Iron ore sintering is a high-energy-consuming industry, and its high dependence on fossil fuels and the low concentration of CO in the sintering flue gas conceal the truth of the large total amount of CO emissions, which leads to the continuous emission of CO in the sintering flue gas has been harmful to the atmosphere and human health, and it is facing the great pressure of CO emission reduction. On the basis of commercially applied sintering technologies, the mechanism and characteristics of CO emission from sintering flue gas are discussed, and feasible ways to control CO emission in multiple aspects of source control, process emission reduction and end-of-pipe treatment are summarized. The core of source abatement is to reduce the fuel ratio, process abatement is to improve the combustion conditions of fuels to enhance the conversion rate of CO to CO₂, and end-of-pipe treatment is to separate or oxidize CO to CO₂ by physical or chemical means. Hydrogen sintering technology is the future development direction for source abatement, steam blowing sintering technology is introduced for process control, and catalytic oxidation technology has great prospects for removing CO from flue gas in end-of-pipe treatment. CO has great prospects, but efforts are needed to develop highly active catalysts with anti-poisoning and long-standing stability. Finally, feasible technical routes for sintering flue gas CO reduction and their challenges are analyzed, and a coordinated multifaceted control of source-process-end sintering technologies is proposed to achieve the goal of high-efficiency sintering flue gas CO reduction.

The competition between the ferrite and austenite for nucleation in the melt can result in various solidification sequences in the Fe-based alloy. This study demonstrates that the austenite solidification was initiated by metastable ferrite nucleation followed by ferrite-austenite transformation even in Fe-22mass%Mn-0.7mass%C, where the austenite is the primary phase in equilibrium. Time-resolved X-ray diffraction measurements were performed using a time-resolved X-ray tomography apparatus to identify the metastable ferrite nucleation followed by the austenite solidification. X-ray radiography was performed to observe the microstructure evolution through the metastable ferrite nucleation followed by the austenite solidification. The metastable ferrite nucleation was preferably selected when the completely melted specimen was cooled. During subsequent cooling, the ferrite massively transformed to the austenite in the solid state, and multiple austenite grains were produced in a single ferrite grain through ferrite-austenite transformation. The ferrite-austenite transformation was immediately followed by the coarsening of multiple austenite grains. When the ferrite-austenite transformation occurred in a semisolid state consisting of the ferrite and liquid phase, the liquid phase, which isolated the austenite grains, suppressed the coarsening of austenite grain. The typical austenite grain size ranged from 100 to 500 µm. Thus, the present results suggest that the ferrite-austenite transformation following the metastable ferrite nucleation has the potential to control the austenite grain size in as-cast microstructures.

Currently, research and developments are underway for steel production using hydrogen-direct reduced iron and large-scale electric arc furnace (EAF). Fe₃C has attracted attention as a carburizing agent and clean source of iron for EAF steel production to lower the concentration of impurities. However, production capacity of cementite is low since the carbonization reaction rate of reduced iron pellet is limited by gas diffusion inside micropores in the pellet.

In this study, the carbonization reaction rate of porous iron whisker with approximately 95% of porosity was examined. The porous iron whisker can be produced through carbothermal reduction of fine iron ore and biochar mixture. The carbonization reaction rate of the porous iron whisker was approximately three times faster than that of fine iron particles. The porous iron whisker has advantageous for rapid cementite production compared to fine iron particles since the effective surface area is larger in the porous iron.

The copper was the main manufacturing material to produce the coherent lance for enhancing the cooling effect. Due to the low hardness of copper and high-temperature environment, the exit of Laval nozzle would be worn off, resulting in suppressing the impaction ability of supersonic oxygen jet. In order to investigate the effect of wear length on the behavior of coherent jet, both high-temperature experiment and numerical simulation have been carried out, and the axial velocity, total temperature and oxygen fraction were measured in the experimental test to verify the accuracy of simulation model. Based on the result, the overexpand phenomenon was generated due to the Laval nozzle exit wear off, which improved the shock wave intensity at the tip of Laval nozzle, resulting in a lower axial velocity at the velocity potential core. With a longer wear length, the vorticity of the coherent jet periphery is increased, which causes more thermal energy of combustion flame being released prematurely near the coherent lance tip, leading to a shorter velocity potential core.

Under certain conditions, the whole roll flatness meter outputs a bimodal waveform signal, which is clearly different from the conventional unimodal waveform signal. Since detection relies on the extraction of crest values and the values of the two waveforms do not have the same linearity, the presence of the two waveforms of different channels will clearly give rise to errors in the calculated flatness distribution. To develop an effective extraction method, it is necessary to accurately analyze the evolution of the waveforms. In this paper, the finite element method is used to calculate the load of the sensor, the stress distribution of each analysis surface and the deformation of the sensor mounting hole during the real-time detection to analyze the mechanism of the waveforms. The results show that unimodal and bimodal waveforms are produced under different strip tension and wrap angle conditions. In addition, the radial stress of the roll surface always presents two stress wave distributions. With increasing strip tension or wrap angle, the phase difference between the two waves increases. The stress distribution will change the deformation trend of the mounting hole and affect the stress distribution state of the sensor. When the phase difference of the stress waves exceeds the covering range of the sensor, the output signal changes from a unimodal waveform to a bimodal waveform. Finally, by setting up an experimental platform with variable tension and wrap angle, the relationship between the output waveforms and the working conditions in the simulation is reproduced.

Thermal hysteresis in fusion welding causes significant weld deterioration in medium- and high-carbon steels. Therefore, the development of an effective alternative welding process is required. Friction stir welding (FSW) is a solid-state welding process performed in an atmosphere that reduces the risks associated with melting and solidification of metals, making it an effective alternative method. Furthermore, it facilitates a flexible in-process control of heat input, which can be achieved by controlling the welding parameters. Considering these, the authors conducted a series of studies to elucidate the characteristics of FSW for medium- and high-carbon steels, including high-strength tempered steels.

This paper presents the results of applying FSW to 1.4 GPa-grade tempered JIS-S55C steel plates. Five distinct weld types were created by varying the welding parameters, including tool rotation and welding speed. The temperature of the interface between the tool and in-process material was measured using a thermal imaging camera. The microstructure of the welds was evaluated using optical microscopy and field-emission scanning electron microscopy (FE-SEM) with an electron-backscatter diffraction (EBSD) measurement system. The mechanical properties of the welds were evaluated through Vickers hardness and tensile tests. Digital image correlation analysis was employed to analyze the local deformation during the tensile test.

To investigate the factor that cause the variation in friction coefficient by sliding conditions in commercially pure titanium coated titanium oxide film, in-situ observation of sliding interface during ball on block test and EBSD analysis of a sliding cross-section were performed. At the vertical load of 0.1 N, the friction coefficient stabilized at a low level of approximately 0.12. However, at 0.5 N, the friction coefficient varying widely in the range of 0.20–0.80. At 2.0 and 4.0 N, the friction coefficient stabilized at a high level, approximately 0.30 and 0.40, respectively. At the vertical load of 0.5 N, the friction coefficient was negatively correlated to the Taylor factor for the uniaxial compression of the titanium grains directly beneath the film. Thus, it can be presumed that the ploughing term of friction coefficient increased due to the enhancement of compressive strain of titanium. On the other hands, at vertical loads of 2.0 and 4.0 N, the ball is always in contact with multiple grains due to the larger contact area. As a result, it is considered that the influence of Taylor factor was equalized and the variation of friction coefficient got smaller.

The effect of MnS inclusions on the localized corrosion of low-alloy steel in a 0.5 mol/kg (3%) NaCl solution was investigated to propose countermeasures for inhibiting localized corrosion initiated by MnS inclusions. Low alloy steels without MnS inclusions did not corrode in a 0.5 mol/kg (3%) NaCl solution, regardless of the addition of Cu. That is, no matrix improvement effect due to solute Cu was confirmed. Slight corrosion occurred in the Cu containing steel with MnS inclusions; however, the MnS inclusions remained. Cu_7.2S₄ precipitated on the MnS in contact with a 0.5 mol/kg (3%) NaCl solution. Therefore, Cu_7.2S₄ precipitates on the MnS inclusions during immersion, which could suppress the localized corrosion initiated by the MnS inclusions because Cu sulfide is not dissolved based on potential-pH diagram. The addition of Cu in a 0.5 mol/kg (3%) NaCl solution does not improve the corrosion resistance of the matrix due to solute Cu but does suppress localized corrosion initiating from MnS by precipitating Cu sulfide on MnS.

This study investigates the effect of P addition on the corrosion resistance of steels before and after rust formation. Electrochemical measurements and surface analysis of P-containing steels (Fe-0.5 mass% P, Fe-1.0 mass% P, and Fe-1.5 mass% P) were conducted to analyze the contribution of P to their initial corrosion resistance before rust formation. The results showed that the initial corrosion resistance of the steel worsened with increasing P content. According to the surface analysis conducted by SEM/EDS, more P segregations at the grain boundaries occurred with higher P content. Polarization measurements indicated that these P segregations became initiation sites for localized corrosion, resulting in a decrease in the initial corrosion resistance.

Although the initial corrosion resistance was worse with higher P content, the long-term corrosion resistance showed the inverse trend, improving with increasing P content. Atmospheric exposure tests at Miyakojima and surface analysis of the rust layers showed that P was incorporated into the rust layer, and it promoted the protective ability against corrosion.

This work demonstrated that the silicon carbide addition to pre-alloyed Fe–Mo powder could result either in the formation of steel or iron microstructure depending on the added silicon carbide content. With 1.0 wt.% silicon carbide addition, slowly cooled sintered Fe–Mo–Si–C alloys showed steel microstructures consisting of proeutectoid ferrite and eutectoid transformation product in the form of ferrite + carbide mixture. With 2.0 wt.% silicon carbide addition, slowly cooled sintered Fe–Mo–Si–C alloys with Mo contents of ≥ 0.85 wt.% microstructures comprised ferrite + austenite constituents in the forms of either degenerate upper bainite or ausferrite. With ≥ 3.0 wt.% silicon carbide addition, ductile iron-like microstructures were developed in sintered Fe–Mo–Si–C alloys. The change of microstructures in experimental sintered alloys was attributed to the combined effect of alloying molybdenum, silicon, and carbon elements. Tensile strength and hardness increased with increasing added SiC content while ductility varied with microstructural components.

Ferritic stainless steels are used for automobile exhaust parts because of their high heat and corrosion resistance. Among them, parts located upstream near the engine, so-called hot-end parts, for example, exhaust manifolds, are required to show excellent heat resistance. Since thermal fatigue is induced by repeating heating and cooling with mechanical strain restriction, thermal fatigue resistance is one of the most important properties of upstream exhaust-parts materials.

In this study, the effect of Al addition on thermal fatigue deformation morphology was investigated for high heat-resistant ferritic stainless steel SUS444 which has been used for automobile exhaust parts. In contrast with the steel without Al addition, which fracture morphology in thermal fatigue under the maximum temperature of 1173 K was necking, cracking was predominant in the steel with Al addition without necking. Al addition has the effect to prevent necking in thermal fatigue under the maximum temperature of 1173 K due to solid solution strengthening by Al.

In general, the stress-strain relationship of materials obtained by standard uniaxial tensile test, which can identify the hardening behavior only up to necking. Beyond necking, the material behavior is usually estimated by extrapolating or numerical modelling based on hardening behavior prior to the uniform elongation. This study investigated the post-necking hardening behavior of a fully martensitic steel by in-situ synchrotron X-ray diffraction during tensile deformation. From the in-situ results, the dislocation density, lattice strain and phase stress were calculated within the necked region and outside the necked region. A near steady-state flow with some hardening was observed within the necked region of a martensitic steel. However, beyond uniform elongation, outside the necked region the dislocation density and phase stress decreased slightly, suggesting stress relaxation. Steady-state flow and dislocation densities at large strains suggest dynamic recovery occurs in the martensitic steel at room temperature.