Two low‐C CrNiMnMoB ultrahigh‐strength steels, one Nb‐free (0Nb) and one microalloyed with 0.04 wt.% Nb (4Nb), were developed to investigate the role of Nb in hot deformation behaviour, strain‐induced precipitation, and microstructural evolution. Isothermal single‐hit compression tests were conducted over 850–1250 °C and strain rates of 0.01–50 s −1 using a Gleeble 3800 simulator, complemented by Thermo‐Calc predictions and EBSD/TEM analyses. Nb addition significantly modified the thermomechanical response by increasing flow resistance, delaying dynamic recrystallization (DRX), and elevating the deformation activation energy. Processing maps revealed that Nb shifted DRX domains toward higher temperatures and lower strain rates while suppressing regions of flow instability. Quantitative precipitation‐kinetics analysis demonstrated that the solubility of Nb in austenite is negligible at 850 °C (≈0.00049 wt.%) and increases progressively with temperature, reaching full dissolution (≈100% of total Nb, 0.04 wt.%) at 1250 °C. Increasing strain rate significantly suppressed strain‐induced NbC precipitation, reducing the normalized precipitation fraction ( X p ) from nearly 50% at 0.01 s −1 to below ~10% at 1 s −1 and 3%–5% at 50 s −1 . These results confirm that NbC precipitation is strongly temperature‐ and strain‐rate‐dependent and governs hot deformation resistance in Nb‐microalloyed CrNiMnMoB steels.
The uniform dispersion of carbon black in the mold flux matrix is critical for the stability of the continuous casting process. During the preparation of mold flux slurries, Na + ions generated from the hydrolysis of Na 2 CO 3 interact with surface functional groups on the carbon black, thereby influencing its dispersion state. The results indicate that as the Na 2 CO 3 content increases, the aggregate particle size enlarges, reaching a maximum of 0.759 μm at 8 wt% before stabilizing. Molecular simulations demonstrate that Na + induces a charge screening effect on the carbon black surface functional groups. As the Na 2 CO 3 concentration rises from 1 to 12 wt%, the intensity of the radial distribution function decreases, indicating a weakening of short‐range enrichment and interfacial structuring. The diffusion coefficient exhibits a distinct transition near 8 wt%, suggesting that under high ionic strength, charge screening is enhanced and adsorption–desorption exchanges become more frequent. Furthermore, the Na + number‐density profile ρ ( z ) shows pronounced tail shrinkage with increasing concentration, indicating compression of the electrical double layer and reduced electrostatic repulsion, which ultimately deteriorates dispersion stability. Reducing the dosage of Na 2 CO 3 contributes to improving the melting uniformity of the mold flux.
This study investigates the effect of mold geometry on carbon segregation in 20‐ton low‐alloy steel ingots by combining industrial experiments with numerical simulations. Polygonal and rectangular ingots were compared to clarify how geometry‐dependent heat transfer, melt flow, and grain evolution affect macrosegregation. The industrial results show that the rectangular ingot has a markedly smaller carbon segregation range, with a maximum Δ C of 0.27, compared with 0.53 in the polygonal ingot. The polygonal ingot exhibits more severe positive segregation at the head, with a maximum carbon content of 1.00 wt%, and stronger negative segregation at the tail, with a minimum carbon content of 0.409 wt%. In contrast, the rectangular ingot shows milder segregation and a smaller affected region. Numerical simulations indicate that these differences are associated with variations in the temperature field, melt flow pattern, solidification front morphology, and grain growth behavior. In the polygonal ingot, unstable convection, narrow remaining liquid channels, and dendrite bridging restrict solute transport and aggravate local segregation. By contrast, directional heat extraction through the broad faces of the rectangular ingot produces a wider and more regular solidification front, a more stable flow pattern, and smoother solute redistribution, thereby reducing macrosegregation.
This study examines how deformation temperature paths affect martensitic hierarchy and the strength–ductility balance of an experimental low‐carbon Ti–Zr microalloyed ultrahigh‐strength steel. Isothermal three‐pass compression at 950, 1000, or 1050 °C (routes A–C) was compared with decreasing‐temperature paths of 1050–1025–1000 °C and 1050–1000–950 °C (routes D and E). After water quenching, the microstructures were characterized by scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), and transmission electron microscopy (TEM), together with microtensile testing and hardness measurements. The 1050 °C isothermal route coarsened prior‐austenite grains and martensitic packets/blocks, whereas decreasing‐temperature deformation suppressed coarsening and enhanced martensitic subdivision. Route D produced the most homogeneous hierarchical structure, the highest high‐angle‐boundary fraction, and coordinated kernel average misorientation (KAM) and geometrically necessary dislocation (GND) distributions, yielding 915.3 MPa yield strength, 1043.0 MPa ultimate tensile strength, and a Vickers hardness of 315.4 HV. Route E produced the finest hierarchy and greater dislocation‐associated stored energy, with 766.4 MPa yield strength, 928.9 MPa tensile strength, and 25.2% elongation. These results show that the deformation temperature path balances boundary‐network homogenization against stored‐energy retention, while Ti/Zr‐rich carbide precipitates provide auxiliary strengthening.
The scrap‐based electric arc furnace (EAF) steelmaking route, using steel scrap as the primary metallic charge with a supplement of ore‐based metallics (OBMs), will be increasingly employed to produce low‐nitrogen steels that conventionally are made by the blast furnace (BF)‐basic oxygen furnace (BOF) integrated route. To support such trends with minimized environmental impact and low costs, this paper critically reviews the relevant literature from both research and industrial practice on controlling steel nitrogen content in steelmaking processes. It covers the entire scrap‐based EAF steelmaking process from raw materials, through primary EAF steelmaking (scrap melting, slag foaming and tapping) and secondary refining (ladle furnace treatment and vacuum degassing), to continuous casting. The paper identifies future work to advance fundamental understanding and improve industry practices for producing low‐nitrogen steels via the scrap‐based EAF steelmaking route.
In this article, the mechanism of boron in mitigating the heat‐affected zone (HAZ) softening in hot‐rolled ultra‐low‐carbon (C < 0.07 wt%) martensitic steels was investigated. The thermal cycles corresponding to different HAZs were simulated for 1000 MS steels with low (5 ppm) and high (12 ppm) boron contents. Results indicated that welding thermal cycles induced varying degrees of softening and strength reduction across all HAZs. The addition of 12 ppm boron effectively suppressed softening in both the fine‐grained zone (FG) and intercritical zone, increasing their hardness by 79 and 59 HV and yield strength by 262 and 219 MPa, respectively. This enhancement is attributed to boron segregation at prior‐austenite grain boundaries, which hinders carbon diffusion, prevents the formation of carbon‐depleted zones, and consequently inhibits ferrite precipitation, promoting martensite formation during the cooling stage. Furthermore, boron addition altered the softening hierarchy, shifting the most severely softened region from the FG (336HV) to the sub‐critical zone (SC, 288HV).
This study investigates the effects of Cu content (1.35, 3.10, and 6.01 wt.%) on hydrogen diffusion behavior and hydrogen embrittlement resistance in Cu x Ni 2.7 Mn low‐carbon steel, supplemented by numerical simulations using a cellular automata (CA) model. Through hydrogen permeation experiments, mechanical property testing, and fracture surface analysis, this study systematically analyzed hydrogen diffusion parameters, hydrogen trap density, and hydrogen embrittlement susceptibility at different Cu contents. CA simulations revealed hydrogen accumulation at grain boundaries and Cu‐rich precipitation interfaces, along with copper’s reversible regulation of hydrogen distribution. Results indicate that increasing Cu content leads to grain refinement, enhanced Cu‐rich precipitation, elevated hydrogen trap density, reduced effective hydrogen diffusion coefficient, and significantly diminished hydrogen embrittlement susceptibility. Optimal hydrogen embrittlement resistance is achieved within the 3.60–5.40 wt.% Cu content range. This study provides theoretical and experimental foundations for the composition design and engineering application of Cu‐containing steels with high hydrogen embrittlement resistance.
Laser quenching technology is widely applied in the aerospace and defense industries for surface strengthening of high‐performance steel components. However, multiple overlapping processing often leads to the formation of local softened zones in the secondary tempering zone, and the crystallographic mechanisms of grain orientation evolution and lattice distortion remain insufficiently clear. In this study, a disc‐type laser system was used to perform rectangular point laser quenching treatment on 12Cr2Ni4A aviation gear steel. The morphological evolution characteristics and local softening behavior were characterized through electron backscatter diffraction, polar plots, inverse polar plots, orientation distribution function, scattering topological analysis, scanning electron microscopy, and microhardness testing. The results show that laser quenching promotes the transformation of grain orientation from a dispersed distribution to a concentrated structure dominated by the enhanced (110) related components. In the second tempering zone, the repeated thermal cycling results in a significant enrichment of the A1 grain structure, an expansion of anisotropic orientation scattering, an increase in the proportion of low‐angle grain boundaries, and a decrease in local hardness. It reveals the phenomenon of cumulative lattice distortion and residual stress concentration in overlapping areas, providing a crystallographic basis for optimizing laser quenching processes and enhancing the reliability in service.
Integrating renewable carbon sources into electric arc furnace (EAF) steelmaking requires an understanding not only of their reaction chemistry but also of their injectability under realistic process conditions. Biocarbon has emerged as a promising candidate, yet its physical delivery to the slag and its capacity to initiate foaming remain largely unquantified. This study introduces a novel laboratory‐scale setup featuring a scaled‐down industrial injector combined with an induction furnace to simulate EAF steelmaking. The setup enabled the evaluation of biocarbon injection behavior and slag foaming response. Experimental results demonstrate that biocarbon can be successfully injected to penetrate the molten slag and initiate foaming. However, slag foaming performance exhibits a pronounced decline beyond a critical injector working distance (WD), rather than a gradual decrease. Computational fluid dynamics (CFD) simulations, used to interpret this behavior, revealed a sharp drop in particle velocity past this distance. These findings provide a systematic evaluation of biocarbon injection behavior for slag foaming and offer practical insights for its implementation in sustainable electric steelmaking.
This study systematically investigates the effects of heating rate and temperature on the high‐temperature oxidation behavior of industrial X70 pipeline steel in the range from 700 to 1000 °C. Thermogravimetric experiments were conducted to simulate the heating and holding processes during hot rolling, combined with characterization techniques such as SEM, EDS, and EBSD. The non‐isothermal and isothermal high‐temperature oxidation behavior of industrial‐grade X70 pipeline steel was systematically investigated in the hot‐rolling heating range from 700 to 1000 °C. The results show that increasing the heating rate can induce a significant oxidation hysteresis effect, delaying the onset temperature of intense oxidation from 805 °C (10 °C/min) to 850 °C (50 °C/min). The apparent oxidation activation energies during the heating and isothermal stages were calculated to be 140.327 and 12 256.04 J/mol, respectively. A layered evolution characteristic was identified, with Fe 2 O 3 , Fe 3 O 4 , and FeO arranged sequentially from the outermost layer inward, along with Si–Cr alloy oxides enriched at the interface. For the first time, a coherent cogrowth mechanism was quantitatively revealed between the persistent strong {001} texture in the Fe 3 O 4 layer and the {111} plane texture in the FeO layer that intensifies with increasing temperature. This study provides a theoretical foundation for optimizing the heating process and controlling oxide scale defects in the hot rolling of X70 pipeline steel.
As a link between mold oscillation and the slab shell mechanical response, slag channel pressure directly influences shell morphology and slag film lubrication. This study investigates longitudinal pressure distribution in the slag channel by developing a coupled model that incorporates multiphase flow, heat transfer, and solidification. The study reveals a functional zoning of pressure between the meniscus and submeniscus region and analyzes how pressure variations influence oscillation mark depth and slag channel lubrication under different mold oscillation parameters. Results show that meniscus pressure governs mark formation: larger pressure fluctuations deepening the marks. Conversely, submeniscus pressure regulates channel lubrication: higher pressure maintains wider channels and enhances lubrication. Parametric analysis indicates that lower amplitude or higher frequency reduces meniscus pressure fluctuations and deepens marks. However, the same parameter changes also decrease submeniscus pressure, producing narrower channels and decreased lubrication. Implementing nonsinusoidal waveforms achieves synergistic optimization by simultaneously reducing meniscus pressure differentials and raising pressure below the meniscus, which diminishes mark depth and improves lubrication. These insights elucidate the longitudinal pressure mechanisms in slag channel and provide theoretical guidance for optimizing continuous casting parameters.
To efficiently characterize the impact of random corrosion on the mechanical properties of steel, the random corrosion morphology and equivalent constitutive model of high‐performance steel (HPS) Q550E are studied in this paper. First, 3D scanning is performed on Q550E HPS specimens to explore their corrosion morphology and pit distribution characteristics. The mechanical property parameters and degradation laws of the specimens are obtained by static tensile tests. Subsequently, a finite element simulation method for random corrosion is proposed to assess the effects of pit morphology on mechanical responses. Finally, an equivalent thickness method is developed, incorporating the three‐dimensional geometry, type, and proportion of corrosion pits. Model parameters are recalibrated and validated against the three‐stage constitutive model. Results show that the mean value of rectangularity is negatively correlated with the corrosion rate, but positively correlated with the average cross‐sectional area. Key mechanical indicators degrade linearly with rising corrosion severity. The equivalent thickness model is proved to be superior to the traditional method, and the developed constitutive model can accurately reproduce the stress‐strain response of corroded HPS. The research results provide a reference for the performance evaluation and safety design of HPS structures in corrosive environments.
This study systematically investigated the precipitation behavior and strengthening mechanisms of MX and M 23 C 6 in 9–12Cr martensitic heat‐resistant steels by combining first‐principles calculations with experiments. The results show that the primary precipitates in 9–12Cr martensitic heat‐resistant steels are (Cr,V)N and (Fe, Cr) 23 C 6 phases, which are dispersed along the prior austenite grain boundaries and martensite lath boundaries, forming rigid obstacles that impede dislocation motion. This microstructural feature yields a yield strength of 636 MPa and an elongation of 21% at room temperature. First‐principles calculations reveal that, except for Fe 23 C 6 , the formation enthalpies of all other precipitates are negative, with NbN and Cr 22 FeC 6 being thermodynamically the most stable among the MX and M 23 C 6 . NbC exhibits brittle characteristics, while the other precipitates exhibit ductile behavior. This study clarifies the stability rules of precipitates and their strengthening mechanisms, providing theoretical guidance and experimental support for the composition design of 9–12Cr martensitic heat‐resistant steels.
The characteristics of slag films and their influence on the hot‐tearing susceptibility of advanced high‐strength steel (AHSS) were investigated by combining mold simulator technology, single hot thermocouple technology (SHTT), scanning electron microscopy (SEM), JMatPro calculation, and ProCAST simulation. The results show that the slag film formed by YH mold flux in AHSS 1 has a thickness of 1.78 mm, which is significantly greater than the 1.06 mm obtained for CH mold flux in AHSS 2, owing to a larger solidification shrinkage of AHSS 1. Compared with CH slag, YH slag exhibits a much higher crystalline layer fraction (84.5% vs. 37.1%) and a lower liquid layer fraction (9.4% vs. 14.7%). Quantitative thermal resistance analysis further indicates that the total thermal resistance of the YH slag film is approximately twice that of the CH slag film, mainly due to its thicker crystalline layer. ProCAST simulations further reveal that the hot‐tearing indicator of AHSS 1 is markedly lower than that of AHSS 2. The reduced hot‐tearing susceptibility of AHSS 1 is attributed to the coupled effect of larger shrinkage‐induced slag infiltration, higher slag film thermal resistance, and more uniform shell solidification.
Low friction and wear of diamond‐like carbon (DLC) coatings strongly depend on the running‐in phase, which is significantly affected by surface pretreatment. In tool steels, differences in hardness and sputtering rates between carbides and the steel matrix may cause carbide protrusion during polishing and ion etching, leading to increased coating roughness. Although considerable attention has been devoted to optimizing DLC deposition parameters, the influence of surface pretreatment is often overlooked despite its significant effect on tribological performance. In this study, a TiNb‐DLC coating consisting of an amorphous hydrogenated carbon matrix (a‐C) doped with titanium and niobium was deposited on X153CrMoV12 (AISI D2) tool steel by reactive magnetron sputtering. Tribological properties were evaluated using a pin‐on‐disc test, while chemical and structural characterization was performed by EDS, XRD, Raman spectroscopy, and XPS. Reducing the ion etching time decreased the coefficient of friction by 18% and coating wear by 70% during the running‐in phase. Post‐deposition polishing further reduced the coefficient of friction by 51%, wear of the steel counterpart by 71%, and wear of the TiNb‐DLC coating by 91%. The results demonstrate the critical role of surface pretreatment in controlling the tribological behavior of DLC coatings.
Blast furnace processes have traditionally dominated ironmaking; however, multistage smelting reduction iron bath reactors offer a promising alternative. The optimization of these reactors is currently hindered by an inadequate understanding of gas-liquid-solid interactions and pellet distribution dynamics. To address this, the present study employs a coupled Volume of Fluid (VOF) and Discrete Phase Model (DPM) approach to simulate multiphase flow within the reactor. This methodology systematically evaluates pellet distribution, concentration gradients, and flow-field interactions under varying lance diameters and bottom blowing configurations. Key findings indicate that implementing a spiral feeding method reduces the pellet sedimentation rate by 44% compared to conventional feeding techniques. In the absence of bottom blowing, pellet settling is minimized, resulting in the highest local concentration. The single-hole configuration ranks second in mitigating the settling rate and maintaining concentration. Consequently, operating no bottom blowing combined with a lance diameter of 125 or 175 mm yields the optimal concentration. Furthermore, the single-hole configuration achieves superior uniformity in pellet distribution, corresponding to a coefficient of variation (CV) between 23.7% and 29.6%. Conversely, double-hole configuration induces severe pellet segregation, with the CV reaching up to 37.1%.
Steel recycling is fundamental for advancing a circular economy and green steel mission, as producing steel from scrap substantially reduces energy consumption and CO 2 emissions compared with ore‐based steelmaking. However, the uncontrolled retention of residual Cu in recycled steels poses a significant challenge known as copper contamination. During hot working, Cu enrichment at surfaces and near‐surface grain boundaries can lead to the formation of low‐melting Cu‐rich liquid films, which result in hot shortness and surface cracking. Moreover, depending on Cu content, precipitate size, and processing conditions, Cu segregation and precipitation of Cu‐rich phases during cooling or aging may cause embrittlement and reduced toughness. In contrast, when Cu incorporation is carefully controlled and combined with appropriate alloy design and processing parameters, it can enhance mechanical properties through nanoscale precipitate strengthening, improve corrosion resistance via the formation of protective patina layers, and impart antibacterial functionality in specific steel grades and environments. This work reviews the dual role of Cu as both a detrimental residual element and a beneficial alloying addition in steels and provides important considerations for the design of high‐performance, sustainable, and multifunctional Cu‐bearing steels with potential applications in automotive, construction, marine, pipeline, medical, food, and sanitary sectors.
Ferro-coke is an emerging ironmaking fuel that can reduce both blast furnace fuel consumption and CO2 emissions. This study investigates the effect of metallurgical dust on the gasification behavior of ferro-coke and elucidates its catalytic mechanism. Results indicate that the addition of dust decreases the initial gasification temperature of ferro-coke, with a further decline observed as the dust dosage increases. When the dust addition amount increases from 0 to 20%, the initial gasification temperature decreases from 808.8 degrees C to 729.5 degrees C. The rate-limiting step of the ferro-coke gasification reaction shifts from chemical reaction control to internal pore diffusion control. Scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS) characterization demonstrates that dust increases the internal porosity of ferro-coke, consistent with the random pore model. Meanwhile, X-ray diffraction (XRD) and Raman spectroscopy analyses show that dust decreases the degree of carbon graphitization, increases the amorphous carbon content, and enhances gasification reactivity. First-principles calculations confirm the synergistic catalytic effects of Fe and Ca in the dust; the reaction energy barrier is reduced from 196.65 kJ & centerdot;mol-1 to 115.26 kJ & centerdot;mol-1, indicating a pronounced catalytic effect.
This study focused on the relationship between the microstructure and mechanical properties of a Cu-bearing steel treated by quenching and tempering. The evolution of strengthening and toughening mechanisms at different tempering temperatures was discussed in detail. The influence of tempering temperature on the quantity, morphology, and thermal stability of reversed austenite (RA) was systematically explored, thus revealing its mechanism in enhancing the low-temperature toughness. At a tempering temperature of 650 degrees C, an optimal microstructure was obtained, characterized by a high content (15.3%) of film-like RA, along with the appropriately sized Cu-rich precipitates (about 11 nm) and fine lath structures. The steel achieved a yield strength of 824 MPa, tensile strength of 894 MPa, elongation of 23.60%, and impact energy of 204 J at -80 degrees C, demonstrating a remarkable combination of mechanical properties. On the contrary, only a small amount of blocky RA was formed at 630 degrees C, while tempering at 680 degrees C caused the decomposition of RA, both of which led to a significant decrease in toughness. These results revealed that the mechanical properties were significantly improved through optimized composition design and process refinement, providing theoretical support and practical approaches for designing high-performance low-carbon Cu-bearing steels.
