multi-model integrated prediction framework for FeO content during the iron ore sintering process was presented. By applying the affinity propagation clustering algorithm, different working conditions were efficiently classified and the support vector machine algorithm was utilized to identify these conditions. Comparison of several models under different working conditions was carried out. The regression prediction model characterized by high precision and robust stability was selected. The model was integrated into the comprehensive multi-model framework. The precision, reliability and credibility of the model were validated through actual production data, yielding an impressive accuracy of 94.57% and a minimal absolute error of 0.13 in FeO content prediction. The real-time prediction of FeO content provided excellent guidance for on-site sinter production.

Dissolution kinetics of CaO·2Al₂O₃ (CA₂) particles in a synthetic CaO-Al₂O₃-SiO₂ steelmaking slag system have been investigated using the high-temperature confocal laser scanning microscope. Effects of temperature (i.e., 1500, 1550, and 1600 °C) and slag composition on the dissolution time of CA₂ particles are investigated, along with the time dependency of the projection area of the particle during the dissolution process. It is found that the dissolution rate was enhanced by either an increase in temperature or a decrease in slag viscosity. Moreover, a higher ratio of CaO/Al₂O₃ (C/A) leads to an increased dissolution rate of CA₂ particle at 1600 °C. Thermodynamic calculations suggested the dissolution product, i.e., melilite, formed on the surface of the CA₂ particle during dissolution in slag with a C/A ratio of 3.8 at 1550 °C. Scanning electron microscopy equipped with energy dispersive X-ray spectrometry analysis of as-quenched samples confirmed the dissolution path of CA₂ particles in slags with C/A ratios of 1.8 and 3.8 as well as the melilite formed on the surface of CA₂ particle. The formation of this layer during the dissolution process was identified as a hindrance, impeding the dissolution of CA₂ particle. A valuable reference for designing or/and choosing the composition of top slag for clean steel production is provided, especially using calcium treatment during the secondary refining process.

The thick layer and graded feeding technology of a belt roasting machine is an effective method for improving the production efficiency and quality index of pellet production, and a reasonable design of the mechanical structure of the layer is the basis for optimizing the heat andmass transfer performance of the layer. Janssen effect and von Mises yield criterion were used to establish a simplified mathematical model describing the elastic and plastic deformation of the green pellet under the action of an external force. The mechanical characteristics of extrusion, contact, and elastic-plastic deformation between green pellet particles in the material layer of the belt roastingmachine weremodeled usingEDEMsoftware.For a green pellet size of 12mm,as the layer height increases from 300 to 1000 mm, the maximum vertical pressure on the pellets increases from 11.64 to 24.01 N, and the porosity decreases from 27.04% to 22.01%. As the layer height increases, the contact between the green pellets becomes more intense, and the force chain structure of the layer becomes more stable; the Janssen effect is observed when the layer reaches 700 mm. The compressive strength of the green pellets is linearly related to the particle size, and the compressive strength increases with an increase in particle size.At a layer height of 600 mm, as the particle size of the green pellets increases from 8 to 20 mm, themaximum vertical pressure increases from 7.54 to 44.16 N, and the porosity increases from23.20% to 31.47%,while the yield per unit of the layer decreased by 12.1%. Small particles have a more stable force chain structure, larger comparative area, and higher production efficiency; however, their compressive strength is lower. Large particles have higher compressive strength and good permeability in the layer, but the production efficiency is relatively low. In actual production, a variety of factors should be integrated to optimize the feeding, and a multi-granularity graded feeding is the most ideal feeding.

In response to the new mechanism of direct vortex melting reduction of vanadium-titanium magnetite, the reaction control mechanism and the migration regularity of valuable components in the process of direct melting reduction were inves-tigated using kinetic empirical equation by fitting and combining with X-ray diffraction, X-ray fluorescence, scanning electron microscopy, energy-dispersive spectrometry, and optical microscopy. The results show that iron reduction is controlled by the mass transfer process of (FeO_x) in the slag, while vanadium reduction is controlled by both the mass transfer of (VO_x) in the slag and the mass transfer of [V] in the molten iron, and the slag-metal interfacial reaction is the only pathway for vanadium reduction. The reduction of iron and vanadium is an obvious first-order reaction, with activation energy of 101.6051 and 197.416 kJ mol^-1, respectively. Increasing the vortex rate and reaction temperature is beneficial to improving the reaction rate and reduction efficiency. The mineral phase variation of iron and vanadium in the slag during the reduction process is Fe₂O₃→Fe₃O₄/FeV₂O₄→FeTiO₃ and FeV₂O₄→MgV₂O₅; titanium in slag is mainly in the form of Mg_xTi_3-xO₅ (0≤x≤1) and CaTiO₃. As the reaction time went on, the molar ratio (n_Ti/n_Mg)in MgxTi₃-xO₅ (0≤x≤1) and the Ti₂O₃ content in the slag gradually went up, while the area proportion of MgxTi₃-xO₅ (0≤x≤1) went up and then down, and the porosity of the slag and the grain size of MgxTi₃-xO₅ (0≤x≤1) got smaller.

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

To optimize the comprehensive utilization of vanadium titanomagnetite by direct reduction-smelting processes, it is essential to acquire titanium slag with a higher TiO2 content of 45-60 wt.%. A thermodynamic model was developed based on the ion and molecule coexistence theory, specifically targeting the CaO-SiO₂-Al₂O₃-MgO-TiO_2-V₂O₃-FeO slag system. The impact of slag composition on the smelting of vanadium titanomagnetite was assessed, and the thermodynamic model was utilized to identify the optimal high-titanium slag. The results revealed that increasing the basicity, MgO content, and FeO content within the slag effectively suppressed the reduction of titanium and silicon oxides. Furthermore, the calculated activity coefficient of TiO2 decreased with higher basicity, MgO, and FeO levels. While an increase in basicity significantly enhanced the reduction of vanadium oxides, the effects of MgO and FeO contents on vanadium oxide reduction were comparatively less significant. Notably, higher basicity and FeO content promoted the formation of calcium titanates, whereas an elevated MgO content favored the formation of magnesium titanates. The smelting results indicated that a lower V₂O₃ content and higher TiO₂ activity corresponded to a smaller titanium mass fraction in the iron alloy, while the opposite trend was observed for vanadium.

5052 Al and carbon fiber-reinforced polyamide 6 composite (CF-PA6) were jointed via ultrasonic welding with the assistance of temperature compensation device. The effects of the ultrasonic welding time and temperature compensation on the microstructure and mechanical properties of the joints were investigated. Through analysis of the wettability and fluidity of the molten carbon fiber-reinforced thermoplastic composites (CFRTP), the bonding mechanism and failure path of Al/CFRTP were clarified. The results show that under the conditions of temperature compensation of 220 °C and welding time of 1500 ms, the joint strength of the two components reaches 2480.4 N, which is 813.6% higher than that of Al/CFRTP components obtained at room temperature. Overall, temperature compensation prolonged the wetting time of molten CFRTP on the aluminum alloy surface. When the fluidity and wettability were coordinated with each other, a high- quality joint was formed. In addition, the ultrasonic welding process of Al/CFRTP mainly relies on ‘‘physical adsorption,'' ‘‘diffusion effect,'' and ‘‘mechanical locking effect'' to achieve sufficient bonding, and the effect of hydrogen bonding is weak.

Cleanliness control of advanced steels is of vital importance for quality control of the products. In order to understand and control the inclusion removal during refining process in molten steel, its motion behaviors at the multiple steel/gas/slag interfaces have attracted the attention much of metallurgical community. The recent development of the agglomeration of non-metallic inclusions at the steel/Ar and steel/slag interfaces has been summarized, and both the experimental as well as theoretical works have been surveyed. In terms of in situ observation of high-temperature interfacial phenomena in the molten steel, researchers utilized high-temperature confocal laser scanning microscopy to observe the movement of more types of inclusions at the interface, i.e., the investigated inclusion is no longer limited to Al₂O₃-based inclusions but moves forward to rare earth oxides, MgO-based oxides, etc. In terms of theoretical models, especially the model of inclusions at the steel/slag interface, the recent development has overcome the limitations of the assumptions of Kralchevsky-Paunov model and verified the possible errors caused by the model assumptions by combining the water model and the physical model. Last but not least, the future work in this topic has been suggested, which could be in combination of thermal physical properties of steels and slag, as well as utilize the artificial intelligence-based methodology to implement a comprehensive inclusion motion behaviors during a comprehensive metallurgical process.

The phase volume fraction has an important role in the match of the strength and plasticity of dual phase steel. The different bainite contents (18-53 vol.%) in polygonal ferrite and bainite (PF + B) dual phase steel were obtained by controlling the relaxation finish temperature during the rolling process. The effect of bainite volume fraction on the tensile deformability was systematically investigated via experiments and crystal plasticity finite element model (CPFEM) sim-ulation. The experimental results showed that the steel showed optimal strain hardenability and strength-plasticity matching when the bainite reached 35%. The 3D-CPFEM models with the same grain size and texture characters were established to clarify the influence of stress/strain distribution on PF + B dual phase steel with different bainite contents. The simulation results indicated that an appropriate increase in the bainite content (18%-35%) did not affect the interphase strain difference, but increased the stress distribution in both phases, as a result of enhancing the coordinated deformability of two phases and improving the strength-plasticity matching. When the bainite content increased to 53%, the stress/strain difference between the two phases was greatly increased, and plastic damage between the two phases was caused by the reduction of the coordinated deformability.

Creep rupture of the reduced activation ferritic/martensitic (RAFM) steel and 316L steel dissimilar joint by friction stir welding was investigated. The creep rupture time of the dissimilar joint was 1941 h at 600 °C/100 MPa and 120 h at 650 °C/100 MPa. The creep fracture occurred in heat affect zone (HAZ) of RAFM steel side where coarse Laves phase was detected. The formation and coarsening of the Laves phase particles in HAZ of RAFM steel side were the main reasons that caused the creep fracture of the dissimilar joint. The Laves phase particles nucleated adjacent to the large M₂₃C₆ particles at the grain boundaries where W element segregated and grew fast during creep exposure. The large Laves phase would deteriorate the pinning effect of M₂₃C₆ carbides and weaken the solid solution strengthening effect. Besides, the size of the Laves phase in HAZ of RAFM steel side was bigger than that in stir zone of RAFM steel side. These reasons explain the creep fracture in HAZ of RAFM steel side of dissimilar joint.

An industrial experiment was conducted at a certain steel plant in China to compare and analyze the effects of Ca treatment and Mg-Ca treatment on inclusions in 45MnVS non-quenched and tempered steel. Through scanning electron microscopyenergy dispersive scanning analysis of the morphology and composition of inclusions, as well as Aspex quantitative analysis of their quantity, type and size, the formation mechanism of MnS-oxide (MnS inclusions with oxide cores) was intensively studied. The influence of sulfide morphology on the impact properties of steel was also analyzed. The results show that the quantity percentage of spindle-shaped sulfides in Ca-treated steel is 19.99%, and that in Mg-Ca-treated steel is 35.38%. Compared with Ca-treated steel, there are more MnS-oxide inclusions in Mg-Ca-treated steel. Controlling the content of Ca and Mg in the oxide core of MnS-oxide inclusion above 10 wt.% and the area ratio below 5 would contribute to the formation of spindle-shaped inclusions after rolling. The mismatch between MnS and oxides decreases with the increase in MgO content in the oxides, which is beneficial to nucleation and precipitation of MnS with this type of oxides as the core. Under the same deformation conditions, the size of sulfide does not affect its aspect ratio. Under the experimental conditions, the inclusion containing a certain amount of MgO can enhance its sulfur capacity, facilitating the formation of composite sulfides. The transverse impact energy of Ca-treated steel is 25.785 J, and that of Mg-Ca-treated steel is 32.119 J. Compared with the traditional Ca-treatment, Mg-Ca treatment can increase the number of spindle-shaped sulfides in the steel, thereby improving the transverse impact toughness of the steel and reducing the anisotropy of the mechanical properties of the material.

High-temperature confocal scanning laser microscopy (HT-CSLM) is a potent methodology for investigating various phenomena in the field of metallurgy. Initially applied to the observation of solid phase transformations and solidification, this method has gained traction in the field of non-metallic inclusion in steels in recent years. An overview of the experimental capabilities of HT-CSLM and the most important results of recent investigations regarding the topics of clean steel production are provided. It includes the formation of intragranular acicular ferrite (IAF) from the surface of nonmetallic inclusions during the continuous cooling and heat treatment, which can be especially beneficial in the toughness of heat-affected zones of welded pieces. Furthermore, the investigation of agglomeration mechanisms of non-metallic inclusions (NMIs) in liquid steel is discussed to improve the insight into attraction forces between particles and clogging phenomena during continuous casting. Also, the dissolution of NMIs in various steelmaking slags can be observed by HTCSLM to compare dissolution rates and mechanisms of NMI, where significant influences of temperature and chemical composition of the slag were shown. Last but not least, the experimental work regarding the interface between steel and slag is discussed, where novel techniques are currently being developed. A comprehensive summary of experimental techniques using HT-CSLM equipment to investigate different interactions of NMIs with steel and slag phases is compiled.

Understanding the solidification characteristics and microsegregation under varying cooling rates is essential to comprehend the formation of center cracks in large section round billets. P91 high-alloy steel was taken as the research object. The peritectic solidification process, steel solidification shrinkage and microsegregation of solute elements at different cooling rates were studied and revealed by high-temperature confocal scanning laser microscopy, Thermo-Calc thermodynamic software, hybrid laser microscopy and electron probe microanalysis. The results showed that as the cooling rate increased from 10 to 100 °C/min, the percentage of δ-Fe involved in peritectic reaction decreased from 98.6% to 36.4%, the surface roughness of the sample decreased from 8.59 to 5.14 lm, and the volume shrinkage decreased from 5.92% to 2.18%. Moreover, the solidification path enters the crack sensitivity area at lower cooling rates (10 and 50 °C/min), while the solidification path is far from the crack susceptibility area at higher cooling rate (100 °C/min). With the increase in cooling rate, the segregation deviation parameters of the elements V, C, Mo and Cr were decreased by 9.52%, 22.2%, 29.4% and 70.5%, respectively. Solidification path changed and microsegregation weakened by adjusting cooling mode might be a way to improve central crack.

Diamond tools have been widely used in national defense military, automobile manufacturing, resource exploitation and other fields. Laser brazing diamond technology is often applied to the preparation of diamond tools. However, the formation and expansion of cracks in the process of laser brazing diamond seriously affect the mechanical properties of diamond tools. In order to solve the crack problem of laser brazing diamond, many scholars are committed to the research on improving the solder, optimizing the laser process parameters, improving the laser brazing equipment, optimizing the design of joint form, and developing ultrasonic-assisted laser brazing technology, etc. These studies have achieved certain results. Aiming at the research status of laser brazing diamond crack problem, the crack characteristics of brazing diamond are firstly introduced, and the formation reasons of laser brazing diamond crack are elaborated. Then, the elemental characteristics of brazing filler metals used in brazing diamond are introduced. The influences of Ni-Cr and Ag-Cu-Ti alloy solder and laser process parameters on the crack problem are viewed. Finally, the solutions to the crack problem by scholars at home and abroad in recent years are summarized, and the future research directions to solve crack problem are prospected.

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 metastable retained austenite (RA) plays a significant role in the excellent mechanical performance of quenching and partitioning (Q&P) steels, while the volume fraction of RA (V_RA) is challengeable to directly predict due to the complicated relationships between the chemical composition and process (like quenching temperature (QT)). A Gaussian process regression model in machine learning was developed to predict V_RA, and the model accuracy was further improved by introducing a metallurgical parameter of martensite fraction ðfa0 Þ to accurately predict V_RA in Q&P steels. The developed machine learning model combined with Bayesian global optimization can serve as another selection strategy for the quenching temperature, and this strategy is very efficient as it found the ‘‘optimum’’ QT with the maximum V_RA using only seven consecutive iterations. The benchmark experiment also reveals that the developed machine learning model predicts V_RA more accurately than the popular constrained carbon equilibrium thermodynamic model, even better than a thermokinetic quenching–partitioning–tempering–local equilibrium model.

The void closure behavior in a central extra-thick plate during the gradient temperature rolling was simulated and a back propagation (BP) neural network model was established. The thermal-mechanical finite element model of the gradient temperature rolling process was first developed and validated. The prediction error of the model for the rolling force is less than 2.51%, which has provided the feasibility of imbedding a defect in it. Based on the relevant data obtained from the simulation, the BP neural network was used to establish a prediction model for the compression degree of a void defect. After statistical analysis, 80% of the data had a hit rate higher than 95%, and the hit rate of all data was higher than 90%, which indicates that the BP neural network can accurately predict the compression degree. Meanwhile, the comparisons between the results with the gradient temperature rolling and uniform temperature rolling, and between the results with the single-pass rolling and multi-pass rolling were discussed, which provides a theoretical reference for developing process parameters in actual production.

Brazing, an important welding and joining technology, can achieve precision joining of materials in advanced manufacturing. And the first principle calculation is a new material simulation method in high-throughput computing. It can calculate the interfacial structure, band structure, electronic structure, and other properties between dissimilar materials, predicting various properties. It plays an important role in assisting practical research and guiding experimental designs by predicting material properties. It can largely improve the quality of welded components and joining efficiency. The relevant theoretical foundation is reviewed, including the first principle and density functional theory. Exchange-correlation functional and pseudopotential plane wave approach was also introduced. Then, the latest research progress of the first principle in brazing was also summarized. The application of first principle calculation mainly includes formation energy, adsorption energy, surface energy, adhesion work, interfacial energy, interfacial contact angle, charge density differences, density of states, and mulliken population. The energy, mechanical, and electronic properties were discussed. Finally, the limitations and shortcomings of the research in the first principle calculation of brazed interface were pointed out. Future developmental directions were presented to provide reference and theoretical basis for realizing high-throughput calculations of brazed joint interfaces.

The vacuum diffusion bonding method was used to introduce Al foil as the middle layer, and 6061 aluminium alloy was vacuum diffusion bonding together. The typical microstructure characteristics and mechanical properties of 6061/Al/6061 welded joints were studied in detail, the effects of process parameters and Al intermediate layer on the microstructure and mechanical properties were revealed, and the diffusion bonding mechanism of 6061/Al/6061 welded joints was described. Al foil middle layer welded joint had the best performance at the temperature of 540 °C, the holding time of 120 min, and the welding pressure of 4 MPa. The bonding ratio is 95.91%, the shear strength is 79 MPa, and the deformation rate is 8.05%, and the introduction of Al intermediate layer improves the element distribution and microstructure, so that the bonding ratio of the welded joint is increased by 10.86%, the shear strength is increased by 5.55 MPa, and the deformation rate is reduced by 1.58%. The fracture morphology has typical ductile fracture characteristics.

The effect of Zr on the microstructure and mechanical properties of 304 stainless steel joints brazed with Ag-Cu fillers was studied. The incorporation of Zr had little effect on the solid-liquid phase line of the fillers, and the melting temperature range of the fillers was narrowed, which enhanced their fluidity and wettability. The presence of Zr in the form of heterogeneous particles augmented the nucleation rate during solidification, transforming the intermittently distributed gray-black coarse dendrites into cellular crystals. This structural transformation led to fragmentation and refinement of the microstructure. The dissolution of Zr into Ag and Cu promoted the transformation of low-angle grain boundaries to high- angle grain boundaries (HAGBs), hindering crack propagation. Zr element in the brazing seam led to grain refinement and increased density of grain boundaries. The grain refinement could disperse the stress, and HAGBs could resist the dislocation movement, improving the joint strength. The results display that when Zr content was 0.75 wt.%, the maximum strength was 221.1 MPa. The fracture occurred primarily at the brazing seam, exhibiting a ductile fracture.

The mechanism of strength and toughness variation in Ti microalloyed steel within the range of 0.04-0.157 wt.% was investigated. By adding 0.13 wt.% Ti, the steel achieves higher strength while maintaining a certain level of elongation and low-temperature impact toughness. With increasing Ti content, the grain size in the steel decreased from 17.7 to 8.9 lm. This decrease in grain size is accompanied by an increase in the percentage of low-angle grain boundaries and dislocations, which act as barriers to hinder crack propagation. The Ti microalloyed steel exhibits a 20% increase in yield strength and a 14% increase in tensile strength. The transformation of steel plasticity occurs when the Ti content exceeds 0.102 wt.%. The low-temperature impact toughness of the steel gradually decreases with increasing Ti content. At low Ti content, the low-temperature impact toughness is reduced due to crack initiation by large-size inclusions. At high Ti content, the low-temperature impact toughness of the steel deteriorates due to several factors. These include the narrower tough-brittle transition zone, grain boundary embrittlement caused by small-sized grains, and the decrease in the solid solution strengthening effect.

304 stainless steel (SS)/Q235 carbon steel (CS) bimetallic composite shafts were prepared by the cross wedge rolling (CWR). The bonding interface welding mechanism was investigated through CWR rolling experiments and finite element simulation, as well as element diffusion, microstructure analysis, and mechanical property tests. According to simulation studies, the bonding interface is primarily subjected to three-directional compressive stresses at the tool–workpiece contact zone. As compression ratio increases from 0.25 to 0.35, the interface of the stress penetration area increases, while the diameter and wall thickness of CS/SS bimetallic shaft decrease, and hence, thickness-to-diameter ratio remains unchanged, which is conducive to the coordinated deformation of inner and outer metals and the interface of welded joints. The microstructure analysis of the interface shows that there are no obvious defects and cracks in the attachment, and that the microstructure on CS side is dominated by ferrite and martensite phases. Caused by the decarburization effect, Q235 steel microstructure features coarse ferrite, accompanied by a carburized layer with a thickness of about 20 lm on SS side near the interface where grains are refined. As radial compression ratio increases, the diffusion distance of Cr, Ni, and other elements increases, the average thickness of the decarburized layer decreases, the interfacial bonding strength increases from 450 to 490 MPa, and metallurgical bonding at the interface is thus improved. The study demonstrates that it is feasible to use 304 SS and Q235 CS for cross wedge rolling composite shafts.

The use of an alternative magnetic field during vacuum arc remelting (VAR) can have significant effects on the primary carbide and mechanical properties of M50-bearing steel. The solidification structure and the primary carbide morphology of the VAR ingot were analyzed by optical microscopy and scanning electron microscopy. Characterization and analysis of the growth direction of primary carbides were conducted using high-resolution rapid electron backscatter diffraction. Solute elements segregation was analyzed using an electron probe microanalyzer. FLUENT was utilized to conduct numerical simulations to validate the experimental findings and elucidate the underlying mechanism. Compared to tra-ditional VAR, magnetic-controlled VAR generates a horizontal circulation, which makes a shallower and flatter molten pool and a more even temperature distribution. In the time dimension, the local solidification time is shortened, and the concentration of solute elements will be alleviated. In the spatial dimension, the secondary dendrite arm spacing decreases, alleviating the degree of inter-dendritic segregation. Consequently, the possibility of forming a segregation diminishes. Both aspects promote the even distribution of solute atoms, resulting in less segregation and hindering the development of primary carbide. This leads to the refinement of primary carbide size and its uniform distribution. The magnetic-controlled vacuum arc melting not only refines the dendritic structure in the M50 ingot, causing it to expand more axially along the ingot, but also refines primary carbides and improves tensile and wear-resistant mechanical properties.

Accurate prediction of strip width is a key factor related to the quality of hot rolling manufacture. Firstly, based on strip width formation mechanism model within strip rolling process, an improved width mechanism calculation model is delineated for the optimization of process parameters via the particle swarm optimization algorithm. Subsequently, a hybrid strip width prediction model is proposed by effectively combining the respective advantages of the improved mechanism model and the data-driven model. In acknowledgment of prerequisite for positive error in strip width prediction, an adaptive width error compensation algorithm is proposed. Finally, comparative simulation experiments are designed on the actual rolling dataset after completing data cleaning and feature engineering. The experimental results show that the hybrid prediction model proposed has superior precision and robustness compared with the improved mechanism model and the other eight common data-driven models and satisfies the needs of practical applications. Moreover, the hybrid model can realize the comple-mentary advantages of the mechanism model and the data-driven model, effectively alleviating the problems of difficult to improve the accuracy of the mechanism model and poor interpretability of the data-driven model, which bears significant practical implications for the research of strip width control.

Press hardened steel (PHS) plays a key role in the manufacture of anti-collision structural components. The formation of d- ferrite is a suffering issue for the laser welding of Al–Si coated PHS. Oscillating laser was used to weld Al–Si coated 1.5 GPa PHS and novel 2 GPa PHS, and the effect of laser offset on the microstructure and properties of the dissimilar welded joints was studied. The results showed that a perfect weld profile was achieved by laser offset welding (LOW), without any welding defects. The d-ferrite formed in as-received welds of laser alignment welding (LAW) with high Al content (up to 2.9 wt.%), but it disappeared with the laser offset to 2 GPa PHS, and the maximum Al content in the segregation zone reduced to 1.2 wt.%. After post-welding heat treatment, the d-ferrite was coarsened and the a-ferrite formed in the secondary Al-rich area for the high Ac3 temperature, but the a-ferrite was few and fine in LOW welds. The hardness in the LAW welds was lower than that in the LOW welds, due to the presence of d-ferrite, as well as less carbon content and Ti and V alloying elements. The tensile strength (1561 MPa) and elongation (5.4%) with LOW were higher than those with LAW (1490 MPa, 3.1%), and the fracture occurred in the Al–Si coated PHS. It is indicated that adjusting the laser offset is effective to prevent the formation of d-ferrite and is potential to avoid the formation of a-ferrite. It also provides a wide heat treatment temperature window for the dissimilar welds of 1.5 GPa PHS and novel 2 GPa PHS.