Hydrogen dissolved from the moisture or the wire filler is formed on the surface of welded joint due to the driving of high-energy heat source. The diffused hydrogen in the welded joint could cause hydrogen embrittlement (HE). The important factors determining the HE resistance of welded joints are microstructure style, dislocation distribution, grains characteristics, precipitate particle, and residual stress. Different welding technologies show various heat sources and heat cycles, which result in different characteristics of fusion zone and heat-affected zone. Thus, the HE fracture behavior of welded joint produced by different welded technologies differs greatly. The current stage of HE behavior of welded joint was reviewed to provide fundamental reference for the scientists and engineers engaging in welding. The appearance of hydrogen atoms in the surface or interior of welded joint could weaken the bonding strength and change the fracture mode from ductile to sudden brittle fracture. Generally, the controlling of filler wire and heat input is a practical route to obtain the excellent welded joint with high HE resistance. The inhibition of hydrogen diffusion via the formation of fine coating and the aggregation of hydrogen atoms via the control of microstructure and precipitates are the effective routes to improve HE resistance.

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.

Erosion-corrosion (EC)-induced damage is a primary contributor to premature failures in hydraulic transport structures involving sudden changes in flow patterns, especially the hydraulic pipeline (tee, reducer, pipe bend, etc.), pumps, and valves. A comprehensive exploration of EC behavior of steels subjected to high tensile stress was provided, as most engineering structures are operated under high stress. The stress-accelerated erosion (SAE) and stress-accelerated corrosion (SAC) behaviors of highly stressed steel and their synergistic effect were mainly focused. SAE, SAC, and their synergistic mechanisms, existing debate, and possible reasons, as well as available analytic models with their advantages and limitations, are thoroughly discussed. The multiphysics simulation methods for modeling EC interactions with both static and cyclic stresses are also summarized, and EC mitigation strategies, especially the bionics-based strategies, were also summarized in detail.

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 continuous growth behavior of austenite grain in 20Cr peritectic steel was analyzed by experiment and theoretical modeling. The peculiar casting experiment with different cooling rates was achieved by multigradient operation scheme, and different morphologies in austenite grain were observed at the target location. The increase in austenite grain size with increasing cooling rate was firstly revealed in steels. The anomalous grain growth theoretically results from the mechanism of peritectic transformation transiting from the diffusional to massive type, and the additional energy storage stimulates the grain boundary migration. A new kinetic model to predict the growth behavior of austenite grain during continuous cooling process was developed, and the energy storage induced by massive type peritectic transformation was novelly taken into account. The parameters in the model were fitted by multiphase field modeling and experimental results. The kinetic model was finally verified by austenite grain size in laboratory test as well as the trial data at different locations in continuously cast bloom. The coarsening behavior of austenite grain during continuous casting was predicted based on the simulated temperature history. It is found that the grain coarsening occurs generally in the mold zone at high temperature for 20Cr steel and then almost levels off in the following process. The austenite finish transformation temperature T_γ and primary cooling intensity show great influence on the grain coarsening. As T_γ decreases by 1 ℃, the austenite grain size decreases by 4 μm linearly. However, the variation of T_γ against heat flux is in a nonlinear relationship, suggesting that low cooling rate is much more harmful for austenite grain coarsening in continuous casting.

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.

A novel Al-alloyed press-hardening steel (PHS) was developed, which exhibits excellent tensile, bending and antioxidation properties. Al is a ferrite-forming element that can hinder the formation of cementite and enhance the stability of austenite. The incorporation of Al not only induces the formation of ferrite within martensitic matrix but also enhances the stability of retained austenite (RA). The microstructure of novel steel consists of martensite, ferrite, and RA after press hardening. Investigations into the role of Al in RA development were supported by thermo-kinetic calculations. The simultaneous introduction of ferrite and RA into the martensitic matrix via tailored chemical compositions significantly enhances the elongation and bending toughness of the novel PHS. Additionally, Al can form a dense Al oxide at the bottom of oxide layer, resulting in the improved antioxidant properties. Compared to 22MnB5 steel, it is an exciting discovery as there is a significant improvement in total elongation and bending toughness of novel PHS without compromising strength. The novel PHS, with its exceptional balance of strength and ductility, will play a crucial role in reducing weight when it replaces the existing class 22MnB5 PHS in different structural components of vehicle bodies.

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

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 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.%.

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.

The effect of rare-earth cerium on impurity P-induced embrittlement for an advanced SA508Gr.4N reactor pressure vessels steel is investigated by virtue of microstructural characterization, Auger electron spectroscopy (AES), and spin-polarized density functional theory (DFT) calculations. The ductile-to-brittle transition temperatures (DBTTs) are evaluated by Charpy impact testing, and grain boundary segregation (GBS) of P is quantified by AES. Trace addition of Ce can effectively reduce GBS level of P, thereby substantially decreasing the embrittlement induced by P. A linear correlation between DBTT (℃) and GBS level of P (C_p, at.%) is observed for both undoped and Ce-doped samples, being expressed as DBTT=13.13C_p-335.70 (undoped) and DBTT=12.67C_p-350.78 (Ce-doped). In the absence of GBS of P, the incorporation of Ce appears to play a pivotal role in augmenting the intrinsic toughness. These results imply that the impact of Ce on impurity P-induced embrittlement may be attributed to a combination of increasing the intrinsic toughness and lowering GBS of P. DFT calculations indicate that there is a negligible interaction between Ce and P in the ternary alloy, and thus GBS of P and Ce is mainly site-competitive.

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.

Microwave pre-oxidation and biomass reduction were adopted to enhance the separation of titanium and iron in vanadium-titanium magnetite. The effects of microwave pre-oxidation temperature and time, as well as biomass reduction temperature and time, were investigated. The results showed that the average particle size of vanadium-titanium magnetite decreased, and the specific surface area increased with the increase in pre-oxidation temperature and time. The reaction pathway (Fe_3-xTi_xO₄ → Fe_2-xTi_xO₃ → Fe₂TiO₅) was proved in microwave pre-oxidation process. The results of biomass reduction roasting showed that biomass reduction could effectively reduce ferric oxide to metallic iron while Ti was enriched in a solid solution of magnesium anosovite, which was beneficial to the subsequent grinding and acid leaching separation. The combined process of microwave pre-oxidation and biomass reduction achieved a high separation efficiency of titanium and iron in vanadium-titanium magnetite without forming complex titanium minerals. The titanium grade in the vanadium-titanium-rich material was 32.10%, and the recovery rate was 91.51%. The iron grade in the iron concentrate (metallic iron) was 90.90%, the recovery rate was 93.47%, and metallization rate was 93.87%.

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.

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

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 unclear interfacial characteristics of Ag/Cu interface during diffusion welding limit the improvement of mechanical properties of Ag/Cu bimetallic strips. The growth orientation and evolution of Ag and Cu crystals between Ag and Cu strips were investigated by electron backscatter diffraction (EBSD) analysis, and the interfacial properties of various Ag/Cu interfacial configurations were calculated using first-principles calculations to elucidate the diversified interfacial char-acteristics. Three interface bonding states, including Ag(100)/Cu(100), Ag(110)/Cu(110) and Ag(111)/Cu(111), were preferentially formed in Ag/Cu bimetallic strips during roll bonding. The intensity of Ag(100)/Cu(100) interface increases with the increasing deformation amounts during cold rolling, accompanied by the decreased intensity of Ag(110)/Cu(110) and Ag(111)/Cu(111) interfaces. The largest adsorption work and lowest interface energy of Ag(100)/Cu(100) interface at the “center” position reveal the transition from Ag(110)/Cu(110) and Ag(111)/Cu(111) interfaces to Ag(100)/Cu(100) interface.

Under the background of the strategic goal of ‘‘double carbon,’’ the carbon reduction and consumption reduction of the iron and steel industry, especially in the ironmaking process, need to be further improved. The raceway of tuyere provides the chemical environment, fuel and power source for blast furnace smelting. The research on the characteristics of its action mode and mechanism is of great significance to clarify the way of reducing carbon and consumption of blast furnace. In general, the formation mechanism, energy distribution, research progress, extended resource injection and directional regulation are studied and expounded. The research results of various scholars on the characteristics of the raceway show that the raceway is a complex process including multiphase turbulent flow, heat, momentum, mass and homogeneous and heterogeneous chemical reactions. With the development of multi-source fuel injection technology, the complexity of problem research is more obvious. Therefore, the collection of multi-factor, multi-directional and multi-process characteristic information in the raceway can provide guarantee for the stability, smooth operation, high yield, carbon reduction and consumption reduction of blast furnace and provide new ideas for the green and low-carbon development of iron and steel industry.

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 mathematical model between laser cladding parameters and coating properties was established by the response surface method (RSM). Ni-WC-reinforced CoCrNiFeAl high-entropy alloy (HEA) composite coatings were prepared on the surface of 0Cr13Ni5Mo steel by laser cladding to study the addition of Ni-WC on slurry erosion resistance of coatings. The optimal parameters obtained by RSM are laser power of 1450 W, scanning speed of 4.3 mm/s, powder feeding speed of 1.3 r/min and overlap rate of 60%, respectively. The grains of CoCrNiFeAl composite coatings are refined by adding Ni-WC-reinforced powder. 15 wt.% Ni-WC composite coating presents the maximum microhardness with the value of 655 HV_0.3. The cumulative mass loss of the composite coatings at different erosion angles is lower than that of the pure CoCrNiFeAl coating. In addition, at low erosion angles, the cumulative mass loss of the composite coatings gradually decreases with the increase in the mass fraction of Ni-WC. Ploughing and microcutting are the primary erosion mechanisms of CoCrNiFeAl composite coatings at low erosion angles. When erosion damage occurs at high erosion angle, the erosion mechanisms of composite coating material loss are dominated by lip formation and craters. The proposed high-entropy alloy composite coatings can be applied to improve the erosion resistance of components in contact with high-speed fluids, such as ship propellers and centrifugal pump blades.

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%.

The top-bottom combined blowing converter mainly adopts the blowing method of top-blowing oxygen and bottomblowing nitrogen. In the production process, there are some disadvantages, such as a significant temperature difference between the top and bottom of the molten pool, inadequate gas permeability of bottom blowing, and low decarburization efficiency. Therefore, we propose a novel bottom-blowing gas doped oxygen process to enhance the smelting conditions in the converter. The 500 kg medium frequency induction furnace with top and bottom-blowing function was used to explore the influence of the proportion of bottom-blowing gas doped oxygen on the smelting effect in different smelting cycles. Subsequently, industrial experimental verification was carried out on a 60 t converter. The results of intermediate frequency furnace experiments demonstrate that the bottom-blowing gas doped oxygen process exhibits a superior heating rate and decarburization efficiency during the initial and final stages of blowing compared to pure N₂ used for bottomblowing. Simultaneously, the dephosphorization efficiency exhibited an initial increase followed by a subsequent decrease as the bottom-blowing oxygen content increased. The industrial test of 60 t converter validates the findings above. Moreover, when the oxygen content in bottom-blowing gas is 5%, the average blowing time reduces by 54 s, and the minimum endpoint carbon-oxygen equilibrium reaches 0.00219 under this condition. The results demonstrate that the appropriate amount of oxygen doped in bottom-blowing gas can effectively enhance the metallurgical conditions of the converter and improve production efficiency.

The 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.

The variations in the mechanical and magnetic properties of cold-rolled 20Mn23AlV non-magnetic structural steel after annealing at different temperatures were investigated. The microstructure and precipitation changes during annealing were studied by optical microscopy, scanning electron microscopy, and transmission electron microscopy. The results show that recrystallization completed after annealing at 620 ℃, resulting in grain sizes of approximately 800 nm and the best combination of strength and plasticity. The yield-to-tensile ratio of the non-magnetic structural steel after cold rolling continuously decreases from low to high temperatures after annealing, with the highest value being 0.89 and the lowest value being 0.43, indicating a wide range of yield-to-tensile ratio adjustment. The introduction of numerous dislocations during cold rolling provided favorable nucleation sites for precipitation, leading to abundant precipitation of the fine second-phase V(C, N). The phase composition of the samples remained unchanged as single-phase austenite after annealing, and the relative permeability values were calculated to be less than 1.002, meeting the requirements for nonmagnetic steel in terms of magnetic properties.

The free-surface vortex is a rotational flow phenomenon characterized by two-phase coupling, formed by the rupture of surface fluid in the final stage of discharge. It is a significant concept with broad applications in engineering fields like metallurgy and hydraulics. The basic concepts and characteristics of free-surface vortices were introduced, and their hazards in various fields were discussed. The development of theoretical and numerical models over recent decades was reviewed, and the factors affecting vortex formation and existing suppression methods were outlined. Finally, the key challenges and focus areas on the study of free-surface vortex were summarized. With the ongoing advancements in computational fluid dynamics and experimental technology, research on free-surface vortices will become more in depth and precise. Additionally, interdisciplinary cooperation and technological innovation are expected to achieve precise control and optimal design of free-surface vortices, offering more efficient and sustainable solutions for metallurgy and related engineering fields.

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.

The corrosion behaviors of an as-cast FeCoNiAl_0.75Cr_1.25 high-entropy alloy (HEA) in acidic Na₂SO₄ solution with different pH values were investigated. The results indicate that the as-cast FeCoNiAl_0.75Cr_1.25 HEA is mainly composed of face-centered cubic phase, body-centered cubic (BCC1) phase (Co-Cr-Fe) and ordered BCC (B2) phase (Ni-Al), in which BCC1 phase and B2 phase have a eutectic microstructure. Moreover, the corrosion of B2 phase occurs preferentially in a 0.05 mol/L SO₄^2- acidic solution. The electrochemical measurement results show that the corrosion resistance of the investigated HEA significantly changes as the solution pH increases from 2 to 2.5. This indicates that there is a critical pH in the range of 2-2.5 that affects the corrosion of HEA. In addition, the results of X-ray photoelectron spectroscopy prove that the surface film of FeCoNiAl_0.75Cr_1.25 in SO₄^2- solution is formed with Al₂O₃ and Cr₂O₃ as the main components, and The content of Al₂O₃ and Cr₂O₃ increases with increasing solution pH.

Rare earth La was introduced into 40Cr steel in industrial experiments to achieve the purpose of modifying inclusions. The impact of La on the inclusion modification was studied, and its infiuence on the solidification structure was further investigated. With adding 0.0023% La, the Al₂O₃・CaO・CaS inclusions were modified to the LaAlO₃・CaO・CaS inclusions. Additionally, the morphology tended to be more spherical, and the proportion of small-sized inclusions increased sig-nificantly from 77.8% to 93.5%. The large-sized inclusions were almost completely eliminated. Based on experimental results, a dynamical model elucidating the process of inclusion modification by La was developed. Furthermore, the ratio of equiaxed zone of the solidification structure increased from 22.9% to 31.0%, and the average primary dendrite arm spacing decreased significantly from 288.4 to 226.2 lm. Two-dimensional lattice mismatch analysis results determined that LaAlO₃ can serve as an effective heterogeneous nucleation core, leading to solidification structure refinement. The beneficial transformation of inclusions and refinement of solidification structure are conducive to the cold heading process of 40Cr steel.

An opposite combined vertical linear electromagnetic stirring (CV-LEMS) was proposed, which is applied in the final solidification zone of bloom continuous casting. The melt flow, heat transfer, and solidification under CV-LEMS were investigated by establishing a three-dimensional numerical simulation model and a pilot continuous casting simulation experiment and compared with the conventional rotary electromagnetic stirring (REMS). The results show that a longitudinally symmetric linear magnetic field is formed in the liquid core of the bloom by applying CV-LEMS, which induces a strong longitudinal circulation flow both on the inner arc side and the outer arc side in the liquid core of the bloom. The height of the melt longitudinal effective mixing range under CV-LEMS reaches 0.9 m, which is greater than that of the REMS and makes up for the deficiency of REMS sensitivity to the position of the final solidification zone. CV-LEMS strongly promotes the mixing of upper melt with high temperature and the lower part melt with low temperature in the liquid core, improves the uniformity of melt temperature distribution and significantly increases the melt temperature near the solidification front, and the width of the liquid core increases by 4.2 mm at maximum. This shows that the appliction of CV-LEMS is more helpful to strengthen the feeding effect of the upper melt to the solidification shrinkage of the lower melt than the conventional REMS and inhibits the formation of porosity, shrinkage cavity and crack defects in the center of the bloom.

The failure analysis was conducted on unqualified torsion bar spring in automobile suspension system used for light vehicles during engine test. The effects of through hardening, surface induction hardening, quenching and tempering, and tempering temperature on the microstructure and fatigue life of 45CrNiMoVA steel torsion bars were also investigated. Results showed that only the torsion bar spring after through quenching and tempering is subjected to surface induction quenching and tempering to achieve the fatigue life of the qualified torsion bar. The fatigue life of torsion bar spring reaches 3×10⁵ cycles more than the required 2×10⁵ cycles. This is because the distribution of gradient microstructure was helpful to relieve the applied stress during the fatigue process. The microstructure of the non-hardened region, which consists of tempered sorbite regardless of whether it is tempered at 330 or 430 °C, contributes to minimizing the impact of temper brittleness on the fatigue life of the torsion bar. Consequently, the fatigue life of the torsion bar is relatively unaffected by temper brittleness due to the presence of tempered sorbite in its non-hardened regions. And the reason for the unqualified fatigue life was that the depth and hardness of the hardened region did not meet the standard requirements of 5-7 mm and 47-52 HRC, respectively.

Understanding the motion behaviors of non-metallic inclusions in the liquid metal is important for clean steel production. High-temperature confocal laser scanning microscopy is applied to investigate the effect of different Ti and Al contents on the agglomeration behavior of non-metallic inclusions in low carbon steels. Furthermore, the agglomeration mechanism of inclusions was investigated through quantitative analysis of in-situ observation experiments and a modified Kralchevsky- Paunov model. The obtained results indicate that Al₂O₃ is the main type inclusion in the low-alloys steels with both Al and Ti addition. This type of inclusion is more likely to absorb surrounding small-size inclusion particles, leading to a further growth for the cluster formation and contributing to a serious engineering problem, nozzle clogging. Besides, TiO_x is the main type inclusion in the molten steel with only Ti addition, and this type of inclusion is less likely to agglomerate and the individual inclusion particles show a ‘free’ motion with the fluid of molten steel. The difference between these two types of inclusions is due to the difference in attractive force and action distance at the meniscus created by the inclusion/steel/Ar multiple interfaces and influenced by the physical parameters, e.g., contact angle and interface energy between inclusion and steel, and surface tension of the melt.

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.

Herein, the effect of direct current (DC) attached the mold on refining the microstructure and alleviating the central segregation of a tin-bismuth (Sn-10 wt.% Bi) alloy ingot during the solidification process has been investigated. The experiment used a self-made device, which can achieve the effect of refining the solidified structure and alleviate the segregation of the metal casting. Numerical simulations were performed to calculate the Lorentz force, Joule heating and induced melt vortex flow for the magneto-hydrodynamic case. Our results show that the maximum velocity of the global electro-vortex reached 0.017 m s^-1. The DC-induced electro-vortex was found to be the primary reason of refining the equiaxed grain and alleviating the segregation of the b-Sn crystal boundary. The grain refining effect observed in these experiments can be solely attributed to the forced melt flow driven by the Lorentz force. DC field attached the mold can lead to grain refinement and alleviate the segregation of the ingot via a global vortex. The technology can be applied not only to opened molds, but also toward improving the quality in closed molds.

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 production of ferroalloys is a resource-intensive and energy-consuming process. To mitigate its adverse environmental effects, steel companies should implement a range of measures aiming at enhancing the utilization rate of ferroalloys. Therefore, a comprehensive ferroalloy model was proposed, incorporating a prediction model for alloying element yield based on case-based reasoning and support vector machine (CBR-SVM), along with a ferroalloy batching model employing an integral linear programming algorithm. In simulation calculations, the prediction model exhibited exceptional predictive performance, with a hit rate of 96.05% within 5%. The linear programming ingredient model proved effective in reducing costs by 20.7%, which was achieved through accurate adjustments to the types and quantities of ferroalloys. The proposed method and system were successfully implemented in the actual production environment of a specific steel plant, operating seamlessly for six months. This implementation has notably increased the product quality of the enterprise, with the control rate of high-quality products increasing from 46% to 79%, effectively diminishing the consumption and expenses associated with ferroalloys. The reduced usage of ferroalloys simultaneously reduces energy consumption and mitigates the adverse environmental impact of the steel industry.