Isij International最新文献

In steel rail production, complex deformations can induce non-uniform changes in cross-sectional profiles along the rail's length, resulting in unevenness and safety implications. It is essential to perform dimensional testing to ascertain compliance with standard requirements. Currently, profile inspection results are manually evaluated, posing efficiency challenges and a lack of standardized criteria.To address this challenge, this paper proposes an online automatic steel rail segmentation and evaluation method (online-ASE) based on pattern matching and complex networks to enable automatic rail profile assessment. This method initially utilizes offline high-dimensional time series data for conducting Toeplitz Inverse Covariance-based Clustering (TICC) training and constructs a standard quality characterization pattern library through distinct inverse covariance structures between abnormal and normal high-dimensional quality characterization indicators of steel rails. When applied online, the Viterbi shortest path dynamic programming algorithm is utilized to match steel rail data with the pattern library, swiftly identifying anomalous rail segments. Additionally, the algorithm computes the contribution of steel rail quality parameters to the segmentation results using complex network betweenness centrality, thereby explaining the reasons for segment formation. These explanations provide a reference basis for subsequent steel rail repairs. Finally, the effectiveness of the proposed method is validated using real-world steel rail data from a specific steel factory in China.

Vanadium composite electrogalvanized (Zn–V hydroxide) steel sheets were prepared by electroplating using a horizontal flow cell. The structure of the Zn-V plating layer depended on the flow rate of electrolyte and the current density, and the performance of Zn-V steel sheets depended on the structure of plating films. The Zn-V plating films composed of two-phase structure without cracks showed the high corrosion resistance and high adhesion. The two-phase layer consisted of the field-oriented fiber and non-field oriented texture. The field oriented fiber phase was mainly formed from the amorphous V compound. The V compound in the non-field oriented phase seems to hydrogen evolution during Zn-V composite plating. The Zn-V steel sheets had a black and low-gloss appearance compared to the conventional electrogalvanized steel sheet (EG). Since the V compound in the non-field oriented texture was black and the field oriented texture formed the surface roughness, the lightness and gloss of the Zn-V steel sheets decreased with increasing V content in plating films.

This paper reports an improved method for sample preparation of a stainless steel sample for inductively coupled plasma mass spectrometry. Conventional digestion methods using a digestion agent containing hydrochloric acid affect chlorine spectral interference such as that by ³⁵Cl¹⁶O⁺ or ⁴⁰Ar³⁵Cl⁺. Alternatively, a microwave digestion method using an acid mixture of nitric acid and hydrofluoric acid can fully eliminate these interferences. The suggested procedure can contribute to more reliable quantification of titanium, vanadium, arsenic, niobium, tin, and antimony in stainless steel samples using a low-resolution quadrupole mass spectrometer.

The contribution of dislocation-slip stability and carbide precipitation morphology to the hydrogen embrittlement (HE) property of tempered martensitic steels with low and high silicon contents (L-Si and H-Si) and oil-quenched martensitic steel (As-OQ), was evaluated by conducting slow strain rate tests. The order of dislocation-slip stability was the H-Si specimen > L-Si specimen > As-OQ specimen. The H-Si and As-OQ specimens had finely dispersed carbides inside prior austenite (γ) grains, whereas the L-Si specimen had coarsely dispersed carbides inside prior γ grains and on the boundaries. Notched specimens were charged with hydrogen in a range of low (0.19-0.31 ppm), medium (1.04-1.49 ppm), and high (2.17-2.33 ppm) hydrogen contents. The H-Si specimen had the highest HE property under the three hydrogen charging conditions. With the low and medium hydrogen charging conditions, the HE property of the L-Si specimen was higher than that of the As-OQ specimen, whereas their HE properties markedly declined to a similar level under the high hydrogen charging condition. The HE property of the L-Si specimen with increased dislocation-slip stability by applying stress relaxation was equivalent to that of the L-Si specimen under the high hydrogen charging condition. These results revealed that increasing dislocation-slip stability improved the HE property in the range of low to medium hydrogen charging. Under the high hydrogen charging condition, dislocation-slip stability did not contribute to improving the HE property, but it was found that the carbide precipitation morphology, particularly coarse carbides precipitated on prior γ grain boundaries, influenced the HE property.

An 11 mass% Cr ferritic/martensitic steel was subjected to a standard heat treatment consisting of normalizing and tempering and subsequently, a thermomechanical treatment (TMT) process involving austenization at 1100 °C for 1 hour, warm-rolling with 93% deformation at 650 °C and tempering at 650 °C for 1 hour. The precipitate phases of the TMT-processed steel were qualitatively analyzed using transmission electron microscopes and energy dispersive X-ray spectrometers in combination of lattice parameter calculation. Nb-rich MC carbides and Nb-rich M(C,N) carbonitrides pre-existing in the normalized-and-tempered steel were also observed in the TMT-processed steel. Eight types of precipitate phases introduced by the TMT were identified in the TMT-processed steel. They are Nd-rich MC carbide with a face-centered cubic crystal structure and lattice parameter a = 1.1408 nm, Cr-rich M₂C carbides/Cr-rich M₂X (Cr₂C type) carbonitrides/Cr-rich M₂X (Cr₂N type) carbonitride with a hexagonal crystal structure, Cr-rich M₇C₃ carbides/Cr-rich M₃C₂ carbide/V-rich M₂(C,N) carbonitride with a simple orthorhombic crystal structure, and Mn-rich M₅C₂ carbide with a base-centered monoclinic crystal structure. Among these identified precipitate phases, Nb-rich MC carbides, Nb-rich M(C,N) carbonitrides, Cr-rich M₂C carbides and Cr-rich M₂X (Cr₂C type) carbonitrides are dominant phases, while the other six precipitate phases are minor phases, in the TMT-processed steel. The identified precipitate phases are also discussed.

In this study, a non-isothermal reduction kinetics model has been developed for a single self-reducing iron ore pellet (SRP) to enhance the understanding of the reduction kinetics especially in the thermal reserve zone (TRZ) of the blast furnace (BF). The model simulates the mass changes and chemical processes during reduction, incorporating the effects of temperature, gas composition, and pellet composition on the reduction kinetics of different iron oxide phases, including Fe₂O₃, Fe₃O₄, and FeO. A mathematical model, comprising a comprehensive set of ordinary differential equations (ODEs), has been developed and solved using numerical methods and MATLAB software. The model has been rigorously validated against previous studies, specifically under non-isothermal conditions. It enables the calculation of mass loss and the reduction extent of specific phases of iron oxide, with the rate constant (k-value) curve across different temperatures. Moreover, the model adaptability is highlighted by its effective application in various BF conditions, as demonstrated by its use with data from the reference plants.

This work aims to study the effect of pH₂O in the atmosphere during hydrogen reduction of iron oxide over a temperature range relevant to industrial practice. To further the industrial context, industrially produced hematite iron ore pellets are utilized. A resistance heated furnace was employed to conduct experiments, in the temperature range 873 K – 1173 K. A water vapor generator was used to control water vapor partial pressure during hydrogen reduction in the range 0-15% pH₂O. The system was carefully designed to ensure precise control of the water content in the reaction gas. Thermal Gravimetric Analysis (TGA) was used to follow the reduction of the iron ore pellets. To understand the reaction mechanisms, Scanning Electron Microscopy (SEM) was used to study the microstructure of partially reduced pellets. Results suggest the reduction rate is profoundly affected by water at 873 K, less so when the temperature is increased. The microstructure is also highly affected by pH₂O at 873 K, at higher temperatures the microstructure is less affected. The influences of gas dilution and chemical reaction rate on these aspects are discussed.

In this study, to elucidate the agglomeration mechanism of various inclusions in molten steel based on their interfacial chemical interactions, the agglomeration forces exerted between the solid-phase oxides of MgO, MgAl₂O₄, ZrO₂, SiO₂, and TiO₂ in molten steel, in addition to those between the reference material Al₂O₃ have been measured directly. We experimentally verified for the first time that the agglomeration force due to the cavity bridge force in molten steel acts in a relatively stable manner between all solid-phase oxides that are difficult to wet with molten steel. Furthermore, this force decreased with increasing O concentration in molten steel, which is attributed to the interfacial activation effect caused by the adsorption of oxygen at the interface between the oxides and molten steel. The agglomeration properties of various oxide inclusions in the deoxidized molten steel were further evaluated from the perspectives of both agglomeration force and thermodynamics. Quantitative analysis indicated easy agglomeration of oxide inclusions in the order MgO < TiO₂ < SiO₂ < MgAl₂O₄ < ZrO₂ < Al₂O₃. A comparative evaluation of the agglomeration and external forces acting on the oxide inclusions in molten steel suggests that any oxide inclusion in the deoxidized state forms cavity bridges and agglomerates and retains that state under intense molten steel flow. However, these agglomerated inclusions may separate again under a molten steel flow at a high O concentration. The extent of separation depends primarily on the type of oxide used.

The influence of MC-type carbide formation on pitting corrosion resistance in weld metal of austenitic stainless steel was investigated. The relationship between the microstructure such as carbides and element distribution, and pitting corrosion resistance of the simulated weld metal of austenitic stainless steel was studied. The addition of molybdenum improved the pitting corrosion resistance. The effect of niobium addition on the pitting resistance was negligible. However, the addition of titanium significantly reduced the pitting corrosion resistance. The addition of niobium or titanium induced the formation of MC-type carbides, such as TiC and NbC, at the cellular boundaries. The pits were mainly initiated near or at carbides. The chromium depletion zone was formed near M₂₃C₆ coexisting with TiC only in the specimen added titanium. Thus, TiC formed during solidification accelerated the chromium diffusion-associated M₂₃C₆ precipitation on TiC. The depletion zone deteriorated the pitting corrosion resistance of the titanium-containing specimen.

This paper proposed an innovative electrochemical method for copper recovery from spent sulfide slag (Na₂S-FeS-Cu₂S), generated during copper removal from iron-based melts. It aims to reduce the high decopperization agents' consumption caused by low copper distribution ratio during the copper removal process, address the cost issues by recycle of slag and recovery of copper, and expand the application potential of the emerging copper removal method using the sulfide slag systems. The feasibility of electro-recovery of copper is verified by cyclic voltammetry tests and potentiostatic electrolysis experiments. The results show that in the Na₂S-FeS-Cu₂S melt, although copper cannot be reduced alone without reducing iron, rough separation can be achieved by controlling the temperature. The current efficiency of Cu⁺ reduction in the molten sulfide is about 9.1% due to electronic conduction in the sulfide melt, which needs further improvement. The slag treated by the innovative electrochemical process can be reused, as the XRD results show that it has a similar composition to the primary slag unused.