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The microstructure of the B1-type TiC formed during solidification and its mechanical properties were investigated using arc-melted Fe–Ti–C ternary alloys. The TiC formed at relatively high temperatures in the liquid as the primary phase exhibited a dendritic shape. With decreasing temperature and/or decreasing Ti and C content in the liquid, the morphology of the TiC changed to a cubic shape with a {001}_TiC habit plane, a plate shape with a {011}_TiC habit plane, and a needle shape with a preferential growth direction of <001>_TiC. The morphology of the TiC was characterized by the anisotropy of its surface energy and its growth rate. The cubic shape with a {001}_TiC habit plane was formed as a result of the {001}_TiC surface exhibiting the lowest surface energy among the TiC surfaces. However, the plate shape with a {011}_TiC habit plane and the needle shape with a <001>_TiC preferential growth direction likely formed because the slowest and fastest growth rates corresponded to the <011>_TiC and <001>_TiC directions, respectively. At room temperature, the alloy with dendritic TiC was fractured in the elastic deformation region because TiC exhibited no plastic deformation. However, the results obtained at 800°C suggested that the TiC exhibited plastic deformability and that the alloy with the dendritic TiC was also plastically deformed.

In the continuous casting process, the temperature of liquid steel in tundish determines the casting speed and secondary cooling conditions, and then influences the billet quality. It's very important to measure the temperature of liquid steel in tundish quickly and accurately. However, the initial response lag of blackbody cavity sensor is inevitable since the time is required for the sensor inner wall and the liquid steel reaching thermal equilibrium by heat transfer. In this paper, in order to eliminate the initial response lag of sensor, a heat transfer model of sensor is established. The heat transfer characteristics and cavity integral emissivity of sensor with different depths immersed into liquid steel are analyzed. The analytical solution of sensor temperature is derived by separation of variables method and superposition principle, and is verified by the actual temperature measurement data. Then an innovative method of liquid steel temperature rapid identification is deduced and validated by the actual measurement data. The results show that the initial response lag of sensor is greatly shortened and the temperature measurement efficiency is improved. This study provides a theoretical method for improving the initial response speed of sensor.

The interfacial tension between the liquid steel and molten slag is one of the key properties to control the entrapment of mold flux in molten steel in the continuous casting process. A dynamic change of the interfacial tension is observed when deoxidized iron and silicate slag are in contact, which can be explained by the oxygen absorption and desorption at the iron/slag interface. However, the dynamic change of the interfacial tension is influenced by other surfactant components of the molten iron and slag. Fluoride ions are fundamental component of mold flux, and recognized as the surface active component of molten slag. The effect of fluoride ions in slag on the interfacial tension has not been critically evaluated. Here, the effect of fluoride ions in slag on the interfacial tension between molten iron and molten silicate slag was evaluated at 1823 K, where the fluoride-containing slag compositions were designed to exhibit the same SiO₂ activity and slag viscosity as those of the fluoride-free slag. Compared with the case of molten iron and fluoride-free slag, the interfacial tension between the molten iron and fluoride-containing slag was initially lower. Except the effect of oxygen adsorption, fluoride ion was considered to directly decrease the interfacial tension. However, as the fluoride content in slag was higher, the interfacial tension tended to show the higher value at the final state. This behavior was attributed mainly to fluoride vaporization as SiF₄, which reduce the SiO₂ activity in slag and thus equivalent oxygen content at the iron/slag interface.

The increase of hydrogen usage in a blast furnace is expected to affect the reduction degradation of ferrous burden materials and influence the gas permeability inside the furnace. Previous studies show a disagreement on the effect of H₂ on reduction degradation, with the extent of degradation depending on the H₂ content and type of ferrous burden materials. In this study, the reduction degradation of sinter, lump, and pellet was compared using the reduction degradation test under different gas mixtures containing CO and H₂, covering the gas composition of conventional and H₂ injection blast furnaces. Lump (Newman Blend Lump NBLL) and pellets show a lower RDI_-2.8 than sinter under all the gas compositions tested. Higher RDI_-2.8 values were obtained for all burden materials with a reducing gas containing both CO and H₂ compared to CO or H₂ only. The addition of H₂ to CO increases the pore diffusion rate allowing reducing gas to reach the centre part of the particles, leading to the reduction of hematite to magnetite and subsequent crack formation across the whole particles. Compared to the conventional blast furnace case, NBLL lump and sinter show a lower degradation for the H₂ injection case while it was the opposite for the pellet, suggesting the necessity of reviewing overall burden materials to optimise the hydrogen injection in the blast furnace.

The hardness of martensitic steels with high M_s temperatures is reduced by auto-tempering after transformation, therefore the true hardness of martensite with carbon in fully solid solution is not known. In this study, we investigated a method to quantitatively evaluate the true hardness of quenched martensite unaffected by auto-tempering and the effect of auto-tempering was quantitatively evaluated by the diffusion area of carbon in bcc iron at temperatures below 400°C. As a result, it was clarified that the effect of auto-tempering is more pronounced in steels with an M₅₀ temperature higher than 300°C and that the softening behavior of martensitic steels can be uniformly evaluated regardless of the carbon content if the activation energy of carbon diffusion is known. Furthermore, it was clarified that the degree of auto-tempering can be quantitatively evaluated by calculating the integral diffusion area S (= ∑Dt) below the M₅₀ temperature during quenching.

Automotive suspension springs are required to be high-strength and lightweight, and currently have a maximum strength of 2000 MPa. In addition, they must have high resistance to hydrogen embrittlement in the service environment. From previous research, Si addition or rapid tempering improves the hydrogen embrittlement resistance of low alloy steel. In this study, we investigated the hydrogen embrittlement properties of steel samples with different Si contents and tempering rates and the effects of the fine iron carbides and retained austenite on its properties for 2000 MPa suspension spring steel. JISSUP7 (2.0Si) and SAE9254 (1.4Si) spring steels were tempered at different tempering rates by induction (IH) and furnace heating (FH) methods. Four-point bending tests under corrosion cycles were performed on these steels, and the time to failure was measured. The results show that the 2.0Si-IH steel with higher Si content and higher tempering rate has the longest fracture life and highest resistance to hydrogen embrittlement, even with relatively high diffusible hydrogen content. The size and volume fraction of iron carbides and retained austenite were evaluated by TEM, EBSD, and synchrotron XRD, and the 2.0Si-IH steels were found to have the smallest size and the highest volume fraction of fine iron carbides Fe_2-3C(ε) and the highest amount of retained austenite. It is considered that the fine iron carbides of Fe_2-3C(ε) work as hydrogen trap sites and that their high dispersion suppresses dislocation movement. They suppress hydrogen accumulation in stress concentrated areas and are expected to improve resistance to hydrogen embrittlement.

This study focuses on the fracture mode of 201 austenitic steel at room temperature (RT) and at -40 °C for one hour and three hours. The results reveal that at room temperature, the fracture is dominated by ductile behavior. At - 40 °C, the fracture mode is a mix of ductile and brittle behavior. Type 201 austenitic stainless steel has a low stacking fault energy value (about 16 mJ.m^-2 at RT), leading to the activation of the transformation-induced plasticity (TRIP) effect. When the sample is soaked at -40 °C for three hours, deformation-induced martensite transition (DIMT) formation with the volume fraction rises significantly to 19.9 %. At -40 °C for 3 hours, the alloy's impact energy absorption is reduced by 39%. The interaction of deformed austenite grains with previous austenite grain boundaries results in the formation of serrated grain boundaries in samples soaked at -40 °C. Serrated grain boundaries prevent crack propagation and reduce crack expansion at the grain boundary during the fracture of this alloy. The width of the crack at serrated grain boundaries is 38% less than that of the straight grain boundary.

This study reports a case of cold cracking along welds, which arises from solidification cracking within the crater during the laser welding of high-strength steel sheets. In this investigation, we aimed to delineate the factors influencing cold cracking that originates from solidification cracking in the crater. This was achieved by using steel sheets whose mechanical properties (tensile strength: 0.6 to 1.5 GPa) and chemical composition (carbon content: 0.20 to 0.55%) were individually adjusted. The evaluation method involved performing laser welding in a stitch pattern on an oiled steel sheet, with variations in welding length. The evaluation focused on the maximum welding length at which cold cracking occurred (L_MAX). The results indicated that while a high tensile strength of the steel sheet marginally increased the L_MAX, the impact remained limited. Conversely, the carbon content of the steel sheet significantly influenced cold cracking; the L_MAX for carbon contents of 0.30% and 0.45% was substantially greater than that for 0.20%. However, an unusual behavior was observed at a carbon content of 0.55%, where the L_MAX was smaller than that for 0.45%, despite the significant hardening of the weld metal. This phenomenon was hypothesized to occur because the tensile residual stresses in the welds decreased as martensitic transformation starting temperature lowered and the expansion strain during the transformation increased with higher carbon content.

Reasonable gas flow distribution plays a decisive role in the smooth operation of blast furnace smelting, but it is difficult to detect the gas flow distribution in blast furnace in real time. An intelligent prediction and identification system of central gas flow distribution based on infrared image of blast furnace and cross-beam temperature measurement is constructed(C-GFD). The system is mainly composed of two models, namely the image model and the prediction and recognition model. In the image model, three kinds of derived parameters, namely, central gas flow area, temperature and offset, are extracted by the image entropy and neighbourhood valley-emphasis (ENVE) Otsu, thermodynamic heat transfer and grey scale centroid algorithms, and then the statistical relationship between the change of image information and the distribution of gas flow is investigated. In the prediction and recognition model is established by the algorithms based on convolutional neural network long and short-term memory (CNN-LSTM) and Euclidean-weighted fuzzy C-mean clustering (E-FCM) to complete the prediction of the three types of derived parameters, and the prediction data is transferred to the recognition model to complete the recognition of the central gas flow distribution pattern. The test results show that the system provides real-time and reliable gas flow reference information for blast furnace operators with 95% accuracy in model prediction and more than 90% accuracy in pattern recognition of various types of central gas flow distribution.

To develop a H₂ production and CO₂ fixation process using scrap iron, the characteristics of iron and steel particles that react efficiently were investigated. The reaction of commercial pure iron and alloyed steel powders were compared, and their reactivity was evaluated based on the specific surface area, apparent density, and crystal lattice strain. The efficient reactivity in porous iron powders was attributed to crevice corrosion. To investigate the effect of alloy composition, we added Ni to pure iron powder by pretreatment, which resulted in enhanced H₂ production and CO₂ fixation. The results indicated that galvanic corrosion contributes to Fe oxidation, because Fe is less noble than Ni based on their electrode potentials. This study provides guidelines for improving the efficiency of reactions that produce H₂ while fixing CO₂ using steel scrap.