Mortar blocks to heal coastal environments were prepared with cement and fine aggregates composed of steel slag and wood chips. Inorganic and organic species leached from the pulverized mortar blocks prepared in this work. Fe, Si, Mg, Al, Mn, Ca, and S were contained in the leachate as inorganic species. Among them, Fe, Si, Mg, Al, and Mn mainly leached from the steel slag in the mortar block. The elution of these elements was facilitated by the wood chips. Because Ca and S mainly leached from the cement component, the ratio of steel slag and wood chips added to the mortar block gave no effects on the elution of these elements. The leachate of the mortar block also contained not only vanillin and benzoic acid derived from lignin, but also sugar derived from cellulose. These organic substances evolved from the wood chips in the mortar blocks during the preparation process. The steel slag added in the mortar blocks facilitated leaching these organic components. Because the organic and inorganic components feed nutrients to aquatic lives in coastal areas, the prepared mortar blocks could recover damaged coastal environments.

In this study, neutron diffraction mapping was performed on linear friction welded joints of a 12 mm thick high-phosphorus weathering steel (SPA-H) to evaluate the distribution of residual stress, dislocation density and crystallographic orientation. Linear friction welding (LFW) was conducted under two applied pressures (100 MPa and 250 MPa). The welded interface primarily consisted of refined ferrite with minor retained austenite and martensite, suggesting that peak temperatures during welding exceeded the A₁ point (the eutectoid transformation temperature) and induced reverse transformation to austenite. However, the joint produced at 250 MPa exhibited a lower welding temperature. At the weld region, grains near the specimen surface were elongated along the oscillation direction (OD), whereas equiaxed grains appeared at the center in both thickness and width directions. Inhomogeneous microstructural distributions were observed near the interface along OD. Both joints exhibited high tensile residual stresses in all directions at the weld center, while compressive residual stresses developed near the surface in the direction perpendicular to the weld interface. The applied pressure had minimal influence on the overall residual stress distribution trend within the tested welding conditions. Dislocation density at the weld interface was higher than that in base metal, and the increase was more pronounced under higher applied pressure. This is attributed to suppressed dynamic recovery caused by the lower welding temperature at higher pressure. Finally, strong texture formation was observed at the welding interface due to plastic flow during welding. The applied pressure had only sa limited effect on texture development.

Recycling of metallic products is one of the important technologies for the formation of a resource-recycling society to reduce carbon dioxide emissions. Because most metal waste is an alloy and it usually consists of various elements, an efficient method to separate these elements from the metal waste is required. Separation of solid and liquid under two phase co-existing condition is one of the promising methods since their chemical components are different. Electromagnetic separation is expected for this purpose because large difference between the solid and the liquid in electrical conductivity induces relatively large difference in the electromagnetic force than that in the gravitational force. Thus, solidification experiment using a low melting point binary Sn-10 mass% Pb alloy under different electromagnetic field imposition conditions has been done, and eutectic ratio adopted as an index of solute separation or segregation was evaluated. Obvious segregation was not observed under a static magnetic field imposition condition because it has a flow suppression function. Segregation was enhanced under the condition of simultaneous imposition of the static magnetic field and an alternating current. The degree of the segregation under the no-electromagnetic field condition was intermediate between those under the magnetic field imposition condition and the simultaneous imposition condition. The eutectic size under the simultaneous imposition condition was larger and this might become easier the liquid motion in the latter stage of the solidification.

In steel works, flammable gas which generated in the manufacturing process, are used as fuel in the factory. Long pipeline is land to convey these flammable gases. Because serious accidents such as leakage of flammable gases may occur due to pipe corrosion and wall thinning, so periodic inspection of pipe is conducted. Generally, flammable gas pipes are inspected by ultrasonic thickness gauge, but the inspection area is limited.

Therefore, a remote-control wireless inspection robot is developed to expand the pipe inspection area. A robot capable of circumferential and extensive screening inspection on pipes with a diameter of 500 mm or more has been developed by combining eddy current testing using a permanent magnet, which consumes less power and does not require a contact medium, with a design that allows the body to move along the diameter of the pipe using a link mechanism. And the crawler, equipped with permanent magnets in its four wheels, is held to the surface of the steel pipe by suction. Additionally, a function to estimate self-position using an IMU (Inertial Measurement Unit) and encoders has been incorporated, enhancing the robot's practicality by visualizing the moving path on the pipe, weld beads, and thickness reduction on the inspection color map.

The robot moved on the pipe, generated the inspection color map, and successfully detected the simulated weld bead and the simulated defect on the moving path.

The permanent strengths of interstitial-free (IF) steels with different grain sizes and dislocation densities processed by severe plastic deformation (SPD) and subsequent annealing are systematically investigated. Permanent strength, which is athermal and time-independent, corresponds to the fundamental capability to bear stresses caused by external forces. Sufficiently long-time (24 h) stress relaxation tests were carried out and experimental stress–relaxation time relationships were extrapolated to estimate the permanent strength that remained after an infinite time passed. The flow stresses observed in standard uniaxial tension tests increased with repeated SPD processes, and the fraction of permanent strength to the observed flow stress was mostly above 65%. The permanent strength also increased with repetition of SPD processes, and subsequent low-temperature annealing further augmented the permanent strength. During SPD processes, the dislocation-related strengthening was dominant, while the grain-size-related strengthening was minor, i.e., the Hall–Petch relation does not hold. On the other hand, after low-temperature annealing, the grain-size-related strengthening became dominant, quickly replacing the dislocation-related strengthening. In a coarse-grain region, the grain-size-related strength was consistent with the classical Hall–Petch relation. It was confirmed that the original Hall–Petch relation holds only in the coarse-grain region and it indicates “softening with grain coarsening due to annealing”, not “strengthening by grain refinement due to SPD”.

The work to remove the defects generated on the steel pipe surface by grinding is required to be automated because of the large load on the worker. Although automatic machining by large equipment is carried out, there is a problem of low efficiency. The authors proposed a system to automatically remove only surface defects using a 3D camera and a grinder held by a robot arm.

This system is composed of a 3D camera capable of measuring the shape of the steel pipe surface, including defect areas to be maintained, a processor and controller that automatically generate grinding operations, a robot arm as an actuator, and a pressure control device that maintains a constant grinding pressure, which is the grinding device. In this system, the shape of the grinding object is extracted by combining three-dimensional shape measurement and point group processing with two-dimensional image processing, and the machining locus including the tool contact attitude and the motion of the robot are automatically generated based on the shape.

In addition, it became possible to obtain a smooth and high-quality grinding profile by controlling the grinding depth by a pressure control device and controlling the feed rate during machining. By introducing this system into the factory, work efficiency has increased by approximately 2.5 times. And, the production process was made safe, and the engagement of the workplace was improved, because the worker did not handle the dangerous grinder directly.

CO₂ methanation over Ni-based catalysts was studied under conditions simulating steelworks off-gas with trace H₂S. Sulfur in the feed gas deactivated the catalyst, but high-pressure operation suppressed the deactivation. Highly crystalline Ni formed under these conditions may enhance sulfur tolerance. High-temperature calcination also improved crystallinity and durability.

The authors have studied integrated steelworks that are able to achieve carbon neutrality. The process used in the study was a combination of a blast furnace and a pre-reducing furnace. The cases where hydrogen and ethylene were used as fuel were compared based on numerical simulations. As a result, it was found that when hydrogen was used, the reduction in CO₂ emissions from the entire steelworks was only 45%, whereas when ethylene was used, CO₂ emissions from the entire steelworks could be reduced by 86%. Ethylene can be obtained by the dehydration reaction of bioethanol, and can also be synthesized using surplus renewable electricity, which is expected to increase in the future, and CO₂ emitted from steelworks.

The formation behavior of the plating films of Zn−V composite electroplated steel sheets was investigated using electrochemical techniques, and the paint adhesion and heat absorption/dissipation properties were investigated. In Zn−V composite plating, V compounds were preferentially deposited at the initial stage of plating, subsequently Zn was deposited in the form of an electric field-oriented fiber structure. As plating progressed, Zn−V composite plating films consisting of an electric field-oriented fiber structure of Zn and a non-electric field-oriented structure of V compounds were formed, and V compounds were codeposited in the gaps between Zn platelet crystals. The critical current density for initiating Zn plating was about 20 times higher in Zn−V bath than in Zn bath. In Zn−V bath, at the potential range more noble than that for initiating Zn plating, since V ions were reduced from tetravalent to trivalent along with the hydrogen evolution, the critical current density seems to be higher. The Zn−V composite plated steel sheets had better paint adhesion than EG. The excellent paint adhesion is attributed to the anchor effect caused by the large surface roughness and the formation of chemical bonds between the paint films and the oxide or hydroxide of V in the plating films. The Zn−V composite plated steel sheets had a higher emissivity than electrogalvanized steel sheets (EG). As a result, the emissivity after chemical conversion coating was high, and the sheets had high heat dissipation. This seems to be due to the oxide or hydroxide of V in the Zn−V plating films.

It is known as Al₂O₃ dispersed with Ni particles composite (Ni/Al₂O₃) has self-healing function which recovers mechanical properties by the high-temperature oxidation of dispersoids. Ni/Al₂O₃ appear self-healing function not only by the contribution of high-temperature oxidation of Ni particles exposed on sample surface, but also contribution of grain boundary diffusion of Ni ions through Al₂O₃ matrix. The objective of this study is to investigate the influence of Ni ion diffusion on the growth of NiAl₂O₄ self-healing layers with different Ni volume fractions. Dence Ni/Al₂O₃ were prepared and etched nitric acid to remove surface Ni particles. Samples were heat treated at 1100–1355℃ for 6–48 h in air. NiAl₂O₄ self-healing layer is observed on the sample surfaces with and without etching. The NiAl₂O₄ self-healing layer grows with parabolic manner with respect to the heat treatment time, indicating that the diffusion of Ni ion through the Al₂O₃ grain boundary is the rate-controlling. The contribution of surface Ni to the growth of NiAl₂O₄ layers is independent of heat treatment conditions due to the surface Ni particles are defined by the Ni dispersion ratio. The contribution of Ni ion diffusion increases linearly with increasing Ni volume fraction. It indicates that the amount of Ni ions diffused through the grain boundary is proportional to the Ni volume fraction.

This study investigates the phase stability and decomposition behavior of SFCA (Silico-Ferrite of Calcium and Aluminum) at 1573 K under varying oxygen partial pressures. SFCA, a key mineral phase in sintered ore, plays a critical role in enhancing the mechanical strength and reducibility of sinter. Understanding its stability under different conditions is essential for optimizing sinter production processes. Equilibrium and decomposition experiments were conducted under oxygen partial pressures ranging from atmospheric levels to 10^-6 atm. The results revealed that SFCA remains stable up to 5×10^-3 atm, while it decomposes at lower oxygen partial pressures. The decomposition products include magnetite, melilite, and other SFCA groups, indicating that SFCA undergoes a stepwise transformation rather than direct breakdown. Additionally, the liquid phase in equilibrium with SFCA shifts toward the CA₆ (CaAl₆O₁₀) region of the CCC plane as oxygen partial pressure decreases, resulting in an expansion of the liquidus-only region. The findings highlight the narrow stability range of SFCA, with an estimated oxygen partial pressure limit around 10^-3 atm. These results provide valuable insights into the formation and transformation of SFCA under sintering conditions, where local oxygen partial pressures fluctuate due to coke combustion.

Fire and explosion accidents with equipment troubles directly lead to long-term shutdowns and labor accidents related to human lives in ironworks. Panoramic thermal monitoring that can synthesize multiple thermal images at different viewpoints is strongly demanded for wide-area infrastructures such as material yards. In this study, we develop a mirror-drive pan-tilt telephoto infrared camera that enables quick viewpoint switching to different directions without moving its heavy camera body and realize to capture a panoramic thermal image of 8320×4320 pixels in the view angle of 93×46 degrees by stitching 117 thermal images at intervals of 24 s in the fastest case. We demonstrate its effectiveness by verifying panoramic thermal images for material yards in ironworks and superimpose the panoramic thermal images on their 3D point cloud data toward digital-twin-based thermal monitoring.

The chemical analysis and structural evaluation for the multi-component calcium ferrites were carried out, focusing on the microstructural classifications 1H-ACF, 2H-CF and M-FCF used in the 'Development of environmentally friendly steelmaking process technology (COURSE 50)'. The synthesis was carried out with reference to the multi-component calcium ferrite compositions observed in 1H-ACF, 2H-CF and M-FCF. The crystal structure of 1H-ACF and 2H-CF is strongly influenced by the final temperature reached during sintering. And the crystalline phases observed in 1H-ACF and 2H-CF are SFCA and SFCA-I, with a small amount of SFCA-III. On the other hand, the structure of the SiO₂-rich M-FCF was SFCA. The crystal structure of 2H-CF in "sinter 5" was evaluated by single-crystal X-ray diffraction analysis. The multicomponent calcium ferrites in the 2H-CF region of the actual sintered ores reflect the fact that SFCA, SFCA-I and SFCA-III are of the M_14+6nO_20+8n (M = Si, Fe, Al, Ca, Mg) polysomatic series, and are therefore either SFCA with structural defects or SFCA-I. In the 2H-CF region, SFCA-III, rich in Fe₂O₃ and poor in MgO, was also found and the model structural composition was Ca_6.66Fe_39.43Al_3.28Mg_2.63O₇₂, with the MgO component playing an important role in the formation of spinel sheets. SFCA-III, described in detail for the first time in this report, is richer in Fe₂O₃ than those of SFCA and SFCA-I, suggesting an interesting active role as a new component operating in a more reducing environment with Fe²⁺ present.

This study investigated low-temperature linear friction welding (LFW) of Ti-17 alloy, performed below the β transus temperature (applied pressure: 550 MPa), and compared its microstructures and mechanical properties with conventional LFW joints fabricated above the β transus temperature (applied pressure: 50 MPa). Both joints were sound without joining defects. At an applied pressure of 50 MPa, the joint interface consisted of equiaxed β grains　with a grain size of 5 μm, and Vickers hardness measurements indicated significant softening at the interface region. In contrast, at 550 MPa, the joint interface contained ultrafine equiaxed β grains having a grain size of 0.7 μm with a small fraction of α phase, exhibiting hardness comparable to the base material. Tensile tests showed that at 50 MPa, fracture occurred at the softened joint interface region, whereas at 550 MPa, fracture occurred in the base material, indicating the improved joint efficiency of about 100%. In cyclic fatigue tests of specimen at 550 MPa, the joint fractured at the interface but exhibited a fatigue life nearly equivalent to that of the base material. In cold dwell fatigue tests, the joint at 550 MPa exhibited the base material fracture, and the fatigue life was extended by a factor of 3.2 compared to the base material. These results demonstrate that the low-temperature LFW joint (550 MPa) possesses superior mechanical properties compared to conventional LFW joints (50 MPa). This improvement highlights its potential applicability to high-performance aerospace components such as blisks, where enhanced strength and fatigue resistance are critical.

This study explores a method for the synthesis of formic acid from CO₂ through the utilization of biomass-derived bio-oil, specifically focusing on leveraging levoglucosan (LGA) as a key intermediate. Formic acid has the potential to be a feedstock for the synthesis of oxalic acid, a key chemical compound in an iron-making method proposed by the authors. The research investigates the pyrolysis of lignocellulosic biomass, emphasizing the effects of oxalic acid washing on the yield of LGA and its content in bio-oil. By employing a fixed-bed pyrolyzer, the study demonstrates a significant increase in LGA yield when using oxalic acid-treated biomass compared to untreated sample. The pyrolysis with a fluidized-bed pyrolyzer successfully prepared bio-oil rich in LGA during 30 min of continuous operation. Additionally, the produced bio-oil is applied in a CO₂ alkaline hydrothermal conversion process to synthesize formic acid, highlighting the potential of LGA as both a reducing agent and a formic acid precursor. The findings indicate that the LGA-rich bio-oil not only enhances the formic acid yield but also exhibits superior performance compared to conventional reducing agents such as glucose. The study also considers challenges associated with improving CO₂ conversion efficiency, suggesting that the application of bio-oil could be a promising pathway for sustainable CO₂ utilization. The results pave the way for further optimization of bio-oil production and its integration into carbon capture and utilization (CCU) processes.

This study systematically investigates the catalytic performance of Ni‐supported metal oxide catalysts in CO₂ methanation, focusing on seven supports: ZrO₂, α-Al₂O₃, γ-Al₂O₃, MgO, TiO₂, ZnO, and CeO₂. In response to carbon utilization demands, CO₂ methanation, converting CO₂ and H₂ into synthetic methane, provides a promising route for renewable fuel production and energy storage.

An integrated approach of experimental evaluation and quantum chemical calculations was employed to examine adsorption stabilities of key intermediates (e.g., OH, OCHO, and other species) and to correlate these findings with catalytic activity. Experimental results indicated that ZrO₂ achieved the highest CO₂ conversion (49.2%) and CH₄ selectivity (73.5%), followed by α‐Al₂O₃ (46.0%) and CeO₂ (42.9%), while MgO displayed moderate performance. In contrast, TiO₂ and ZnO were nearly inactive under the tested conditions. Computational findings confirmed these observations, demonstrating that adsorption energy and bond order are strong predictors of efficiency.

Notably, ZrO₂ and CeO₂ were predicted to stabilize multiple reaction pathways, highlighting their versatility; Computational results provided insight into α‐Al₂O₃'s high activity in specific routes. By comparing single‐metal‐atom and twelve‐metal‐atom models, it was shown that smaller systems capture essential trends, thereby reducing computational requirements.

In conclusion, these results illuminate the critical role of adsorption stability in determining CO₂ methanation performance. Optimizing electronic properties and adsorption characteristics is crucial for enhancing catalytic efficiency. The combined experimental-computational analysis provides a basis for designing Ni‐supported metal oxide catalysts that advance sustainable CO₂ utilization and energy solutions. These findings offer valuable guidelines for optimizing catalyst design and improving catalytic efficiency for industry.

For reducing CO₂ emissions from blast furnace, carbon recycling blast furnace has been proposed. In carbon recycling blast furnace, reducing agents are synthesized from CO₂ by carbon recycling technology and injected into blast furnace. It has been reported that by synthesizing methane from CO₂ in the blast furnace gas and using it as a reducing agent, CO₂ emissions could be reduced by about 30 % compared to conventional blast furnace. However, it has not been investigated what type of reducing agent is suitable for carbon recycling blast furnace. Therefore, this study aims to examine what reducing agents are effective for CO₂ emission reduction of carbon recycling blast furnace. First, candidate chemical species for the reducing agent of carbon recycling blast furnace were investigated and extracted. Then, the amount of carbon consumption of carbon recycling blast furnace when different candidate reducing agents are injected into carbon recycling blast furnace was evaluated by using Rist diagram analysis. The effect of blast oxygen concentration on the amount of carbon consumption were also evaluated. Based on these results, it was clarified that the amount of carbon consumption of carbon recycling blast furnace is mainly affected by the calorific value of partial combustion of reducing agent and blast oxygen concentration. It was found that by using hydrocarbons with higher calorific value of partial combustion than 4000 kJ/kg as reducing agents of carbon recycling blast furnace, carbon consumption and CO₂ emissions could be reduced by up to 40 % compared to conventional blast furnace.

In this study, influence of crystal structure and chemical composition for Silico-Ferrite of Calcium and Aluminum (SFCA) on its reducibility are examined. Eight types of the powder samples containing SFCA and SFCA-I phases were prepared using chemical reagents by the heat treatments in air. The samples were heated up to 800℃ in the different atmospheres of CO–CO₂–H₂–H₂O systems. The reducibility of the samples was evaluated using the peak intensity ratio identified by XRD before and during the reduction experiment. The intensity of SFCA peak is not decreased up to 700℃ in CO–CO₂ atmosphere, whereas the intensity become weak in CO–CO₂–H₂–H₂O atmosphere. The intensity of SFCA-I peak is decreased above 500^oC in all atmospheric condition and the reduction reactions are enhanced by the addition of H₂–H₂O gas. Decrease in intensity of SFCA peak is independent of Fe composition, whereas that of SFCA-I is decreased with decreasing Fe concentration. The difference in reducibility is attributed to the difference in the crystal structure of multi-component CF. SFCA and SFCA-I are composed of pyroxene and spinel units. Since the pyroxene unit contains more gangue minerals than spinel unit, it implies that the pyroxene unit shows low reducibility than the spinel units. Since SFCA-I contains more the spinel units than SFCA, SFCA-I is easily reduced than SFCA.

Reduced Multicomponent Calcium Ferrite was analyzed using STEM-EDS(scanning transmission electron microscope - energy dispersive spectrometer) and 3DAP(three-dimensional atom probe) in order to clarify the reducibility of SFCA(silico-ferrites of calcium and aluminum) based on the microstructure analysis. The morphological observation and crystal structure analysis using STEM-EDS revealed that the amorphous Ca-Si-O oxides, spinel phase (Fe,Mg)(Fe,Al)₂O₄ and brownmillerite phase (Ca,Fe)₂(Fe,Al)₂O₅ were formed in the metallic iron obtained by the reduction of SFCA. Since the relatively reducible spinel phase was observed after reduction, it is suggested that the formation of spinel phase (Fe,Mg)(Fe,Al)₂O₄ by the dissolution of Mg into spinel phase affect the reducibility of SFCA. It was also found that each oxide was dispersed in metallic iron in granular form, either singly or in complex form. The three-dimensional analysis by performing 3DAP clarified that the presence of the Fe-O enriched region with a width of about 2 nm existed at the interface between amorphous Ca-Si-O oxide and metallic iron. This result suggests that the morphology of amorphous Ca-Si-O oxides affect the reducibility of SFCA.

The declining quality of iron ore fines and increasing re-use requirement of steelmaking slag have led to higher Al₂O₃ content in sinter products. High grade concentrated hematite ore (concentrate) has been emerged as a potential solution for reducing Al₂O₃ levels of sinter. However, research regarding on the melting and assimilation behavior of concentrates in sintering process is limited. On the other hand, our previous work demonstrated that Parallel Granulation with Inclined Mixing of Limestone, based on the creation and mixing of pseudo-particles with high and low CaO/Fe₂O₃ ratios, can improve the sinter strength and productivity. To investigate the melting and assimilation characteristics of concentrates, we conducted melt dripping tests various kind of iron ore, revealing that adhesive layers with high concentrate content have low melt retention capacity. Furthermore, sinter pot tests under single granulation condition showed that when a large amount of concentrate is blended, fragile sinter cake is formed due to insufficient melting and assimilation. Sinter pot tests using Inclined Mixing of Limestone demonstrated that melting and assimilation are promoted by positioning concentrate near abundant melt sources.

REMO-tec, developed by Nippon Steel, is the sintering technique of re-igniting sintering packed bed at certain intervals after first ignition. This method improves sinter yield while maintaining high reducibility, thereby making REMO-tec a technology that contributes to reduce CO₂ emissions in both sintering and blast furnace operations. This study aims to investigate the effects of re-ignition and coke breeze reduction on the mineral phase and pore structure of sintered ore through pot tests, providing a comprehensive evaluation linked to sintering operational parameters. Sinter pot tests were conducted with a 130 mm layer of raw materials, focusing on the upper part of the sintering layer. Experimental conditions included a base condition with single ignition and REMO-tec with re-ignition under three levels of coke breeze blending ratios (4.1, 3.3, and 2.9%). Microstructure observation and pore structure analysis were conducted using an optical microscope and image processing, respectively. REMO-tec extended the high-temperature holding time while maintaining the maximum bed temperature, leading to the formation of an acicular calcium ferrite under low coke conditions (3.3 and 2.9%) with a peak temperature of approximately 1250℃. Additionally, pore structure analysis revealed that the reducibility of sintered ore correlates with the volume of pores smaller than 200 µm. Consequently, producing high-FeO sintered ore with an acicular calcium ferrite matrix and a large volume of pores smaller than 200 µm through REMO-tec under low bonding agent conditions is the most desirable approach for balancing sintering operational parameters and reducing CO₂ emissions in the ironmaking process.

In this study, the method to extract multi-component calcium ferrite (CF) into actual iron ore sinter is proposed and its reducibility is investigated under N₂-CO-CO₂ atmosphere. Actual iron ore sinter are pre-reduced at 500°C for 3 h in N₂-CO-CO₂-H₂-H₂O atmosphere and then sample particles containing mainly multi-component CF are successfully obtained through crashing and wet magnetic separation. In the isothermal reduction at 700-800°C, the reduction rate shows positive correlation with compositions of SFCA-I and SFCA-III up to early stage of reduction, and the negative correlation is obtained with SFCA. However the relationship is reversed, for example at 750°C for approximately 90 s. After approximately 380 s, there is no longer any correlation between SFCA and the reduction rate. It indicates that SFCA-I and SFCA-III are already reduced to intermediate products up to 90 s and the reduction of SFCA affects the reduction rate up to 360 s at 750℃. In the heating reduction using in-situ XRD, the formation of wustite is identified along with the decrease in the intensity of multi-component CF from around 600°C. The intensity of SFCA-III decreases from around 550℃ and disappears at 760℃, whereas the SFCA-I decreases more gradually. It is known as the multi-component CF consists of series of spinel and pyroxene structure. Since the proportion of S units is SFCA-III > SFCA-I > SFCA, it implies that the reduction of Fe ions advances in S units than in P units.

In this study, the influence of Fe²⁺/Fe³⁺ ratios in SFCA-I on its reducibility are examined. Five types of powder samples containing SFCA-I with different Fe²⁺/Fe³⁺ ratios were prepared using chemical reagents by solid phase reaction at high temperature. The samples were heated up to 800℃ in the different atmospheres of CO-CO₂-H₂-H₂O systems. The reducibility of the samples was evaluated using the integrated intensity ratio identified by XRD before and during the reduction experiment. The integrated intensity ratio of SFCA-I is not decreased up to 700℃ in CO-CO₂ atmosphere, whereas the intensity become weak in CO-CO₂-H₂-H₂O atmosphere. The integrated intensity ratio of SFCA-I remains at 800°C under CO-CO₂ atmosphere. On the other hands, the integrated intensity ratio disappears under the CO-CO₂-H₂-H₂O atmosphere. The increase in the Fe²⁺/Fe³⁺ ratio in SFCA-I leads to the increase in the concentration of Fe in SFCA-I and significant decrease the integrated intensity under different reducing gas conditions at 750℃. The increase in the amount of Fe²⁺ may lead to enter Fe²⁺ into the spinel unit, and this may contribute to the reduction of SFCA-I.

Conventionally, it has been known that the product yield of the upper part of the sintering layer is extremely low, because of the heat loss caused by transferring heat toward the space above sintering layer, and of the large amount of unburned carbon in upper sintering layer.

As a countermeasure, REMO-tec (Re-ignition Method for Optimization of Total Energy Consumption) has been developed. Here, REMO-tec, is the sintering technique of re-igniting sintering packed bed at certain intervals after first ignition. This method has an effect on improving sinter yield with maintaining high sinter reducibility.

This paper focuses on gas flow rate control between first ignition and re-ignition for the purpose of further improving product yield.

It has been clear that certain decrease of gas flow rate between these two ignitions, has an effect on increasing heat storage amount in coke combustion zone at re-ignition caused by controlling vertical position of coke combustion zone.

This method has been applied in Kimitsu No.3sinter plant. Product yield improves by 0.3% with increasing high temperature holding time.

The reduction disintegration index (RDI) of sintered ore, which is the main raw material of blast furnaces, greatly affects blast furnace operation. In order to improve RDI without deteriorating the reducibility index (RI), sintered ore having a CaO concentration of 20 mass%, which is higher than the conventional 10 mass% when using porous Australian iron ore, was produced, and its effects on the mineral structure, porosity, RI and RDI were evaluated. In the sintered ore having a CaO concentration of 20 mass%, hematite decreased and calcium-ferrite (sum of other component system calcium-ferrite and binary calcium-ferrite), the SFCA-I/SFCA ratio and porosity increased in comparison with that having a CaO concentration of 10 mass%. When Australian iron ore was used as a raw material for sintered ore, RI increased in sintered ore having a CaO concentration of 20 mass% compared with the one having a CaO concentration of 10 mass%. In addition, RDI was improved in the sintered ore having a CaO concentration of 20 mass% compared with the that having a CaO concentration of 10 mass%. This is due to the formation of binary calcium-ferrite instead of secondary hematite, which deteriorates RDI.

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.

Multi component calcium-ferrites (CFs) including in iron ore sinter are key component of sinter properties, such as strength and reducibility. Those in a sinter are crystallized from oxide melts and form various morphologies such as columnar, needle, and fine textures depending on the formation process. Ca₂(Fe,Ca)₆(Fe,Al,Si)₆O₂₀ (SFCA), Ca₃(Ca,Fe)(Fe,Al)₁₆O₂₈ (SFCA-I) and SFCA-III phases are representative multicomponent CFs, which are included in a sinter. Those texture and types of the crystal structure are not matched one by one. Since their compositional ranges and chemical properties have not yet been fully clarified, and they have micron ordered grain size, it is difficult to determine CF phases only by EPMA chemical composition analysis. In this study, phase determination of CFs in sinter was conducted by Electron backscatter diffraction (EBSD) analysis, which has better spatial resolution than Electron Probe Micro Analyzer (EPMA). Needle like CFs in the sinter with size of several microns were analyzed and confirmed presence of SFCA, SFCA-I and SFCA-III with the needle like texture. Crystal grains determined as SFCA showed higher Si content compared to those of SFCA-I, and this result is consistent with phase diagram. Mg concentration of SFCA-III found in sinter was in the range of 0.6－2.6mass%, which was lower than that of previously reported single crystal structure analysis sample.

The reducibility and mechanical properties of iron ore sinter in blast furnace is critical to effective plant operation. The reduction reaction of sinters progresses heterogeneously owing to microstructures with various mineral phases and pore networks. The reduction process was investigated by semi-microbeam synchrotron X-ray multimodal analysis. Heterogeneous chemical state evolution of Fe and trigger sites of crack formation were visualized using two-dimensional Fe K-edge X-ray absorption near-edge structure analysis and were discussed based on reduction gas transfer. The elemental composition map and X-ray diffraction microanalysis were also combined to reveal the microprocesses during the reduction, such as calcium ferrite decomposition and crystal grain growth.

Friction stir welding (FSW) was applied to a 10 mm-thick plate for the Fe-15Mn-10Cr-8Ni-4Si seismic damping alloy. A sound FSW joint was obtained successfully without macro-defects such as groove-like defects and tunnel holes. However, small pores with diameters of 1–5 μm were formed owing to the wear of the FSW tool during the FSW. The decrease in the heat input suppressed the tool wear. Consequently, the distribution of small pores was limited to the border of the stir zone at the advancing side under smaller heat input conditions. The stir zone of the FSW specimen produced at 125 rpm showed a higher tensile strength of 759 MPa owing to the grain refinement and the high elongation of 50% compared with the base metal. In addition, the stir zone exhibited a remarkable fatigue life of 9,723 cycles. This was higher than that of the base metal (8,908 cycles). Grain refinement occurred by discontinuous dynamic recrystallization (DDRX) via high-angle boundary bulging and direct nucleation in the high-dislocation area. The increase in the heat input suppressed the DDRX owing to the promotion of dynamic recovery.

To reduce the reducing agent ratio and CO₂ emissions in blast furnace operation, it is important to control the material structure of sintered ore, which affects its metallurgical and mechanical properties. Multicomponent calcium ferrites (also called CF or SFCA (silico-ferrite of calcium and aluminum)), which is a type of melting and solidification structure, has attracted considerable interest recently, and the chemical composition and crystal structure of each CF have been researched. Although the crystal structure of CF has conventionally been analyzed mainly by XRD, the atomic arrangement could not be observed directly. Therefore, in this study, CF was investigated at the atomic level by scanning transmission electron microscopy (STEM). This research revealed that acicular CF, which was previously understood to be SFCA-I, has a SFCA (≠ SFCA-I)structure. It was also found that columnar CF had a non-periodic SFCA structure induced with a magnetite-like structure. Furthermore, a CF in which SFCA and SFCA-I were alternately stacked repeatedly was also discovered. This research clarified the fact that CF has a non-periodic structure at the atomic level.

The effect of Al₂O₃ on the compositional region of silico-ferrite of calcium and aluminum (SFCA) and the liquid phase and the phase equilibria, including SFCA, was investigated in a CaO-SiO₂-Fe₂O₃-5mass%Al₂O₃ system at 1240 ^°C in air. To obtain the desired composition, reagent-grade CaCO₃, SiO₂, Fe₂O₃, and Al₂O₃ powders were weighed, mixed, and equilibrated at 1240 ^°C in air. Each obtained sample was divided into two parts: one was pulverized into a powder and analyzed by XRD, and the other was subjected to microstructural observation and compositional analysis using EPMA. The results revealed that the compositional region of SFCA lies on the CF₃-CA₃-C₄S₃ plane and is C/S = 2.77–7.60 for 5 mass% Al₂O₃. Compared with the SFC composition region for 0 mass% Al₂O₃, the compositional range of SFCA extended in the CF₃-C₄S₃ direction, suggesting that the addition of Al₂O₃ contributes to the stability of SFCA. Furthermore, the liquid-phase region was divided into a ferrite melt with a high Fe₂O₃ concentration and a silicate melt with a high SiO₂ concentration, both of which shifted to the lower Fe₂O₃ side compared to the liquidus isotherm in the CaO-SiO₂-Fe₂O₃ system. Unlike CaO-SiO₂-Fe₂O₃, SFCA-I (SFC-I) was observed in the CaO-SiO₂-Fe₂O₃-5mass%Al₂O₃ system, thus indicating that the addition of Al₂O₃ contributes to the stability of SFCA-I.

Conventionally, it has been known that the product yield of the upper part of the sintering layer is extremely low, because of the heat loss caused by transferring heat toward the space above sintering layer, and of the large amount of unburned carbon in upper sintering layer.

As a countermeasure, REMO-tec (Re-ignition Method for Optimization of Total Energy Consumption) has been developed. Here, REMO-tec, is the sintering technique of re-igniting sintering packed bed at certain intervals after first ignition. This method has an effect on improving sinter yield with maintaining high sinter reducibility. This effect leads to improving sinter reducibility without decreasing sinter yield by decreasing control of coke breeze content in sinter mixture.

This paper focuses on coke combustion efficiency as combustion ratio of carbon in coke breeze for considering improvement of sinter yield through sinter pot test. Here, carbon combustion ratio is defined as proportion of actual heat generation at combustion to ideal heat generation as complete combustion (C+O₂→CO₂) of all carbon in coke. And it can be calculated based on component analyses of exhaust gas.

As the result, it was confirmed as shown bellows.

1) By re- ignition, the unburned coke remaining in the upper layer of the sinter packed bed was burned, which has a role of extending keeping time over 1200℃ especially in the upper layer of sinter packed bed.

2) Due to the effect of 1), the increasing amount of heat supply at “REMO-tec” case was equivalent to the same as the experimental case of increasing coke breeze content, at which increasing heat amount at blending coke breeze content was four times larger of the heat amount at re-ignition. (For a 430 mm layer pot test)

3) In addition, since the re-ignition heat is donated to the upper layer (surface layer), the amount of heat consumption in the upper layer of the sinter packed bed increases and the amount of heat consumption in the lower layer decreases compared to the case of increasing coke breeze content, which results in decrease of the difference between heat consumption in upper layer and that in lower layer.

In addition, these effects have been also confirmed at the commercial sinter plant.