bluuebunny/crossref_metadata_2025 huggingface dataset:
Contribution on the influence of transformation structures under consideration of austenite deformation
Authors: Peisker Dieter , Doktorowski Annett , Dittrich Dirk
Published: December 2016

Hot forming represents a substantial part of the manufacturing process of many steel products. The crucial microstructural transformation process, which influences the characteristics of a steel considerably, is undisputed the γ/α‐transformation. A successful aid to the interpretation of possible microstructural transformation processes during cooling from the austenitizing or deformation temperature is the determination and handling of CCT diagrams. In this article two steels are examined which differ only in their titanium content. Dilatometric investigations were performed varying the three parameters' transformation temperature, strain and cooling strategy. The insights gathered are illustrated and discussed with the aid of CCT diagrams. An additional transformation below Ac1 with a brief curing reheat up to Ac3 + 20 K leads to a substantially finer structure. The exploitation of this effect may be of great industrial importance.
Determination of aluminium nitride or free nitrogen in low carbon steel
Authors: Guetaz Virginie , Massardier Véronique , Merlin Jacques , Ravaine Daniel , Soler Michel
Published: December 2016

As the aluminium nitrides play an important role in the manufacturing of steel sheets, a specific methodology was developed based on the thermoelectric power (TEP) technique, in order to determine the AIN nitrogen by an indirect method. The free nitrogen was determined and then the AIN nitrogen was calculated by the difference between the total nitrogen and the free nitrogen. Indeed, it is easier to determine the dissolved nitrogen, the content of which gradually decreases during the AIN precipitation, than the AIN nitrogen. A low carbon aluminium killed steel was employed with 580 ppm of aluminium and 50 ppm of nitrogen. A comparison of the results obtained by TEP with those obtained by other techniques (hot hydrogen extraction, electrochemical dissolution followed by a mineralization, electrochemical dissolution followed by a sodic decomposition and the Beeghly method) was conducted, in order to determine a reliable technique likely to quantify the amount of aluminium nitrides in aluminium killed steels. With these techniques, it is possible to determine either free nitrogen or precipitated nitrogen. From an experimental point of view, the precipitation kinetics of AIN was followed during an annealing performed at 973 K (700 °C) by TEP and then different precipitation states of AIN were investigated to compare the different techniques: three annealing states (when no nitrogen, half the nitrogen and the total nitrogen has precipitated) and two soaking states (1403 and 1523 K). Thus, it was possible to compare states where the AIN precipitates are in various forms (different shapes, crystallographic structures, sizes, distributions in the matrix). This work showed that the quantification by TEP, hot hydrogen extraction and electrochemical dissolution followed by a mineralization seem reliable whereas the Beeghly method gives good results only for the precipitates formed at high temperatures. In contrast, the quantification by electrochemical dissolution followed by a sodic decomposition does not seem reliable.
An improved method for determining the continuous cooling transformation diagram of C‐Mn steels
Authors: Mesplont Christophe , Zhao Jiu Zou , Vandeputte Sven , De Cooman Bruno C.
Published: December 2016

Dilatometry is often used to study the decomposition of austenite in steels, but the analysis of dilatometric data is often limited to the determination of transformation temperatures. The well‐known lever rule is not applicable when more than one phase transformation occurs. A model accounting for the carbon partitioning effects was developed to extract the phase transformation kinetics of a C‐Mn steel cooled using a wide range of cooling rates. The model is shown to be suitable to analyze the phase transformations in C‐Mn steels and it can be used to obtain a detailed CCT diagram for those steels.
Formation of metal droplets from gas bubbles bursting on iron melt
Authors: Han Zhijun , Holappa Lauri
Published: December 2016

The bursting of gas bubbles on the free surface of liquid iron produces iron droplets that are ejected into the surrounding atmosphere. The bubble bursting phenomenon was detected in situ by applying X‐ray transmission techniques and by collecting and measuring the metal droplets formed. The effect of equivalent bubble diameter on the mass of ejections was studied. A critical bubble diameter was found which produces the maximum quantity of droplets. The critical diameter was about 9 mm for argon/liquid iron system with a surface tension of around 1.4 N/m. The effect of an equivalent bubble diameter on the size and the number of jet droplets formed was also investigated.
Strip formation and process stability in twin roll strip casting
Authors: Badowski Mark , Hentschel Lars , Kopp Reiner , Schmitz Willi , Senk Dieter
Published: December 2016

Process stability in the thin strip casting process of steel has been investigated with a laboratory pilot caster. Depending on the steel grade and the process parameters irregular process states could be observed. It has been proved experimentally that the observed behaviour is not caused by the regulation system. Investigations of microsections on the cast strips have shown evidence of periodical changes in heat flux during solidification and strip formation as the reason for observed oscillating process variables. Similar to conventional flat rolling forward and backward slip between strip and casting rolls during the joining of the shells can occur. Under certain combinations the process parameters and the cast material a backward‐slip can lead to local lift‐offs of the solidified shells. This circumstance significantly disturbs the heat flux and consequently the solidification, even periodically.
Chemistry effects on the crack susceptibility of structural steels during continuous casting
Authors: Bleck Wolfgang , Dahl Winfried , Picht Gunnar , Pariser Gerhard
Published: December 2016

This work is a review of research results, which have been determined in recent years in order to reveal the effects of the chemical compositions on the high temperature properties of structural steels. Special emphasis has been laid on the solidification structure, phase reactions and precipitates. For this comparison exemplary different structural steel grades have been chosen. The effect of the chemical composition on the solidification structure is shown by increasing Ni mass contents up to 10 %, the influence on the phase transformation is illustrated on the basis of a steel with a Mn mass content of 1.6 % and varying carbon contents. The influence of precipitates has been investigated both on the basis of the Mn/S‐ratio and by microalloyed structural steels with different Nb, V and Ti additions. For all these steel grades the laboratory testing conditions were the same. The high temperature properties of steels can be investigated by high temperature tensile tests; the range of good ductility is determined by the measurement of the reduction of area, e.g. RoA > 50 % or >70 %. The upper limit of the ductility range is the temperature of zero ductility, TZD%. The lower limit of the good ductility range is marked by the transition to the ductility minimum II. The experiments for a series of different structural steels show that the hot ductility properties are affected by the metallurgical phenomena mentioned before.
Development of Zn‐Mg alloy coatings by JVD
Authors: Schmitz Bruno
Published: December 2016

To promote continuous dry coatings for steel strip by PVD, CRM develops its own JVD (jet vapour deposition) simulator and applies an economical integration strategy combining continuous annealing of steel and vapour deposition by JVD.

The JVD system is a very compact system, characterised by a high productivity, a very high metal yield, possibility of working at high partial pressure (up to 1 mbar), homogeneous metal distribution and alloy composition and good coating adherence. It was verified that continuous annealing is a very efficient surface pre‐treatment for steel strip in a wide range of industrial dew points. No additional thermal energy is needed for strip heating since this PVD system is introduced in the end section just after continuous annealing. Application to the Zn‐Mg system is described. Influence of annealing parameters, residual gas pressure, coating speed, steel strip temperature and chemistry are discussed.
Effects on the cementite distribution in low carbon enamelling steels
Authors: Bleck Wolfgang , Diederichs Roman
Published: December 2016

To enamel modern LC‐steels it is necessary to provide a sufficient amount of hydrogen recombination sites as well as hydrogen traps within the materials microstructure to keep the hydrogen inside the steel. Hence surface defects like fish scaling, which are related to the effusion of hydrogen, can be avoided. Therefore it is necessary to produce internal surfaces inside the steel In form of hard and brittle particles which can be fractured during cold rolling and produce voids. For LC‐steels these particles could be formed by iron carbides. Aiming at an increased amount of cementite particles inside the steel, the carbon content could be raised or the parameters of the thermomechanical treatment (TMT) could be adjusted for a given carbon content to form coarse cementite particles. In this investigation the TMT‐parameters were systematically varied in hot compression tests and the results were evaluated by quantitative metallography. The focus was laid on the variation of the final deformation temperature, the coiling temperature and the cooling rate after coiling.
Inhibiting the reoxidation of directly reduced iron by vapour phase inhibitors
Authors: Zhang Jianqiang , Grabke Hans J. , Müller‐Lorenz Else
Published: December 2016

The inhibition of the reoxidation of direct reduced iron was investigated by establishing different contents of vapour phase inhibitors in oxidising gas mixture He‐O2 at 150 and 200 °C. The raw materials were iron oxide powder and iron ore pellets which were first pre‐reduced by H2 at 500 °C and then reoxidised. Three stages of oxidation are identified, a rapid initial stage, an intermediate stage in which the rate of reoxidation decreases significantly, and a final stage, in which the rate of oxidation is very low. The length of each stage and the rate of reoxidation are related to temperature and to the status of raw materials.

Four inhibitors were tested. Benzylamine, ammonium benzoate, and the commercial VCI cortec 101 exert a good inhibition on the reoxidation of iron. The inhibition by ammonia, however, is not significant. Presence of water vapour enhances the reoxidation. XPS analysis reveals amines on the surface when benzylamine is added in the oxidation gases.

The ignition temperature of reduced iron decreases with the addition of inhibitors in the oxidation gas atmosphere. This unwanted effect probably is due to organic deposits on iron surface, initiating the burning of iron. The extent of reoxidation, however, is significantly diminished by the inhibitors, thus heating of the material is suppressed and the danger of ignition is decreased.
Modelling the effects of off‐centered ladle streams on fluid flow of liquid steel in a slab tundish
Authors: Aguilar‐Corona A. , Morales Rodolfo D. , Díaz‐Cruz Manuela , Palafox‐Ramos Jorge , Rodríguez‐Hernández H.
Published: December 2016

The effects of off‐centered ladle streams on fluid flow of liquid steel in a two‐strand slab tundish were studied using water modelling techniques and particle image velocimetry (PIV) measurements. Fluid flow in an off‐centered ladle stream was compared with a centered ladle stream. In a centered position the proposed arrangement (turbulence inhibitor plus dams) yields higher fractions of plug flow than the current arrangement (baffles). This effect is stronger at the high casting rate. An off‐centered position increases dead volumes at a low casting rate of 1.7 t/min. At the high casting rate of 3.8 t/min, effects of the off‐centered position are decreased although the TI‐D arrangement always renders better flow characteristics. Velocity fields determined with PIV measurements, demonstrated that the TI‐D arrangements provide the fluid with a plug flow characteristic.
Determination of residual stress and critical rolling temperatures in a microalloyed steel with low carbon and niobium contents
Authors: Gómez Manuel , Hernanz Oscar , Medina Sebastián F. , Tarín Pascual
Published: December 2016

Using torsion tests, residual stress (Δσ) and critical rolling temperatures (Tnr, Ar3, Ar1) have been determined for a low Nb content microalloyed steel by means of simulation of rolling cycles and subsequent representation of mean flow stress versus the inverse of the temperature. The above magnitudes were determined as a function of interpass time for two strains applied in each pass (0.20, 0.35), respectively. Among the results found, it is notable that Δσ decreases with longer interpass times until it reaches zero, and is greater the smaller the strain applied. With regard to the cooling transformation temperatures Ar3 and Ar1, these were found to be practically independent of the interpass time and were higher for smaller applied strains. Temperatures Ar3 and Ar1 were also determined by dilatometry, and comparison of these values showed that both methods yield similar results, except in the value of Ar1.
Mathematical modelling of decarburisation and degassing during vacuum circulation refining process of molten steel: mathematical model of the process
Authors: Wei Ji‐He , Yu Neng‐Wen
Published: December 2016

Based on the mass and momentum balances in the system, a new mathematical model for decarburisation and degassing in the vacuum circulation refining process of molten steel has been proposed and developed. The refining roles of the three reaction sites, i.e. the upsnorkel zone, the droplet group and steel bath in the vacuum vessel, have been considered in the model. It was assumed that the mass transfer of reactive components in the molten steel is the rate control step of the refining reactions. And the friction losses and drags of flows in the snorkels and vacuum vessel were all counted. For the refining process of molten steel in a 90 t multifunction RH degasser, the parameters of the model have been discussed and more reasonably determined.
Investigations of the bonding mechanism at the joining region of a steel sandwich sheet
Authors: Bian Jian , Bleck Wolfgang , Karduck Peter
Published: December 2016

A steel sandwich sheet was produced by a high temperature dipping process. An unalloyed steel was used as substrate and an alloyed steel as coating. At the interface of the sandwich sheet a good bonding between the two different steels could be achieved by a bonding process, which was caused by the formation of a diffusion induced liquid phase. Since the bonding is connected to the formation of the liquid phase at the interface, this is similar to a conventional welding process. This welding process was investigated at the interface of well and partially bonded specimens. Based on these investigations the bonding mechanism could be explained.
Development of the Continuous Dephosphorization and Decarburization Process Using BOF
Authors: Ogawa Yuji , Yano Masataka , Kitamura Shin‐ya , Hirata Hiroshi
Published: December 2016

The authors propose a new refining process, by which hot metal is dephosphorized and decarburized continuously in the same basic‐oxygen furnace, with intermediate deslagging following dephosphorization. After decarburization, slag is kept inside the furnace and reused to dephosphorize the next charge so as to minimize the quantity of slag discharge. Experiments were made to clarify the properties of this process, using an 8‐ton experimental converter. The results confirmed high productivity or a higher rate of dephosphorzation achievable with an increased rate of oxygen blowing and the addition of iron ore. Because of the dephosphorization by low‐basicity slag and the hot recycling of decarburizationslag to dephosphorize the next charge, lime consumption was relatively low. The proper conditions of this process, such as the slag composition for dephosphorization, rate of oxygen supply, bottom agitation, and rate of intermediate deslagging, are also discussed, based on the experimental results.
Thermodynamic Assessment to Chromium Oxidation in the Production of Stainless Steel
Authors: Ma Zhongting , Janke Dieter
Published: December 2016

A solution model called ε approach is applied to predict the thermodynamic solution behaviour of Cr in steel melts. The calculated results are supported by the available experimental results. Further predictions on chromium scorification are achieved in view of melting and refining processes for Cr‐containing steels. Chromium reduction from slags after meltdown during EAF melting and AOD or VOD refining treatment is important for the production of Cr‐containing steels. It is thermodynamically predicted that chromium is inevitably oxidized during decarburization process which coincides with the industrial and experimental results. Minimum oxidation of chromium can be reached by lowering the partial pressure of CO gas at high temperatures.
Finite‐Element Simulations of the Intercritical Deformation of a Low‐Carbon Steel
Authors: Burghardt André , Bodin Andre
Published: December 2016

A mathematical model has been developed to describe the intercritical deformation of a low‐carbon steel under compression. It applies the finite‐element method in a 2D axially symmetric computation domain. By means of a special algorithm different types of microstructures to be used by the deformation model can be constructed, as far as ferrite and austenite phase fractions and distributions are concerned. Calculated results on the basis of constructed microstructures deviate significantly from mixture‐rule predictions. Compression curves exhibit a decreasing strength with increasing connected areas of either phase. The corresponding strain ratios demonstrate the difference in strain behaviour between the ferrite and the austenite phase. In the case of larger connected areas the contribution of the soft ferrite phase to the total strain is much more pronounced than that of the hard austenite phase.
Development of an Aluminized Multi‐Phase Steel with Dual Phase Properties for High Temperature Corrosion Resistance Applications
Authors: Mahieu Jan , Maki Jun , De Cooman Bruno C. , Fiorucci Mauri , Claessens Serge
Published: December 2016

A high strength, high Mn, Cr‐Mo containing multi‐phase steel grade was aluminized with a 90 wt% Al – 10 wt% Si alloy coating, using a laboratory hot‐dip simulator. The adhesion of the coating to the steel strip was evaluated and the microstructure of the as deposited material was assessed. The coated sheet steel was tested at high temperatures by monitoring the weight gain of the samples and their mechanical properties as a function of time. It was found that the thermal properties of the aluminized sheet were excellent. The analysis of the coating/substrate interface revealed the dissolution of brittle intermetallic phases, explaining the excellent high temperature resistance performance of the Al‐Si coating up to temperatures as high as 900°C. In addition, the use of a continuous annealing cycle common in current aluminizing lines, resulted in a dual phase microstructure.
A Survey of the Morphology of Surface Features during Metal‐Forming Operations
Authors: Rasp Wolfgang , Wichern Christian Matthew
Published: December 2016

The morphology of the workpiece surface during and after metal forming operations is dependent on the type and magnitude of the forming operation, the lubrication and the initial surface condition. The current work is a survey of the surfaces that result from mechanical forming of workpieces with different initial surface conditions. The mechanical forming, the bulk material properties and the lubrication condition were maintained as constant as possible. Polished, as rolled, etched, coarsely ground and model surfaces were deformed under plane strain and the surface changes were digitally recorded and examined.
Micromechanical Modelling of TRIP Steels
Authors: Van Rompaey Tim , Furnémont Quentin , Jacques Pascal J. , Pardoen Thomas , Blanpain Bart , Wollants Patrick
Published: December 2016

The combined thermodynamic‐micromechanical model of Fischer [1] is applied to a low‐alloyed TRIP steel with a volume fraction of 16% of retained austenite. The model is implemented in a finite element code. The mesh consists of 9 by 9 by 9 cubical elements, each representing a single grain with a random crystallographic orientation. The retained austenite grains are randomly dispersed through the entire mesh. The extent of the martensitic transformation in all austenite grains is calculated. A large spread in transformation rate is observed. The most favourably oriented grains reach a full martensitic structure, while the martensite volume fraction of less favourably oriented grains is less than 50%. When the chemical driving force is more negative, the onset of the transformation is delayed and the increase of the martensite volume fraction is slower. The calculated results are compared with experimentally obtained values. Although in general a reasonable agreement is found, Fischer's approach leads to some discrepancies with experimental observations.
Statistical Design and Evaluation of Experiments in Steel Production
Authors: Lundberg Sven‐Erik
Published: December 2016

Making experiments under industrial production conditions gives many times difficulties in varying the important parameters in a relevant way in order to significantly Influence the process and thus make it possible to measure the result. The common way of varying one parameter at a time, gives rise to many experiments and mostly, large difficulties in the evaluation.

The statistical design method, on the other hand, where the parameters are varied systematically and simultaneously, gives possibilities to influence the process in a more efficient way, thus reducing the necessary number of experiments, and at the same time to obtain more reliable results. In spite of the linear approach presented here, it is always possible to evaluate any kind of influence on a process, by choosing the studied parameters in a relevant way. This is simply done by means of a suitable variable transformation before the experimental matrix is set.

Analytical evaluation of the experiments often raises a voluminous mathematical treatment of the results. However due to the linearity of the primary functions, the experiments can be evaluated by means of a simplified linear procedure, and even large experimental matrices can easily be evaluated only by means of a simple spread sheet program.

By application of the method to industrial problems, a calculation model was developed for the prediction of process parameters for quenching and self tempering of rebar, as a function of requirements and chemical composition of the steel. Alternately the required chemical composition can be predicted when required mechanical properties and quenching parameters are given, or the mechanical properties can be predicted when composition and quenching parameters are given. Another use of the method has been to optimize the finish rolling and coiling temperatures for on line treated high carbon steel wire rod.
Numerical and Experimental Investigations of Curved Fatigue Crack Growth under Proportional Cyclic Loading
Authors: Theilig Holger , Wünsche Michael , Bergmann Rolf
Published: December 2016

The present paper demonstrates that the common computer‐aided two‐dimensional crack path prediction can be considerably improved in accuracy by using a new predictor‐corrector procedure in combination with the modified virtual crack closure integral (MVCCI) method. The numerical crack growth simulation is still based on a step‐by‐step technique, but uses a piecewise curved approximation of the crack path. By this method, both the new locus of the crack tip and the slope of the crack path at the crack tip can be computed simultaneously by the mode I and II stress intensity factors for only one virtual tangential crack extension with respect to the previous step. Furthermore, the paper presents a new finite element technique of calculating stress intensity factors of mixed mode problems by MVCCI Method. The procedure is devised to calculate the separated strain energy release rates by using the convergence of two separate calculations with different element sizes in the neighbourhood of the crack. The method provides robust calculation ability, even in the case of very coarse meshes. In order to evaluate the validity and efficiency of the proposed higher order crack path simulation method in relation to the well‐established basic strategies, experiments of curved fatigue crack growth are carried out with a specially designed specimen under proportional lateral force bending. In all investigated cases the computationally predicted crack trajectories show an excellent agreement with the different types of curved cracks that are obtained in the experiments as a function of the position of crack initiation.
Modelling of Nitrogen Intrusion into an AOD Converter at the Reduction Stage Caused by Suction Oscillation in the Ventilation Hood
Authors: Tang Yong , Fabritius Timo , Härkki Jouko
Published: December 2016

Some AOD operators doubt that unusual high nitrogen content in low nitrogen grade stainless steel may come from the entrapped nitrogen of air through the gap between hood and AOD converter under some unsteady conditions. This paper modelled the unsteady condition caused by pressure jumping in the ventilation system of an AOD vessel in order to investigate the possible nitrogen intrusion inside the converter. Commercial CFD code, FLUENT6.1, was applied to study the gas flow field, thermal conditions and species transfer in the computing domain. The stainless steelmaking converters in AvestaPolarit's stainless steel plant in Finland, named AOD1 and AOD2, were simulated respectively. The modelling was carried out at the reduction stage of the AOD process, in which only argon is blown from the bottom tuyeres. The results show that most hot gas from the AOD converter escapes to the atmosphere as the local relative pressure in the ventilation hood jumps to a high value. The temperature inside the hood climbs suddenly when the suction ability of the ventilation system drops and the direction of the exhaust gas flow reverses. Because of different geometric location between hood and converter, the air can intrude further into AOD1 converter than into AOD2. Therefore, the high nitrogen fraction area also projects deeper inside AOD1. Although gas containing a high nitrogen fraction can be entrapped inside the converter due to a dramatic drop in suction ability in the ventilation system, the present research suggests that the area rich in nitrogen is so limited inside AOD that the mass fraction of nitrogen does not exceed 5% near the melt bath surface.
Direct Smelting of Metallurgical Dusts and Ore Fines in a 125t DC‐HEP Furnace
Authors: Tzevelekou Theofani V. , Geck Hans Günter , van Hüllen Peter , Höfer Friedrich , Papamantellos Demetrios C.
Published: December 2016

In the metallurgical plant of LARCO at Larymna, approximately 200000t/y of nickelferrous dust are collected in the gas cleaning systems of the Rotary Kilns (R/Ks) corresponding to an annual production of 100000t FeNi20%. In addition, a stockpile of one million tons of old R/K dust lies close to the plant and the community of Larymna. A “one‐stage” environmentally friendly process has been developed for the recycling of this dust by direct reduction smelting in a DC arc furnace. The industrial adaptation of this process was tested in the 125t DC‐HEP (Direct Current — Hollow Electrode Powder) furnace at Georgsmarienhütte steelwork (GMH) in Germany. About 70t of dust were directly smelted by injection through the hollow electrode of the furnace. The nickel recovery in the metal bath was 93‐99.9%. Final products were low nickel alloyed steel grades and slag suitable for special cement types production. Main cause of the dust generation in the R/Ks is the disintegration of laterite and the ore fines fraction after the ore crushing. Their separation, collection and metallurgical exploitation prior to their feeding in the R/Ks would significantly reduce the amount of the generated dust. Therefore, the smelting of untreated laterite ore fines in the DC‐HEP furnace was also indicatively tested. Thus, a zero residues industrial production process was developed for the recycling of nickel bearing dust and ore fines by smelting in a DC‐arc furnace, since the finally produced FeNi‐alloy and slag are 100% utilized in the steel and cement industry respectively.
Formation of Aluminide Coatings by a Low Temperature FBCVD Process
Authors: Christoglou Christos , Bulancea Catalin , Angelopoulos George N.
Published: December 2016

The formation of aluminide coatings on Ni, Inconel 738, NiCr23Fe, SS304 and ARMCO Fe by a Fluidised Bed Chemical Vapour Deposition (FBCVD) process at low temperatures (550‐650°C) was studied. Aluminium powder and a HCl activator were used to form precursor halide vapours of Al. This led to the aluminide coating formation on the substrate's surface. The examination of the treated samples by means of optical microscopy and SEM/EDX indicated the deposition of dense and homogeneous coatings over the entire surface even for small treatment times. Coating thickness growth and coating morphology were evaluated for various treatment times and temperatures. The low temperature process has advantages compared to the high temperature process since the mechanical properties of the treated parts are not affected, although the coating thicknesses achieved are smaller.
Evaluation of a New Process for Ironmaking: a Productivity Model for the Rotary Hearth Furnace
Authors: Fortini Otavio , Fruehan Richard
Published: December 2016

In order to address the key issues of capital costs and CO2 emissions in ironmaking operations, a new process was proposed combining a Rotary Hearth Furnace (RHF) and a Bath Smelter. This paper describes the construction of a productivity model for the RHF based on previous studies concerning the reduction behaviour of pellets of carbon and iron oxides. The model was used to estimate changes in RHF productivity according to the type of carbon used in the RHF pellets, numbers of layers of pellets, final metallization degree of the direct reduced iron (DRI) produced, and initial sizes of the pellets. The results indicate that productivity gains between 33 and 46% can be achieved replacing coal with wood charcoal, a carbon source virtually free of net CO2 emissions. Also, the productivity of the RHF can be doubled by reducing the charge only up to 70% metallization. The model allows the study of changes in overall energy consumption due to changes in the extent of primary oxidation of the gas at the pellet level showing that the use of wood charcoal increases the total amount of carbon consumed by less than five percent relative to operations with coal.
Observation and Measurement of Bubble Separation at Liquid‐Liquid Interfaces
Authors: Chevrier Vincent , Cramb Alan W.
Published: December 2016

Incomplete separation of bubbles at liquid‐liquid interfaces during steel casting can lead to subsurface problems in castings that can ultimately result in product defects. An oil‐water model was used to study the separation of bubbles at an oil‐water interface. It was found that rest times of droplets and bubbles at the interface are quite variable with average rest times a function of chemistry and temperature (due to viscosity and interfacial tension changes) and bubble size. The results of these studies were compared to a study of bubbles separating at a steel‐slag interface conducted by X‐Ray Fluoroscopy. All of the phenomena noted in the separation of bubbles at an oil‐water interface were also documented in high temperature experiments. The low temperature results were repeatable and allowed a better understanding of the factors controlling separation. It is postulated that the mechanism of film rupture after drainage is responsible for the variation in measured rest times and accounts for the fact that observed rest times are significantly greater than observed or calculated drainage times.
Oxidation and Characterization of As‐Cast TRIP Steel Surfaces
Authors: Senk Dieter , Sridhar Seetharaman , Safi Mohammad , McDonald Neill J. , Krings Miriam
Published: December 2016

This paper presents recent results from a collaborative study between the Department of Ferrous Metallurgy at RWTH‐Aachen University and the Department of Materials Science and Engineering at Carnegie Mellon University on high temperature oxide scale formation of Al and Si containing as cast TRIP steel surfaces under conditions similar to that of continuous casting and hot rolling. A combination of experimental studies consisting of (i) electron microprobe analysis and metallographic studies of the cast steel surface, (ii) direct visualization of the oxide formation through high temperature confocal scanning microscopy and (iii) Tammann furnace oxidation tests were carried out. It was found that internal oxidation of Al and Si takes place along the inter‐dendritic boundaries, where Al and Si were found to have been enriched after casting. The scale formed on the steel surface was a complex mixture of solid fayalite ((FeOn)2(SiO2)), wüstite (FeOn), magnetite (Fe3O4), hematite (Fe2O3), and Fe‐particulates and the rate of scale growth appears to have been controlled at high temperatures by the formation of a liquid slag layer that allows for rapid oxygen transport to the steel/scale interface.
Phenomenological Description of the Surface Morphology and Crack Formation of Continuously Cast Peritectic Steel Slabs
Authors: Weisgerber Bernadette , Harste Klaus , Bleck Wolfgang
Published: December 2016

The surface quality of continuously cast material is strongly depending on the initial solidification of the steel. Oscillation marks are formed at the very early stages of the strand shell growing process, thus influencing the microstructure and cracking behaviour of the surface and subsurface region. An industrial study of the oscillation mark morphology and the surface structure of peritectic medium carbon steel slabs was performed. The formation of oscillation marks and their effect on the surface quality was examined by metallographic investigations of slab samples. Although constant casting and oscillation conditions were applied, a variation of oscillation mark geometry along the narrow faces of the slabs was measured. A relation between the depth of the oscillation marks and the thickness of a layer of segregated melt situated inside the bottom of the marks was found. Measuring the distribution and length of surface and subsurface segregated cracks in the vicinity of the marks, existing theories of oscillation mark formation could be confirmed. The austenite grain size was found to increase with increasing oscillation mark depth. There was no clear correlation between the austenite and the δ‐ferrite grain size.
Finite Element Modelling of TRIP Steels
Authors: Papatriantafillou Ioannis , Aravas Nikolaos , Haidemenopoulos Gregory N.
Published: December 2016

A constitutive model that describes the mechanical behaviour of steels exhibiting “Transformation Induced Plasticity” (TRIP) during martensitic transformation is presented. Multiphase TRIP steels are considered as composite materials with a ferritic matrix containing bainite and retained austenite, which gradually transforms into martensite. The effective properties and overall behaviour of TRIP steels are determined by using homogenization techniques for non‐linear composites. The developed constitutive model considers the different hardening behaviour of the individual phases and estimates the apportionment of plastic strain and stress between the individual phases of the composite. A methodology for the numerical integration of the resulting elastoplastic constitutive equations in the context of the finite element method is developed and the constitutive model is implemented in a general‐purpose finite element program. The prediction of the model in uniaxial tension agrees well with the experimental data. The problem of necking of a bar in uniaxial tension is studied in detail.
Experimental Studies of Gas‐Liquid‐Powder Flow in Moving Particles
Authors: Pinson David , Pham Thinh , Yu Ai‐Bing , Zulli Paul
Published: December 2016

An experimental study has been carried out of gas‐liquid‐powder flow in moving particles in one‐ and two‐dimensional packed beds, simulating the complex four‐fluid flow conditions in an ironmaking blast furnace which involves the upward flow of gas and unburnt coal/char and the downward flow of coke and molten iron and slag. It is shown that the contacts between packed particles are important for powder entrapment, and the presence of a liquid phase can significantly increase the powder hold‐up and gas pressure drop. Only when the packed particles have significant downward velocity can the flow of powder and liquid be maintained without flooding. Depending on the flowing conditions, both steady and unsteady flows can be observed, giving the so‐called operational and non‐operational regimes. For the gas‐glass powder‐water system considered, the effects of solid, liquid, powder and gas flow rates on the two regimes have been quantified. The non‐operational regime stems from the flooding caused by high gas and liquid flowrates and/or hanging caused by high powder and low gas flow rates. The operational regime expands with solid flow rate, and contracts with an increase in gas, liquid and/or powder flow rates. Implications of the findings to blast furnace operations are also discussed.
Correlation between Surface Structure and Iron Nucleation in the Wustite Reduction
Authors: Bahgat M. , Sasaki Yasushi , Ishii Kuniyoshi
Published: December 2016

The effects of the orientations of surface grains on the iron nucleation process during the wustite reduction at 1073 K were studied. The orientation of grains in polycrystalline wustite was measured by applying electron backscattering patterns technique. Comparing the numbers of the formed iron nuclei in the grains with different orientations, the reactivity of iron nuclei formation was established as a function of grain orientation. The highest number of iron nuclei was observed in the grain with the orientation of (649). The nucleation behaviour was discussed based on the BCF (Burton‐Cabrera‐Frank) model of crystal growth. The step density in the surface structure of the grains was found to be the dominant controlling factor for the iron nuclei formation during the wustite reduction process.
Study of the Effect of Hellenic Diasporic Bauxite Addition on Blast Furnace Operations
Authors: Karamoutsos Spyridon , Alexopoulou Irene. E. , Papanastassiou Dimitri , Papamantellos Demetrios C.
Published: December 2016

The blast furnace (BF) operation, as well as the steel‐shop downstream, can derive benefits from adjusting the slag alumina content with the proper addition of bauxite flux to its burden. Additions of 5‐15 kg of bauxite/t hot metal lead to a raise of the alumina content of the resultant BF‐slag from 10% to the level of about 12%. In Hellas extensive deposits of diasporic bauxite exist which, however, are under‐utilized by the alumina refineries due to their rather low solubility during the Bayer‐process. The above BF application, therefore, as an alternative use of the diasporic bauxite, is of great interest to the bauxite producers of Hellas.

The influence of the bauxite additions on the metal/slag reactions under BF‐conditions was simulated in the laboratory by smelting BF‐slag with diasporic bauxite additions in a graphite crucible. It was achieved the production of BF‐slags with higher alumina contents under the condition of constant slag basicity. The results show the beneficial effect of the bauxite addition to the quality of the produced hot metal. In accordance to its desulphurization and desiliconization as well as the increase of BF‐slag sulphur capacity and fluidity, a thermodynamic evaluation of the metal/slag reaction in respect of SiO2 reduction and S‐transfer to the slag in relation to its Al2O3 content was carried out. This evaluation led to simple algebraic functions and graphs easily applicable by the BF operators. The attained metallurgical results were verified in comparison to industrial test heats with bauxite additions in the BF‐burden in USA, Canada and Europe.
Effect of Annealing Conditions on the Texture and Normal Anisotropy of Al‐Killed Steels in Simulated Batch Annealing
Authors: Juntunen Pasi , Karjalainen Pentti , Peltola Ari
Published: December 2016

Three commercial cold rolled Al‐killed steels were investigated to study the effect of annealing conditions on the crystallographic texture and the resulting plastic anisotropy. The heating rates, maximum temperatures and isothermal holding times were varied in 18 laboratory scale thermal cycles applied to all steels. The annealed and skin‐passed samples were tensile tested to determine mechanical properties and anisotropy parameters. Grain structures and average grain sizes were examined by an optical microscope and the textures were measured by X‐ray diffraction.

It was found that the chemical composition of the steel had a significant effect on the texture and normal anisotropy obtained at certain heating rates. The differences between the current steels were discussed in the light of the competition between the kinetics of AIN precipitation and recrystallization. Excess heating rates led to a low normal anisotropy, which was not improved by extending the isothermal time of annealing. Pancake grain structure and the grain size larger than 20 mm were found to be indicators of the properly chosen heating rate and resulting in high normal anisotropy. At the proper heating rate high normal anisotropy was attained at low annealing temperatures and in short isothermal times, but a longer isothermal annealing was required to obtain a low yield strength.
Effect of a Phase Formation on Mechanical Properties of Stainless Steel SUS309L after Isothermal Aging
Authors: Lin Dong‐Yih , Chang Tao‐Chih
Published: December 2016

The effect of σ phase formation on mechanical properties, such as the tensile strength, hardness and reduction of area, of SUS 309L stainless steels with various Si content after isothermal aging was investigated. The experiments were performed using tensile and Rockwell hardness tests and scanning electron microscopy. The tensile strength of SUS 309L stainless steels with 0.17, 0.34 and 0.73 wt% Si content increased with increasing aging time from 0 to 200 h. The hardness also increased after the same aging parameters. However, the reduction of area of these materials with different Si content decreased significantly.
New Developments for Powder Coal Injection into the Blast Furnaces
Authors: Assis Paulo Santos , Vieira Cláudio Batista , Nolasco Sobrinho Pedro José
Published: December 2016

Experiments and results concerning Powder Coal Injection into blast furnaces are presented. A pilot plant, similar to a blast furnace tuyere, with a high thermal gradient, developed at Escola de Minas‐UFOP, Brazil, is described. Several tests have been performed in this pilot plant, using a mixture of three coals and preheating the coal, giving the following conclusions: preheating of coal and the mixture of more than two coals, not commonly practised by now, are appropriate for improving the combustion rate and thus enhancing the coal injection technique.
Flow, Thermal and Microstructural Analysis during Cast Rolling of Steel in In‐line Strip Production Process
Authors: Mapelli Carlo , Venturini Roberto
Published: December 2016

A mathematical model was developed to describe the in‐line hot rolling deformation and recrystallization behaviour of austenite after the solidification on a thin slab casting plant. The most significant features of the cast rolling process were taken into consideration: through‐thickness thermal gradients, inhomogeneous stress and strain, temperature discontinuity between the strip and the rolls. A HSLA (High Strength Low Alloy) steel has been chosen to perform the experiments of cast rolling. The characteristic constants ruling the microstructural evolution of that steel were computed and integrated into the computational module which manages the structural stress‐strain and strain rate computation. The developed approach is based on the Navier‐Stokes’ equations which were used to compute the speed field in the strip during the deformation. Then a model providing a proper constitutive equation was structured on the basis of the Yada's model based on evolution of the dislocation populations. The use of the Navier‐Stokes’ formalism allows to reach the resolution of the structural problem from the data measured easily during the industrial practice (i.e. speed of the rolled product at the entry and at the exit of a stand, the temperature of the rolled material). The validation of this computational approach was obtained by a comparison between the prior austenite grain size of the strip in different positions of the hot rolling process, as well as by a comparison between the computed deformation power and the measured one provided by the engines moving the rolls.
The Influence of Rapid Annealing Cycles on the Recrystallisation Behaviour of Cold Rolled Ultra Low Carbon and Low Carbon Steel
Authors: Kizu Taro , Bleck Wolfgang , Lesch Christian
Published: December 2016

For ultra low carbon (ULC) and low carbon steel (LC), the influence of heating rate, annealing temperature, and holding time on the recrystallisation behaviour and the resulting grain size was investigated. For ULC smallest grain sizes of about 9 μm were obtained at the lowest heating rate whereas for LC significant smaller grain sizes of about 5 μm were determined at the highest heating rate. Furthermore, the evolution of the grain size distribution with varying heating rate, annealing temperature, and holding time was studied in dependence of the rolling and normal direction. The state of the as‐hot rolled microstructure as well as the precipitation state exert a strong influence on the development of the recrystallised microstructure along the different directions for both steel grades. The inherent prolonged microstructure due to the cold rolling process is still obvious just after recrystallisation. With ongoing annealing and grain growth, the aspect ratio approaches the equiaxed state. This change proceeds faster for the ULC steel grade. With increasing annealing temperature, the bimodal character of the grain size distribution disappears and the distribution becomes more homogeneous.