Abstract: Hole expansion is one of the most important properties describing the formability of steel sheets, especially those used in automotive industry. In order to determine and emphasize the influence of hole edge conditions and hole surface quality on the results of standardized hole expansion tests, different hole preparation methods such as hole punching, hole drilling and wire cutting were applied to the industrially produced dual–phase and complex–phase steel grades DP800 and CP800. Results of hole expansion testing were discussed with respect to the impact of deformation introduced into the material during the hole preparation and to the material microstructure and mechanical properties. The damage characteristics of every method as well as the fracture surfaces were investigated in detail via light optical microscopy (LOM) as well as scanning electron microscopy (SEM). Qualitative and quantitative analyses of microstructure combined with microhardness measurements were used for the interpretation of the results and are correlated with the mechanical properties and the formability characteristics of the investigated steel grades.

Abstract: By carbon dioxide mineralization, CO2 can be stored safely and leakage-free for very long times. Owing to their high calcium content, steelmaking slags are suitable for mineral carbonation. In a country like Finland, where no suitable geological formations for CO2 storage seem to exist, steelmaking slag carbonation offers an important CO2 emissions reduction option for steel plants. If calcium could be extracted selectively from the slags prior to carbonation, a pure, and possibly marketable, calcium carbonate may be produced. This could replace some of the natural and synthetic CaCO3 used in industry, combining savings in natural resources with CO2 emissions reduction. Development work on the production of pure calcium carbonate from steelmaking slags by carbonation is presented in this study. Selective extraction of calcium from steelmaking slags was investigated using various solvents. Precipitation of CaCO3 from dissolved calcium at atmospheric pressure was also investigated. Amongst the various tested solvents ammonium salt solutions (NH4Cl, CH3COONH4, NH4NO3) were found to be the most promising for selectively extracting calcium from steel converter slag. These solvents dissolved calcium efficiently also from desulphurization slag, while extraction of calcium from two other types of slag was poor. CaCO3 was successfully precipitated from the solution containing ammonium salt and dissolved steel converter slag.

Abstract: Advanced high-strength steels offer a great potential for the further development of automobile bodies-in-white due to their combined mechanical properties of high formability and strength They represent the first choice in material selection for strength and crash-relevant parts with challenging geometries The intensive development of multiphase steels by ThyssenKrupp Steel has led to hot dip galvanizing concepts with an outstanding forming potential Hot rolled, hot dip galvanized complex-phase steels are currently produced in addition to cold rolled dual phase (DP) and retained austenite (RA) or transformation induced plasticity (TRIP) steels New continuously annealed grades of steel are being developed with tensile strength levels of up to 1000 MPa in combination with sufficient ductility for the high demands of structural automobile components These steels make use of the classic advantages of microalloying as well as the principles of DP steels and RA / TRIP steels Further improvement of properties will be reached by the new class of high manganese alloyed steels

Abstract: The application of multiphase steels in the automotive industry has been rapidly increased according to economic, environmental and safety reasons. To determine an optimal combination of high strength and good formability of multiphase steels by using the FE modelling, their complex microstructures have to be considered. Two-dimensional Representative Volume Elements (RVEs) were currently developed based on real microstructures for dual phase (DP) steels. In general, the microstructure of DP steels contains hard martensite particles and a soft ferritic matrix. The strain hardening behaviour of the individual phases was described in the model taking the microstructural constituents and the carbon partitioning during intercritical annealing into account. Two dual phase microstructures with same martensitecontent but different martensite distributions were investigated in experiment as well as in FEM simulation by means of the RVE. The resulting mechanical properties of these steels are strongly influenced by the phase distribution and interaction. As validation, calculated flow curves were compared with the experimental results from quasi-static tensile tests. In addition, the local stress and strain partitioning between both phases depending on the spatial phase distribution and morphology is discussed.

Abstract: The nature of the high work-hardening rate of nitrogen bearing steels was examined focusing on the stacking fault energy (SFE). The dislocation configuration and the width of dissociated dislocations were evaluated in various kinds of austenitic stainless steels with and without nitrogen, using the weak beam method. Nitrogen addition resulted in changing the dislocation configuration from tangled to planar. Nitrogen was, however, found to increase the SFE rather than decrease as reported previously and the SFE can be formulated as a function of chemical composition, SFE(mJ/m2) = 5.53 - 0.16 (wt%Cr) + 1.40 (wt%Ni) + 17.10 (wt%%N). These results indicate that dislocation planarization by nitrogen addition is inadequately explained in terms of SFE.

Abstract: Slags from metallurgical processes are widely used in different fields of application, e.g. in the building industry and as fertilisers. Nevertheless, also these by-products have to be improved to ensure their sustainable use. The treatment of liquid slags, e.g. by changing their composition outside of the steel production process, will lead to interesting new properties of the newly formed products and thus guarantee their use in the future. Moreover, dust and sludges from off-gas cleaning of metallurgical processes are becoming promising resource for coating and alloying elements. The very important element Zn for surface coating is enriched in the dusts, due to the recycling of Zn coated scrap. On the other hand, Zn might run short in the future, so that recovering of Zn from dusts and sludges may become necessary. To improve the efficiency of Zn recovery a dust re-cycling process has been developed for EAF steelmaking by FEhS-Institute. Some interesting side effects are supported by the dust recycling. It has been proved that the slag foaming can be enhanced by dust recycling, even for stainless steelmaking processes. Finally it can be shown that recovery of valuable elements from residues of iron and steelmaking is becoming more and more important. New developed processes are ready to be implemented into the daily steelmaking practise.

Abstract: The stacking fault energy plays a significant role in defining the type of plasticity mechanism which prevails in high-Mn steels. Therefore, a detailed understanding and control over the physical mechanisms that influence the stacking fault energies is crucial for effective design and optimization of such steels. We present results of a first principle study on the influence of the chemical and magnetic ordering on the composition dependence of stacking fault energies in austenitic Fe1-xMnx alloys, which are prototypes for high-Mn steels. Our calculations show that chemical ordering has a significant influence on the intrinsic stacking faults. We have further demonstrated that, although FeMn-alloys have zero net magnetization, the internal magnetic structure significantly changes the properties of the stacking faults. Specifically, we have shown for chemically disordered structures that the dependence of the equilibrium volume and of the SFE on their composition is strongly changed if they are under paramagnetic instead of non-magnetic exposure. These results prove the importance of atomistic simulations for the determination of the SFE and clearly indicate that the magnetic interactions and the chemical ordering in this system must be accurately captured by the theory.

Abstract: The present work aims to study the high-temperature strength of coke. Mechanisms of disintegration were evaluated using basket samples charged into LKAB's experimental blast furnace prior to quench ...

Abstract: A model for viscosity estimation of molten slags in the Al2O2-CaO-MgO-SiO2 system is presented in this work The model is an extension to the viscosity estimation model of molten slags in the CaO-FeO-MgO-MnO-SiO2 system developed before by the present author The present model has explicitly taken charge compensation into consideration It is postulated that Al exists in a structural unit MAl2O4 when MO/ Al2O3 >1 for the Al2O3-MO-SiO2 system (MO=CaO, MgO) MAl2O4 has a similar behaviour as SiO2, ie it can form an Al-O-Al network and be depolymerised by network modifying oxides (CaO, MgO) The present model is applied in viscosity estimation of some slags within the Al2O3-CaO-MgO-SiO2 system A mean deviation of less than 25% is achieved for the present model

Abstract: Iron ore sinter constitutes a major proportion of blast furnace burden. Hence, its quality and consistency have a significant impact on blast furnace performance. Iron ore fines are the main source for sinter, and the chemical composition of the iron ore fines, together with the thermal conditions that blends are subjected to, plays an important role in forming the primary melt during the sintering process and accordingly determines the sinter structure and quality. Therefore, considerable importance has been placed on the chemical composition and consistency of iron ore fines, particularly in terms of alumina content. Due to depletion of high grade iron ore resources, alumina content in the iron ore fines is expected to increase gradually. Ore with higher alumina content is usually expected to be detrimental in forming the sinter matrix, if sintered alone, due to the low reactivity of alumina bearing minerals and the high viscosity of primary melts. The selective granulation process is a new sintering process for high alumina iron ore fines, and can eliminate the adverse effects of ‘hard to sinter’ or ‘unsuitable – for ironmaking’ ores. In the present work laboratory sintering experiments have been carried out with iron ore fines of different alumina level (2.00 to 5.46 mass-%) to know the influence of alumina on mineralogy, productivity, physical and metallurgical properties of sinter prepared by the conventional and the selective granulation process. With increasing alumina content in sinter of both the conventional and selective granulation process, the fractions of hematite and of silico-ferrites of calcium and alumina (SFCA) as well as the pore phase increased whereas the magnetite and silicate phases decreased. With increase in alumina content sinter productivity and tumbler index (T.I.) decreased, and metallurgical properties like sinter RDI and reducibility improved. However, sinter of the selective granulation process showed better results compared to the conventional process.

Abstract: Chromium carbide coatings deposited by the salt bath method have a lot of technologically interesting characteristics. This method produces hard, wear–resistant, oxidation and corrosion–resistant coating layers on steel substrates. In the present study, the kinetics of chromium carbide formation on carburized and uncarburized AISI 1020 steel substrates has been compared. The presence of the Cr7C3 phase on the surface of steel substrates was confirmed by X-ray diffraction. Cross–sectional observation of optical and SEM images showed that chromium carbide layers formed on the steel substrates were rather compact and smooth. The kinetics of chromium carbide coating by salt bath immersion indicated a parabolic relationship between carbide layer thickness and treatment time. The activation energy of the formation of carbide on the surface of carburized and uncarburized steel was calculated to be 87.9 and 225.6 kJ/mol, respectively. Moreover, an attempt was made to present contour diagrams for predicting the thickness of the chromium carbide layer. In addition, the possibility of establishing and using some mathematical relationships between process parameters and chromium carbide layer thickness was investigated.

Abstract: The effect of titanium oxide on iron ore agglomerates is studied by the use of test sinter, test pellets and synthetic briquettes under laboratory conditions. Titanium favours secondary hematite rather than magnetite, which is the main phase in the sinter of Rautaruukki's Raahe plant. Additionally, the effects of sinter RDI and pellet LTD on the blast furnace process are evaluated using the test results of basket trials in LKAB's Experimental Blast Furnace. The effect of titanium in synthetic hematite is studied as hematite is reduced to magnetite in the RDI test. This occurrence causes deterioration in burden permeability. Synthetic titanium-bearing iron oxides under controlled conditions are investigated at the University of Oulu. The effect of TiO2, in solid solution in magnetite, on the magnetite to hematite oxidation is studied separately in order to simulate the final stage of the sintering process. In other experiments, hematite samples doped with various contents of TiO2 are studied using thermogravimetry under a controlled gas atmosphere (CO/CO2/H2/N2). The TiO2 content of hematite has a clear effect on reduction degradation. Also increasing content of TiO2 in solid solution in magnetite radically accelerates the oxidation rate. In the pilot tests, TiO2 content has a similar negative effect on the reduction strength of both sinter and pellets

Abstract: The high strength and formability of steels is based on a large number of competing mechanisms on the microscopic/atomistic scale. Among them are dislocation gliding, dynamic strain aging, mechanical twin formation and local martensitic phase transformations, for which stacking faults play a dominant role. Many of the underlying concepts are based on empirical and experimental data. For a deeper understanding, however, an atomistic simulation of those structural defects becomes more and more crucial. Recent advances in ab initio calculations have sparked a lot of interest in deriving this information from such completely parameter free methods. Employing ab initio methods allows exploring chemical trends, to deliver parameters for phenomenological models, and to identify new routes for the optimization of steel properties. A major challenge in applying these methods to the above questions is the inclusion of all relevant temperature effects on the desired properties. We have therefore developed a large range of computational tools to improve the capability and accuracy of first-principles methods in determining free energies. These combine electronic, vibrational, and magnetic effects in an integrated approach. Based on these simulation tools, we are able to successfully predict mechanical and thermodynamic properties of metals with hitherto not achievable accuracy.

Abstract: Now at Department of Materials Science and Engineering, 6531-G Boelter Hall, University of California, Los Angeles, CA 90095-1595, USA The influence of temperature on the deformation behaviour of a Fe-16.5Cr-8Mn-3Ni-2Si-1Cu-0.25N (wt%) austenitic stainless steel alloy was investigated using transmission electron microscopy and X-ray diffraction measurements. Recrystallized samples were deformedunder tension at -75°C, 20°C, and 200°C and the microstructures were characterized after 5% strain and after testing to failure.Deformation to failure at -75°C resulted in extensive transformation induced plasticity (TRIP) with over 90%
.
-martensite. The sample deformed to 5% strain at -75°C shows that the austenite transformed first to
0-martensite which served to nucleate the
.
-martensite. Transformation induced martensite prohibits localized necking providing total elongation to failure of over 70%. At room temperature, in addition to some TRIP behaviour, the majority of the deformation is accommodated by dislocation slip in the austenite. Some deformation induced twinning (TWIP) was also observed, although mechanical twinning provides only a small contribution to the total deformation at room temperature. Finally, dislocation slip is the dominant deformation mechanism at 200°C with a corresponding decrease in totalelongation to failure. These changes in deformation behaviour are related to the temperature dependence on the relative stability of austenite and martensite as well as the changes in stacking fault energy (SFE) as a function of temperature.

Abstract: In the present work, BaO was used as tracer in the ladle slag to investigate the effect of slag on inclusion composition and the formation of non-metallic inclusions by ladle glaze Experiments wer

Abstract: Decarburization and oxidation have considerable influence on the product properties of spring steels. The investigations in part I of this paper concentrate on the experimental determination of the influence of different thermal cycles on the decarburization process. With the thermo-mechanical simulator Gleeble 1500, the influence of different process parameters, such as the time between furnace reheating and hot rolling, the hot rolling temperature, finish rolling temperature, laying temperature, and the α→γ phase transformation temperature range, is systematically investigated. In part II of this paper [15], numerical simulation techniques are applied to simulate the decarburization behavior under the experimental conditions, which are described in the present part I.

Abstract: The popularity of hot sheet metal forming processes in the recent years has necessitated research efforts to improve tool life and control the friction level during hot forming operations. In this work, the tribological properties of tool steel and ultra high strength boron steel (UHSS) pairs at elevated temperatures have been studied by using a special hot sheet metal forming test rig that closely simulates the conditions prevalent in the real process. This test involves linear unidirectional sliding of a preheated UHSS sheet between two tool steel specimens where new workpiece material is continuously in contact with the tool surface. The study is aimed at investigating different surface treatments/coatings applied on either the tool or sheet surface or on both. The results have shown that it is possible to control the coefficients of friction through surface treatments and coatings of the tool and workpiece materials. The application of a coating onto the sheet material has a greater influence on the friction compared to changing the tool steel surface. After running-in, the investigated tool steel variants show almost similar frictional behaviour when sliding against the same sheet material. Although coating the UHSS sheet reduces friction, it abrades the tool surface and also results in transfer of the sheet coating material to the tool surface.

Abstract: Semisolid processing of aluminium and magnesium alloys has matured to become a well established manufacturing route for the production of intricate, thin-walled parts with mechanical properties as good as forged grades. However, this innovative forming technology faces a major challenge in the case of steels. The tool materials must withstand the complex load profile and relatively higher forming temperatures which promote chemical interaction with steel slurries. Thixoforming tools ought to last thousands of forming cycles for industrial application to be attractive. Hot work tool steel dies proved to be entirely inadequate when thixoforming steels. In spite of extensive research on tool materials for the semisolid processing of steels, there is yet no material to fulfil this critical role. The present work was undertaken to explore the potential of a novel CrNiCo alloy as the tooling material in semisolid processing of steel.

Abstract: Microstructure and mechanical properties were studied in CORRAX maraging steel during prolonged ageing up to 300 h at 798 K. Strengthening of maraging steel was caused by the formation of an intermetallic phase enriched in Ni and Al which exhibits an ordered B2 (CsCl) superlattice structure. Precipitation hardening was accompanied by an increase in micro-hardness with peak hardness after about 12 h of ageing. After 300 h of ageing, the micro-hardness value is still high, corresponding to 94% of the peak hardness. The reverse transformation of martensite to austenite does not take place during prolonged ageing as shown by X-ray and electron backscatter diffraction analyses. The experimentally determined amount of austenite (1-2 vol.%) is in good agreement with the calculated value (about 2.5 vol.%).

Abstract: For production of fluxed sinter the use of dolomite and other MgO bearing materials has increased in the recent past. Flux materials influence the microstructure and chemical properties of the resultant sinter. Improvement in raw material quality and use of alternative raw materials play an important role for improving the sinter quality and overall economics of iron and steel making. The physical and metallurgical properties of sinter mainly depend on the mineralogy of the sinter. Dolomite is composed of calcium magnesium carbonate and dunite consists of magnesium silicate. In the present work laboratory sintering experiments have been carried out with different MgO level (1.40 to 2.60 mass%) to know the influence of MgO on the mineralogy, productivity, physical and metallurgical properties of sinter prepared by using dolomite and dunite. Microstructural examinations of the produced sinter revealed that dunite sinter is bounded with higher amounts of hematite and less calcium ferrites when compared to dolomite sinter. Hematite and calcium ferrite phases decreased whereas magnetite phase increased with increase of magnetite content in sinter using both dolomite and dunite. From the test results it was found that dunite sinter showed better metallurgical properties whereas dolomite sinter showed better physical properties.

Abstract: The effects of carbon on general and pitting corrosion behaviour of Fe-18Cr-10Mn-(0.33∼0.44)N-(0∼0.38)C alloys were investigated using potentiodynamic tests. Carbon made the nitrogen-bearing alloys inert and thus promoted general corrosion resistance. These results were supported by experimental findings, such as elevated corrosion potential, reduced active dissolution rate, lowered passive potential and accelerated hydrogen evolution rate in sulphuric acid solution. The resistance to pitting corrosion in chloride solution was also enhanced by the addition of carbon, which was attributed to the improvement of the stability of the passive film. XPS analysis revealed that the cationic fraction of chromium in the passive film was increased and hence the protection ability of the film was improved by the carbon addition.

Abstract: When producing thin ultra high strength steel components with the press hardening process, it is essential that the final component achieves desirable material properties. This applies in particular to passive automotive safety components where it is of great importance to accurately predict the final component properties early in the product development process. The transfer of heat is a key process that affects the evolution of the mechanical properties in the product and it is essential that the thermal contact conditions between the blank and tool are properly described in the forming simulations. In this study an experimental setup is developed combined with an elementary inverse simulation approach to predict the interfacial heat transfer coefficient (IHTC) when the hot blank and cold tool are in mechanical contact. Different process conditions such as contact pressure and blank material (22MnB5 and Usibor 1500P) are investigated. In the inverse simulation, a thermo-mechanical coupled simulation model is used with a thermo-elastic-plastic constitutive model including effects from changes in the microstructure during quenching. The results from simulations give the variations of the heat transfer coefficient in time for best match to experimental results. It is found that the pressure dependence for the two materials is different and the heat transfer coefficient is varying during quenching. This information together with further testing will be used as a base in a future model of the heat transfer coefficient influence at different conditions in press hardening process.

Abstract: Semisolid processing, already a well established manufacturing route for the production of intricate, thin-walled aluminium and magnesium parts with mechanical properties as good as forged grades, faces a major challenge in the case of steels. The tool materials must withstand complex load profiles and relatively higher forming temperatures for thousands of forming cycles for industrial application to be attractive. Since the forming pressures are much lower than those encountered in conventional forging, the principle die failure mechanism in steel thixoforging is expected to be thermal fatigue. Hence, suitable materials able to withstand the steel thixoforming environment for an economically acceptable life, can be best identified with a thermal fatigue test. Such a test is described in the present work. A novel CrNiCo and a nickel-base superalloy, reported to exhibit superior thermal fatigue resistance in demanding tooling applications, was tested under thermal fatigue conditions encountered in the thixoforming of steels.

Abstract: The amount of heat supplied to the electric arc furnace affects the melting rate. Power delivery in a three-phase EAF is influenced not only by the electric parameters such as arc length and voltage but also by thermal properties of the gases that form the plasma in the arc region. Application of the Channel Arc Model (CAM) suggests that power delivery is enhanced with long-arc, maximum tap operation and plasma gases with high heat capacity. It is also suggested that foaming improves power delivery due to the presence of gases with high heat capacity.

Abstract: Wrought magnesium alloys are interesting materials for automotive and aeronautical industries due to their low density in comparison to steel and aluminium alloys, making them ideal candidates when designing a lower weight vehicle. However, due to their hexagonal close-packed (hcp) crystal structure, magnesium alloys exhibit low formability at room temperature. For that reason, in this study a high velocity forming process, electromagnetic forming (EMF), was used to study the formability of AZ31B magnesium alloy sheet at high strain rates. In the first stage of this work, specimens of AZ31B magnesium alloy sheet have been characterised by uniaxial tensile tests at quasi-static and dynamic strain rates at room temperature. The influence of the strain rate is outlined and the parameters of Johnson-Cook constitutive material model were fit to experimental results. In the second stage, sheets of AZ31B magnesium alloy have been biaxially deformed by electromagnetic forming process using different coil and die configurations. Deformation values measured from electromagnetically formed parts are compared to the ones achieved by conventional forming technologies. Finally, numerical study using an alternative method for computing the electromagnetic fields in the EMF process simulation, a combination of Finite Element Method (FEM) for conductor parts and Boundary Element Method (BEM) for insulators, is shown.

Abstract: The mechanical properties of twinning-induced plasticity (TWIP) steels are often assumed to be solely due to the reduction of the mean free path of glide dislocations resulting from deformation twinning. Other mechanisms may also play an essential role: Mn-C cluster formation, planar glide, pseudo-twinning, short range ordering, and dynamic strain ageing. The present contribution offers a critical analysis of the mechanical properties of high-Mn TWIP steels, especially in terms of Dynamic Strain Aging (DSA) and Static Strain Aging (SSA). The presentation offers new insights into the properties of TWIP steels which were obtained by using new experimental techniques such as in-situ strain analysis and high sensitivity infrared thermo-graphic imaging.

Abstract: For demanding applications high steel cleanliness and strictly controlled inclusions are required. Primary inclusions are formed during steel treatments in the ladle. Most of these are removed to the ladle slag or on the lining. However, the rest of the inclusions still remain through the successive process stages, and additionally new inclusions are formed during casting and solidification due to decreasing thermodynamic solubility of oxygen in the steel at lower temperatures, reactions with surrounding slag, refractory materials and eventual contact with air. Inclusions formation and transformation are simulated by thermodynamic calculations in the steel/inclusions/slag system taking into account the solidification phenomena. In this paper inclusions in Si/Mn-deoxidised steel and Al-deoxidised Ca-treated steels are contributed. Calculations are compared with experimental results from steel plants.

Abstract: In part I of this paper, the decarburization and oxidation behavior of spring steel during simulated thermal cycles resembling the conventional production process have been investigated experimentally. In part II, the results obtained from part I are studied theoretically and numerically by various computational methods. The phenomena discussed in this study include the influence of composition on phase transformation and on diffusion behavior of carbon, decarburization process calculations by simulations of diffusion controlled phase transformations with the software DICTRA, and the development of a simple integrated model to describe simultaneously the decarburization and oxidation kinetics. The simulations show good agreement with experimental results. Moreover, the simulation methodologies can be used to optimize processing parameters and steel composition.

Abstract: In the context of forward bulk extrusion, where product defects are frequently observed, the effect of counter pressure on damage accumulation materializing a Continuum Damage Mechanics (CDM) approach is presented. A Lemaitre variant damage model accounting for unilateral damage evolution coupled with a multiplicative finite plasticity is utilized for this purpose. After a presentation of the crack governing mechanism, it is demonstrated that application of counter pressure introduces a marked decrease in the central damage accumulation, which in turn increases the formability of the material through keeping the tensile triaxiality in tolerable limits. It is also shown that, for a crack involving process, through systematic increase of the counter pressure, the crack sizes diminish; and at a certain level of counter pressure chevron cracks can be completely avoided.