Low ductility is the intrinsic cause of cracking in slab, and cooling rate is a key factor affecting the hot ductility of steel. This article focuses on low carbon V-N steel, and explores the growth characteristics of carbonitride precipitation and microstructure at different cooling rates through thermal simulation tensile experiments. The results show that increasing the cooling rate can improve the ductility in the third brittle zone. The cooling rate increases from 0.5°C/s to 7°C/s, the minimum of the reduction of area increases from 38.1% to 38.9%, 39.8%, 44.9%, and 48.4%, and the third brittle temperature zone shrinks from 725 ~ 860°C to 725 ~ 820°C. Increasing the cooling rate has little effect on austenite grain size, but it will significantly reduce the proeutectoid ferrite formed at austenite grain boundary. With the cooling rate increasing, due to the accelerated transition from austenite to ferrite, the average thickness of the proeutectoid ferrite film decreases from 38μm to 4μm, and no proeutectoid ferrite is formed at some grain boundaries. The cooling rate ≤5°C/s, the carbonitrides are distributed in a chain like manner at austenite grain boundary, and the size is large. However, when the cooling rate is ≥5°C/s, the time for the microstructure to remain in the austenite temperature zone and the high fluidity of the γ/α interface cause some carbonitrides to precipitate in the ferrite matrix, with small and uniform distributions in the original austenite grains.

This study investigates the oxidation behavior of MgO-C refractories containing a combined antioxidant system of Al (2wt%) and B₄C (0~4wt%). Oxidation tests were conducted under air conditions at 1200°C, 1300°C, and 1400°C for 60 and 180 minutes. As the temperature was increased from 1200°C to 1400°C, the non-oxidized area increased by 1.4, 3.3, and 14.1 times, respectively. The weight loss ratio decreased with the B₄C content and the temperature. Above 3wt% of added B₄C, the weight loss ratio remained the same. At 1200°C, the weight loss ratio decreased from 14.2% to 9.9% as the addition of B₄C was increased to 3wt%. At 1300°C, the weight loss ratio decreased from 14.8% to 6.7%. At 1400°C, the weight loss ratio decreased from 16.0% to 1.88%. These findings demonstrate that the effect is significant as the temperature increases. After the experiments, an XRD analysis confirmed the formation of Al₂O₃, B₂O₃, Mg₂B₂O₅, Mg₃B₂O₆, and MgAl₂O₄. Thermodynamics analysis indicates that Mg₃B₂O₆ melts at 1400°C, enabling effective pore sealing. At 1300°C, however, the combined reaction between Al₂O₃ and magnesium borates generates low-melting phase that provides a remarkably strong antioxidation effect even at this lower temperature, making 1300°C the critical point where the Al-B₄C system becomes highly effective. However, at 1200°C, only B₂O₃ is present as a liquid and subsequently forms solid magnesium borates with MgO, offering only a limited improvement in oxidation resistance.

This work deals with the development of new Compacted Graphite Cast Iron Composite Castings as an alternative to Si-Mo ductile iron. The new material is a silicon-molybdenum cast iron (Si-Mo), transformed into a cast composite using the Self-propagating High-temperature Synthesis in Bath (SHSB) method, which synthesizes ceramic carbide particles of metals such as Ti, W, Nb, Mo, Zr. SHSB is used to ensure the formation of thermodynamically stable ceramic phases, in this case, carbide phases. Among the listed metals, titanium was selected for the SHSB synthesis process due to the exceptionally favorable physicochemical properties of titanium carbide and its highly exothermic enthalpy of formation. The described process strengthens the matrix of the material, changing its characteristic operational properties. The resulting composite is designated as Si-Mo TiC. Conventional Si-Mo cast iron is widely applied in the automotive industry, where it is used, for instance, in the production of exhaust manifolds and turbocharger components, where high resistance to thermal shock and excellent heat resistance are required. Transforming this material into a composite material improves many physicochemical parameters. Additionally, titanium desferoidizing effect helps stabilize graphite in the compacted (vermicular) form. Castings of both conventional Si-Mo iron and the TiC-reinforced Si-Mo composite with compacted graphite were produced with varying wall thicknesses. The microstructural characteristics and thermophysical properties, such as thermal conductivity and thermal stability, of the classical and composite materials were compared. The new Si-Mo cast iron reinforced with thermally stable TiC particles has been demonstrated to exhibit excellent structural integrity and thermal stability.

Steelmaking slag contains valuable components. Its high phosphorus content hinders its reutilization in the steelmaking process. This study proposes an efficient phosphate removal process using molten CaCl₂ as the reaction medium, aiming to enable slag recycling and P recovery. Experimental results show that nearly all P-bearing phases in steelmaking slag are leached into molten CaCl₂ under the tested conditions (850 to 1000 °C, slag/CaCl₂ mass ratios 1:10 to 1:2.5). The leaching mechanism involves the reaction of slag's P-bearing phases with CaCl₂ to form intermediates (Ca₂PO₄Cl and Ca₃SiO₄Cl₂), which dissociate into PO₄^3– and other ions in the melt. For other elements: Si(IV) leaches continuously but incompletely; Fe(II) and Mn(II) concentrations in the melt first increase then decrease, attributed to the evaporation of volatile FeCl₂ and MnCl₂; Mg and Al remain nearly unleachable. After leaching, adding carbon to the P-enriched melt achieves complete P(V) removal via carbothermal reduction. This molten CaCl₂-based approach provides a sustainable alternative to conventional technologies, offering valuable insights for the comprehensive utilization of P-bearing solid wastes.

The formation and evolution of plastic strain concentration zones and surface damage introduced by tensile testing of dual-phase steel were investigated by tracking precise markers on the specimen surface using electron beam lithography and a focused ion beam (FIB). Following tensile test at a stress approaching the tensile strength, areas of concentrated plastic deformation and extremely dark surface cracks (surface damage) appeared on the specimen surfaces. Regions of strain concentration with equivalent plastic strain exceeding 0.15 were identified from the displacement of precise markers. These regions appeared within the ferrite, near the ferrite-martensite interface, and within the martensite. Within the ferrite and at the ferrite-martensite boundary, strain concentration due solely to plastic deformation was observed, rather than displacement due to surface damage. The Taylor factor for ferrite grains within these strain concentration areas tended to be lower than those for ferrite grains within the surface damage regions. Furthermore, after we applied the new markers via the FIB and performed additional tensile testing until fracture, new plastic deformation concentration zones appeared within the ferrite, and the Taylor factor of the ferrite was relatively low. The Taylor factor is determined solely by the crystallographic orientation of the ferrite and the tensile deformation conditions. The effects of the ferrite crystallographic orientation on the ductile fracture process were also examined.

COREX shaft furnace adopts screws and corresponding guiding flow insert for burden discharge. To understand and then control burden flow in the furnace, it is essential to study the influence of discharge conditions and other factors on granular flow. Common CFD method cannot predict the orientation and size of stagnant zone formed by discharge in lower part of the furnace and thus is not easy to reasonably examine the effect of distribution of discharge conditions. Although the influence of discharge conditions could be studied by DEM, numerical studies of COREX shaft furnace by the method had obvious deviations in predicting descent velocity and resident time of burden in the furnace due to limitation of computational cost. In this paper, appropriate boundary conditions were used to describe lower screw discharger and guiding flow insert in moving bed, and a new CFD method based on novel potential flow model was used to numerically study 3D granular flow field including stagnant zone in a physical simulation bed of COREX shaft furnace. With the movement times of granular materials in bed reasonably predicted, the influences of not only screw discharger and guiding flow insert but also shaft angle of furnace on granular flow were investigated by the method in detail. Present work may provide a more reliable numerical basis for studying and then controlling burden flow in COREX shaft furnace.

Material applied in low-temperature liquefied gas storage tanks is required to have sufficient toughness. In recent years, high Mn austenitic steel has attracted attention for use in this application. In this study, the basic deformation characteristics and toughness of high Mn steel containing about 25% Mn were compared with those of 9% Ni steel in order to investigate the applicability of high Mn steel to LNG tanks. The high Mn steel showed larger uniform elongation than the 9% Ni steel due to higher strain-hardening, but elongation after the maximum load was significantly smaller. The plastic flow stress of the high Mn steel increased with decreasing temperature and showed temperature dependence similar to that of 0.2% proof stress in the 9% Ni steel. The Charpy absorbed energy of the high Mn steel was about half that of the 9% Ni steel, with an average value of 86 J at 77 K. Cleavage fracture surfaces were not observed in the fracture surfaces obtained at any temperature, indicating the micro-void coalescence type of fracture. The characteristics of ductile damage in the high Mn steel were discussed based on observation of micro-voids.

The objective of this study was to predict the hydrogen content entering steels during immersion in NaCl solutions, using finite element method (FEM) simulations. FEM simulation models were constructed by appropriately defining the boundary conditions for electrochemical reactions, diffusion coefficients of chemical species, and dissolved oxygen concentrations. The simulated polarization curves for carbon steel in various NaCl solutions were in good agreement with experimental results, indicating the high accuracy of the simulation models in representing actual phenomena.

Based on FEM simulations, the cathodic current for the hydrogen evolution reaction (HER) increased as the solution pH decreased. In particular, the HER cathodic current at pH 1 was approximately twice as large as that at pH 2. Considering that the HER cathodic current is correlated with the amount of hydrogen entering the steel, it is predicted that the hydrogen content entering steel at pH 1 is twice that at pH 2. This prediction was well supported by experimental thermal desorption spectroscopy results, suggesting that calculating the HER cathodic current by FEM simulations is an effective approach for predicting hydrogen entry behavior in steels.

This research aimed to investigate the influence of Fe-based addition on the solution-loss kinetics of coke in hydrogen-enriched blast furnace. The solution-loss reactions of base coke (BC) and Fe-based coke (BC+Fe) in the CO₂ + 20%H₂O atmosphere across the temperature 1000-1200 °C were carried out by a homemade coke reactivity measurement device with continuous water inflow. The kinetics of the Boudouard reaction (C + CO₂ = 2CO) and the water-gas reaction (C + H₂O = CO + H₂) were assessed by monitoring the outlet gas composition (CO and H₂) to quantitatively evaluate the catalytic influence of Fe₂O₃ on the solution-loss reaction. The results indicate that the solution-loss rates of BC+Fe coke are more those of BC coke, and the solution-loss ratios of BC+Fe coke are 10.5-26.8% for the Boudouard reaction and 12.1-42.2% for the water-gas reaction higher than those of BC coke. Furthermore, Fe₂O₃ lowers the apparent activation energy (E_a) of the Boudouard reaction by 4.2% and that of the water-gas reaction by 7.8%, which shows that the catalytic effect of Fe₂O₃ is stronger for the water-gas reaction than for the Boudouard reaction. SEM analysis shows that the BC+Fe coke has a more varied pore structure and wider range of pore sizes on the surface. XRD analysis indicates that Fe₂O₃ reacts with Si and Al species in the minerals to form Fe-based silicates and aluminosilicates, which could contribute to the catalytic effect of the coke solution-loss reaction.

This study has analyzed the growth and removal mechanisms of Al₂O₃, MgO, MgAl₂O₄, ZrO₂, SiO₂, and Ti₃O₅ inclusions in molten steel formed through the addition of various deoxidizing elements by dividing them into single inclusions and cluster inclusions resulting from the agglomeration of these inclusions with a focus on kinetics. Additionally, we have evaluated the maximum particle diameter of cluster inclusions from both thermodynamic and agglomeration force perspectives to examine the agglomeration properties and mechanisms of various inclusions. The growth mechanism of various single inclusions, measuring several micrometers in diameter and suspended in molten steel, is governed by Ostwald ripening with collision agglomeration due to Brownian motion and turbulent stirring. Contrarily, cluster inclusions with diameters of 10 µm or more float in molten steel agglomerate with suspended single inclusions. Depending on the inclusion type, they also agglomerate with other clusters along their floating paths, growing larger and undergoing floating separation. Furthermore, the agglomeration strengths of various inclusions in molten steel follows the order MgO < Ti₃O₅, SiO₂ < MgAl₂O₄ < ZrO₂ < Al₂O₃. The kinetic mechanism of agglomeration growth is explained in a unified manner by the interparticle interactions of agglomeration force driven by cavity bridge forces.

The effect of B on the surface oxidation behavior and phosphatability of cold-rolled steel sheets was investigated using 0.001 wt% B-added and B-free steels containing 0.6 wt% Si and 2.0 wt% Mn. The specimens were annealed at 800 °C in a 5 vol% H₂-N₂ atmosphere with a dew point of -50 °C. The surface oxides of the annealed samples were analyzed by GD-OES, FT-IR, SEM-EDX and TEM. The annealed steel sheets were then subjected to zinc phosphate treatment, and the effect of the surface oxides on phosphatability was evaluated by SEM-EDX. In the initial stage of annealing, fine granular Mn₂SiO₄ mainly formed and film-like SiO₂ partly formed on both steels. As the soaking time at 800 °C increased, the granular Mn₂SiO₄ increased in the B-free steel. In contrast, in the B-added steel, the granular Mn₂SiO₄ coarsened, MnSiO₃, MnO and B₂O₃ formed, and the film-like SiO₂ formation area expanded. Addition of B reduced the melting point, causing coarsening of Mn₂SiO₄, exposing the base steel. This results in a difference in the oxygen potential between the exposed area of the steel and the oxide covered area. This local inhomogeneity of the oxygen potential changes the surface oxide species of the B-added steel. To elucidate the reason for the poor phosphatability of the B-added steel, a SEM-EDS analysis of the steel surface in the initial stage of zinc phosphate treatment was conducted, revealing that the coarse Si-Mn complex oxides and large film-like SiO₂ inhibited the zinc phosphate reaction.

The reactivity of metallurgical coke is a key contributory factor to its integrity in the ironmaking blast furnace. Herein, the factors that influence the CO₂ gasification reactivity of individual coke inert maceral derived components (IMDC) and reactive maceral derived components (RMDC) were examined, including: Parent inertinite types, degree of microtextural anisotropy, accessibility of the IMDC; and ash chemistry.

Individual IMDC and RMDC components were formed by coking inertinite group concentrates (IC) and vitrinite group concentrates (VC), respectively. Cokes were also formed from head coals and by using different proportions of IC and VC in the coking blend. Coke lump and intrinsic gasification kinetics were compared for each case, where "intrinsic" refers to the gasification behaviour of powdered samples. The most influential factors on which the reaction rate was dependent were distinctly different between lump and powdered samples. The degree of isotropy of the carbon structure was the most important parameter controlling coke lump gasification kinetics with CO₂ at 1100 °C, followed by the basicity index of head coal. Conversely, intrinsic reactivity was closely correlated with microporosity.

Importantly, the isotropy of the carbon structure was not found to be a critical parameter controlling the intrinsic gasification kinetics up to the 40 % carbon conversion point. These results suggest that in the lump form where gas diffusion limits the reaction rate, carbon structure and catalytic effect of coke minerals play the dominant role in coke gasification. Such behaviour leads to a selective reaction of gas with IMDC in coke lumps due to the isotropy of carbon and greater association with minerals.

Utilizing the greater momentum inertia and higher specific surface area of powder lime, top-blown CaO-O₂ technology has been proposed to further improve the mixing ability of the molten bath and to increase the slagging rate in the Basic Oxygen Furnace (BOF) steelmaking process. This research presented the development of a simulation model designed for investigating the effect of centre CaO-O₂ mixed injection method on the flow field within the molten bath. The result showed that, compared to the traditional jet, the CaO-O₂ jet improved axial impaction ability of top-blown jet, while reducing its impaction ability in the radial direction. Furthermore, the CaO-O₂ jet not only improved the impaction depth, but also exhibited a smaller decrease rate in impaction depth as the lance height increased. In the conical protrusion area, a greater amount of kinetic energy from the CaO-O₂ jet was transferred into the molten bath, which enhanced the dynamic condition within the molten bath.

To address the critical problem of erosion and rupture in the tundish weir, this study employs numerical simulation to systematically explore the effects of casting speed, the distance between the weir and the long nozzle, and the distance between the weir bottom and the tundish bottom on upstream impact stress distribution. An optimization strategy to mitigate weir impact stress is proposed. The results show that the impact stress on the weir upstream surface increases with casting speed. A greater distance between the weir and the long nozzle significantly increases the average impact stress at the upstream bottom, while a larger distance between the weir bottom and the tundish bottom gradually decreases it. For the 65-ton two-strand slab tundish, under the conditions of the casting speed being 1.5 m/min, the distance between the weir and the long nozzle being 1 200 mm, and the distance between the weir bottom and the tundish bottom being 300 mm, the impact stress on the upstream surface of the weir is minimized, the average residence time of molten steel in the tundish is extended, and the metallurgical performance of the tundish is significantly improved.

Pearlitic steels achieve an exceptional balance of strength and ductility through the lamellar stacking of ferrite and cementite. While this synergy enhances mechanical performance, cementite also serves as a preferential site for crack initiation, making its thickness and the extent of deformation localization caused by dislocation pile-ups critical factors in the plasticity–fracture transition. In this study, molecular dynamics simulations were performed to clarify how cementite thickness and dislocation pile-ups govern deformation and fracture. The results reveal that thinner cementite or smaller pile-ups promote dislocation emission across the interface, whereas thicker cementite and larger pile-ups facilitate crack initiation within cementite. Comparison with a conventional continuum model showed qualitative agreement but also highlighted nanoscale effects—such as core relaxation of penetrated dislocations in cementite—that are beyond continuum descriptions. These findings provide atomistic insights into the mechanisms controlling the plasticity–fracture transition in pearlitic microstructures.

This study systematically investigates the reduction behavior of biochar-containing briquettes under varying heat-treatment parameters (temperature, time, and C/O ratio), with a focus on metallization rate, mechanical strength evolution, and microstructural transformations. The results indicate that with increasing heat-treatment temperature, the strength of the biochar-containing briquettes first decreases then increases. Within the 600-800 °C range, the Fe₃O₄ phase remains stable, wherein carbonaceous networks derived from binder carbonization effectively preserve structural integrity. The critical 900-1100 °C interval exhibits significant strength deterioration, attributed to attributed to lattice distortion induced by the Fe₃O₄→Fe_xO phase transition and proliferation of iron whiskers. Above 1100 °C, the onset of metallic iron nucleation enhances strength (up to 0.68 MPa  ) and achieves a metallization rate of 91.97%. A 40-minute holding time at 1100 °C further increases reduction efficiency from 69.36% to 87.64%, driven by the formation of a dense metallic iron network. The C/O ratio exerts a pronounced influence: high-C/O-ratio (0.8) briquettes develop porous architectures due to gas escape, yielding 40% lower strength than low-C/O-ratio (0.4) specimens. Conversely, the limited reducing agents at C/O = 0.4 restrict metallization to even 68.7% at 1150°C. These findings validate potential of biochar as a sustainable reductant substitute, establishing technical prerequisites for low-carbon ironmaking through optimized biochar-containing briquettes production.

This study systematically investigates the dual effects of Sb on the oxidation behavior of 65Mn steel, combining laboratory experiments with industrial-scale validation. Key findings demonstrate that Sb additions significantly suppress both continuous and isothermal oxidation, with 0.03 wt% Sb reducing mass gain by 15.9% (continuous oxidation) and achieving maximal suppression of 85.2% at 800°C (isothermal oxidation), while increasing the oxidation activation energy from 184.0 kJ·mol^-1 (Sb-free) to 200.7 kJ·mol^-1. Notably, Sb nearly eliminates IGO at the "nose temperature" of 777.6°C, where IGO depth peaks at 18.5 μm in Sb-free specimens. However, excessive Sb (0.21 wt%) induces hot shortness due to grain boundary segregation of low-melting-point Sb-rich phases (Fe-ε(FeSb) eutectic phase), causing edge cracking during hot rolling, where industrial trials reveal local Sb enrichment exceeding 26–29 wt% at crack sites (>120× bulk content). Incomplete descaling coverage‌ at edge regions ("descaling shadow zones") combined with localized ‌undercooling‌ (ΔT ≈ 120°C) promotes Sb enrichment beyond its solid solubility limit, which elucidates why Sb-induced cracking occurs exclusively at strip edges. Mechanistically, Sb enrichment at oxide/substrate interfaces blocks Fe^2-/O^2- diffusion, while its volatility prevents stable oxide formation, creating a kinetic barrier. The study identifies an optimal Sb content of 0.03 wt% that balances oxidation inhibition (IGO suppression >90%) with hot shortness.

A hydrogen visualization technique based on Prussian blue (PB), a fully reversible hydrogenochromic material, was developed for detecting hydrogen distribution in a pure Fe sheet. A PB layer was electrochemically formed on a Pd-coated Fe sheet. The Pd intermediate layer acted as a catalyst for the reduction of PB by hydrogen atoms diffusing through the Fe sheet. During hydrogen charging, the PB layer exhibited a color change from deep blue to light blue, effectively visualizing the hydrogen distribution in the Fe sheet. The color gradually recovered in air via oxidation by O₂ in air, and the color restoration was significantly accelerated by heating at 70°C. The PB layer exhibited excellent reversibility of color change over multiple hydrogen charging and heating cycles. This study highlights the potential of PB as a reusable sensor for the in situ monitoring of hydrogen distribution in metals.

Fatigue crack initiation and subsequent crack propagation behaviour in as-quenched low-carbon low-alloy steel were examined using a rotating-bending fatigue test and electron backscatter diffraction analysis to clarify the relationship between the fatigue limit and the microstructural heterogeneity of martensite. The as-quenched low-carbon low-alloy steel exhibited a low fatigue limit relative to its ultimate tensile strengths. The fatigue fracture was originated from slip deformation due to dislocation glide in the matrix. Furthermore, a tensile test revealed a low elastic limit in the steel, which can be explained by the movement of high-density mobile dislocations introduced during the transformation. These findings suggest that the low fatigue limit of as-quenched low-carbon low-alloy steel is due to its low elastic limit. Fatigue cracks initiated at prior austenite grain boundaries (PAGBs), at packet boundaries, and parallel to the block boundaries. These crack initiations were triggered by the preferential activation of slip systems parallel to the habit plane in the coarse martensite, which was nucleated at the PAGBs in the early stage of transformation and satisfied the Kurdjumov–Sachs orientation relationship (K–S OR), with not only its own parent austenite grain but also the adjacent austenite grain (i.e. the double K–S OR). Additionally, the initiated cracks were arrested at the fatigue limit. This is probably due to plasticity-induced crack closure stemming from the significant plastic deformation of the early transformed coarse martensite.

In the steelmaking process, lime is usually fed into the bath as a lump through the charging holes at the top of the furnace, the slag-making material floats on the slag surface, and the melting speed is slow, resulting in deep dephosphorization of molten steel is difficult. In order to improve the kinetic conditions of the molten pool and increase the velocity of the powder impacting the molten pool, this paper designs a cluster-type oxygen lance containing supersonic gas-solid blowing, which effectively solves the above problems. The jet law of supersonic gas-solid blowing oxygen gun is investigated by numerical simulation with the following results: i) Supersonic gas-solid injection reduces the peak velocity of the gas-phase jet but effectively mitigates the decay of the gas-phase velocity and extends the jet length; ii) The low-temperature gas in the center of the jet acquires energy from the high-temperature environment generated by the external ring-seam gas through convection, and thus expands sufficiently to provide sufficient energy for particle acceleration; iii) When the powder particles are larger than 0.3 kg/s, the gas-solid jet will flow at subsonic speed, greatly reducing the ability to accelerate particles, the design of supersonic gas-solid spray gun need to consider the appropriate powder-gas ratio. These findings will provide a certain research basis for supersonic lime powder delivery in the steelmaking process, which is of significance for efficient dephosphorization smelting with less slag in electric arc furnaces.

We employed the high-resolution digital image correlation study to investigate the plastic deformation of low-carbon lath martensite. The strain localization bands were mainly categorized into two types: boundary slips and intra-block deformation. Misorientation angle and inclination angle with respect to loading direction primarily determines the slip activation at boundaries. The competitive relationship between the activation of in-lath-plane and out-of-lath-plane slip systems follows the Schmid effect. The in-lath-plane slip systems were only activated in blocks with high in-lath Schmid factor (SF) value. The out-of-lath-plane slip systems were activated only when its SF is much higher than the maximum in-lath SF, offsetting the effect of the higher critical resolved shear stress (CRSS) for in-lath-plane slip systems. Moreover, the block morphology also affects the slip activation behaviour: in-lath-plane slip systems in columnar blocks were preferentially activated due to both crystallographic dynamics and strain accommodation. In contrast, out-of-plane slip systems were only observed in equiaxed blocks where the boundary effect is weakened.

A deep understanding of the chemical structure evolution during coal pyrolysis and coking is crucial for expanding coking coal resources and developing more rational coal blending schemes. Two samples of fat coal at different pyrolysis stages were prepared by using a thermogravimetry-plastometer-swelling pressure apparatus and a muffle furnace. The samples were characterized by FTIR, ¹³C NMR, XRD and Raman spectroscopy to systematically investigate the evolution of the carbon structure during pyrolysis. The results indicate that the Feibei sample, which contains a higher content and longer length of aliphatic side chains, exhibits a slower formation rate of aromatic ring systems with≥6 rings in the later stages of pyrolysis. During the pyrolytic coking process of both coal samples, the content of aliphatic structure groups initially increased and subsequently decreased. Meanwhile, the aromatic ring systems underwent three distinct stages: initial longitudinal stacking dominated by 3-5 rings, followed by lateral expansion into larger systems comprising≥6 rings, and subsequent vertical growth centered on≥6 ring architectures, accompanied by a continuous reduction in the d₀₀₂ of the carbon microcrystals. This study elucidates the evolution pathway of aromatic carbon structures during the pyrolytic coking of the tested coal samples.

This report describes improved X-ray fluorescence analysis to quantify chromium as a major constituent of stainless steel and cobalt–chromium alloy samples. Stainless steel can be digested rapidly using hydrochloric and nitric acids, including aqua regia, for wet chemical analyses using atomic absorption spectrometry, inductively coupled plasma atomic emission spectrometry, and inductively coupled plasma mass spectrometry. Nevertheless, because of chromium volatilization as chromyl chloride in fusion processes during glass bead preparation, this acid digestion is inapplicable for glass bead specimens of chromium-containing materials intended for use in X-ray fluorescence spectrometry. For the work described herein, microwave digestion using nitric and hydrofluoric acids was used to prepare appropriate glass bead specimens. The X-ray absorption and enhancement were negligible for the present glass bead specimens. An extremely high 2000-times dilution of 4000 mg lithium tetraborate and 2 mg sample was used. Reliable analytical values of chromium were obtainable using the suggested X-ray fluorescence analysis without matrix correction calculation.

This study presents a semi-analytical model to accurately predict roll force and setup roll gap (G_set) in the finishing stage of H-beam rolling. The model modifies Sims' classical strip rolling formula to capture the unique geometric and deformation characteristics of H-beam sections. The cross-section is divided into web and flange regions using a rectangular approximation. A geometry-dependent correction function is then introduced to account for the effects of reduction ratio, reduction balance, and contact geometry. This function is calibrated through finite element (FE) simulations under varying rolling conditions. Parameters such as web and flange thickness reduction, junction radius, and flange inclination are systematically adjusted, and the resulting roll forces are used to optimize the function via the Nelder–Mead method.

The model is validated using two H-beam specifications from Hyundai Steel. Compared to the company's empirical model, the proposed model reduces web and flange thickness deviations by up to 71%, demonstrating improved prediction accuracy. Statistical analysis also shows substantial reductions in standard deviation and mean error, confirming better dimensional control. This semi-analytical model provides a fast, reliable alternative to full FE simulations and manual adjustment procedures, improving both efficiency and product quality in industrial H-beam rolling.

The rotary hearth furnace (RHF) process is widely employed for the efficient recycling of iron- and zinc-bearing dusts. However, the formation and deposition of secondary dust in the flue gas system significantly impair its operational availability. In this study, a laboratory-scale simulation of the RHF reduction process was conducted to collect and characterize the secondary dust formed under different temperature conditions. The distribution patterns and deposition behavior of secondary dust were systematically investigated. Results indicate that dust deposition predominantly occurs in the medium-temperature zone (873 ~ 1073K), where ZnO and alkali metal chlorides are the dominant components, accounting for up to 76.1% of the total deposited mass. The particle size of the secondary dust first decreases and then increases with decreasing flue gas temperature. The elemental composition of the secondary dust includes Zn, Pb, K, Na, Sn, In, O, and Cl. Specifically, the Zn content decreases from 73 mass% to 44 mass%, while Cl increases sharply from 0.2 mass% to 41 mass% as the temperature drops. Minor increases in K and Pb concentrations and a slight decrease in Na are also observed. Thermodynamic modeling was applied to interpret the phase transformations and deposition mechanisms at various temperature intervals. This study provides fundamental insights into the generation and deposition behavior of secondary dust in RHF systems, offering theoretical guidance for the mitigation of dust-related issues and improvement of process reliability in industrial applications.

The reduction disintegration index (RDI) of sintered ore, which is the main raw material of blast furnaces, greatly affects blast furnace operation. In order to improve RDI without deteriorating the reducibility index (RI), sintered ore having a CaO concentration of 20 mass%, which is higher than the conventional 10 mass% when using porous Australian iron ore, was produced, and its effects on the mineral structure, porosity, RI and RDI were evaluated.

In the sintered ore having a CaO concentration of 20 mass%, hematite decreased and calcium-ferrite (sum of other component system calcium-ferrite and binary calcium-ferrite), the SFCA-I/SFCA ratio and porosity increased in comparison with that having a CaO concentration of 10 mass%.

When Australian iron ore was used as a raw material for sintered ore, RI increased in sintered ore having a CaO concentration of 20 mass% compared with the one having a CaO concentration of 10 mass%. In addition, RDI was improved in the sintered ore having a CaO concentration of 20 mass% compared with the that having a CaO concentration of 10 mass%. This is due to the formation of binary calcium-ferrite instead of secondary hematite, which deteriorates RDI.

This paper introduces the implementation of an advanced intelligent billet distribution system at a recently built steel plant, specifically designed to address the complex challenge of synchronizing multi-strand continuous casters with three high-speed wire production lines through various integrated strategies in direct rolling scenarios. The residence-time model and C# language were used for simulation, offering real-time temperature control and dynamic adjustment capabilities that address variations in production conditions and process demands. The innovative approach of incorporating iron oxide scale trenches also significantly reduces maintenance and improves operational safety and environmental conditions. The latest statistics show that the average direct rolling rate has reached over 93%. The findings highlight the practical significance and potential of this system for wider adoption in the steel industry, providing an efficient and sustainable production solution that adapts to evolving market demands and environmental challenges.

Bloom continuous casting is widely used because of its high efficiency and superior product quality. Electromagnetic stirring (EMS) technology can improve casting quality and reduce defects. However, in bloom casting, the electromagnetic force generated by traditional mold electromagnetic stirrer (M-EMS) is comparatively weak. Moreover, these stirrers are often plagued by issues such as uneven distribution of stirring force, low energy efficiency, and considerable electromagnetic losses. To address these problems, this study introduced the cross-winding electromagnetic stirrer (C-EMS). By optimizing the magnetic circuit design and current control strategy, the C-EMS improved the distribution of stirring force and reduced electromagnetic loss. The results showed that the maximum magnetic flux density at the center of the bloom for C-EMS was significantly higher than that of M-EMS and annular-winding electromagnetic stirrer (A-EMS) under the same current conditions. Moreover, the maximum electromagnetic volume force at the bloom corners for C-EMS was 34,586 N/m³, which was approximately 470% and 220% greater than that of the conventional and annular stirrers, respectively. Furthermore, the optimized C-EMS demonstrated a total electromagnetic loss of 18,470 W at 225 A, compared to the 19,121 W loss observed with the conventional winding at the same current. This design can enhance stirring efficiency, improve bloom quality, and significantly reduce electromagnetic loss, offering an energy-saving solution for bloom continuous casting.

As Sweden transitions to hydrogen-based steel production, excess O₂ generated as a byproduct of H₂ production through water electrolysis is likely to be available. This presents an opportunity to use extra O₂ for reducing fuel consumption during production of iron ore pellets. Considerable heat is released as magnetite is oxidised to hematite during induration. Increased O₂ content in the process gas is expected to accelerate the exothermic oxidation reaction, allowing faster intrinsic heating of the bed. This study examines various energy scenarios utilising O₂-enriched gas (40 vol% O₂) relative to a base case that uses low-O₂ gas (13 vol% O₂). The focus is the effects of the flow rates and O₂ contents in the inflow gas on the temperature development and physicochemical properties (oxidation degree and cold compression strength) of pellets across a 100-kg pot furnace bed. Enriching the inflow gas with O₂ has advantages with regard to the aforementioned properties. Notably, utilising O₂-enriched gas at a reduced flow rate (in this case, 30% less gas volume compared with the base case) enables improved heat distribution relative to the base case with low-O₂ gas. In addition to the effects on the energy and pellet properties, the microstructures are analysed with respect to the underlying oxidation mechanisms.

The thermophysical properties of four TWIP steels with varying Cu, Al, and Si contents were measured and compared with those of austenitic stainless steel and plain carbon steel over a temperature range of 25 to 1000 °C. The thermal expansion coefficient (β) of the TWIP steels was unaffected by alloying additions, averaging 22.87x10^-6 °C^-1, which is slightly higher than that of austenitic stainless steel (19.74x10^-6 °C^-1) and notably higher than that of plain carbon steel (12.61x10^-6 °C^-1). Density (ρ) decreased linearly with temperature across all compositions and was further reduced by higher Cu, Al, and Si contents due to the lower atomic mass of these elements compared with Fe, with Al showing the most pronounced effect in TWIP steels. Due to the high β of TWIP steel, the ρ reduction with increasing temperature was more pronounced in TWIP steel compared to that of conventional carbon steels and stainless steels. The specific heat capacity (C_p) of TWIP steels increased with temperature, showing a trend similar to that of austenitic stainless steel. Thermal diffusivity (α) and thermal conductivity (k) also increased with temperature but decreased with alloying additions, attributed to increased thermal resistivity by solute atoms. Among the alloying elements, Al had the strongest influence on reducing α and k, followed by Si, with Cu having minimal effect. Compared to other steels, TWIP steels exhibited significantly lower k and higher β, characteristics that may induce thermal stress and increase the risk of thermal cracking during rapid thermal processes such as welding, heat treatment, machining, casting, and hot forming.

SFCA-I, a form of silico-ferrite of calcium and aluminum (SFCA) in CaO-Fe₂O₃-Al₂O₃-SiO₂ system, is the key bonding phase for iron ore sintering and significantly influences sinter quality and carbon emissions in sintering process. The phase equilibria characteristics of SFCA-I are essential for the design and operation of iron ore sintering. However, most SFCA-I samples synthesized in laboratories currently lack SiO₂, indicating that the composition of SFCA-I lies within the CaO-Fe₂O₃-Al₂O₃ ternary system. In this study, the solid solution series, solid solution limits, and stable region of SFCA-I at 1200°C in air in CaO-Fe₂O₃-Al₂O₃ and CaO-Fe₂O₃-Al₂O₃-SiO₂ systems were revealed via phase equilibrium tests. The results indicate that the upper and lower solid solution limits of Al₂O₃ in SFCA-I are 1.31wt% (i.e., 1.67mol%) and 7.65wt% (i.e., 9.10mol%) at 1200°C in CaO-Fe₂O₃-Al₂O₃ system. With the increase of Al₂O₃ content, the upper limit of SiO₂ solid solution in SFCA-I is gradually decreased. The upper limit of SiO₂ solid solution in SFCA-I reaches a minimum value of 0.686wt% when Al₂O₃ content is 7.62wt% at 1200°C in CaO-Fe₂O₃-Al₂O₃-SiO₂ system. In addition, the XRD results prove that SFCA belongs to the solid solution of C(A,F)₃ series. The other phases encountered in the tests include Fe₂O₃, CF, C(A,F)₃, C(A,F)₂ and C₂(A,F). The relevant schematic and calculated phase diagrams are constructed. The position of SFCA-I in the CaO-Fe₂O₃-Al₂O₃ ternary system and the relations among SFCA, SFCA-I and the surrounding phases are presented.

In an extensive flow of studies on material fracture, fracture mechanics has successfully established engineering standards for the safety evaluation of structural components. Vital difficulties in theories have been the management of the crack-tip stress singularity and the existence of incipient crack(s). Plasticity complicates fracture theories, and understanding the microscopic process of fracture is crucial for material design. This paper aims to shed light on the role of plasticity throughout the entire fracture process, remarking mostly brittle-like fracture, both in theory and experiment. Lattice deterioration due to plastic deformation increases potential energy, a key concept in deriving fracture criteria. Studies demonstrating the maturing of strain-induced lattice defects, primarily vacancy clustering, are reviewed to play a crucial role, operating as void source in fracture as a precursor to crack initiation.

Strain localization due to microstructural inhomogeneities are remarked to characterize the material's susceptibility to fracture. The extent of strain localization, coupled with external and local stresses, provides favorable fracture paths through crack nucleation and extension, as exhibited in fracture surface morphology. However, a single type of morphology does not specify a fracture event, and its continuous transition during crack extension suggests operation of an essentially common mechanism between seemingly different morphologies.

Lattice defects generated during plastic deformation persist into later stages, and environmental variations alter dislocation configurations, generating vacancies. As a method to assess the intrinsic material's susceptibility, detecting the progress of lattice deterioration in response to cyclic stressing is proposed.

Building on our previously established trap-free lattice transport framework for Ni–X binary model alloys, we extend the analysis to multicomponent Fe–Cr–Ni austenite and systematically evaluate how Ni, Mn, and N influence lattice expansion, mechanical strength, hydrogen diffusivity, and hydrogen solubility under 100 MPa hydrogen within a temperature range of 160–270°C. Mn showed the most pronounced austenite lattice expansion, whereas N provided the strongest solid-solution strengthening. Ni increased hydrogen diffusivity as measured by the desorption method, while Mn and N had little effect. Across Fe–Cr–Ni and previously studied Ni–X systems, variations in diffusivity are primarily governed by changes in activation energy, with the pre-exponential factor remaining nearly constant across alloys within each system. Hydrogen solubility, assessed by thermal desorption analysis (TDA) after 100 MPa exposure, showed that Mn markedly increased solubility, whereas Ni slightly decreased it and N had a negligible effect. These alloying effects on solubility are also explained by changes in activation energy, consistent with a narrowly distributed pre-exponential factor. TDA spectra computed from the measured temperature dependence of diffusivity reproduced the experimental peaks for almost all alloys, indicating trap-free lattice diffusion; a shoulder observed for the Mn-rich composition suggests ordering-induced trapping during heating. The results highlight the distinct roles of the alloying elements: Ni accelerates hydrogen transport, Mn increases uptake, and N enhances strength with minimal impact on transport, thereby providing composition–property guidelines for hydrogen management in austenitic stainless steels.

Tensile test results obtained from millimetre- and micrometre-scale specimens were correlated using crystal plasticity analysis to examine the microstructural factors dominating the mechanical properties of the as-built maraging steel produced by the laser powder bed fusion (LPBF) method for repairing die-casting tools. Micrometre-scale tensile tests revealed that the mechanical properties of single prior austenite grain (PAG) structures are dominated by the deformation of the coarse block according to Schmid's law rather than by habit-plane-orientation-dependent slip deformation. This is owing to the low aspect ratio of the lath structure in the maraging steel produced by the LPBF method. In the millimetre-scale tensile specimens consisting of multiple PAGs in the gauge section, anisotropy of the ultimate tensile strength and elongation-to-failure was not observed, which was attributed to the high energy density in LPBF process. It was revealed that the specimen with the loading direction (LD) parallel to the build direction exhibited earlier work softening than the specimen with the LD perpendicular to the build direction, regardless of the energy density. This anisotropy was examined using crystal plasticity analysis with material parameters obtained through the fitting analysis of micrometre-scale specimens. The analysis results indicated that the anisotropic work-hardening behaviour related to the build direction was due to differences in the overall Schmid factor and the degree of lattice rotation, both of which stemmed from the texture. As the anisotropic mechanical properties observed in this study were insignificant, the application of the high-energy-density LPBF method to maraging steel is useful for repairing mechanical components.

The strength at 600 °C in fire-resistant steel exhibits a significant dependence on strain rate, likely attributed to a shift in deformation mechanism from slip deformation to grain boundary sliding (GBS) with increasing temperature. In this study, GBS was observed using a grid method, and the strain distribution introduced by a high-temperature tensile test in a carbon steel was visualized. The characteristics of the strain distribution in the grains composing the grain boundary where GBS occurred were discussed. Although the test temperature was 500 °C, high-temperature tensile tests with strain rates of 10^-3 and 10^-5 s^-1 orders were successfully conducted. Strain rate dependence of strength was comparably small at 500 °C. The discontinuous slide of the grid line at the grain boundary was observed after the tensile tests at 500 °C, regardless of strain rate, indicating that GBS occurred. The strain was distributed inhomogeneously during the high-temperature tensile tests. The grain boundary generating GBS lay 45 ° from the tensile direction and consisted of a pair of high- and low-strain grains. The m' value, which represents the ease of slip transfer between adjacent grains, was low at the grain boundaries generating GBS. This suggests that GBS was induced by pile-up dislocations at the grain boundary.

The detection of hydrogen that permeates the steel specimen is crucial in the study of the mechanism of hydrogen embrittlement. However, the applicable analytical methods have been limited. In this study, we developed an experimental system of photoelectron yield spectroscopy (PYS) measurements to detect hydrogen in steel. The PYS measurement can evaluate the work function of a specimen under atmospheric conditions by detecting photoelectrons emitted from its surface. The measurement system was applied to monitor the work function of the nickel-plated surface on the hydrogen detection side of iron during a hydrogen permeation test. The initial value of the work function was 4.72 eV, indicating the presence of nickel hydroxide on the detection side. It was found that the work function of the detection side decreased by 0.35 eV after the introduction of hydrogen. In addition, the shape of the photoelectron yield spectrum changed, indicating a mixed phase of the nickel hydroxide and other substances with a smaller work function. It demonstrated that the PYS can detect the hydrogen at the specimen surface and can be a powerful tool in the study of hydrogen permeation.

The intergranular crack growth in an Fe-25Cr-1.1N austenitic steel (in wt.%) was examined by in situ scanning electron microscopy and three-dimensional tomographic reconstruction based on Xe-focused-ion beam serial sectioning. The intergranular crack growth exhibited discontinuity, crack deflection/branching along {111}, and crack tip blunting. These features could be interpreted by considering the effects of planar dislocation slip that causes stress concentration at grain boundaries and Lomer-Cottrell sessile dislocations. The models explaining the intergranular cracking and associated crack deflection were proposed based on an assumption of intense planar slip and no cross slip until near-fracture, which was observed by in situ electron channeling contrast imaging under mechanical loading in the present study. In this context, because crack tip deformation is significantly constrained in the specimen interior (plain strain condition), the dislocation-driven intergranular crack growth occurred preferentially in the specimen interior, and subsequently, surface crack propagation occurs in a ligament portion. After blunting of the main crack tip, the coalescence of the main crack and planar-slip-induced brittle crack allows further crack growth.

By using finite element method for crystal plasticity, we investigated the accumulation behavior of dislocation and atomic vacancies introduced by non-uniform deformation in pure iron polycrystals. Dislocation density was calculated from the increment of plastic shear strain and spatial gradient of the slip systems for SS and GN dislocation densities. Vacancy density was calculated from the edge component of SS dislocation density and the incremental plastic shear strain by expanding the theory of Essmann and Mughrabi, in which atomic vacancies are released by the annihilation of edge dislocations, for each slip system. The cyclic loading analysis was performed under strain-controlled with 10 cycles between a tensile process up to 0.5 % nominal strain and a compressive process down to 0 %. For comparison, a monotonic loading analysis was also performed. The macroscopic mechanical responses were significantly different under the two conditions, and the work hardening rate under cyclic loading was less than half that under monotonic loading. The localization of plastic strain was more pronounced in the cyclic loading deformation than in the monotonic one. The low work hardening rate for cyclic loading deformation was attributed to the low accumulation of GN dislocations due to the relaxation of the plastic shear strain gradient caused by the load reversal. The average vacancy density was twice higher for monotonic loading deformation than for cyclic loading deformation. On the other hand, the maximum value of vacancy density was almost the same in both conditions, indicating that the cyclic loading deformation was more localized.

This study investigates the effect of Ca addition on the brittle-to-ductile transition (BDT) and grain boundary decohesion by S segregation in as-quenched low-carbon fully martensitic steel. Temperature dependence of the impact absorbed energy was examined in two kinds of steels with different Ca content (Ca-added steel and Ca-free steel). The BDT temperature of the fully martensitic steel was significantly decreased with the Ca addition. The temperature dependence of the 0.2% proof stress was measured to discuss the decrease in the BDT temperature based on shielding theory. The temperature dependence of 0.2% proof stress was compatible between the two steels, indicating that Ca addition did not affect the dislocation mobility regardless of the Ca content. Observations of brittle fracture surface revealed that intergranular fracture was prominent in the Ca-free steel, whereas it was suppressed in the Ca-added steel. Auger electron spectroscopy further revealed that S was segregated at prior austenite grain boundaries in the Ca-free steel. These results suggest that the improvement in low-temperature toughness in the Ca-added steel is attributed to the increase in surface energy for intergranular fracture, resulting from the suppression of S segregation by Ca addition.

The strain distribution developed during high-cycle fatigue bending tests exceeding 10⁶ cycles was visualized in 780 MPa high-strength steels with various microstructures using the digital image correlation (DIC) method for the secondary electron images of the specimen surface. The tensile stress was approximately identical among the steels with ferrite (F), bainite (B), and ferrite + pearlite (FP) microstructures. Microcracks were detected in the B and FP steels after the fatigue bending test, whereas no cracks were present in the F steel even after 10⁶ cycles. The strain distribution developed in the high-cycle fatigue bending test was successfully visualized using the DIC method for the first time. The strain was inhomogeneously distributed for up to 10² cycles even under an applied stress less than the yield stress. The average strain along the loading direction was approximately zero regardless of the number of cycles for all specimens. The standard deviation calculated from the strain histogram continuously increased with an increasing number of cycles for all steels. This suggests that strain gradually accumulated during the fatigue test. Microcracks tended to nucleate in high-strain regions. The plane of the microcrack was the slip plane, and its Schmid factor was high. Therefore, the microcracks were generated through intrusion and extrusion mechanisms with local slip deformation at the specimen surface.

The effects of stress, plastic strain, and hydrogen on hydrogen embrittlement fracture of hole-expanded transformation-induced plasticity-aided martensitic steel were investigated. The hydrogen embrittlement properties were evaluated by means of cathodic hydrogen charging to the hole-expanded specimen. The residual stress and plastic strain distributions in the hole-expanded specimens were analyzed using finite element analysis. The hydrogen content was measured using a thermal desorption spectrometer. Hydrogen embrittlement cracking occurred approximately 3 mm from the hole edge in the radial direction. As the crack propagated, it diverged in the circumferential direction. The fracture morphology primarily consisted of a mixture of intergranular and quasi-cleavage fractures. The tensile stress in the circumferential direction at the position where the hydrogen embrittlement crack was initiated was the highest, and the tensile stress in the radial direction and hydrostatic stress were also high. The hydrogen content in the vicinity of the hole edge of the hole-expanded specimen was the highest owing to the large amount of plastic strain applied by hole punching and hole expanding whereas the hydrogen content at the positions where the hydrogen embrittlement crack was propagated was not very high. Thus, the highest tensile stress in the circumferential direction is the controlling factor in the location of the crack initiation site and the direction of the initial crack and its growth during the initial phase. The high hydrostatic stress that causes hydrogen accumulation could also assist the crack initiation.

In this study, the effect of hydrogen on the spot-welded tensile shear strength of transformation-induced plasticity (TRIP)-aided martensitic (TM) steel sheet was investigated. The tensile shear tests were carried out on an Instron-type universal testing machine using the tensile shear specimen which was spot-welded at the lapped portion of 30×30 mm² using specimens with dimensions of width of 30 mm and length of 170 mm at crosshead speeds of 0.5-100 mm/min without and with hydrogen. The results were summarized as follows.

(1) The ultrahigh-strength TM steel without and with hydrogen charging possessed an excellent tensile shear stress (τ_f) in comparison with the hot-stamped (HS1) steel. This might be attributed to the TRIP effect of the TM steel which exhibits volume fraction of retained austenite of 1.52 vol% and low absorbed hydrogen concentration compared with that of the HS1 steel.

(2) The τ_f decreased with decreasing the deformation speed in the TM and HS1 steels with hydrogen, whereas the τ_f was hardly changed by the crosshead speed in the HS1 steel without hydrogen. The decrease in τ_f at slow strain rate might be caused by the occurrence of hydrogen diffusion to crack initiation site and crack tip to accelerate hydrogen embrittlement crack propagation.

(3) The hydrogen embrittlement crack was initiated at heat affected zone (HAZ) due to the hydrogen diffusion and hydrogen concentration at the HAZ which is softer than its surroundings, so the deformation is concentrated and HAZ becomes the origin of fracture, resulting in the stress concentration.

The warm V-bendabilities and hydrogen embrittlement properties of ultrahigh-strength Quenching and Partitioning (QP)-Transformation-Induced Plasticity (TRIP) steel sheets were investigated to apply the QP-TRIP steel sheets for automotive structural parts manufactured by cold or warm press forming. V-bending tests were carried out at a crosshead speed of 1 mm/min at V-bending temperatures of 25, 100 and 150°C using a hydraulic servo testing machine with a 88-deg. V-punch (punch tip radius R = 2 mm, R/t₀ = 1.7) and a V-dice (dice groove size l = 12 mm, dice shoulder diameter 0.8 mm) using V-bend specimens with dimensions of 5-mm width, 50-mm length and 1.2-mm thickness without and with hydrogen charging. Hydrogen charging was conducted by means of cathodic charging using a 3 wt% NaCl + 3 g/L NH₄SCN solution at a current density of 10 A/m² for 48 h before V-bending. The main results were obtained as follows.

(1) QP-A steel enabled to conduct V-bending at a V-bending temperature T = 25°C although the bending angle after unloading (θ₂) was less than 90-deg.

(2) When V-bending tests were carried out at T = 100°C, QP-B, C, and E steels without hydrogen and QP-B steel with hydrogen charging enabled to conduct V-bending. In addition, QP-B steel was also possible to carry out the V-bending at T = 150°C. These results implied that the V-bending at warm temperatures can improve the V-bendabilities of the QP-TRIP steels.

Strain-induced lattice defects that form during the incubation stage of hydrogen embrittlement fracture in the plastic region were quantified and their relationship with mechanical properties and fracture morphologies was investigated. Pure iron was subjected to plastic strain by tensile testing at various strain rates and hydrogen charging conditions. After charging tracer hydrogen as a probe for detecting lattice defects under conditions that reached equilibrium, specimens were quickly cooled with liquid nitrogen to prevent hydrogen desorption, and total tracer hydrogen was detected using low-temperature thermal desorption spectroscopy (L-TDS), which is capable of continuously elevating the temperature and subsequently performing measurement from that temperature. Dislocation density was not affected by the strain rate or hydrogen content. However, the vacancy concentration increased in the presence of hydrogen and displayed strain rate dependence even at the same strain level. A comparison of the mechanical properties with/without hydrogen showed that the flow stress with hydrogen increased with a decreasing strain rate compared with that without hydrogen, i.e., dislocation mobility decreased. It was established that strain-induced vacancies, which were excessively generated in the presence of hydrogen and formed complexes with it, were responsible for reducing dislocation mobility. Furthermore, fractures, albeit predominantly quasi-cleavage ones, along the {001} plane, which is the cleavage plane in body centered cubic iron, were present on the fracture surfaces, and their proportion increased with decreasing dislocation mobility. This suggests that vacancy-hydrogen complexes contribute to cleavage fracture by inhibiting dislocation motion.