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.

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.

Steels are widely used as structural materials, making them essential for supporting our lives and industries. However, further improving the comprehensive properties of steel through traditional trial-and-error methods becomes challenging due to the continuous development and numerous processing parameters involved in steel production. To address this challenge, the application of machine learning methods becomes crucial in establishing complex relationships between manufacturing processes and steel performance. This review begins with a general overview of machine learning methods and subsequently introduces various performance predictions in steel materials. The classification of performance prediction was used to assess the current application of machine learning model-assisted design. Several important issues, such as data source and characteristics, intermediate features, algorithm optimization, key feature analysis, and the role of environmental factors, were summarized and analyzed. These insights will be beneficial and enlightening to future research endeavors in this field.

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.

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.

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.%.

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 lanthanum on the characteristics of inclusions in the slab of non-oriented electrical steels was investigated through industrial trials and thermodynamic analysis. The number, size, and chemical composition of inclusions in the surface, one-quarter of thickness and the center of slabs with and without lanthanum addition were statistically analyzed using an automatic inclusion analysis system. In the lanthanum-free slab, inclusions were predominately MgO[1]Al2O3, MgO, and AlN as well as a small number of Al2O3–MgO–CaO and MgS. The number densities of oxide inclusions and AlN decreased from the surface to the center of the slab, which was ascribed to the difference in cooling intensity during the continuous casting. In the steel with lanthanum addition, inclusions were modified into LaAlO3 and La2O2S and gradually transformed into dual-phase MgO–La2S3 with an increasing distance from the slab surface due to the reaction between the lanthanum-containing inclusion and the steel matrix. The uneven distribution of oxide inclusions along the thickness of the slab was eliminated in the lanthanum-bearing slab because the dissolved oxygen was remarkably decreased by lanthanum. Lanthanum-bearing inclusions were more likely to agglomerate AlN by inducing the heterogeneous nucleation of AlN on their surface, while small-size MgO-Al2O3 inclusions hardly showed a coarsening effect on the size of AlN.

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.

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 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.

MgO participates in all stages of sintering, pelletizing, and blast furnace ironmaking, and synergistically optimizing the distribution of MgO in ferrous burden can effectively enhance the interaction within the ferrous burdens and optimize the softening–melting properties of the mixed burden. Magnesium-containing pellets mixed with low-MgO sinter or mixed with high-MgO sinter in the blast furnace ferrous burden structure have opposite softening–melting performance laws. When the structure of the ferrous burden is magnesium-containing pellets mixed with low-MgO sinter, the magnesiumcontaining pellets can enhance the interaction of the ferrous burden in the process of softening–melting, which can optimize the composition of the slag phase and improve the slag liquidity. When the structure of the ferrous burden is magnesium-containing pellets mixed with high-MgO sinter, the magnesium-containing pellets weaken the interaction of the ferrous burden in the process of softening–melting, increase the content of the high melting point solid-phase particles in the slag, lead to an increase in the viscosity of the slag and difficult separation of the slag and iron, and decrease the permeability of the charge layer. Therefore, to ensure good permeability of the mixed burden, the following measures are suggested: optimizing the MgO distribution of the ferrous burden, reducing the MgO content of the sinter to 1.96 wt.%, increasing the MgO content of the pellets to 1.03–1.30 wt.%, controlling the MgO/Al2O3 ratio of the mixed burden within 1.15–1.32, narrowing the position of the cohesive zone, and maintaining an S value (permeability index) of approximately 150 kPa °C.

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.

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.

Zinc extraction residue, a solid waste generated from the treatment of zinc-containing dust in rotary kilns, is commonly stockpiled in steel companies for extended periods. It poses significant disposal challenges and environmental pollution risks. So far, research on the treatment of zinc extraction residues has been slow, inadequate, and sporadic. For this gap, a novel approach was proposed to effectively treat the zinc extraction residue via the iron ore sintering process. It was feasible to add 1 wt.% of zinc extraction residues to the sintering raw materials. The more adequate mineralization reaction resulted in higher yield and tumbler indexes, despite a slight decrease in sintering speed. Although this may result in a slight decrease in sintering speed, the more complete mineralization reaction leads to improved sintering yield and tumbler index. Interestingly, the addition of zinc extraction residues reduced the CO and NOx concentrations in the sintering flue gas. Thus, the iron ore sintering process provided a viable solution for resource utilization and environmentally friendly treatment of zinc extraction residues.

Proportioning is an important part of sintering, as it affects the cost of sintering and the quality of sintered ore. To address the problems posed by the complex raw material information and numerous constraints in the sintering process, a multiobjective optimisation model for sintering proportioning was established, which takes the proportioning cost and TFe as the optimisation objectives. Additionally, an improved multi-objective beluga whale optimisation (IMOBWO) algorithm was proposed to solve the nonlinear, multi-constrained multi-objective optimisation problems. The algorithm uses the constrained non-dominance criterion to deal with the constraint problem in the model. Moreover, the algorithm employs an opposite learning strategy and a population guidance mechanism based on angular competition and two-population competition strategy to enhance convergence and population diversity. The actual proportioning of a steel plant indicates that the IMOBWO algorithm applied to the ore proportioning process has good convergence and obtains the uniformly distributed Pareto front. Meanwhile, compared with the actual proportioning scheme, the proportioning cost is reduced by 4.3361 ¥/t, and the TFe content in the mixture is increased by 0.0367% in the optimal compromise solution. Therefore, the proposed method effectively balances the cost and total iron, facilitating the comprehensive utilisation of sintered iron ore resources while ensuring quality assurance.

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.

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.

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.

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.

Horizontal segregation has been a constraint to the development and application of super-high bed sintering. To eliminate the horizontal segregation of super-high bed sintering, several typical sintering machines were sampled and analyzed, and theoretical calculation was made to compare the bed depth and their differences in different areas within the mixture bin. Then, solutions were proposed and applied to a 265 m2 sintering machine. The results showed that the horizontal segregation of the 265 m2 sintering machine was dominated by particles larger than 8 mm with horizontal segregation degree of 0.48, while 360 and 550 m2 sintering machines were affected by 5–8 mm and 1–3 mm particles with horizontal segregation degree of 0.27 and 0.31, respectively. Causes analysis indicated the different segregation distribution results from the matching of the bed depth of each area within the mixture bin. Finally, the horizontal segregation degree not larger than 0.06 was achieved by optimizing the time parameters and the division of three zones on the 265 m2 sintering machine.

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.

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.

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.

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 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.

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.

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 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.

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.

To comprehensively utilize the low-iron high-vanadium–titanium magnetite, a new method of vortex smelting reduction of vanadium–titanium magnetite was proposed, and the enrichment and reconstitution regularity of Ti-bearing phases in the slag was investigated through X-ray fluorescence spectrometry, X-ray photoelectron spectroscopy, X-ray diffraction analysis, and optical microscopy. The phase diagram revealed that the preferential crystallization of MgTi2O5 can be achieved by adjusting the CaO, MgO, and TiO2 contents of slag. The predominant Ti-bearing phases in the slag obtained from the reduction process are MgxTi3-xO5 (0 B x B 1) and CaTiO3. FeTiO3 is present at carbon–iron ratio (CR) = 1.3, while MgTi2O4 and TiC are formed at CR = 1.3. The enrichment of TiO2 in the slag increases first and then decreases as the CR increases, and at CR = 1.1, the enrichment of TiO2 in the slag reaches 51.3 wt.%. Additionally, the concentrations of MgxTi3-xO5 (0 B x B 1) and CaTiO3 in the slag, along with the grain width of MgxTi3-xO5 (0 B x B 1), decrease with the increase in CR.

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.

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.

The strip casts of cobalt-free maraging steel were fabricated using a twin-roll strip casting simulator, and its characteristics of sub-rapid solidification were studied. Subsequently, the confocal laser scanning microscope (CLSM) was employed to in situ observe the phase transformation during the heat treatment of maraging steel strip cast such as austenitization, solution treatment, and aging processes. It was found that due to the high cooling rate during the twin-roll strip casting process, the sub-rapid solidified strip cast possessed a full lath martensitic structure, weak macrosegregation, and evident microsegregation with a dendritic morphology. During austenitization of strip cast, the austenite grain size increased with the austenitization temperature. After holding at 1250 °C for 250 s, the austenite grain size at the high temperature owned a high similarity to the prior austenite grain size of the strip cast, which effectively duplicates the microstructure of the strip cast after sub-rapid solidification. During the solution treatment process, the martensitic structure of the strip cast also underwent austenitic transformation, subsequently transformed into martensite again after quenching. Due to the low reheating temperature during solution treatment, the austenite grain size was refined, resulting in the fine martensitic microstructure after quenching. During the aging process of strip cast, some of martensite transformed into fine austenite, which was located in the interdendritic region and remained stable after air cooling, resulting in the dual-phase microstructure of martensite and austenite. The solute segregation of Ni and Mo elements during the sub-rapid solidification of strip cast caused the enrichment of Ni and Mo elements in the interdendritic region, which can expand the austenite phase region and thus enhance the stability of austenite, leading to the formation of austenite in the interdendritic region after aging treatment.

The microstructure and mechanical properties of the compact strip production (CSP) processed quenching and partitioning (Q&P) steels were investigated through experimental methods to address the challenge of designing high-performance Q&P steels. Compared with the conventional process (CP) produced samples, with slightly reduced strength, the total elongation of the CSP produced samples was increased by nearly 7%. Microstructural analysis revealed that variations in austenite stability were not the primary cause for the differences in mechanical properties between the CSP and the CP. The CSP processed Q&P steel exhibited milder center segregation behavior in contrast to the CP processed Q&P steel. Consequently, in the CSP processed Q&P steel, a higher proportion of austenite and a lower proportion of martensite were observed at the center position, delaying the crack initiation in the central region and contributing to the enhanced ductility. The investigation into the CSP process reveals its effect on alleviation of segregation and enhancement of mechanical properties of the Q&P steel.

Metallographic microscopy, scanning electron microscopy and TiN growth thermodynamic and kinetic equations were used to investigate the morphology, quantity, and size of TiN in the center of high-titanium high-strength steels under different solidification cooling rates. The results showed that TiN in the center of the experimental steels mainly existed in three forms: single, composite (Al2O3–TiN), and multi-particle aggregation. TiN began precipitating at around 1497 °C (solidification fraction of 0.74). From the end of melting to solidification for 180 s, the cooling rates in the center of the experimental steels for furnace cooling, air cooling, refractory mold cooling, and cast iron mold cooling tended to stabilize at 0.17, 0.93, 1.65, and 2.15 °C/s, respectively. The size of TiN in the center of the experimental steel cooled using furnace cooling was mainly concentrated in the 5–15 lm range. In contrast, the size of TiN in the center of the experimental steels cooled using air cooling, refractory mold cooling, and cast iron mold cooling were mainly concentrated in the 1–5 lm range. In addition, their density of TiN in the center of the experimental steels is significantly higher than that of the furnace-cooled experimental steel. Thermodynamic and kinetic precipitation models of TiN established predicted the growth size of TiN in a high-titanium high-strength steel when the solidification cooling rates are not below 0.93 °C/s.