steel research international最新文献

Ferritic–martensitic (F–M) steels are widely used for high-temperature pressure vessels and reactor cladding structures in power plants. The high operating temperatures and pressures, as well as the radiation environment, significantly challenge the mechanical stability of these steels. Here, the degradation mechanisms in F–M steels during creep and thermal aging under these harsh environments are reviewed. The exceptional mechanical properties of F–M steels are mainly attributed to their well-constructed microstructures and chemical compositions. Microstructural barriers such as dislocations, solid solution atoms, and precipitates play key roles in resisting degradation. During the long-term service, the microstructures undergo gradual evolution, resulting in a deterioration of mechanical properties at the macrolevel. In addition to the degradation mechanisms, some recent advancements in strengthening methods, including microalloying strengthening, thermomechanical treatment (TMT), and oxide dispersion strengthening, are summarized, aimed at the development of next-generation F–M steels. The strengthening of the F–M steels is mainly achieved by enhancing the thermal stability of their microstructures. Insight into both the deterioration mechanisms and strengthening methods of F–M steels may pave the way for new approaches in developing high-performance steels for applications in next-generation power plants operating at ultrahigh operating temperatures and pressures.

The impact of silicon and aluminum on phase transformation behavior, particularly bainite, and microstructure evolution in Fe–0.2C–2.5Mn steel are presented. Continuous–cooling–transformation (CCT) and time–temperature–transformation (TTT) diagrams are determined experimentally. An aluminum extended empirical formula is introduced to estimate the martensite start temperature (M_s) with a thorough assessment of existing formulae. Results show that aluminum significantly increases M_s and has a stronger influence on promoting ferritic microstructures than silicon. During continuous cooling, alongside bainite, formation of Widmanstätten structures is induced in aluminum-alloyed steel at higher cooling rates due to increased prior austenite grain size. Silicon decelerates bainite transformation kinetics by enhancing austenite's chemical stability through carbon enrichment via preventing carbide precipitation and by strengthening austenite against displacive phase transformation via solid solution hardening. Although aluminum has similar effects, incubation time is shortened during isothermal treatment because of the increased driving force, which overcompensates for the retardation effects. A finer carbide-free bainitic microstructure is achieved in aluminum-alloyed steel with more pronounced film-like retained austenite (RA) formation and superior carbon enrichment, improving RA stability and suppressing martensite–austenite island formation. Finally, with the proposed formula, an accurate approximation to experimental M_s is accomplished.

In this research, the reduction of iron ore sinter in a blast furnace (BF) simulator in CO–CO₂–N₂-reducing gas, simulating conditions at the BF center and wall, is investigated. Measurements from an operating BF guide the study, ensuring realistic reduction parameters. Reduction rate and extent, along with physical properties, are assessed under a temperature range of 700–1100 °C. In isothermal reduction experiments, the BF center exhibits superior conditions, particularly at 900 °C, achieving an 83.78% reduction degree compared to 27.17% at the wall for the same temperature. In this study, it is highlighted that basic iron ore sinter demonstrates higher reduction efficiency compared to acid iron ore pellets under identical BF center reducing conditions. Specific surface area and porosity measurements unveil a contrasting trend in specific surface area and porosity evolution between the BF wall and center. Surface morphology analysis reveals that the reduction in specific surface area and porosity of sinter samples at the BF center conditions at 1000–1100 °C is attributed to the sintering of the formed metallic iron. Carbon analysis confirms no carbon deposition took place during reduction. Mineralogical and physical property analyses provide detailed insights into the evolving phase composition during sinter reduction.

This study examines the dependent relationship between microstructure, mechanical properties, and corrosion performance on the wire arc additive manufactured (WAAM) ER2209 duplex stainless steel (DSS). DSS is renowned for its corrosion resistance and mechanical strength, making it favorable for various applications. This study uses the gas metal arc welding (GMAW)- based WAAM technique to fabricate the wall structure using ER2209 DSS filler wire. Fine, equiaxed dendrites are formed along the build direction, with the austenite phase exceeding 70% due to the repeated heating and slow cooling inherent to WAAM process. X-ray diffraction (XRD) confirms no brittle intermetallic phases. The results shows that varying austenite-ferrite fractions significantly influences the anisotropy in mechanical properties between build and deposit directions. Along the build direction, the varying phase fraction causes difference in hardness of 19.59 HV_0.3 and tensile strength of 20 MPa. The maximum tensile strength (787.08 MPa) is observed in the deposit direction, with a 52 MPa difference between the build and deposit directions. Tafel and EIS measurements indicated that WAAM samples corrosion resistance was almost close to wrought 2205 DSS. This study highlights WAAM's potential for defect-free DSS parts and suggests post-heat treatment to optimize microstructure and mechanical properties.

The oxide scale on the surface of hot-rolled low-carbon steel strips is subjected to isothermal reduction in 10 vol%H₂–Ar and 20 vol%H₂–Ar environments to simulate the reduction process that occurs in a continuous annealing furnace. The influence of hydrogen concentration on the reduction kinetics and the microstructural evolution of the oxide scale after reduction at temperatures ranging from 450 to 850 °C for a duration of 20 min are investigated in detail. The mass changes of the oxide scale in the two gases are quantified using a thermogravimetric analyzer. This data is then employed to calculate the reduction rate constant and the apparent activation energy. To examine the microstructure and element distribution, electron probe microanalysis and energy-dispersive spectrometry are employed. An novel approach is also undertaken to assess the reduction degree of the oxide scale by measuring surface microhardness. In the findings, it is indicated that an increase in hydrogen concentration served primarily to accelerate the reduction reaction within the temperature ranges of 450–550 and 800–850 °C. Meanwhile, the mechanism of physical transformation of oxide scale, the microstructure of reduction layer, and hydrogen concentration on reduction efficiency under different reaction stages are proposed.

The production of high-carbon hard wire steel at high speeds necessitates the use of appropriate technical support to ensure cost-efficiency and optimal performance of the special steel casting machine. This study investigates the industrial application of single-roller hard reduction technology in a domestic steel plant for the production of high-carbon hard wire steel billets, specifically of section 165 × 165 mm. The produced billets meet all customer specifications and demonstrate the benefits of this approach, including lower comprehensive costs, suitability for modification, and advanced technical concepts. These features make this method compatible with a wide range of billet casting machines, from standard to specialized. In this research, discussion is done on the reduction process, the layout of withdrawal and straightening units (WSUs), and the optimal casting speed. It is concluded that bow-type billet casting machines using rigid dummy bars can achieve single-roller hard reduction by only three WSUs, offering lower comprehensive costs and suitability for modification. This approach is particularly beneficial for small billet casting machines undergoing an upgrade from general to high-quality and ultimately to special steel. During the process of increasing the central density of the billet and improving central defects using single-roller hard reduction technology, it is observed that defects in the central region gravitated toward the center. For billet casting machines with a bow radius of 10 m, considering process tolerance, the maximum casting speeds achievable with single-roller hard reduction are 2.95–3.40 m min⁻¹ for a section of 150 × 150 mm, 2.60–3.0 m min⁻¹ for a section of 160 × 160 mm, and 2.45–2.80 m min⁻¹ for a section of 165 × 165 mm. To achieve higher casting speeds for high-carbon hard wire steel, it is necessary to modify the machine configuration to flexible dummy bars.

The steel/aluminum dissimilar metal welding plays a significant role in lightweighting automotive structures. However, the formation of hard and brittle intermetallic compounds (IMCs) in steel/aluminum welded joints severely compromises their mechanical performance. Nano ceramic particles such as TiC possess characteristics that inhibit the diffusion of Fe and Al, thereby exhibiting a significant advantage in suppressing IMCs formation in steel/aluminum welded joints. In this study, an optimized laser-welding process is employed to investigate the mechanical properties of steel/aluminum dissimilar metal joints with different concentrations of TiC nanoparticles. It is aimed to determine the optimal TiC addition concentration by comparing the mechanical performance. Additionally, the inhibitory effect of TiC particles on the formation and growth of brittle Fe–Al IMCs is explored through an analysis of IMCs growth kinetics. In the research results, it is shown that the optimal TiC addition concentration is 1%. At this concentration, the tensile strength of the steel/aluminum welded joint reaches 98.29 MPa, showing a remarkable improvement of 32.65% compared to the sample without TiC addition. The addition of TiC particles suppresses the mutual diffusion between Fe and Al, reduces the generation of brittle IMCs, and enhances the mechanical performance of the steel/aluminum joint.

The prediction of the martensite start temperature ($��M_s�$) for steels based on their chemical compositions is a complex problem. Previous work has developed empirical, thermodynamic, and machine learning models to estimate $��M_s�$. However, the empirical models are limited to specific steel grades, the thermodynamic models rely on different model assumptions, and the machine learning models are based on a small number of data, are limited to specific steel grades, as well or are not available for easy use to the public. Herein, a new machine learning model for the prediction of $��M_s�$ is developed on the basis of two publicly available datasets consisting of 1800 steels from different steel grades. Extensive hyperparameter tuning is performed to find the best artificial neural network for the dataset. The best model improves prediction accuracy compared to previous state of the art. Despite a very good prediction accuracy of the model, unexpected behavior is observed in specific unseen data. This opens up the discussion for the requirements of new metrics. The dataset and the model are freely available at https://github.com/EAH-Materials. An easy-to-use web tool to estimate $��M_s�$ without the need of programming based on the chemical composition can be found at https://eah-jena-ms-predictor.streamlit.app/.