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In this study, linear friction welding is applied to join JIS-S45C medium carbon steel with ferrite and pearlite structures at temperatures above and below the A₁ point. Additionally, low-strain-rate tensile tests are conducted both in air and with a cathodic hydrogen charge to evaluate the hydrogen-embrittlement susceptibility of the linear friction-welded joints under both joining conditions. Results of hydrogen thermal-desorption analysis show that the hydrogen-charging conditions in this study simulated atmospheric corrosion conditions. The joining zone of the above-A₁ joint comprises fine martensite and ferrite, whereas that for the below-A₁ joint comprises ultrafine ferrite and cementite. In air tensile tests, both joints fractured in the base-metal region, thus suggesting the high reliability of the joints. In the hydrogen-charged tensile test, the above-A₁ joints exhibit premature fracture at the joining zone. By contrast, the below-A₁ joints exhibit base-metal fractures, thus suggesting that the joints are highly reliable in a hydrogen environment. Fracture-surface observations show that the above-A₁ joints exhibit cleavage fractures in the martensite-dominated region. Tensile tests on heat-treated martensite S45C specimens show that their fracture strength decreased significantly in a hydrogen environment. Therefore, the joint fracture is due to the significant decrease in the fracture strength of martensite formed in the above-A₁ joints in the hydrogen environment. The linear friction-welded medium carbon steel joints below the A₁ temperature can ensure reliability even in a hydrogen environment.

The role of impurities introduced to the steel melt through ferrosilicon addition is of considerable importance in determining the steel cleanness of Si-killed, Si-alloyed steel grades. The silicon requirement is often met with FeSi addition at the industrial scale. In the present study, a detailed investigation of commercial purity ferrosilicon (FeSi) alloy has been conducted to assess its impurity content. Aluminium and titanium were found to be the main impurities among others. Si-O equilibria in liquid steel has been established at 1873 K using FeSi alloy for a wide range of silicon concentration to examine the influence of its impurities. The actual Si-O equilibria established through FeSi addition was compared with true Si-O equilibria which was established using High-purity silicon (HPS) addition. It has been observed that impurities (mainly aluminium and titanium) from FeSi perturbed the true Si-O equilibria. Thermodynamic and kinetic considerations pertaining to this deviation have been elaborated in the present study.

In ferritic steels, solute carbon (C) causes two types of discontinuous stress fluctuations that are accompanied by local deformation bands in the stress–strain curves. One is the yield drop with the Lüders band at yielding, and the other is the serrated flow stress with Portevin–Le Chatelier (PLC) bands during the strain hardening stage, that is, the PLC effect. Lüders band and PLC bands can be explained by static strain aging and dynamic strain aging, SSA and DSA, respectively. These difference in strain aging mechanics distinguish the Lüders band and PLC bands and qualitatively explain when they appear in the stress–strain curve at the yielding and strain-hardening stages. Nevertheless, Lüders band and PLC effect occur in carbon steels at room temperature and 373–473 K, respectively. Therefore, fundamental difference between these bands remains unclear because it is difficult to compare them under the same tensile conditions. In this study, low-strain-rate tensile tests were performed on ultralow-carbon ferritic steel at ambient temperature to compare the bands under the same deformation conditions. In addition to the Lüders band, the formation and propagation of PLC bands were observed at strain rates lower than 1.0 × 10^-4 s^-1, and the PLC effect became more pronounced as the strain rate decreased and the carbon content increased. Furthermore, local strain analysis using digital image correlation revealed that the dislocation movement was much faster than C diffusion only in the Lüders band, which is attributed to the difference in the strain-aging mechanism.

This study investigates the impact of paint baking on the macro and micro-mechanical properties of resistance spot welds in quenched and partitioned 980 steels. It is observed that paint baking enhances both peak load and energy absorption during cross-tension tests, as indicated by load-displacement curves. Four different regions were identified from the load-displacement curves after paint baking. An intriguing observation was a quick increase in the loading rate following a prior decrease, attributed to change in crack propagation behavior rather than improved work hardening. The study further simulated the upper-critical heat-affected zone using a Gleeble thermo-mechanical simulator to evaluate flow strength and work hardening. The Kocks-Mecking strain-hardening model was employed to analyze work hardening behavior in the studied conditions.

This paper reports new research progress on characterizing the burden surface particles of the blast furnace. An algorithm is proposed to extract the contour of the particles on the burden surfaces from their digital elevation models. The statistical distributions of particle size corresponding to the coke and sintered ore burden surfaces are counted from the extraction results of the particle contours. The statistical results obtained in the former research are compared with those of here. The particle surface height distributions can be approximated based on the burden particle size distributions. The peak positions of the estimated particle surface height distribution are consistent with that of the burden surface height distribution.

Recycled scrap is used as a raw material in an electric arc furnace (EAF). Certain EAF systems preheat the scrap using its exhaust gas to save energy. However, the actual operations cannot recover sufficient thermal energy of gas owing to non-uniform flow distribution such as blow-out and stagnation to cause the portion that is not melted. This study investigated the relationship between packed structure and gas permeability in a tank filled with random- and multiple-shaped solids. Visualization and flow measurement experiments were conducted. The packing structure was measured using laser-induced fluorescence by scanning a laser sheet through the tank to measure the three-dimensional distribution of the packed structure. The flow velocity distribution was measured using particle image velocimetry by preparing multiple directions of the laser sheet with respect to the water tank and reconstructing a three-dimensional three-component velocity distribution. Under high packing ratio, the flow structure was obstructed by the packing material, resulting in stagnation areas with low flow velocity. In contrast, at low packing ratio, the stagnation area was smaller, and the global flow field was stable. Furthermore, histograms of the flow velocity distributions suggested that stagnation occurred under high packing ratio conditions, while a global flow field occurred at low packing ratios. These results are applicable in the design of preheating equipment, such as exhaust gas recycling, preheating furnace, or clamshell. Thus, this study provides valuable insights into flow nonuniformity and the design of preheating equipment to improve operational efficiency and safety.

Used plastic waste flowing into oceans has become a worldwide problem. Since international trade in used plastics has been regulated in recent years, a large amount of used plastic now requires domestic disposal. On the other hand, used plastics with a high calorific value could be used as an energy source. Therefore, the authors developed a new used plastic gasification process utilizing a fluidized bed. In this process, used plastics are decomposed in a fluidized bed reactor at around 600 °C, which is a lower temperature than that used in current commercial processes. A higher calorific value gas could be obtained by gasification reaction control at the lower temperature. Hydrogen enriched gas generated by the water-gas shift reaction (WGSR) of basic oxygen furnace gas was used as the fluidizing or gasifying agent, since hydrogen was considered to have an effect of promoting the decomposition reaction of the hydrocarbons in used plastics. As the fluid medium in the reactor, catalysts were used to improve gasification efficiency. In this study, the effect of the gasification temperature and type of catalyst on the calorific value of the produced gas and gasification efficiency were investigated. High calorific value gas (LHV: 5000 kcal/Nm³) could be successfully produced by pyrolysis of used plastics by using an appropriate gasification temperature and catalyst.

Controlling the shape, size, and arrangement of residual defects (pores) in additive-manufactured materials is essential for improving their strength and reliability. However, quantifying the shape and arrangement of individual pores in such materials remains a challenge. This study aimed to clarify the effect of pore configurations that determine the tensile properties of laser powder-based fusion (L-PBF) materials. First, the 3D pore-configurations of pure titanium L-PBF materials fabricated under different beam energy densities were visualized using high-intensity X-ray computed tomography (CT). Subsequently, the porosity, volume equivalent diameter, and sphericity of each pore were quantified by 3D analysis of each CT image, and their correlations with the tensile properties were analyzed. The results showed that, unlike conventional sintered materials, the 0.2% yield stress did not correlate with the porosity of the specimen, suggesting heterogeneity in the hydrostatic component of stress acting on pores. This was connected to periodic fluctuation in the local porosity of the layers sliced perpendicular to the building direction. Furthermore, for specimens fabricated under relatively low beam energy densities, the porosity of the lowest density sliced layer was negatively correlated with tensile strength and total elongation, whereby the local low-density layer dominated the tensile properties. For specimens fabricated under the high energy densities where keyholes were generated, the maximum pore diameter rather than the local layer porosity was more predominate. Thus, it is evident that local structures such as local low-density regions or larger pores dominate the ductile properties of Ti L-PBF materials in terms of their tensile properties.

Previous research has shown that Fe–Mn–Cr–Ni–Si alloys offer excellent low-cycle fatigue resistance via reversible bidirectional transformation between face-centered cubic (FCC) γ-austenite and hexagonal closed-packed (HCP) ε-martensite. The alloy shows superior low-cycle fatigue life and is used for seismic damping applications, but there have been concerns over their resistance to highly corrosive environments. In this study, Fe–15Mn–aCr–bNi–4Si alloys were prepared with different Cr and Ni concentrations to evaluate the effects on the fatigue and corrosion resistances: Z1 with (a, b) = (14, 10.1), Z2 with (a, b) = (12.5, 8.8), Z3 with (a, b) = (11, 7.5), Z4 with (a, b) = (9.5, 6.1), and Z5 with (a, b) = (8, 4.8). Z2 had the longest fatigue life. The alloy showed Gibbs free energy difference between γ-austenite and ε-martensite phases close to the ideal of zero and the α′-martensitic transformation was suppressed well, which agreed with the design criteria for achieving bidirectional transformation-induced plasticity. The developed alloys showed superior corrosion resistance in seawater. Local pitting corrosion was observed that was attributed to the high Mn concentration of the alloys, although this was greatly mitigated by adjusting the Cr and Ni concentrations, especially with Z1 and Z2.

The substitution of fossil coal with biocarbon in the metallurgical processes can help to decrease fossil CO₂ emissions. Biocarbon's characteristics, such as high volatile matter contents and high reactivities with CO₂, are beneficial for increasing the reduction degrees and reduction rates of iron oxides in carbon composite agglomerates (CCA). This study compared the reduction of hematite by of two types of carbonaceous materials (CM): hydrochar (high-volatile biocarbon) and anthracite (a low-volatile coal) in the form of CCA. CM, hematite, and binder (starch) were mixed together to obtain mixtures with C/O molar ratios equal to 0.4-1.2. The mixtures were reduced non-isothermally in nitrogen atmosphere up to 1003 K or 1373 K. Up to 1003 K, the volatiles released from CMs and starch reduced hematite by 18-35%. Between 1003 K and 1373K, both hydrochars (produced from lemon peels and rice husks) reacted with iron oxides more rapidly than anthracite below 1360 K, when the samples had C/O ratios in the range of 1.0-1.2. In this temperature range, rice husk hydrochar promoted a slower reaction with iron oxides than lemon peel hydrochar, which was possibly influenced by its higher ash content which decreased the rate of Boudouard reaction. Samples with C/O ≥ 1.0 achieved complete reduction at 1373 K, regardless of the type of CM used, whereas samples with C/O equal to 0.4-0.5 achieved 63-86% reduction. It can be concluded from this study that hydrochar can fully substitute anthracite for direct reduction of iron oxide to decrease fossil CO₂ emissions during ironmaking processes.