Isij International最新文献

In the gas wiping process used in hot-dip galvanizing, the coating thickness has two thinning limits. The first is the limit due to splashing of the liquid film of molten zinc, and the second is the thinning limit of the wiping capacity of the equipment.

In this study, we investigated the possibility that wiping efficiency is reduced by the effect of zinc solidification due to gas jet cooling by conducting a gas wiping experiment under various temperature conditions.

A galvanized steel strip with a width of 100 mm was immersed in a molten zinc bath in the air atmosphere. The steel strip was heated by induction heating or a gas burner, and the wiping gas was also heated.

The results clarified the fact that high temperature conditions improved gas wiping efficiency. It is suggested that high wiping efficiency is prevented by an increase in viscosity due to an increasing solid volume fraction in the liquid zinc film surface caused by microscopic solidification. In addition, it was also found that the development of the initial alloy layer reduced the amount of liquid phase, which inhibits wiping.

Thermal mixing during the gas stirring operation and arc heating in a steel ladle is analyzed through the modern tools of a physical model using PIV (Particle Image Velocimetry) and thermal PLIF (Planar Laser Induced Fluorescence), whose velocity and temperature fields were used to fine-tune and validate a multiphase Eulerian two-phase mathematical model. Agreement on both fluid dynamics and thermal evolution is reasonably good between experiments and the predictions obtained by the mathematical model of the physical model. The analysis coming from the numerical model validated by the physical model measurements included the thermal mixing and energy efficiency of single nozzle injection in centric and eccentric (4/5R) gas injection. It turned out that energy efficiency in the centric gas injection is 20% more efficient than in eccentric injection. Then, under the same heat flux provided, the maximum temperature of the water in the centric gas injection would be higher than the maximum temperature reached in the eccentric mode with the same gas flow rate. Good heat transfer happens when the heat source impinges in a fluid region with high circulation and turbulent dispersion.

Air-quenched electric arc furnace slag (AEAFS) is a black sphere or spheroid particle prepared by an air quenching theology using electric arc furnace steelmaking slag as raw materials, possessing the characteristics of small particle size, moderate density and high hardness Combined with the tight supply and demand of the existing abrasive market and the continuous increase in price, AEAFS is tried to be used as a free abrasive for sandblasting processing according to its physical characteristics. In order to make sure that the AEAFS meets the requirement of free abrasive blasting, it is necessary to conduct a comprehensive and in-depth analysis of its physical and chemical properties. The research shows that the AEAFS is a spherical particle with weak magnetism and particle size being mainly 2.8 mm (accounting for more than 90%). Its Vickers hardness is in the range of 600–1000 HV; its compressive strength is between 20 and 465 N and increases first and then decreases with particle size. The water content is more than 0.019%, except that the particle size is less than 0.5 mm. All the others meet the requirements of ISO-11126-6: 2018 standard. The content of f-CaO is between 1.122% and 1.612% increasing with the particle size, AEAFS has good chemical stability and weak acid resistance. In summary, AEAFS meets the performance requirements of the medium used in the sandblasting process and is a potential alternative product for sandblasting abrasives.

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.

To investigate the factors that cause variations in the friction coefficients of commercially pure titanium sheets with titanium oxide films, the sliding deformation during ball-on-block sliding tests was observed in situ and compared with electron backscatter diffraction analyses of the same regions. Under a vertical load of 0.1 N, the friction coefficient was stable at a low level of approximately 0.12. By contrast, at 0.5 N, the friction coefficient fluctuated widely between 0.20 and 0.80. At 2.0 and 4.0 N, the friction coefficient was stable again at a high level of approximately 0.30 and 0.40, respectively. The fluctuation in friction coefficient at a vertical load of 0.5 N was investigated further based on the Taylor factor for the uniaxial compression of the titanium grains directly beneath the contact point. Notably, the friction coefficient was negatively correlated with the Taylor factor of the underlying grains. Thus, it can be presumed that the plowing term of the friction coefficient increases as the compressive strain on titanium increases. At vertical loads of 2.0 and 4.0 N, the contact area is larger, so the ball is always in contact with multiple grains. Thus, the influence of the Taylor factor of individual grains can be assumed to be averaged, thereby reducing the variation in friction coefficient.

Assuming that heat is transported by lattice vibrations (phonons) in silicate glasses, their thermal conductivity is correlated with the product of sound velocity, volumetric heat capacity, and phonon mean free path (MFP). The sound velocity and heat capacity have been studied extensively, but the origin of the composition-induced variation in the MFP remains unclear. The present study investigated MFP in M_2/nO–SiO₂ (Mⁿ⁺: Li⁺, Na⁺, Ca²⁺, Sr²⁺, or Pb²⁺) glasses with a variation of M_2/nO content. The MFP of the silica glass decreased with the addition of M_2/nO. The effect of the type of metallic cation on the MFP was minimal for the selected alkali and alkaline-earth silicate glasses. By contrast, the MFP of lead silicate glasses was higher than those of alkali or alkaline-earth silicate glasses when the metallic cation contents were comparable. Previous studies have demonstrated that alkali and alkaline-earth cations act as nonframework species that break the silicate network structure, whereas lead cations have inconclusive structural roles. Our data indicate that lead cations partly act as framework cations and that phonons tend to be scattered near nonframework cations in silicate glasses. Thus, the phonon MFP is a useful parameter for determining the structural role of metallic cations in silicate glass via phonon propagation.

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.

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.

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.

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 1,173 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 1,173 K due to solid solution strengthening by Al.