Showing papers in "Steel Research International in 2014"
TL;DR: In this article, an overview of possible ways to recognize a reasonable improvement in iron and steel making industry is summarized, focusing on the following approaches: replacing expensive coke with relatively less expensive alternate fuels having carbon as well as significant amount of hydrogen such as coal, waste plastic and biomass materials.
Abstract: Coke constitutes the major portion of iron-making cost and its production causes severe environmental concerns. In addition, lower energy consumption, lower CO2 emission and waste recycling are driving the Iron and steel making industry to develop “coke free, zero waste or green processes”. In the present article, an overview of possible ways to recognize a reasonable improvement in iron and steel making industry is summarized. The present discussion is focusing on the following approaches:
Replacing expensive coke with relatively less expensive alternate fuels having carbon as well as significant amount of hydrogen such as coal, waste plastic and biomass materials.
Producing agglomerates from cheaper raw materials (secondary resources) as well as improving their performance in BF.
Making the process towards higher carbon utilization by shifting the wustite equilibrium towards lower CO/CO2 ratio by using high reactive coke or catalytic activated one.
Recycling the unused CO in the top gas by removing CO2 from the gas stream.
Much attention has been paid to carbon composite agglomerates (CCA) as a promising raw material for future iron making. Production, mechanical and chemical suitability, reduction behavior, etc. are being elaborated. In addition, other possible ways to utilize CCA in alternate iron-making process has been explored.
56 citations
TL;DR: In this article, the characteristics, origin, and controlling method of stringer shaped B type non-metallic inclusions were studied for linepipe steel, and a new strategy for control of B type inclusions in steel plates was adopted.
Abstract: The stringer shaped B type non-metallic inclusions in linepipe steel plates deteriorates the properties of low temperature toughness, hydrogen induced crack, etc. At present the formation mechanism and controlling method of B type inclusions in mass production are rarely reported. In this paper, the characteristics, origin, and controlling method of stringer shaped B type non-metallic inclusions were studied for linepipe steel. The stringer shaped B type non-metallic inclusions in API X80 linepipe steel plates, produced through “BOF-LF-RH-Ca treatment” steelmaking route, were mainly of CaO–Al2O3 system with lower melting temperatures, which formed because the presence of: (i) small sized liquid inclusions of CaO–Al2O3 system in liquid steel after the secondary refining and Ca treatment. These small inclusions could aggregate to larger ones of 10–20 μm in continuous casting and be deformed into stringer shaped inclusions in steel plates during rolling. (ii) The large sized low melting temperature CaO–Al2O3 inclusions, in Ca treatment, their surface layers could be modified into high melting temperature CaO, CaS, or CaO–CaS system, but the centers were still of CaO–Al2O3 system. During rolling, these inclusions could also be elongated to stringer typed ones because of their soft CaO–Al2O3 centers. A new strategy for control of B type inclusions in linepipe steel plates was adopted. The key of the control was shifted from removing low melting temperature inclusions of CaO–Al2O3 system after Ca treatment to removing as much as possible inclusions especially large sized inclusions before the Ca treatment. With the new strategy, amount of inclusions after RH refining was remarkably decreased and the efficiency of Ca treatment significantly improved. The inclusions found in steel plates were all of high melting temperature CaO–CaS system and the severities of B-type inclusions have been lowered from “≤2.0” to “0”(ASTM E45 standard).
53 citations
TL;DR: In this paper, a mathematical model of a top blown converter, which was based on a physical model of 30 t vessel, was developed in order to run a large number of tracer calculations within a short time, compared to solving for the entire flow evolution each time.
Abstract: A mathematical model of a top blown converter, which was based on a physical model of a 30 t vessel, was developed in this study. A simplified model consisting of the converter was used in the mathematical simulation. With the simplified model, it is possible to run a large number of tracer calculations within a short time, compared to solving for the entire flow evolution each time. A cavity depth and radius comparison has been done between the physical model and the mathematical model, which showed a good relative difference of 2.5% and 6.1% for the cavity depth and radius, respectively. The velocity change in the bath of the converter was monitored by setting several monitoring points in the physical model. A fully developed flow field was assumed to occur when the fluctuations in these points were small or periodic. It took approximately 25 s to get a developed flow field. In addition, the predicted mixing time showed a good relative difference of 2.8% in comparison to the experimental data. A simplified model consisting of the converter has been used in the mathematical simulation. The comparison between the physical model and the mathematical model shows that the simplified top blown model can successfully be used to calculate long-time simulations, and the mixing time calculations in frozen field can save a large amount of time compared to the simulation time using a transient flow field.
45 citations
TL;DR: In this article, a data-driven model was constructed for the Productivity, CO2 emission, and Si content for an operational Blast furnace using evolutionary approaches that involved two recent strategies based upon bi-objective genetic programming and neural nets evolving through Genetic Algorithms.
Abstract: Data-driven models were constructed for the Productivity, CO2 emission, and Si content for an operational Blast furnace using evolutionary approaches that involved two recent strategies based upon bi-objective genetic Programming and neural nets evolving through Genetic Algorithms. The models were utilized to compute the optimum tradeoff between the level of CO2 emission and productivity at different Si levels, using a Predator–Prey Genetic Algorithm, well tested for computing the Pareto-optimality. The results were pitted against some similar calculations performed with commercial softwares and also compared with the results of thermodynamics-based analytical models.
43 citations
TL;DR: In this article, the effect of precipitation of TiN, MgO, and "TiN-MgO" hybrid inclusion on the formation of fine equiaxed crystals was evaluated.
Abstract: The effect of Mg–Ti deoxidation on the solidification structure of advanced high strength steel was investigated by observing the solidification structure and also the inclusion particles. The effect of precipitation of TiN, MgO, and “TiN–MgO” hybrid inclusion on the formation of fine equiaxed crystals was evaluated. The composition of inclusions was observed to change in the order of MgO “MgO(core) + TiN(surface)” Ti2O3 by reaction time, which corresponded to the change of solidification structure as “columnar equiaxed columnar.” This could be understood from the concept of lattice disregistry in between delta iron and MgO (3.97%), TiN (3.91%), and Ti2O3 (18.9%). However, even with very low disregistry between delta iron and MgO, the MgO itself did not work as an effective catalyst, indicating that there is another criterion for determining a good catalyst. The mechanism of the formation of TiN on MgO surface was schematically described. The precipitation of TiN on MgO surface was feasible although the content of Ti and N was lower than the equilibrium solubility product for the formation of TiN. Because disregistry between TiN and MgO is very low (0.05%), the precipitation of TiN on the surface of MgO is energetically more favorable.
41 citations
TL;DR: In this paper, a new model for the simulation of the converter steelmaking process was developed after the detailed study of existing thermodynamic and kinetic models and approaches, which consists of the reaction model and models for charge materials melting and dissolution.
Abstract: A new model for the simulation of the converter steelmaking process was developed after the detailed study of existing thermodynamic and kinetic models and approaches. This model consists of the reaction model and models for charge materials melting and dissolution. The reaction model is based on the coupled reaction model, which includes the combination of both thermodynamics and kinetics of the involved phases. The models of charge material melting and dissolution include the definition of the driving force for the melting and dissolution, and the mass transfer coefficients in the metal and slag phases.
41 citations
TL;DR: In this article, 316L steel syntactic foams incorporating different mass percentages of soda lime borosilicate glass microspheres (3M™) as porosity-introducing particles are produced via metal powder injection molding.
Abstract: 316L steel syntactic foams incorporating different mass percentages of soda lime borosilicate glass microspheres (3M™) as porosity-introducing particles are produced via metal powder injection moulding. Sintering is performed at 1200°C under controlled atmosphere for 1.5, 3, and 6 h. Microstructural features are examined using optical and scanning electron microscopy (SEM) as well as focused ion beam (FIB) preparation and EDX analysis. Response to quasi-static compressive and tensile loads is studied and interpreted based on structural characterization results. Melting of microspheres is observed, but cavities originally occupied by microspheres are maintained, while glass inclusions form in the surrounding matrix. A qualitative explanation of the underlying process is given. Evaluation of the stress–strain curve reveals a comparatively weak expression of the stress plateau matching the relatively low porosity. Analysis of tensile fracture surfaces indicates a shift of failure initiation sites from spinel type MnCr2O4 phases in the reference material to glass inclusions in foam samples. No major influence of sintering time on structural or mechanical characteristics is identified. Despite the adverse effects of microsphere melting, mechanical performance of 316L syntactic foams matches similar materials having Fe and Fe-based alloy matrices.
40 citations
TL;DR: Bussetta et al. as discussed by the authors used the Arbitrary Lagrangian-Eulerian (ALE) formulation to preserve a good mesh quality throughout the computation and showed that these two formulations essentially deliver the same results in terms of pressures and temperatures.
Abstract: Philippe Bussetta, Narges Dialami, Romain Boman, Michele Chiumenti,Carlos Agelet de Saracibar, Miguel Cervera, and Jean‐Philippe PonthotFriction stir welding (FSW) process is a solid‐state joining process during which materials tobe joined are not melted. As a consequence,the heat‐affected zone is smaller and the qualityof the weld is better with respect to more classical welding processes. Because of extremelyhigh strains in the neighborhood of the tool, classical numerical simulation techniques haveto be extended in order to track the correct material deformations. The ArbitraryLagrangian–Eulerian (ALE) formulation is used to preserve a good mesh quality throughoutthe computation. With this formulation, the mesh displacement is independent from thematerial displacement. Moreover, some advanced numerical techniques such as remeshingor a specialcomputation of transition interface is needed to take into account non‐cylindricaltools. During the FSW process, the behaviorof the material in the neighborhood of the tool isat the interface between solid mechanics and fluid mechanics. Consequently, a numericalmodel of the FSW process based on a solid formulation is compared to anotherone based ona fluid formulation. It is shown that these two formulations essentially deliver the sameresults in terms of pressures and temperatures.
39 citations
TL;DR: In this paper, the authors consider the compliance of roll forming mill in simulation models and show options to respect this compliance in the form of new measuring methods, e.g., contact normal stress, standardized, and new measurement methods are applied.
Abstract: Metal forming companies are confronted with increasing customer requirements and qualitative demands. In the course of tighter tolerances and use of harder materials the roll forming process need to be aligned optimally to the profile's specification. Especially in the case of complex cross-sections the simulation of the forming process is a valuable aid. One challenge of reliable simulations is the consideration of the interaction between sheet metal and tools. Due to their simplification, e.g., missing roll compliance, rigid body models cannot describe the profile – tool interaction sufficiently. This can lead to big differences between experimentally and numerically obtained loads and stresses. Since verification possibilities are unavailable, a consideration of the mill compliance in simulation models has rarely been considered, if at all. This paper shows options to respect the compliance of roll forming mills in simulations. For verification of the load parameters, e.g., contact normal stress, standardized, and new measuring methods are applied.
38 citations
TL;DR: In this paper, endogenous inclusions formed in Fe-25Mn-3Si-3Al TWIP steels in laboratorial ingot, mold casting after AOD steelmaking and electroslag remelting (ESR) process at industrial plant, respectively.
Abstract: Twinning induced plasticity (TWIP) steels with excellent strength and elongation properties are expected to be the next generation of automotive high-strength steels. The present work investigates endogenous inclusions formed in Fe–25Mn–3Si–3Al TWIP steels in laboratorial ingot, mold casting after AOD steelmaking and electroslag remelting (ESR) process at industrial plant, respectively. The research shows that AlN and Al2O3 inclusions are found as dominating inclusions, and most of them are AlN, but the number, distribution, size shape of inclusions have big differences in different metallurgical processes. The AlN inclusions in laboratorial ingot mainly present cluster states and have larger size, but after AOD or ESR process most of AlN inclusions are uniformly distributed, this would reduce harm to steel quality. From the point of view of thermodynamics, the research finds that the generation of AlN inclusions in Fe–25Mn–3Si–3Al steels is different from that of most of other high-Al steels or Al-killed steels, because many publications reported that the precipitation of AlN inclusions took place at solidifying front or solid phase, but AlN inclusions formed in Fe–25Mn–3Si–3Al steels generate in liquid steel, and related experimental results prove this point.
35 citations
TL;DR: In this article, the kinetics and thermodynamics of bottom blowing CO2 were investigated and several mathematical models for kinetic study were established, which indicated that it could lead to a little oxidation of elements in molten steel with the processing of bottom-blowing CO2 compared with Ar stirring.
Abstract: In order to explore the metallurgical behavior and mechanism of bottom blowing CO2 in ladle furnace (LF), CO2 was introduced in the LF refining process. The kinetics and thermodynamics of bottom blowing CO2 were investigated and several mathematical models for kinetic study were established. Some exploratory industrial experiments have been conducted with different proportion of CO2 in a 70 ton LF. The results indicated that it could lead to a little oxidation of elements in molten steel with the processing of bottom blowing CO2 compared with Ar stirring. The average oxidation amount of C was in the range of 0.3–0.8 kg. The average oxidation amount of Mn was reduced by 0.0067% and the average oxidation of Al was increased by 0.003%, while the mass fraction of FeO was less than 0.5% in the slag hence it could meet requirements of reductive reaction. Mass transfer of CO in bubble interface or chemical reaction was the possible rate-determining step by comparing calculated results with experimental results. Compared with bottom blowing Ar, types and compositions of inclusions have no big change, plus, the equal yield density of inclusions has decreased and the cleanness of steel was improved. Therefore, it is possible to use CO2 in LF.
TL;DR: In this article, a two-step strategy was preceded using software THERCAST, which was coupled macroscopic segregation with thermal-mechanical GNS method firstly according to the real production condition of superheat, casting speed and spray intensity, the depth of mushy zone and the terminal end of solidification in width direction.
Abstract: Limited by reduction radio, heavy plates manufactured from slabs are always subjected to deterioration of soundness and mechanical properties. For overcoming these defects, in the current works, a new approach, named heavy reduction process to improve segregation and porosity, was presented. The aim this study was to fix the dividing position of improving centerline segregation or porosity. Based on the world's maximum thickness vertical-bending type caster, a two-step strategy was preceded using software THERCAST, which was coupled macroscopic segregation with thermal-mechanical GNS method firstly. According to the real production condition of superheat, casting speed and spray intensity, the depth of mushy zone and the terminal end of solidification in width direction were modeled. After this, the distribution of pressure and bulging were presented, and four positions were preliminarily determined based on the curves. Finally, the element concentration, cracks and reduction rate at these different reduction positions were discussed further. The results indicate that the division point of improving centerline segregation or porosity is confirmed ultimately.
TL;DR: In this paper, a multilevel recursive regression model was used to complete the prediction of end-point phosphorus content during BOF steelmaking process, based on large amount of production data.
Abstract: Removal of phosphorus is a reaction, which plays an important role in combined converter steelmaking process, and the precise control of end-point phosphorus content during BOF steelmaking process would greatly improve the quality of liquid steel. Therefore, the relation between dephosphorization ratio and temperature of liquid steel, FeO content of slag, slag basicity is clearly clarified through thermodynamic analysis of dephosphorization process in this paper. Besides, by means of combining the methods of multivariate regression analysis and multi-level recursive completely, the multi-level recursive regression model, which is used to complete the prediction of end-point phosphorus content during BOF steelmaking process, is established based on large amount of production data. The verification of the model with the data taken from three steel plants indicates that the hit rate of the multi-level recursive regression model is above 84% when predictive errors of the model are within ±0.005%, and it could provide a relatively good reference for real production.
TL;DR: In this paper, the influence of cold rolling on the microstructural changes of 2205 duplex stainless steel was investigated, and the steel samples revealed the presence of almost equal volume fraction of δ-ferrite and austenite phase after hot rolling.
Abstract: The influence of cold rolling on the microstructural changes of 2205 duplex stainless steel was investigated. The steel samples revealed the presence of almost equal volume fraction of δ-ferrite and austenite phase after hot rolling. During cold rolling, the above phase constituents became flattened, fragmented as well as transformed into acicular microstructural constituents with increasing amount of cold deformation. The transmission electron microscopy revealed the presence of strain-induced α′ martensite, Moire fringes, elongated worm-like closed slip band channels and poorly developed dislocation cell structures. The volume percent of the constituent phases has been quantified by X-ray diffraction analysis, which has also been substantiated by the image analysis result. The micro-hardness measurement establishes that the work hardening capacity of austenite is more compared to ferrite.
TL;DR: In this paper, the results of a computer simulation and laboratory experiments carried out to describe the hydrodynamics of steel active flow in the tundish are presented and validated using the commercial program Ansys-Fluent.
Abstract: This paper presents the results of a computer simulation and laboratory experiments carried out to describe the hydrodynamics of steel active flow in the tundish One of the parameters describing the correct influence of FCDs on the tundish operation is the description of the active flow zone (dispersed plug flow and well mixed volume flow) The facility under investigation is a single-nozzle tundish designed for casting concast slabs Computer simulations of liquid steel flow were performed using the commercial program Ansys-Fluent For the validation of the numerical model and verification of the hydrodynamic conditions occurring in the examined tundish furniture variants, obtained from the computer simulations, a physical model of the tundish was employed During laboratory tests simulating the process of steel flowing through the tundish, E type RTD curves were recorded, which were then juxtaposed with results obtained from computer simulations In order to obtain a complete hydrodynamic picture in the tundish furniture variants tested, the computer simulations were performed for both isothermal and non-isothermal conditions
TL;DR: In this article, the effect of different electrical parameters on the type and content of nonmetallic-inclusions in the ESR material X38CrMoV5-1 was investigated.
Abstract: This paper describes the effect of different electrical parameters on the type and content of non-metallic-inclusions in the ESR material X38CrMoV5-1. For these investigations, six ingots were remelted with two DC polarities (cathodic and anodic) and with low frequency (1 Hz) AC power supplies under otherwise comparable remelting conditions, in an open laboratory ESR plant. The investigations included automated SEM-analysis combined with EDX. The results show that the cleaning effect of both DC polarities is lower than the one with a low frequency AC power supply, whereas the cathodic DC polarity results in better cleanliness levels than the anodic one. In addition, the oxygen content of the ingots shows a strong increase when remelting with anodic DC polarity. A strong relation between the electric parameters and the types and sizes of inclusion of the ESR ingots could be found. The most pronounced differences occur with the oxide-type inclusions. Thereby, the amount of the originally dominating (Al,Mg)-spinel-type-oxides is further increased when remelting under DC− and AC conditions, but were rather eliminated in favor of Al2O3-type inclusions when DC+ polarity is used. All oxysulfides, except Al-oxysulfides, were strongly decreased or eliminated. Furthermore, a significant reduction of sulfides, especially CaS took place under all electrical parameters.
TL;DR: In this paper, the IMCT-N-i thermodynamic model was used to calculate the comprehensive mass action concentration NFetO of iron oxides in the selected slag systems.
Abstract: The defined oxidation ability of metallurgical slags based on the ion and molecule coexistence theory (IMCT), i.e., the comprehensive mass action concentration NFetO of iron oxides, has been verified through comparing the calculated NFetO and the reported activity aFetO of iron oxides in the selected FetO-containing slag systems. To calculate the defined comprehensive mass action concentration NFetO of iron oxides in the selected slag systems, a thermodynamic model for calculating the mass action concentrations of structural units or ion couples in CaO-SiO2-MgO-FeO-Fe2O3-MnO-Al2O3-P2O5 type slags, i.e., the IMCT-N-i thermodynamic model, has been developed. The defined comprehensive mass action concentration NFetO of iron oxides is more accurate than the measured activity aFetO of iron oxides to represent the slag oxidation ability of the selected FetO-containing slag systems. The calculated comprehensive mass action concentration NFetO of iron oxides or the reported activity aFetO of iron oxides in the selected FetO-containing slag systems shows an increase tendency with an increase of optical basicity of the slags by taking FeO as 0.93 and Fe2O3 as 0.69, or FeO as 1.0 and Fe2O3 as 0.75, rather than by taking FeO as 0.51 and Fe2O3 as 0.48. The slag oxidation ability represented by the defined comprehensive mass action concentration NFetO of iron oxides or the measured activity aFetO of iron oxides is not only decided by the effects of iron oxides, but also by the comprehensive effects of both iron oxides and basic oxides as CaO or MgO or MnO in the selected FetO-containing slag systems.
TL;DR: The formation of Widmanstatten ferrite was investigated in a 0.036% Nb microalloyed steel at temperatures above the Ae3 using optical microscopy, scanning electron microscopy and electron backscatter diffraction as discussed by the authors.
Abstract: The formation of Widmanstatten ferrite was investigated in a 0.036% Nb microalloyed steel at temperatures above the Ae3 using optical microscopy, scanning electron microscopy, and electron backscatter diffraction. Such strain-induced ferrite appears to form in two consecutives stages: (i) stage I, first observed at strains below 0.5, leads to the presence of Widmanstatten ferrite plates only about 200 nm wide, (ii) stage II, observed at strains >0.5, involves the coalescence of the Widmanstatten plates into grains. Thus the microstructures formed by dynamic transformation are composed of fresh Widmanstatten plates (stage 1) and polygonal grains (stage 2). Over the experimental temperature range of 836–896°C, the ultrafine ferrite plates and grains have areas below 2 µm2 and are difficult to detect using optical microscopy.
TL;DR: In this article, an analysis of the impact of different content of hydrogen and carbon monoxide on the reduction processes equilibrium at the blast furnace conditions was presented, which revealed possible mechanisms of wustite reduction and role of water−gas shift reaction.
Abstract: In recent years, environmental considerations and requirements about limiting of carbon dioxide emissions into the atmosphere again forced researchers to consider hydrogen as an alternative reducer at the ironmaking processes. In those studies, the reduction of iron oxides by a mixture of hydrogen and carbon monoxide mainly was considered, but reducing ability of solid carbon was taken into account rarely. The article presents an analysis of the impact of different content of hydrogen and carbon monoxide on the reduction processes equilibrium at the blast furnace conditions. Calculations were performed by using the FactSage thermochemical software and databases. The study presents influence of hydrogen content in the bosh gas on range of wustite stability at the blast furnace process conditions. The calculations revealed possible mechanisms of wustite reduction and role of water−gas shift reaction and hydrogen itself.
TL;DR: In this paper, the void characteristics in terms of area fraction, density, and average size were examined as a function of thickness strain in the sectioned specimens, and detailed microstructural analysis revealed that interface decohesion at triple junctions of ferrite-ferrite-martensite was the dominant void nucleation mechanism.
Abstract: Ductile fracture mechanism in fine-grained high-strength dual phase steel in sheet form, which incorporated martensite particles in a soft ferrite matrix, was studied through extensive quantitative metallography, scanning electron microscopy (SEM), and electron backscattered diffraction (EBSD) observations of polished sections as well as fracture surfaces analysis of failed specimens. The void characteristics in terms of area fraction, density, and average size were examined as a function of thickness strain in the sectioned specimens. Detailed microstructural analysis revealed that interface decohesion at triple junctions of ferrite–ferrite–martensite was the dominant void nucleation mechanism. EBSD analysis also revealed that void nucleation was predominantly promoted by the increase of ferrite–ferrite grain boundary misorientation with strain, especially at the boundaries incorporating adjacent martensite particles. Moreover, the study of voids nucleation and evolution behavior suggested that ductile fracture in this steel was nucleation controlled such that just before the final fracture incidence, a high density of voids would be nucleated or a sudden accelerated void nucleation could happen. Microscopic observations as well as statistical analysis confirmed this phenomenon.
TL;DR: In this paper, the adverse effect of reoxidation in tundish on non-metallic inclusion in liquid steel and the end product for Ca-treated Al-killed steel were investigated on API-X70 pipeline steel.
Abstract: Reoxidation usually happens during steelmaking, especially in tundish. Severe reoxidation contaminates the steel cleanliness, and detrimentally affects the steel quality and performance. The purpose of this study is to highlight the adverse effect of reoxidation in tundish on non-metallic inclusion in liquid steel and the end product for Ca-treated Al-killed steel. Inclusions of RH refining, tundish, slab, and plate were investigated on API-X70 pipeline steel. To get a more reliable result, automatic scanning electron microscopy ASPEX PSEM EXPLORER was employed to analyze the inclusion with a much larger scan area. It was found that reoxidation in tundish converted the well-modified liquid calcium aluminates into solid Al2O3-rich inclusions, which are more likely to cause nozzle clogging than pure Al2O3, and the inclusion number dramatically increased form 2.8 µm−2 after RH treatment to 13.5 µm−2 in tundish, further decreased to about 6.0 µm−2 in slab and plate. It indicated that reoxidation in tundish put the calcium treatment and strong capacity of inclusion removal during RH treatment in vain. The ratio of liquid inclusions was proportional to average CaO/Al2O3 in inclusions. Big aggregates and stringer shaped inclusions with CaO/Al2O3 locating between 0.08 and 0.13 were found at the 1/2 and 1/4 slab and plate thickness. The stringer shaped inclusions in the plate were the product of big aggregates in the slab after rolling, and made the plate fail to pass ultrasonic testing.
TL;DR: In this paper, a numerical model for the continuous annealing of dual phase (DP) steels was developed and validated using dilatometric tests and physical simulations of various thermal cycles.
Abstract: Manufacturing of dual phase (DP) steels products is a complex process. Application of special thermal cycles during continuous annealing is one of the methods of obtaining DP microstructures. Development and validation of the numerical model for the continuous annealing of DP steels was the objective of the paper. Experimental part include dilatometric tests and physical simulations of various thermal cycles characteristic for the continuous annealing. The former were combined with the inverse analysis and were used for identification of the model. The latter supplied data regarding microstructure and properties after various annealing cycles. Numerical tests of the model confirmed its good predictive capabilities.
TL;DR: In this paper, a comprehensive model for inclusion development in gas stirred ladles developed by the authors is validated in the industrial ladle treatment processes, where important factors like stirring intensity, reaction between steel and slag as well as refractory material, and the conditions needed for separation and floatation of nonmetallic inclusions are taken into account.
Abstract: Steel cleanliness strongly affects the properties of the products. There is an ever increasing requirement of strict control of inclusion composition and amount during ladle treatment. A comprehensive model for inclusion development in gas stirred ladles developed by the authors is validated in the industrial ladle treatment processes. It can be used for the process simulation and optimization. The important factors, like stirring intensity, reaction between steel and slag as well as refractory material, and the conditions needed for separation and floatation of non‐metallic inclusions are taken into account. FactSage and SimuSage packages are employed as the thermodynamics database and simulation tools, respectively. The evolution of steel and slag composition along with the amount and composition of inclusions during the ladle treatment are calculated and compared with results from the industrial process. The comparison between model predictions and actual plant data shows good agreement as well for 210 t heats as for 30 t heats and different steel grades. The present model is a useful tool for simulation and optimization of ladle metallurgical treatments in industry.
TL;DR: The reverse transformation mechanism of martensite to austenite in 00Cr15Ni7Mo2WCu2 super martensitic stainless steel has been studied in this article.
Abstract: The reverse transformation mechanism of martensite to austenite in 00Cr15Ni7Mo2WCu2 super martensitic stainless steel has been studied. The experimental results indicated that the volume fraction of reversed austenite in 00Cr15Ni7Mo2WCu2 super martensitic stainless steel increased first and then decreased with increasing tempering temperature over a range of 550–750 °C after quenching at 1050 °C. The reversed austenite formed along the martensite lath boundaries. When the tempering temperature was below 700 °C, the reversed austenite grew with a Ni-enrichment; when the temperature was above 700 °C, the reversed austenite re-dissolved and transformed to martensite and a part of the reversed austenite divided the original wider martensitic laths into a number of thinner ones. The basic mechanism for formation of the reversed austenite is diffusion in 00Cr15Ni7Mo2WCu2 super martensitic stainless steel.
TL;DR: In this article, the authors investigated the desulfurization of hot metal using different agents, such as fluidized CaO, CaC2, commercial-CaO, Mg, and ZnO.
Abstract: This thesis deals with desulfurization of hot metal using different agents. The aim of this study was to improve the understanding of commonly used desulfurization agents such as fluidized CaO, CaC2, commercial-CaO, Mg, and mixtures of commercial-CaO-Mg. The possibility to use ZnO for desulfurization of hot metal was also investigated. The desulfurization mechanisms and kinetics of these agents were studied. A broad comparison of the desulfurization abilities of the agents was performed under the same experimental conditions. The experimental studies were carried out in a high temperature resistance furnace at 1773 K with good quenching ability and precise control of the oxygen partial pressure.The influence of ZnO in blast furnace slag on the sulfur removal potential was studied. It was found that ZnO does not stay in blast furnace slag under relevant oxygen potentials and consequently has no influence on its sulfur removal capacity.The reaction mechanism of Mg was studied by adding pure Mg into hot metal. It was found that most Mg (about 90 %) escaped as gas in less than two seconds, only providing a little desulfurization. MgS is not formed by homogenous nucleation, but on MgO particles originating from the surface of the added Mg metal.The growth of CaS around CaC2, fluidized CaO and commercial-CaO were measured and compared. The parabolic rate constants were evaluated to be 2.4∙10-7 [cm s-1] for CaC2, and 5∙10-7 [cm s-1] for fluidized CaO particles. The bigger parabolic rate constant of fluidized CaO explains why fluidized CaO achieved a much better desulfurization of hot metal than CaC2 under the same experimental conditions. Commercial-CaO performed less satisfactory in comparison to fluidized CaO powder. This was due to both its less reactive surface and agglomeration of the particles.Agglomerates and large CaO particles lead to 2CaO.SiO2 formation which hindered further utilization of CaO for desulfurization. The 2CaO.SiO2 formation was favored by a high oxygen potential. Since the desulfurization reaction of CaO not only produced CaS but also oxygen, the local oxygen concentration around big CaO particles was higher than around small particles.When small CaO particles were added together with Mg they quickly transformed to CaS. The Mg-gas helped to distribute the CaO particles in the hot metal and improved the kinetic conditions.The desulfurization abilities of some commonly used agents, namely fluidized CaO, CaC2, commercial-CaO, Mg, mixtures of commercial-CaO-Mg, and ZnO were studied and compared under the same experimental conditions. While fluidized CaO showed the best performance, commercial-CaO mixed with 20 mass % Mg achieved the second best desulfurization. Mg-granules performed slightly better than CaC2 and commercial-CaO, but somewhat less satisfactory compared to fluidized CaO and commercial-CaO-Mg mixtures. ZnO does not influence the sulfur concentration of hot metal.
TL;DR: In this paper, the formation of fine-grained mixed microstructure of acicular ferrite and bainite in the simulated coarse grained heated-affected zone was investigated by means of in situ observation and EBSD analysis.
Abstract: The formation of fine-grained mixed microstructure of acicular ferrite and bainite in the simulated coarse-grained heated-affected zone was investigated by means of in situ observation and EBSD analysis. Single, multiple, and sympathetic nucleation of acicular ferrite were observed. Acicular ferrite laths or plates were formed prior to bainite and effectively partitioned austenite grains into many smaller and separated regions. The later formed bainite at lower temperature was confined in those smaller regions, thus resulting in the fine-grained mixed microstructures of acicular ferrite and fine bainite plate.
TL;DR: In this paper, coal, charcoal, and coke breeze were used as embedded reducing agents to decrease the reducing agent rate in a blast furnace (BF) by using self-reducing pellets (SRP).
Abstract: One way to decrease the reducing agent rate in a blast furnace (BF) is the lowering of thermal reserve zone (TRZ) temperature by using self-reducing pellets (SRP). The lower strength requirement of raw materials for small BFs allows the charging of SRP. In the scope of the current study, the behavior of SRP under the TRZ simulated conditions has been investigated. Coal, charcoal, and coke breeze were used as embedded reducing agents. The reduction experiments have been performed under different iso- and non-isothermal scenarios. A Tammann furnace laboratory rig and a simultaneous Thermogravimetric/Differential Thermal Analysis (TG/DTA) experimental set were used for investigations. Mass loss, reduction degree, metallization degree, volume change, and reaction heat flow were examined. The results from experiments with TRZ condition show that embedded reducing agents, especially charcoal, promote iron oxide reduction in pellets. The crushing strengths of SRPs after both methods of hardening, fire-hardening and cement-bonded curing, and the reduction of cement-bonded SRP after curing have been investigated as well.
TL;DR: The material genome of type 316 austenitic stainless steel is presented in this article, which is a set of constitutive equations which describes the microstructure evolution during hot forming.
Abstract: The material genome of type 316 austenitic stainless steel is presented. The material genome is a set of constitutive equations which describes the microstructure evolution during hot forming. Single- and double-compression tests at temperatures of 950–1150°C and with strain rates of 0.01–20 s−1 were performed to obtain the kinetics of dynamic and static events. Inverse analysis, which couples a thermomechanical finite element analysis with experimental data, is used to obtain the flow curves. It compensates the effect of inhomogeneous distributions of deformation and temperature during the compression tests. The sine-hyperbolic law, which relates the flow stress and the Zener–Hollomon parameter, is used to validate the accuracy of the solution. Regression analysis is applied on the coefficients of the flow curves in order to obtain the parameters of the constitutive equations. Microstructure investigations are used to demonstrate the validity of the newly obtained material genome.
TL;DR: In this paper, an electric arc furnace off-gas heat recovery and first experiences with a testing plant based on molten salt as heat transfer fluid was installed inside the existing offgas system of a German mini mill.
Abstract: This paper deals with electric arc furnace off-gas heat recovery and first experiences with a testing plant. The testing plant based on molten salt as heat transfer fluid was installed inside the existing off-gas system of a German mini mill. Targets of the testing plant are to evaluate tube materials and to measure the influence of hot corrosion and dust settlement. First experimental results are presented. Besides experimental measurements numerical simulations were performed. A process simulation was necessary to describe process dynamics. A computational fluid dynamic simulation of the testing heat exchanger was done to calculate the off-gas flow profile around the heat exchanger.
TL;DR: In this paper, a grain-oriented silicon steel as-cast strip was produced by twin-roll strip casting, and the microstructure and texture evolution were investigated by a combination of optical microscopy, X-ray diffraction, and electron backscattered diffraction methods.
Abstract: A grain-oriented silicon steel as-cast strip was produced by twin-roll strip casting. Then the as-cast strip was symmetrically and asymmetrically hot rolled, respectively. The microstructure and texture evolution was investigated by a combination of optical microscopy, X-ray diffraction, and electron backscattered diffraction methods. The microstructure of the as-cast strip consisted of ferrite matrix and martensite, and the texture was characterized by pronounced {001} 〈0vw〉 fiber texture in the outer layers and nearly random texture in the inner layers. After symmetric hot rolling, the microstructure was composed of deformed ferrite grains, proeutectoid ferrite grains and pearlite. The texture was characterized by pronounced {001} 〈0vw〉 fiber texture in the outer layers and mild γ-fiber texture in the inner layers. By contrast, when asymmetric hot rolling was applied, considerably dispersive proeutectoid ferrite and pearlite and relatively strong Goss texture were observed, together with strong {001} 〈0vw〉 fiber texture in the outer layers.