The high-temperature corrosion behaviors of an as-rolled Fe-17.4Cr-12.4Ni-2.63Mo-1.57Mn-0.044C (in wt.%) austenitic stainless steel in nuclear-grade helium environments containing with 10, 100 and 1000 magnification impurity tolerance concentrations at 550 degrees C were investigated and compared. Based on the quantitative relationship between mass gain and corrosion time, the high-temperature corrosion kinetics curves of the alloy in different helium environments were determined. The results demonstrated that for different samples, their mass gains exhibited a parabolic increase over the corrosion time. Raman spectroscopy and GIXRD analyses revealed that the high-temperature corrosion mechanisms of different samples are similar and the formed surface oxide layers were primarily composed of Fe2O3, Cr2O3, Fe3O4 and NiFe2O4. Under the equivalent corrosion damage and mass gain conditions in helium containing with 10, 100 and 1000 magnification impurity tolerance concentrations, the corresponding corrosion time required to achieve a mass gain of 0.5 mg/cm2 were determined to be 200, 600 and 1000 h, respectively. Based on the principle of same damage mechanism and equal damage degree, an acceleration testing method was proposed and the corresponding empirical formulas were established for evaluating the long-term high-temperature corrosion extent of austenitic stainless steels in nuclear-grade helium environments.
Currently, the supply of high Fe grade and low gangue pellet feeds has become increasingly tight due to yearly large-scale consumption of iron ores worldwide, which will inevitably restrict the development of iron ore pelletizing process and carbon dioxide emissions mitigation of the steel industry. To promote utilization of high silica pellet feeds, the roasting behavior of high silica acid pellets with varying binary basicity (w(CaO)/w(SiO2) = 0.01, 0.20, 0.35, 0.50) through the straight-grate process was examined, and its metallurgical performance in blast furnace and gas-based shaft furnace was also evaluated. The results show that all fired pellets achieved optimal strength by roasting at 1225 °C for 10 min at basicity of 0.35. The metallurgical performance tests under blast furnace and Midrex direct reduction conditions indicate that the addition of a proper quantity of calcium flux improves the pellet reducibility and low-temperature reduction degradation performance, decreases the reduction swelling index and narrows the softening and melting range with better bed permeability at desirable basicity of 0.20 and 0.35. However, further increasing the basicity to 0.50 presents negative impacts on the pellet induration characteristics and metallurgical properties due to excessive formation of liquid phase inhibiting interconnection of hematite particles. Thus, the fired pellets exhibit poorer resistance and structural stability to the mechanical stress and lattice transformation during reduction and cooling process.
A coupled numerical model integrating molten steel flow, solidification behavior, matrix deformation behavior, and surface crack tip extension was developed. Following validation of temperature evolution and strain–stress curve, the model was used to investigate slab crack propagation with various strip feeding ratios during continuous casting, accounting for variations in crack positions and types. The results show that the “double roll” flow is formed under the limitations of the mold narrow surface, meniscus, and submerged entry nozzle, inducing an easier propagation of crack at the slab narrow surface where the S32654 matrix exhibits higher temperature and lower yield strength. The feeding strip prevents the jet from washing on the slab narrow surface, significantly reducing the temperature and increasing the yield strength there. As the strip feeding ratio increases, crack propagation becomes more difficult, while surface crack area gradually decreases. Moreover, longitudinal crack propagation occurs most easily, followed by 45° oblique crack propagation, while transverse crack propagation is the most difficult, due to the increasing angle between the directions of stress release and slab casting. The optimal strip feeding ratio should be around 0.75
The influence of Mn/Cr ratio variation in the Mn–Cr-rich body-centered cubic matrix phase on the high-temperature oxidation resistance and mechanical properties of L21-strengthened Al20Fe50CrxMn25−xTi5 (x = 15, 25 at.
A modified Koistinen and Marburger (KM) kinetics model including the average prior austenite grain size (PAGS) variable was proposed. The enhancement was achieved by introducing the relationship between PAGS and temperature point T_0 , at which the transient change rate is the maximum in the evolution of the phase transformation rate parameter α , thereby improving the accuracy of martensitic transformation kinetics prediction. Diverse austenitization temperatures were applied to investigate the effect of PAGS on the martensite transformation of cold-rolled quenching and partitioning (Q P) steel during the decomposition of austenite. An increase in PAGS from 3.8 to 19.3 μm was observed with elevated austenitization temperatures, accompanied by a sigmoidal rise in martensite start temperature M_s . And the relationship between PAGS and M_s was quantitatively described through an exponential function. At the same time, the martensite fraction at the same quenching temperature gradually increased with the increase in PAGS, leading to the development of PAGS-incorporated modified KM model. The model accurately predicts PAGS-dependent martensite transformation kinetics in Q P steels across various austenitization temperatures, enabling multi-process kinetic curve predictions and overcoming the limitation of process-specific and single-curve prediction in existing models, with significantly broadened applicability.
On the basis of 2100 MPa ultra-high-strength bridge cable steel wire designed by our research group in the early stage, we further understand the change of the performance of the steel wire after hot dipping, which paves the way for the optimization of the hot dipping process and the development of higher-strength steel wire. Cold-drawn wires (5.9 and 7.0 mm in diameter) underwent controlled thermal exposures in a salt bath furnace simulating industrial hot dipping conditions (440–460 °C, 10–300 s), followed by multi-scale characterization combining tensile testing, scanning electron microscope and transmission electron microscope, and three-dimensional atom probe tomography. The results revealed a critical time-dependent competition between strengthening and softening mechanisms: short-duration treatments (≤ 30 s) enhanced strength through cementite dissolution and carbon supersaturation in ferrite, while prolonged exposures (> 60s ) degraded performance through lamellar spacing coarsening and dislocation annihilation. It is worth noting that the peak strength is ahead of the elongation in time to meet the standard requirements, which indicates that the process window should be optimized by the hot dipping process. Experiments and kinetic analysis determined that 30−60s was the best processing time, and the balance performance was achieved by controlling the dissolution of cementite.
The photoelectrochemical cathodic protection (PCP) performance of pure TiO2 photoanode is significantly limited by its narrow light absorption range, rapid recombination of photogenerated electron–hole pairs, and inefficient electron transfer. A novel TiO2/RGO (reduced graphene oxide)/CuInS2 (T/G/Cu) photoanode based on TiO2 nanotube arrays modified with RGO and CuInS2 nanoparticles was developed to improve the corrosion resistance of HRB400 rebars. This ternary photoanode featuring heterojunction structures was synthesized through a combination of anodization, potentiostatic deposition, and successive ionic layer adsorption reaction. Comprehensive characterization techniques, including scanning electron microscope, transmission electron microscope, X-ray diffraction, and X-ray photoelectron spectroscopy, confirmed the uniform distribution of layered RGO and CuInS2 nanoparticles on the surface of TiO2 nanotubes, indicating the successful formation of n–n type heterostructures. Photoelectrochemical analyses, such as ultraviolet–visible diffuse reflectance spectrum, photoluminescence spectroscopy, electrochemical impedance spectroscopy, and Mott–Schottky, revealed that T/G/Cu n–n heterojunction films exhibited a reduced bandgap (2.87 eV), significantly suppressed photogenerated electron–hole recombination, and enhanced the charge transfer efficiency. Under visible light irradiation, T/G/Cu-2 exhibited a cathodic shift in potential to −0.78 V vs. SCE (saturated calomel electrode) and generated a photocurrent density of 20.0 μA/cm2, demonstrating significantly enhanced PCP performance compared to the pure TiO2 photoanode. The high electrical conductivity and large specific surface area of RGO, along with the built-in electric field within n–n heterostructure, enabling efficient electron migration and cathodic polarization of HRB400 rebar.
The deformation and stress behavior during shear-compression bonding of intermediate slabs was investigated, and a systematic evaluation index to quantify bonding quality and process efficiency was established. A finite element simulation model based on plastic deformation theory was developed to analyze the influence of key process parameters. Single-factor analysis and an orthogonal experimental design, combined with range and variance analysis, were employed to evaluate the significance and sensitivity of multiple parameters. A quadratic polynomial regression model was further constructed to describe nonlinear relationships between process variables and performance indices. The results indicate that edge width, overlap amount, reduction, reduction speed, and slab temperature are the dominant factors governing bonding quality. The optimal parameter combination was determined as an edge width of 30 mm, overlap amount of 3 mm, reduction of 20 mm, reduction speed of 60 mm/s, and slab temperature of 1060 °C. The proposed integrated approach provides a reliable basis for process parameter optimization and contributes to enhancing bonding performance and consistency in endless rolling operations.
The martensitic transition sequence and microstructure evolution in a homogenized Fe–15Mn alloy under thermal cycling, involving a thermal body-centered cubic α′-martensite, hexagonal close-packed -martensite, and face-centered cubic γ-austenite, were characterized by neutron diffraction and transmission electron microscope. The → α′ transition is observed for the first time during heating. Upon cooling, γ → and γ → α′ transitions occur concomitantly. The transition rate of the γ → is higher than that of the γ → α′ in the early stage of the phase transition. The Fe–15Mn alloy exhibits a pronounced volume effect of phase transition (1.6 → γ, 1.8 → α′), which induces an obvious lattice mismatch. The sharp increase in the volume fraction of -martensite after thermal cycling is attributed to the formation of abundant stacking faults and the pre-existing α′-martensite within the alloy.
Correlation of quenching temperature and bulk carbon content with microstructure-properties evolution in Mn-heterogeneous quenching and partitioning (Q P) steels (0.3C and 0.4C) was systematically investigated. Two critical quenching temperature points were identified where ghost pearlite fraction peaks (70 °C for 0.4C, 130 °C for 0.3C), with low carbon 0.3C steel displaying a smoother decrease in ghost pearlite fraction due to preferential martensite transformation over coalescence at high quenching temperatures. Compared to 0.4C steel ( 110 °C), superior ductility (22
Hydrogen embrittlement has emerged as a critical challenge that restricts the application of high-strength martensitic steel. The hydrogen embrittlement susceptibility and associated fracture morphologies of high-strength martensitic steel subjected to different aging durations were systematically examined via slow strain rate tensile tests, microstructural characterization, thermal desorption spectroscopy, and finite element simulations. The as-charged specimen exhibited predominantly intergranular fracture, governed by hydrogen-enhanced decohesion mechanism. After 3 d of aging, quasi-cleavage fracture features occurred with reduced susceptibility to hydrogen embrittlement, accompanied by transgranular fracture governed by the hydrogen-enhanced localized plasticity mechanism. Extending the aging period to 8 d yielded ductile fracture, indicative of superior hydrogen embrittlement resistance. A diffusion-kinetic finite element model was developed and shown to accurately predict hydrogen diffusion behavior, and finally quantitative correlations among aging duration, hydrogen concentration, and fracture mode transitions were established.
As a core load-bearing component of railway systems, heavy rail steel is prone to crack initiation induced by inclusions during service, which adversely affects its fatigue life. Owing to its excellent deoxidation, desulfurization, and inclusion modification capabilities, the rare earth element Ce is considered an effective approach to improving steel quality. A combined approach of thermodynamic calculations, high-temperature melting experiments, and crystallographic analysis was employed to systematically investigate the modification mechanism of inclusions and the heterogeneous nucleation behavior induced by Ce in heavy rail steel. The results show that the primary inclusions in untreated heavy rail steel are large, irregular MnS particles and nearly spherical Al2O3–SiO2–CaO complex inclusions. After Ce addition, Ce reacts not only with free O, S, and Al in the molten steel but also modifies the existing inclusions into smaller, more spherical or ellipsoidal CeAlO3, Ce2O3, Ce2O2S, and their composite forms. Due to the better toughness of Ce2O3 and Ce2O2S, when they envelop the harder CeAlO3 core, they help alleviate stress concentration at the interface with the steel matrix, thereby improving the mechanical properties of the steel. With the increasing Ce content, the inclusion size shows a trend of first decreasing and then increasing. The optimal modification effect is observed when the Ce content is in the range of 0.0017
A long-term in-situ marine study was carried out to evaluate the corrosion behavior of Q355B carbon steel across various ocean zones in the Dalian Sea. The results reveal significant variations in the rust layers formed in different regions, which in turn influence the progression of the corrosion process. In the atmospheric zone, the primary corrosion products include γ-FeOOH, α-Fe2O3, and Fe3O4, and the development of the rust layer contributes to a reduction in the corrosion rate. In the tidal zone, the main corrosion products were α-FeOOH, γ-FeOOH, α-Fe2O3, and Fe3O4. The irregular distribution of the rust layer in this area resulted in localized corrosion on the steel surface. In the immersion zone, in addition to the previously mentioned corrosion products, the rust layer also fosters an environment conducive to microbial growth. The metabolic activities of these microorganisms compromise the structural integrity of the rust layer, thereby exacerbating the corrosion process.
The three-dimensional multiphase flow and the unreacted core desulfurization kinetic model were coupled to predict the sulfur content in hot metal during the Kanbara reactor (KR) stirring process. The effect of the impeller rotation speed, initial sulfur content, desulfurizer diameter, and desulfurizer addition on the variation of the sulfur content and desulfurization rate was revealed. The accuracy of the current model was validated through industrial trials involving sampling and measurement of the sulfur content in hot metal. Results indicated that the speed of the hot metal and the vortex distribution were primary factors determining the dispersion degree of the desulfurizer and the desulfurization rate. The variation of the average sulfur content during the KR process essentially followed an exponential distribution. The desulfurization rate constant increased with the higher rotation speed, higher desulfurizer addition, and lower desulfurizer diameter. However, the initial sulfur content in the hot metal hardly affects the desulfurization rate constant. A formula for predicting the variation of the sulfur content with the initial sulfur content, impeller rotation speed, desulfurizer diameter, total mass of desulfurizers, total mass of hot metal, and desulfurization time was proposed to provide theoretical guidance for the actual production.
The coupling effect of grain boundary density and dislocation density on the formation mechanism of adiabatic shear band (ASB) during the dynamic failure of high-strength steel was investigated. Though thermomechanical treatment, samples with different grain boundary densities (SS: 0.67 μm–1, 1093-SS: 0.57 μm–1, and 1273-SS: 0.24 μm–1) and initial dislocation densities (SS: 1.3 × 1015 m–2, 1093-SS: 8.1 × 1014 m–2, and 1273-SS: 5.5 × 1014 m–2) were prepared to elucidate the role of grain boundary density and dislocation density on ASB evolution. Experimental results showed that at a strain rate of 3300 s–1, the high grain boundary density samples (SS and 1093-SS) exhibited higher dynamic flow stresses of 1580 and 1491 MPa, respectively, compared to the low grain boundary density sample of 1273-SS with a stress of 1411 MPa. Under lower dislocation density, the high-density grain boundary network exhibited unique inhibitory effects by preventing dislocation aggregation and entanglement and effectively hindering shear localization, thus significantly delaying dynamic recrystallization. ASB composed of recrystallized grains failed to form due to the significant reduction in the recrystallization ratio. In contrast, low grain boundary density samples exhibited shear localization, leading to the formation of an ASB of approximately 24 μm in width. Further studies revealed that at a higher initial dislocation density, dislocation density has a more significant influence on ASB formation compared to grain boundary density. By contrast, the SS sample with high grain boundary density presented an ASB width of 18 μm. As a result, findings demonstrate that precise regulation of grain boundary density and dislocation densities enhances the material’s resistance to dynamic recrystallization and effectively suppresses ASB formation while maintaining high flow stress, offering a promising strategy to mitigate dynamic failure in high-strength steels.
The hot corrosion behavior of Co6Ti11V alloy at 900 °C was studied and compared with that of K417 and Co9Al9.5W alloys. The salt coating method was employed, which is a saturated mixture of 75 wt.
With the increasing quality requirements and demand for rotary steel parts, the lack of research on the centrifugal casting's flow field in semi-filled molds has limited the development of casting parameterization. The development of centrifugal multiphase flow fields, interphase interface formation, and fluid stability in thick-walled pipe fittings were examined. The fluctuation and stability of the flow field during steel and slag co-pouring are innovatively characterized using finite element analysis and casting experiments. The results show that the movement of the conventional semi-filled horizontal centrifugal flow field can be divided into three stages: filling fluctuation period, stable period, and weak instability period. Producers need to control initial solidification during the stable period to avoid defects and performance changes caused by melt instability. The pressure difference due to gravity causes the flow field to shift, and the center of gravity (CG) of the fluid in the stable period deviates nearly vertically and fluctuates in an elliptical shape, tending towards the central axis with increasing mold speed. Experimental castings exhibited eccentric distribution and phase interface fluctuation, while actual oxygen addition, slag fluctuation, and solidification shrinkage caused the CG offset to be smaller than that of ideal pure fluid. Additionally, the instantaneous filling assumption can be used to characterize the stable stage of the melt flow field, with an error of only 1.2% compared to non-instantaneous filling, while reducing computational cost by 30%.
How alloying low-density steel with Cr and Ni enhances marine corrosion resistance is elucidated by modulating the nucleation and growth kinetics governing the development of protective rust layers. How these alloying elements affect rust-layer evolution and the overall corrosion process is systematically elucidated. Specifically, Cr/Ni additions refine the steel's microstructure and elevate the Volta potential across both austenitic grains and their interfaces. Over extended exposure, Cr/Ni alloying facilitates the formation of protective spinel oxides such as FeCr2O4 and NiFe2O4, which markedly reduce corrosion rates and current densities while enhancing polarization resistance. This transformation supports a shift from localized pitting toward more uniform corrosion. Theoretical analysis using a dissolution-diffusion-deposition framework further reveals that Cr promotes heterogeneous nucleation of FeCr2O4 and dense Fe3O4 deposition, forming a compact, defect-suppressing oxide layer. In contrast, Ni slows matrix dissolution and favors homogeneous nucleation of corrosion products. The superior capacity of Cr to suppress local acidification and drive the formation of dense, protective scales accounts for its more pronounced effect compared to that of Ni.
Y2O3-enhanced MgO refractory crucibles were fabricated based on a novel design of Y2O3 crystal boundary-enhanced magnesia raw materials, and the interface reactions between the Y2O3-enhanced MgO refractory crucibles and Ni-TiAl superalloy were explored. Micro-CT analysis revealed no substantial infiltration or structural damage to the crucible after two cycles of melting. Y2O3 was found to uniformly distribute along MgO grain boundaries, forming a protective core-shell structure that effectively isolates MgO grains from direct contact with the alloy melt. This unique core-shell structure significantly enhanced the crucible's corrosion resistance. Furthermore, a dense MgCr2O4 spinel layer formed at the alloy-crucible interface, serving as a robust barrier against further refractory corrosion. The utilization of high-purity magnesia from Salt Lake resources not only minimized impurity-driven interfacial reactions but also endowed the crucible with superior performance.
The influence of tempering temperatures (200, 350, and 500 °C) on the microstructure and mechanical properties of high chromium (Cr) martensitic steel is investigated. The evolution of microstructure and mechanical properties of the heat-treated steels was thoroughly analyzed. The tempering temperature emerged as a key factor influencing the morphology of martensitic laths and the precipitation of carbides, specifically Cr23C6 and Fe3C. Variations in austenite content, essential for enhancing impact toughness and ductility, were observed at different tempering temperatures. Tempered steels showed reductions in Rockwell hardness and tensile strength, along with an increase in yield strength relative to the as-quenched state. The impact toughness was significantly affected by tempering, with impact energy reaching 337 J at 350 °C. Significantly, tempering at 350 °C improved elongation to 10.0
