steel research international最新文献

The goal of this study is to provide new insights into the corrosion mechanism of core-shell carbides containing steels. The corrosion behavior of two heat-treated Cr–W–V–Mo-rich stainless steels is evaluated using electrochemical techniques. The studied steels have different carbides microstructure, the first has core–shell carbides (Cr₇C₃–Cr₂₃C₆) in a ferritic matrix, while the second has conventional Cr₂₃C₆ carbides in a duplex matrix. The open-circuit potential results show a nobler behavior of the duplex sample; it is noticed in the potentiodynamic polarization curves where the core–shell carbides containing steel have an oxidation peak at −0.37 V versus saturated calomel electrode with a current density of 0.19 mA cm⁻², contrary to the duplex steel that shows a passive behavior. Electrochemical impedance spectroscopy demonstrates the presence of two degradation mechanisms in the core–shell carbide steel, while the other steel is governed by charge transfer only. These findings are supported by scanning electron microscopy examination that shows the preferential corrosion of the shell while the core and the duplex matrix are kept intact. The passive film stability is evaluated using Mott–Schottky analysis and it shows the presence of a higher defect density on the passive film of the core–shell carbides containing steel.

This article focuses on the influences of austenitizing temperature and holding time on the grain sizes of 1800 MPa ultrahigh strength steel (UHS-1800). When the austenitizing temperature increases from 900 to 990 °C and the holding time is 5 min, the austenite grain size increases from 12.60 to 20.88 μm. When the austenitizing temperature is 930 °C and the holding time increases from 3 to 9 min, the grain size increases from 13.52 to 17.22 μm. When the austenitizing temperature increases from 900 to 990 °C and the holding time is 5 min, the radiuses of the second-phase particles increase from 15.23 to 25.36 nm. When the austenitizing temperature is 930 °C and the holding time increases from 3 to 9 min, the radius of the second-phase particle increases from 15.72 to 20.50 nm. On this basis, a prediction model for austenite grain growth suitable for UHS-1800 hot stamping process is proposed. The growth model of the austenite grain can accurately predict the grain growth behavior during the hot stamping process, with a maximum error of 5.35% compared to experiments.

The converter is a complex, high temperature, high pressure reactor with limited internal moitoring. At present, data-driven models mainly focus on the prediction differences between algorithms, and there is relatively little analysis of the impact of different hyperparameters on prediction accuracy. Taking a 120 t converter in a Chinese steel plant as an example, this paper explores the application of particle swarm optimization-back propagation neural network (PSO-BP) in converter temperature prediction. First, the Pauta criterion or Box plot method was used to preprocess the data by prescreening. Subsequently, the influence of the activation function, learning rate, and number of hidden layer nodes of BP on the prediction accuracy of the endpoint temperature were explored. Then we investigated the influence of PSO parameters on the optimal result of BP initial value. Comparing the temperature prediction hit rate before and after optimization, the BP model has hit rates of 63.64%, 79.22%, and 87.45% within ±10, ±15, and ±20 °C, respectively, and the PSO-BP model has hit rates of 68.40%, 84.85%, and 94.81%, respectively. In comparison, PSO-BP extracts data features more accurately, has higher stability, and has better accuracy in predicting the endpoint temperature of the converter.

An experimental investigation has been conducted with respect to the effect of permanent magnet stirring (PMS) under different rotation speeds (0, 60, 180 rpm) on the solidification of AH32 shipbuilding steel by analyzing the inclusion evolution, solidification structure, and mechanical properties. As the rotation speed increased from 0 to 180 rpm, the mean size of inclusions (Al₂O₃, MnS, and Al₂O₃–MnS) reduced significantly from 6.23 to 2.92 μm, their number increased from 49 to 82 n mm⁻² and the ratio of complex inclusions increased from 30.6% to 75.6% in the AH32 steel ingot. Besides, the increasing number of small complex inclusion promotes the formation of acicular ferrite in steel, resulting in an elevation of the area ratio from 10.5% to 27.8%. Furthermore, under a rotation speed of 180 rpm, the mean grain size decreased to 99.4 μm and the frequency of high-angle grain boundaries (HAGBs) increased to 86.1%. In addition, the as-cast AH32 steel exhibited an optimized ultimate tensile strength of 532.0 MPa and an improved elongation of 24.2% after an enhanced PMS, which was attributed to more acicular ferrite, higher HAGBs ratio, and refined grain size.

With the thinner of the automobile panel, the press crack defects caused by the large-size calcium aluminate inclusions at the automakers become obvious. Herein, in order to stabilize the control of calcium aluminate inclusions in the molten steel, the vortex slag entrainment (VSE) of a 300 ton ladle is investigated by the numerical simulation. The effects of the steel throughput, cofferdam height close to the nozzle, and ladle bottom structure on the VSE are analyzed. Results demonstrate that the residual molten steel (RMS) in the ladle and the critical height of the vortex increase with the increasing of the steel throughput. The RMS increases with the increasing of the cofferdam height when the VSE occurs. When the cofferdam height is 50, 100, and 150 mm, the RMS are 4.71, 7.19, and 9.62 t at the initial time of the VSE with a 7.5 ton min⁻¹ steel throughput. In addition, the industrial trial of transforming the flat bottom ladle into the slope bottom ladle is carried out to control the VSE and reduce the RMS. The average weight of the RMS after pouring 25 heats of the slope ladle bottom ladle is 1.85 t less than that of the flat bottom ladle.

In this study, the harmful effects of a banded structure on the bending fracture of electroplated fasteners are investigated. The origins and ways to control these structures are also explored. The fracture surfaces of the fasteners exhibit stepwise cracks and numerous intergranular facets associated with ductile tearing, which is a characteristic of hydrogen embrittlement. The origin of these stepwise cracks can be traced to the internal banded structures. Therefore, the internal banded structures promote fracturing during the bending test. The internal banded structures in the fasteners can be traced back to the internal cracks in the bloom, and inappropriate soft-reduction processes lead to internal cracks. Notably, the carbon segregation at the internal cracks is severe. This is attributed to the proximity of the internal cracks to the center of the bloom, causing the enriched liquid in the interdendritic region to be sucked into these internal cracks. The optimal reduction position and amount are determined by employing heat-transfer and soft-reduction models. Fluctuations in superheat and casting speed significantly influence this optimal position and reduction amount.

To clarify the strengthening mechanisms of medium-chromium stainless steels (SSs) with carbides, ferrite, and martensite, 17%Cr SSs with varying martensite contents have been prepared, and the influence of martensite on microstructure, mechanical properties, and fracture has been investigated. According to THERMOCALC calculations, 17%Cr SS undergo a reversible phase transition between austenite and ferrite + M₂₃C₆ through the diffusion of carbon in austenite and M₂₃C₆ in the temperature range of 850–1220 °C. As the martensite content increases, M₂₃C₆ decreases, the martensite grain size increases, and the ferrite grain size initially increases and then decreases. Meanwhile, the yield strength and ultimate tensile strength increase, while both the uniform and post-uniform elongation decrease. It is also found a decrease in work-hardening index and an increase in work-hardening rate with increasing martensite content. Under tensile loading, three types of voids are present in 17%Cr SS: type A only in the grain boundary (GB) area with M₂₃C₆ in martensite-free material and type B and C in ferrite grains close to martensite grains and at ferrite/martensite GBs, respectively. An increase in martensite content leads to more voids, indicating a reduction in material plasticity caused by martensite.

The recrystallization behavior of ferrite single phase in ultrahigh-strength low-alloy (UHSLA) steels, with different titanium concentrations (1000, 1500, and 2000 ppm) is presented. Utilizing detailed dilatometer tests, we identified disparities between the observed austenite onset temperatures and those predicted using the JMatPro 13 program and ThermoCalc. This study accentuates the combined effects of titanium, niobium, and reduced manganese levels on the initiation of the ferrite-to-austenite transformation. The Hall–Petch relationship was used to draw a correlation between titanium concentration, yield strength, and grain size. Moreover, we explored the recrystallization kinetics of these steels using the Johnson–Mehl–Avrami–Kolmogorov (JMAK) model, pinpointing titanium's crucial role in modulating the recrystallization dynamics. These findings have significant implications for advancements in steel manufacturing, enhancing the quality and performance of UHSLA steels in industrial applications.