Showing papers in "Isij International in 2012"
TL;DR: In this article, a life cycle assessment methodology has been used to estimate the greenhouse gas footprint of charcoal production from biomass, as well as the potential reductions in greenhouse gas emissions from the use of charcoal from biomass in the integrated, mini-mill/EAF and direct smelting steelmaking routes.
Abstract: Fossil fuel-based carbon is widely used in iron and steelmaking in a number of forms, and the replacement of these materials with renewable carbon derived from biomass is seen as offering the greatest potential to reduce the greenhouse gas footprint of steel production. Life cycle assessment methodology has been used to estimate the greenhouse gas footprint of charcoal production from biomass, as well as the potential reductions in greenhouse gas emissions from the use of charcoal from biomass in the integrated, mini-mill/EAF and direct smelting steelmaking routes. The results indicated that the use of charcoal in the integrated steelmaking route in likely applications and substitution rates has the potential to reduce the greenhouse gas footprint of steel by 0.69–1.21 t CO2e/t steel (or 31–57%) without any charcoal production by-product (bio-oil and electricity) credits, and by 0.91–1.61 t CO2e/t steel (42–74%) with these by-product credits included. The corresponding reductions for the mini-mill/EAF and direct smelting routes were 0.028–0.056 t CO2e/t steel (5.5–11%) and 0.34–1.70 t CO2e/t steel (16–80%) without by-product credits, and 0.037–0.075 t CO2e/t steel (7.3–14.7%) and 0.45–2.25 t CO2e/t steel (21–106%) with by-product credits respectively. However, the magnitude of the by-product credits depends on the by-product yields in the charcoal retort, which in turn are dependent on a number of factors, in particular, the nature of the pyrolysis process (fast or slow) and the biomass feed composition. Estimates of the potential plantation areas available to grow the biomass required to produce charcoal for steelmaking purposes in a sustainable manner, together with estimates of sources of biomass residues suggest that it is possible that an appreciable amount of the world’s steel production can utilise charcoal in place of coal or coke over the coming decades. However, transportation is expected to be a significant issue affecting the cost of charcoal delivered to steel plants in all biomass source scenarios. Other issues such as technical aspects of charcoal use in steelmaking and economics will also play a significant role in the uptake of charcoal from biomass as a source of renewable carbon for iron and steelmaking.
132 citations
88 citations
TL;DR: In this paper, three kinds of biomass fuels such as charcoal, charred-straw and molded-sawdust were studied as sintering fuels, and the results showed that, with the proportion of biomass replacing coke breeze increasing, the vertical sinterING speed raises, but the yield and the tumble index of sinter decrease.
Abstract: For green production of iron ore sintering, it is significant to substitute fossil fuels by biomass which is a kind of clean and renewable energy. In this paper, three kinds of biomass fuels such as charcoal, charred-straw and molded-sawdust were studied as sintering fuels. The results show that, with the proportion of biomass replacing coke breeze increasing, the vertical sintering speed raises, but the yield and the tumble index of sinter decrease, so the replacement proportion should be appropriate for satisfying the productivity and the quality of sinter. The suitable replacing proportions of charcoal, charred-straw and molded-sawdust are 40%, 20% and 15% respectively, in which the emission of COx can be decreased by 18.65%, 7.19% and 5.39%, SOx by 38.15%, 31.79% and 28.90%, NOx by 26.76%, 18.31% and 15.49% respectively.
82 citations
TL;DR: In this paper, a viscosity model was proposed to represent the slag structure through the different types of oxygen ions formed in the melt, and approximate methods for calculating the concentrations of these different kinds of oxygen ion are proposed and then used to describe the effect of melt structure on visco-ity.
Abstract: A structurally-based viscosity model (using a few optimized parameters) is proposed to represent viscosity as functions of both temperature and composition for the CaO–MgO–Al2O3–SiO2. The model represents the slag structure through the different types of oxygen ions formed in the melt. Approximate methods for calculating the concentrations of these different types of oxygen ions are proposed and are then used to describe the effect of melt structure on viscosity. The model provides a good description of the viscosity behavior varied with composition and temperature within the CaO–MgO–Al2O3–SiO2 system. This includes pure systems: Al2O3 and SiO2; binary systems: CaO–SiO2, MgO–SiO2, Al2O3–SiO2 and CaO–Al2O3; ternary systems: CaO–MgO–SiO2, CaO–Al2O3–SiO2 and MgO–Al2O3–SiO2; quaternary system: CaO–MgO–Al2O3–SiO2. The different roles of CaO and MgO on viscosity are also discussed; these tend to differ in melts with or without Al2O3. In the absence of Al2O3, CaO reduces the viscosity more than MgO. In contrast, when Al2O3 is present, the Ca2+ ions take priority over Mg2+ ions in the charge-compensation of Al3+ ions which leads to the formation of more stable Ca–AlO45– tetrahedral structures, which, in turn, results in an increase in viscosity. However, when there is enough basic oxide (CaO or MgO) present to generate non-bridging oxygens, CaO reduces the viscosity more effectively than MgO.
82 citations
TL;DR: In this paper, the change of structure of calcium aluminosilicate slags with varying Al2O3/SiO2 ratios at a fixed CaO content was investigated.
Abstract: Molecular dynamics simulation was explored to investigate the change of structure of calcium aluminosilicate slags with varying Al2O3/SiO2 ratios at a fixed CaO content. In practice the results of the study are relevant to the significant changes in slag structure caused by the changes in chemical composition during continuous casting of steels containing high amounts of dissolved aluminum. It was found that Q4 tetrahedral species (tetrahedron with four bridging oxygens) increase while NBOs (non-bridging oxygen) decreases with increasing Al2O3/SiO2 mole ratio, suggesting that a more polymerized network was formed. The concentration of oxygen tricluster increased dramatically up to 24% with increasing Al2O3/SiO2 mole ratio, and the coordination number for Al (CNAl–O) was also observed to increase from 4.02 for sample CAS1 to 4.11 for sample CAS11, suggesting that high coordination number of Al presents in the slag melt with the substitution of [AlO4] for [SiO4]. NBOs prefer to be coordinated with Si and Al tends to be localized in more polymerized environment as network intermediate phases. The degree of Al avoidance was calculated and the Al avoidance principle is applicable in the SiO2 rich regions.
78 citations
TL;DR: In this paper, the influence of TiO2 from 0 to 10 mass% on the viscous behavior of slags has been investigated and correlated to the slag structure using XPS (X-Ray Photoelectron Spectroscopy).
Abstract: Iron ores consisting of significant TiO2 such as ilmenite are low cost ores, but due to the high TiO2 content its use may result in significant issues within the blast furnaces such as lower reduction degree,1–4) changes in the liquidus temperature in slag,5–7) lower residual removal by the slag,8–10) and viscosity changes within the bosch and hearth.11–15) However, potential benefits of TiO2 in the blast furnace slags have also been known by forming a protective layer of titanium carbo-nitride on the refractory brick and inhibiting the premature failure and erosion of the hearth.9,15–18) Ohno and Ross13) found TiO2 additions increase the slag viscosity in the CaO–SiO2–Al2O3–TiO2 slags under reducing atmospheres of C/CO equilibrium. Shankar et al.19) revealed the effect of TiO2 in the CaO–SiO2–MgO–Al2O3 slag system, where the viscosity decreased with TiO2 up to 2 mass%. Saito et al.14) found TiO2 lowered the viscosity in the CaO–SiO2–MgO–Al2O3 slag system at 10 mass% and 20 mass% TiO2. However, the viscosity data between 0 to 10 mass% TiO2 is still ill-defined. In this study, the influence of TiO2 from 0 to 10 mass% on the viscous behavior of CaO–SiO2–17 mass%Al2O3–10 mass%MgO slags have been investigated and correlated to the slag structure using XPS (X-Ray Photoelectron Spectroscopy).
78 citations
TL;DR: In this article, phase equilibria in the Fe-Si binary system were investigated experimentally and thermodynamic assessment was carried out, and a four-sublattice split compound energy formalism was applied to calculate the Gibbs energy of the bcc phases.
Abstract: Phase equilibria in the Fe–Si binary system were investigated experimentally and thermodynamic assessment was carried out. The αFe (A2) + α"Fe3Si (D03) two-phase microstructures at 600°C and 650°C were obtained, whose grain sizes were sufficiently coarsened to be analyzed by FE-EPMA with a spatial resolution below 0.5 μm under the condition of 6 kV accelerating voltage. α'FeSi (B2) + α"Fe3Si (D03) two-phase equilibria above 700°C were detected for the first time and equilibrium compositions were determined by the diffusion couple method. The horn-shaped two-phase miscibility gap extends from the low temperature αFe + α"Fe3Si equilibrium along the B2/D03 second-order transition boundary and closes below 1000°C. Four-sublattice split compound energy formalism was applied to calculate the Gibbs energy of the bcc phases, A2(αFe), B2(α'FeSi) and D03(α"Fe3Si), and the thermodynamic parameters in the Fe–Si binary system were evaluated. Equilibrium relations in the binary system were well reproduced, especially the effect of the B2 and D03 ordering on the liquidus and solidus curves and the miscibility gap between bcc phases. Optimized thermodynamic parameters as well as the experimental results are expected to be helpful for developing higher multi-component systems for practical steels.
76 citations
TL;DR: In this paper, the authors investigated the characteristics of hydrogen-related crack propagation in low carbon lath martensite steel through orientation analysis using electron backscattering diffraction, which revealed that the hydrogenrelated fracture surface consisted of the {011}M facets, which were also parallel to the block boundaries or lath boundaries.
Abstract: This study investigated the characteristics of hydrogen-related crack propagation in low carbon lath martensite steel through orientation analysis using electron backscattering diffraction. The orientation analysis revealed that the hydrogen-related fracture surface consisted of the {011}M facets, which were also parallel to the block boundaries or lath boundaries in the lath martensite structure. In addition, micro-cracks were observed on or in the vicinity of the prior austenite grain boundaries. On the basis of the experimental results, we proposed that hydrogen enhanced local plastic deformation occurred in the vicinity of prior austenite grain boundaries. The mechanism of hydrogen-related fracture is characterized by the formation of micro-cracks around prior austenite grain boundaries and subsequent crack propagation along block boundaries or lath boundaries.
74 citations
TL;DR: In this article, the progress of Chinese blast furnace long hearth service life design concept was analyzed deeply from design of hearth structure, selection of hearingth refractory, arrangement of hearths cooling system and establishment of online hearth monitoring system.
Abstract: In recent years, Chinese steel companies suffered a spate of blast furnace hearth incidents, such as hearth sidewall breakout or temperature abnormal increase, causing Chinese blast furnace ironmakers to pay a great deal attention on long hearth service life technology. In this paper, the progress of Chinese blast furnace long hearth service life design concept was analyzed deeply from design of hearth structure, selection of hearth refractory, arrangement of hearth cooling system and establishment of online hearth monitoring system, and the future design proposal for long hearth service life of Chinese blast furnace was put forward.
72 citations
TL;DR: In this paper, an improved immersion-type hydrogen charging method using an ammonium thiocyanate (NH4SCN) aqueous solution was introduced to control the diffusible hydrogen content.
Abstract: When ultra high strength steel (UHSS) sheets with tensile strength over 980 MPa are applied in automobiles, there is a risk that a type of hydrogen embrittlement fracture called delayed fracture may occur while a vehicle is in use. This paper summarizes the effects of stress, strain, diffusible hydrogen content and the forming mode on the hydrogen embrittlement resistance of UHSS sheets for automotive applications. In this study, 1180 MPa grade ferrite-martensite dual phase steel was used. This material was evaluated by the U-bending and drawn cup methods. It was concluded that high strain, high stress and high diffusible hydrogen content reduced hydrogen embrittlement resistance.In addition, an improved immersion-type hydrogen charging method using an ammonium thiocyanate (NH4SCN) aqueous solution was introduced in this paper. The NH4SCN solution enables control of the diffusible hydrogen content from low to high concentrations using the NH4SCN concentration, and dissolution of the specimens during immersion in NH4SCN was minimal, making it possible to maintain substantially the same surface condition as before immersion.
70 citations
TL;DR: In this paper, the authors investigated how the mass ratio between Al2O3 and SiO2 in slag compositions influences the structure, viscosity and crystallization of the slag melts.
Abstract: The present paper investigates how the mass ratio between Al2O3 and SiO2 (mAl2O3/mSiO2) in slag compositions influences the structure, viscosity and crystallization of the slag melts. The objective is to study the variations in viscosity and structure of slags with increasing mAl2O3/mSiO2 ratio. In practice the results of the study are relevant to the significant changes in slag property caused by the changes in chemical composition during continuous casting of steels containing high amounts of dissolved aluminum. The viscosity was found to decrease slightly with increasing mAl2O3/mSiO2 ratio up to 0.56. The degree of polymerization for [SiO4]-tetrahedra was found to decrease with increasing mAl2O3/mSiO2 ratio based on the Fourier Transformation-Infrared Spectra (FT-IR) and Raman spectra, which could explain the observed decrease in viscosity. AtmAl2O3/mSiO2 ratios above 0.56, the viscosity was found to abruptly increase which could be caused by the presence of spinel crystals. The activity coefficient was computed and it was found that the activity coefficient of alumina presents negative deviation when mAl2O3/mSiO2 ratio is less than 0.35, while it shows a positive deviation when mAl2O3/mSiO2 ratio exceeds 0.35. This phenomenon may be related to the change of the primary phase region correlating to the phase diagram to the slag composition.
TL;DR: In this paper, a numerical simulation of blast furnace operation with hydrogen injection through tuyere was carried out under the conditions of constant bosh gas flow rate, adiabatic flame temperature and hot metal temperature.
Abstract: Recent years various trials to decrease carbon dioxide emission from iron and steelmaking industries have been made. One of these trials is utilization of hydrogen in blast furnace process, and this study performed numerical simulation of blast furnace operation with hydrogen injection through tuyere. The simulations were carried out under the conditions of constant bosh gas flow rate, adiabatic flame temperature and hot metal temperature. The simulation results showed that the temperature level in the stack part was decreased with increase in the hydrogen injection ratio. This resulted in the lowering of the top gas temperature and retarded the reduction of iron oxide especially one of magnetite. The injection of the hydrogen remarkably decreased the coke rate. The converted reducing agent rate, that is sum of coke rate and six times (molecular weight ratio of carbon to hydrogen gas) as hydrogen rate showed small change. Although this decrease in coke rate deteriorated the permeability of the burden materials in the furnace, pressure drop in the furnace was reduced. Since the molar flow rate of the reducing gas was kept constant, the decrease in the gas density due to the increase in the hydrogen content was mainly considered to lead the decrease in the pressure drop. The water gas shift reaction played an important role in the generation of the field of gas composition, thus this reaction has to be carefully discussed for further utilization of hydrogen in blast furnace.
TL;DR: In this article, the progress of strip casting technology for steel from a historical perspective is reviewed, and this will be followed by a sequel, reviewing recent technical developments in the field, and two strip casting processes are discussed in detail; Twin-Roll Casting (TRC) and Horizontal Single-Belt Casting (HSBC).
Abstract: With increasing competition in the global steel market, strip casting technology potentially offers an efficient, economical and environmentally-friendly approach to the production of hot-rolled, coiled steel. This review provides a summary of the basic theory and history in the developments of strip casting operations of steels, along with technical discussions regarding various strip casting initiatives that have been carried out in the past, as well as present. Two strip casting processes are discussed in detail; Twin-Roll Casting (TRC) and Horizontal Single-Belt Casting (HSBC). With its inevitable logic, the emergence of strip casting technology could have an enormous impact on the world’s steel industry. This present paper reviews the progress of strip casting technology for steel from a historical perspective, and this will be followed by a sequel, reviewing recent technical developments in the field.
TL;DR: In this paper, Li2O additions up to 1 mass% significantly decreased the viscosity by breaking the [AlO4]-tetrahedral network structure of molten fluxes.
Abstract: The viscous behavior of the CaO–Al2O3–12 mass%Na2O–12 mass%CaF2 based slag system with various concentrations of Li2O has been studied using the rotating spindle method to understand the effects on the viscosity with these additives Li2O additions up to 1 mass% significantly lowered the viscosity by breaking the [AlO4]-tetrahedral network structure of molten fluxes, but Li2O concentrations above this level was comparatively less effective in lowering the viscosity The viscosity was lower at higher temperatures and from an Arrhenius relationship, the activation energy was calculated to be between approximately 180 to 190 kJ/mol Fourier Transform Infra-Red (FTIR) analysis of as-quenched slag samples showed the characteristic Al–O stretching vibration in the wavenumber of 800 cm–1 and 660 cm–1 Slags with higher viscosity showed a slightly wider trough near the 800 cm–1 and 660 cm–1 Al–O stretching bands XPS analysis of slags with various concentrations of Li2O indicated the fraction of bridged oxygen (Oo) decreased and the non-bridged oxygen (O–) increased with higher concentrations of Li2O Li2O additions up to 1 mass% significantly decreased the bridged oxygen fraction, which seem to correlate well with the viscosity measurements
TL;DR: In this article, the main trap sites of TiC and V4C3 precipitates in bcc-Fe were investigated by numerical calculations and the trap states at interstitial site and, carbon vacancy in metal carbide and bccFe/metal-carbide interface were studied by ab-initio calculation.
Abstract: Hydrogen trap states by TiC and V4C3 precipitates in bcc-Fe are investigated by numerical calculations. The trap states at interstitial site and, carbon vacancy in metal carbide and bcc-Fe/metal-carbide interface were studied by ab-initio calculation. The calculated trap energies of these sites for TiC compared with the energy at interstitial site in bcc-Fe were respectively –58 kJ/mol, 125 kJ/mol and 48 kJ/mol and those for V4C3 were respectively –106 kJ/mol, 116 kJ/mol and –6 kJ/mol. The activation energy of detrapping from an isolated carbon vacancy is estimated at 183 kJ/mol for TiC and at 222 kJ/mol for V4C3 from the difference of the calculated energy at carbon vacancy and that at interstitial site in metal carbide. Hydrogen trap energy in coherent strain field around of TiC and V4C3 coherent precipitates in bcc-Fe are also calculated by Finite Element Method (FEM). The calculated energies are respectively less than 29 kJ/mol and less than 15 kJ/mol. These results indicate the main trap site of TiC is TiC/bcc-Fe interface, because TiC contains few carbon vacancies and has large activation energy of detrapping at the sites. That of V4C3 is carbon vacancies because V4C3 contains abundant carbon vacancies and the activation energy of migration between the neighbored carbon vacancy sites is expected to be lower than the calculated value . The estimated main trap sites of TiC is in good agreement with 3 Dimensional Atom Prove (3D-AP) observation results which reported that hydrogen atoms observed at TiC/bcc-Fe interface of TiC precipitate in bcc-Fe.
TL;DR: In this article, the authors investigated the strengthening mechanism of martensite by using an ultra low carbon Fe-18%Ni alloy to eliminate the confusion caused by carbon and found no large difference is found on the nominal stress-strain curves, especially on the yielding behavior.
Abstract: In this paper, the strengthening mechanism of martensite was investigated by using an ultra low carbon Fe–18%Ni alloy to eliminate the confusion caused by carbon. In addition, Fe–18%Ni–C alloys were used to compare with the data of Fe–C alloys already reported and the effect of solute Ni was discussed in terms of solid solution strengthening in martensitic steels. The results obtained are as follows: 1) Microstructure of lath martensite is markedly refined by lowering the solution treatment temperature, nevertheless no large difference is found on the nominal stress-strain curves, especially on the yielding behavior. 2) Low elastic limit of ultra low carbon martensite is due to the existence of high density of mobile dislocation which has been introduced during martensitic transformation. Extra mobile dislocations can be eliminated by charging small amount of pre-strain more than 0.6% and this leads to an increase of 0.2% proof stress. 3) Substantial yield strength of carbon free martensite is determined by only the mechanism of dislocation strengthening without the contribution by grain refinement strengthening depending on microstructural parameters such as prior austenite grain size, packet size and block size. 4) Solid solution strengthening by Ni does not appear in martensitic steels which contains high density of dislocation, even though it is significant in ferritic steels.
TL;DR: In this paper, an ultrafine grained (UFG) ferrite/cementite steel was subjected to intercritical annealing in order to obtain an UFG ferrite and martensite dual-phase (DP) steel.
Abstract: An ultrafine grained (UFG) ferrite/cementite steel was subjected to intercritical annealing in order to obtain an UFG ferrite/martensite dual-phase (DP) steel. The intercritical annealing parameters, namely, holding temperature and time, heating rate, and cooling rate were varied independently by applying dilatometer experiments. Microstructure characterization was performed using scanning electron microscopy (SEM) and high-resolution electron backscatter diffraction (EBSD). An EBSD data post-processing routine is proposed that allows precise distinction between the ferrite and the martensite phase. The sensitivity of the microstructure to the different annealing conditions is identified. As in conventional DP steels, the martensite fraction and the ferrite grain size increase with intercritical annealing time and temperature. Furthermore, the variations of the microstructure are explained in terms of the changes in phase transformation kinetics due to grain refinement and the manganese enrichment in cementite during warm deformation.
TL;DR: In this paper, a combined cellular automaton-finite difference (CA-FD) model was developed to simulate solute diffusion controlled solidification in continuous steel casting, and the effect of the fragmentation of dendrites due to fluid flow induced by EMS in mould on nuclei was taken into consideration by increasing the grain density.
Abstract: A combined cellular automaton-finite difference (CA-FD) model has been developed to simulate solute diffusion controlled solidification in continuous steel casting. Constitutional and curvature undercooling were both solved to determine the equilibrium temperature and growth velocity of the solid/liquid interface. Simulations were firstly performed for both the free dendritic growth from an undercooled melt and the columnar dendritic growth in unidirectional solidification. Finally, competitive dendritic growth and columnar to equiaxed transition (CET) occurring in solidification of continuous casting process were reproduced by the present CA-FD model. The effect of the fragmentation of dendrites due to fluid flow induced by EMS in mould on nuclei was taken into consideration by increasing the grain density. The comparison between the simulated and experimentally observed results shows that the present model can be used to simulate solidification structure formation during the continuous casting process of steel. The influence of superheat on solidification structure was also analyzed, and it was found that increasing superheat increases the columnar dendritic growth and reduces the equiaxed ratio, as it is empirical well known.
TL;DR: In this paper, the authors present an approach to the mathematical modeling of heat and mass transfer processes in a 3-phase, 80 MVA AC, electric arc furnace (EAF) and represent a continuation of their work on modeling the electric and hydraulic EAF processes.
Abstract: The following paper presents an approach to the mathematical modeling of heat and mass transfer processes in a 3–phase, 80 MVA AC, electric arc furnace (EAF) and represents a continuation of our work on modeling the electric and hydraulic EAF processes. This paper represents part 1 of the complete model and addresses issues on modeling the mass, temperature and energy processes in the EAF, while part 2 of the paper focuses solely on the issues related to the thermo-chemical relations and reactions in the EAF. As is generally known, the chemical, thermal and mass processes in an EAF are related to each other and cannot be studied completely separately; therefore, the work presented in part 1 and part 2 is related to each other accordingly and should be considered as a whole. The presented sub-models were obtained in accordance with different mathematical and thermo-dynamic laws, with the parameters fitted both experimentally, using the measured operational data of an EAF during different periods of the melting process, and theoretically, using the conclusions of different studies involved in EAF modeling. In conjunction with the already presented electrical and hydraulic models of the EAF, the heat-, mass- and energy-transfer models proposed in this work represent a complete EAF model, which can be further used for the initial aims of our study, i.e., optimization of the energy consumption and development of the operator-training simulator. The presented results show high levels of similarity with both the measured operational data and the theoretical data available in different EAF studies, from which we can conclude that the presented EAF model is developed in accordance with both fundamental laws of thermodynamics and the practical aspects regarding EAF operation.
TL;DR: In this article, a more comprehensive numerical model which incorporates most of the significant processes and heat transfer modes proposed in earlier models is given, which is available to describe the relationship between airflow rate through the bed and flame front speed, the evaporation and condensation of water ahead of the front, the calcination of fluxes nearer to the front.
Abstract: Iron ore sintering involves the movement of a flame front down a particulate bed, and a series of physico-chemical reactions over a large temperature range. In the literature simple and more sophisticated iron ore sintering models have been reported. In this paper a more comprehensive numerical model which incorporates most of the significant processes and heat transfer modes proposed in earlier models is given. Therefore, sub-models are available to describe the relationship between airflow rate through the bed and flame front speed, the evaporation and condensation of water ahead of the front, the calcination of fluxes nearer to the front, the reactions that occur in the front and cooling of the bed with the departure of the front. Improvements were made to several areas – such as coke combustion, and the melting and solidification processes – to more accurately quantify the phenomena involved. More recent progress in understanding the fundamentals of sintering from BHP Billiton studies have also been incorporated into the model. To date, twelve sinter pot tests have been used for validation studies. Reasonably good agreement was obtained between predicted and measured results – in areas such as bed temperature profiles and waste gas temperature and compositions. Work is continuing to further improve the model, and broaden the validation work to include other bed temperature profile parameters.
TL;DR: In this paper, the authors investigated the relationship between hydrogen embrittlement and lattice defects associated with hydrogen and found that the amount of lattice defect increased gradually with increasing time of applied stress during hydrogen charging.
Abstract: Hydrogen behavior and hydrogen-enhanced lattice defect formation under elastic stress of tempered martensitic steel were clarified with respect to dislocations and vacancies by thermal desorption analysis (TDA) using hydrogen as a probe of defects and a positron probe microanalyzer (PPMA). The relationship between hydrogen embrittlement and lattice defects associated with hydrogen was also investigated. The amount of lattice defects increased gradually with increasing time of applied stress during hydrogen charging. The specimen fractured under elastic stress in the presence of hydrogen macroscopically showed brittle fracture without necking. Whereas fracture surface was attributed to localized plastic deformation, since the morphology of the microscopic fracture surface was mostly quasi-cleavage fracture. The increased lattice defects in the near-fracture area were subsequently removed by annealing at 200°C. The mean positron annihilation lifetime measured with the PPMA for a fractured specimen was longer in the near-fracture area than in other areas. Thus, the most probable reason for the increase in the amount of lattice defects can be ascribed to an increase in the amount of vacancies or vacancy clusters. Regarding hydrogen embrittlement involving microscopic plastic deformation, the localized enhanced vacancies due to interactions between dislocations and hydrogen under elastic stress directly caused ductility loss, because ductility loss occurred even though hydrogen was completely removed by degassing before the tensile test. Besides hydrogen content and applied stress, the time of formation and accumulation of vacancies are also concluded to be important factors causing hydrogen embrittlement.
TL;DR: In this paper, an approach based on a continuum composite view of martensite (CCA) is developed suitable to capture all the experimental features, and it is highlighted that this phase has a very high strain-hardening which increases with carbon content and a large Bauschinger effect.
Abstract: Though as-quenched martensite exhibits a low uniform elongation in tension, it is highlighted that this phase has a very high strain-hardening which increases with carbon content and a large Bauschinger effect. Because usual dislocation storage can not explain reasonably this particular behaviour, an approach based on a continuum composite view of martensite (CCA) is developed suitable to capture all the experimental features.
TL;DR: In this paper, a series of slag modification experiments were designed to investigate the recovery of phosphorus from high P2O5 content dephosphorization slag produced by duplex high phosphorus hot metal refining.
Abstract: Phosphate rock is a vital nonrenewable resource. In order to find new source of phosphorus, the recovery of phosphorus from dephosphorization slag produced by duplex steelmaking process (De–P slag in De–P_De–C steelmaking process) was investigated in the present paper. It was demonstrated that the Prich phase in dephosphorization slag is difficult to recover effectively by magnetic separation as the reason of P enriched phase inlay in the Fe enriched phase in the slag. The relationship between P recovery ratio and magnetic intensity and slag particle size were also obtained. A series of slag modification experiments were designed to investigate the recovery of phosphorus from high P2O5 content dephosphorization slag produced by duplex high phosphorus hot metal refining. It was found that the addition of SiO2, Al2O3 and TiO2 has a positive influence on the P recovery ratio. However, the P recovery ratio and the concentration of P2O5 in unmagnetized slag showed a reciprocal relationship with increasing SiO2 and Al2O3 content. The P recovery ratio was little affected by the addition of FetO and MnO. Furthermore, the P recovery ratio increased under the stirring condition. 74% and 87% P were recovered in the unmagnetized phases with adding 10% SiO2 and Al2O3, respectively. The results demonstrated that most of the phosphorus in the slag could be recovered through slag modification and magnetic separation.
TL;DR: In this paper, the influence of B2O3 on the viscosity of high Ti-bearing BF slag was studied under Ar atmosphere from 1 773 K (1 500 degrees C) to about 1 593 K ( 1 320 degrees C).
Abstract: The influence of B2O3 on the viscosity of high Ti-bearing BF slag is studied under Ar atmosphere from 1 773 K (1 500 degrees C) to about 1 593 K (1 320 degrees C). The results show that the additio ...
TL;DR: Tempering effects on the austenite stability and mechanical properties of 0.2C-5Mn steel were investigated in the temperature range from 100°C to 600°C with 1 hour.
Abstract: Tempering effects on the austenite stability and mechanical properties of 0.2C–5Mn steel were investigated in the temperature range from 100°C to 600°C with 1 hour. It was found that tempering doesn’t result in a significant change of the austenite plus ferrite duplex structure, which was developed in the previous annealing through austenite reverted transformation, whereas significant decreasing of the austenite fraction and carbon concentration was found in the specimens tempered at 200°C and 500°C due to the precipitation of carbides. Correspondingly tempering slightly deteriorates the ductility when the specimens were tempered at 200°C and 500°C without effects on mechanical properties around 400°C. Based on the analysis of relationship between mechanical properties and retained austenite, it was found that the product of tensile strength to total elongation (Rm*AT) was strongly dependent on the product of the volume fraction and carbon concentration of retained austenite (fA*Cγ ). Furthermore, the optimal mechanical properties with tensile strength 1 000 MPa and total elongation 40% could be obtained after tempering at 400°C with 1 hour, which means that galvanization is feasible in the 0.2C–5Mn steel with ferrite and austenite duplex structure.
TL;DR: In this article, the effect of particle properties on interparticle percolation of small particles (pellets) into a layer of larger particles (coke) during burden descent in the blast furnace was studied.
Abstract: Inter-particle percolation at the interface between the burden layers in the blast furnace influences the permeability in the lumpy zone, and, in particular, in the cohesive zone, where the iron-bearing materials start softening to finally melt. This paper presents a simulation study of the effect of particle properties on inter-particle percolation of small particles (pellets) into a layer of larger particles (coke) during burden descent in the blast furnace. An expanding experimental device in small scale was applied to mimic the conditions at burden descent in a shaft with growing radius, and results from these experiments were used as a reference for the simulations and to validate the computational results. The simulations, which were based on the discrete element method, studied the effect of factors such as friction and restitution coefficients, shear modulus, as well as pellet diameter on the extent of percolating particles. It was found that coke shape, pellet diameter, static friction and inter-particle rolling friction and restitution had a marked effect on the percolation, while rate of expansion of the device, density of pellet and shear modulus proved to be of minor importance.
TL;DR: In this article, the effect of uniform distribution of fine cementite on resistance of ultra-high strength steels to hydrogen embrittlement was studied, where the materials used were directly-quenched and tempered 1000-1300 MPa class low carbon steel plates for welded structures with lath martensite structure.
Abstract: The effect of uniform distribution of fine cementite on resistance of ultra-high strength steels to hydrogen embrittlement was studied. The materials used were directly-quenched and tempered 1000–1300 MPa class low carbon steel plates for welded structures with lath martensite structure. Cementite morphology was different at different heating rates to tempering temperatures. Finer cementite was distributed in rapidly-heated steels (20°C/s) than in slowly-heated steels (0.3°C/s). The rapidly-heated steels showed higher resistance to hydrogen embrittlement than the slowly-heated steels for a slow strain rate test (SSRT), whereas they showed almost the same resistance to hydrogen embrittlement for a constant load test (CLT). The specimens fractured in a plastic region for the SSRT, on the other hand, the CLT was conducted in an elastic region. The difference in hydrogen embrittlement resistance between plastic and elastic loading methods was concluded to result from a change in the hydrogen trap state at cementite in association with plasticity. Hydrogen is more strongly trapped at and/or around the strained interfaces between the matrix and cementite after plastic deformation. A close observation of fracture surfaces, hydrogen thermal desorption analysis and hydrogen microprint technique revealed that the high resistance of the rapidly-heated and tempered steels to hydrogen embrittlement for the SSRT is due to a shift of the fracture mode from quasi-cleavage fracture to ductile fracture. This shift was caused by the suppression of the quasi-cleavage fracture due to less hydrogen at lath boundaries accompanied by the uniform distribution of fine cementite.