bluuebunny/crossref_metadata_2025 huggingface dataset:
Hydrogen permeation through oxide and passive films on iron
Authors: Schomberg Karen , Grabke Hans Jürgen
Published: December 2016

Hydrogen permeation through thin films of FeI–Y O on iron and through chemically polished iron were investigated by the sensitive electrochemical technique. The oxide was formed on the exit side of the sample membrane. The hydrogen arriving at the iron/oxide interface is in an atomic or protonic state which renders the hydrogen uptake by the oxide possible.

The wustite films were formed by oxidation in a H2O‐H2‐atmosphere. The dependence of the hydrogen permeation current on temperature and film thickness and different degrees of nonstoichiometry in FeI–Y O was studied. Hydrogen permeation through these oxides is possible, but very low permeation coefficients have been found, of the magnitude of at 25°C. The diffusion coefficient of diffusible hydrogen was determined to be about 4 · 10−10 cm2/s. Measurements of the potential dependence of permeation across the film indicate that hydrogen migrates in the oxide as a charged particle (proton).

In the case of the passive surface film on iron formed by chemical polishing, the dependence of the permeation current on temperature and anodic potential was measured. The electrochemical behaviour of the film was studied by cyclic voltametry. Electron transfer reactions were investigated by means of the hexacyanoferrate (II/III) redox system. Further information on the film composition were obtained by Auger electron spectroscopy. On the one hand, electron transfer across the film can occur, but on the other hand, the film is nearly impermeable for hydrogen, even if the hydrogen is in the atomic or protonic state. Cyclic voltamograms show the formation of an oxygen adsorption layer on the film in a range of anodic potential.
A study on the mechanism of reaction between refractory materials and aluminium deoxidised molten steel
Authors: Brabie Voicu
Published: December 2016

The conditions of formation of inclusions in steel during ladle refining in MgO‐C lined ladles have been investigated in laboratory experiments at 1873 K in MgO‐C crucibles with 50 g iron. From both the experimental results as well those of a thermodynamic study conducted in parallel, the following conclusions can be made about the reaction mechanism between the MgO‐C refractory and aluminium deoxidised molten steel: At steelmaking temperature an internal oxidation‐reduction occurs in the MgO‐C refractory. The formation of a thin oxide layer at the interface is due to the reaction between magnesium vapour and aluminium dissolved into the molten steel and the CO(g) generated by the reaction between MgO and C in the crucible walls. The oxide inclusions formed in the steel have been shown mainly to consist of MgO, Al2O3 or mixture of them. Some of the finest inclusions are considered to be formed as secondary inclusions during cooling and solidification of the steel and they are connected only with the diffusion of magnesium from the crucible to the molten steel. The thermodynamic calculations indicate that during vacuum refining, as the pressure decreases, the chemical compatibility of carbon‐bonded magnesia for ladle lining decreases.
Quantitative study of modification of sulphide inclusions by calcium and its effect on the impact toughness of a resulfurised alloy steel
Authors: Jiang Laizhu , Cui Kun
Published: December 2016

In this paper, the mechanisms of the shape control of sulphide inclusions by calcium in a resulfurised alloy steel and the quantitative effect of the shape factor, the size and the quantity of sulphide inclusions on the transverse impact toughness are investigated. There are three different types of sulphide inclusions in the calcium‐treated resulfurised alloy steel, 58CrNiMnMoVSCa, namely elongated MnS, oval (Mn,Ca)S with and without any calcium aluminate nucleus. The proportion of the former is reduced while that of the two latter raised as the ratio of Ca/S in steel increases. The mechanisms of the shape control of sulphide inclusions by calcium are mainly due to its solid solution hardening effect. Besides, the calcium aluminate, existing as the nucleus of the oval (Mn,Ca)S, restricts the hot deformation of the sulphide inclusions and as a result, enhances further the shape control. Based on the solid solution effect of calcium on sulphide inclusions, the quantitative relationship between the shape factor Λ of sulphide inclusions and the ratio of Ca/S in steel at a hot forging reduction of 85 is developed. Finally, the quantitative relationship between the transverse impact toughness and the parameters of sulphide inclusions, namely the shape factor (Λ), the size (L) and the quantity (N) is also developed.
Microanalytical assessment of solidified slags in view of steel dephosphorization
Authors: Preßlinger Hubert , Antlinger Kurt , Klepp Kurt O. , Hiebler Herbert
Published: December 2016

The process of refining hot metal in the LD‐converter leads to the formation of a slag which according to the theory of ionic dissociation consists of anions, anionic complexes and metal cations. The electroneutrality principle forces local order in the liquid slag ‐ which is transformed to long range order during the solidification of the crystal lattices.

Solid converter slags obtained at the end of blowing consist of mixed crystals of dicalcium silicate, wustite, and dicalcium ferrite phases. Microanalytical investigations and model calculations on mixed crystal formation indicate that the phosphorus of the slag is incorporated into the dicalcium silicate mixed crystal as PO43− partially substituting the SiO44− ‐anions.
Frequency of bubble formation in water and liquid iron
Authors: Thorns Andreas , Tu Shiwei , Janke Dieter
Published: December 2016

In the present work a device for measuring the frequency of bubble formation was developed and tested in water and liquid iron. Using a pressure sensor, the pressure difference induced by bubble formation from a nozzle inserted in the liquid phase is registered and analysed by a frequency analyser. The test results showed a good reliability and accuracy of the device in comparison with the bubble formation theory.
Direct charging of thin slabs of a cold formable HSLA steel
Authors: Bruns Hartmut , Kaspar Radko
Published: December 2016

In the concept of direct charging linking continuous casting with rolling of thin slabs, some differences in the design of process parameters are necessary. By example of a commercial low carbon NbTi‐microalloyed steel, laboratory tests have been carried out by using a thin‐slab continuous casting simulator on‐line with the hot deformation simulator Wumsi. The influence of the temperature of intermediate holding (between casting and rolling), total strain εΣ, finishing temperature and cooling rate after finishing on the microstructure and mechanical properties was investigated on rolling schedules with or without roughing prior to finishing. Conventional cold charging (with reheating of thicker slabs) was simulated as a comparison to this. Whereas the static properties (tensile test) were less influenced by εΣ and by the design of rolling schedule (with or without roughing), the properties measured by the low temperature impact test (at ‐30°C) were more sensitive. By the optimizing process parameters of direct charging (finishing at temperatures of lower austenite, employing accelerated cooling after rolling) mechanical properties superior to those of cold charging (despite of largely reduced εΣ) are attainable.
A contribution to the increase in yield strength during the bake hardening process
Authors: Kozeschnik Ernst , Buchmayr Bruno
Published: December 2016

Bake hardening denotes the controlled aging of steels during a thermal treatment as applied for example by paint baking outer panels of automobiles. Dependent on the duration of the thermal exposure and the temperature, the increase in yield strength can reach up to 80 MPa. The temporal progress is a function of the steel composition and the degree of prestrain and can appear in one or two stages. It seems that the interaction between precipitating ternary iron carbides and the formation of Cottrell atmospheres around mobile dislocations count responsible for the different shapes of the precipitation curves. In the present work an attempt is made to simulate the atmosphere forming and carbide precipitation with the use of classical models and take into account the degree of prestrain. The results are then compared with experimental data on the bake hardening process.
A new way to reduce the edge drop
Authors: Hartung Hans‐Georg , Hollmann Friedrich Wilhelm , Holz Rüdiger , Richter Hans‐Peter
Published: December 2016

Two new ways to reduce the edge drop are being investigated both theoretically and in rolling trials. The edge drop control cooling system (EDC cooling) produces a crown shape with the aid of three cooling beams arranged on stand‐exit side that, on the one hand, feature a very fine spray pattern distribution in the strip edge area and, on the other hand, are applied with differently tempered cooling medium, allowing the edge drop to be reduced. The EDC rolls are more flexible in the strip edge area than in the remaining part of the barrel. The thus created heavier flattening is, on the one hand, sufficiently large and, on the other hand, also excellently suited by its characteristic property to compensate the edge drop. The effects of both systems were evidenced during comprehensive rolling trials in the first stand of a 2‐stand DCR cold tandem mill. For these trials 52 coils of annealed tin plate were used. With the aid of the EDC system, the strip thickness in the immediate strip edge area could be increased by up to 4% of the nominal thickness.
Model experiments of mixing in steel ladles with continuous addition of the substance to be mixed
Authors: Becker Jens‐Ulrik , Oeters Franz
Published: December 2016

The process of alloying steel melts in ladles consists of the three partial steps alloy addition, alloy solution, and alloy mixing. Addition and dissolution together can be simulated approximately by continuous addition of a dissolved substance to be mixed. In this way, the mixing process during alloying can be captured separately. The process was studied in model experiments with continuous addition of NaCl solution to water in a 0.18 m3 cylindrical acrylic glass vessel. The water was stirred by air injection through an eccentrically positioned nozzle in the bottom. The added amount of NaCl was 40 cm3 of a 20% aqueous solution. The addition time was varied. The NaCI concentration in the water vessel was continuously measured with electrical conductivity probes at 12 different positions. From the thus obtained concentration‐vs.‐time curves, the mixing times were determined. They were studied for stirring gas rates between 100 and 700 cm3/min(STP) and for various addition times of the indicator. The measured mixing times depended on the gas stirring rate. They were also functions of the indicator addition time and decreased with increasing addition time until they became zero or negative. Trials where NaCI was added in form of a melting, NaCI containing ice sphere, yielded negative mixing times, which means that melting is slower than mixing. A theoretical model to describe mixing with continuous addition is presented. Besides the measurement of the mixing process, the three main flow directions of the indicator solution when it leaves the injection nozzle were documented by a video camera. They were associated to the concentration curves measured at the conductivity probes to which the flow was directed. It was found that concentration maxima occurred on the curves when the flow was directed to the respective measuring probe. The duration of the maxima coincided almost always with the duration of the flow directions.
UV/VIS‐spectroscopy of molten and solid CaO‐MgO‐SiO2 ‐ slags
Authors: Okretic Stefano , Nowack Norbert , Mausbach Klaus
Published: December 2016

The previously developed high temperature set‐up has been used to monitor the redox state of molten slags at 1500°C directly by UV/VIS spectroscopy. Slags of the CaO‐MgO‐SiO2‐system were doped with Fe2O3 mass contents of 0.80 and 5%. Spectroscopical results at different oxygen partial pressures of the investigated Fe3+ charge‐transfer (CT) transitions in the wavelength range between 200 and 800 nm were found to be representative for the redox state of the slag. The peak positions and shifts give further information about the optical basicity and the structure of molten slags. The time dependence of the oxidation/reduction equilibrium process was measured and evaluated concerning diffusion mechanisms.

In Cr2O3‐doped silicate‐slags in the liquid state CrO3 ‐ and Cr3+‐ species occur. The different CrO3‐species (CrO42‐ and Cr2O72‐) in silicate slags have been indicated spectroscopically and registed quantitatively. Further investigations on Cr2O3‐doped slags uncovered the well known evaporation of chromium out of molten slags as a decrease in the CrO3 concentration in time. In the molten slag the CrO3 slowly evaporates, which can be seen spectroscopically as a decrease in the CT‐band intensity. The results obtained on numerous optical parameters of molten slags will establish the application of reflection spectroscopy at high temperatures.
Mechanisms in fatigue strength improvement of thermomechanically manufactured automotive suspension springs
Authors: Arndt Johannes , Lehmann Gunter , Lehnert Wolfgang
Published: December 2016

In a previous work, application of thermomechanical treatment (TMT) to suspension spring samples led to high increases in fatigue strength (up to 40 %). For the purpose of a better comprehension of these results, further investigations were carried out with major attention to the mechanical properties of quenched and tempered steel 50CrV4 and a Nb‐microalloyed variant of this steel, respectively. First, the samples were ground prior to presetting, stress peening and subsequent dynamic testing. This was done to work out the influence of the surface state on the benefits of TMT. An extended program of materials testing was carried out with particular attention on the crack initiation and growth features of thermomechanically treated steel compared to conventional heat treatment (CHT). One of the results was that grinding of the spring surface causes further improvement of fatigue strength. On the other hand, the advantages of TMT compared to CHT are reduced as a result of surface grinding. The reason for this result is an overproportional increase in fatigue strength of CHT specimens due to grinding. An explanation imaginable for both the improvements caused by TMT and the reduction of these improvements after grinding could be the change in fracture mechanical properties. In particular TMT causes a significantly retarded crack initiation in the finite life range and an increased permissible stress intensity without crack formation.
Thermodynamic study of exchange reactions in the manufacturing of microalloyed steels by the ESR process
Authors: Medina Sebastián F. , Ruiz‐Valdepeñas Francisco , Chapa Modesto , Quispe Alberto
Published: December 2016

With the aim of manufacturing 42CrMo4 steel by the electroslag remelting process (ESR) with a certain Ti and Al content and uniform distribution throughout the ingot, a study has been made of the complex metal‐slag reactions which take place, especially of the most reactive elements. The thermodynamic activities of the elements in the molten metal and of the oxides in the slag were calculated and theoretic oxidation equilibria of the elements with greatest affinity for oxygen were proposed, as well as their exchange equilibria. Comparison of the theoretic equilibria with experimental results permits interpretation of how the system evolves during remelting and adjustment of the slag composition and other parameters in order to manufacture a steel of a certain composition and uniform from the bottom to the top of the ingot.
Investigations on the equilibria between Al‐Ca‐O containing iron melts and CaO‐Al2O3‐FeOn slags
Authors: Schürmann Eberhard , Braun Uwe , Pluschkell Wolfgang
Published: December 2016

The equilibria between liquid CaO‐Al2O3‐FeOn slags and Al‐Ca‐O‐containing iron melts in contact with pure lime (CaO) and pure calcium aluminate (CaO‐2Al2O3) crucibles were investigated at 1600°C. The iron mass content of the metal phase was varied between 0 and almost 100 %. The results show a strong influence of the miscibility gap in the system Fe‐Al‐Ca arising from the Fe‐Ca binary system on the phase equilibria. By these investigations the conditions of solid alumina reduction by dissolved calcium to liquid calcium aluminate were determined.
An inverse analysis of the hot uniaxial compression test by means of the finite element method
Authors: Cabrera José María , Prado José Manuel , Barrön Miguel Angel
Published: December 2016

A computer simulation using the finite element method is carried out in the present work to model a hot compression test. Real constitutive equations of the hot flow behaviour of a medium carbon microalloyed steel, experimentally determined, are implemented in a commercial computer code and an inverse analysis is performed to determine under which conditions the experimental test can be considered as valid. In other words, the degree of strain and strain rate heterogeneity as well as the isothermatility of the test, for the given material, are verified. The effect of the friction coefficient is also included in the current analysis.
Activity of chromium oxide and phase relations for the CaO‐SiO2‐CrOX system at 1873 K under moderately reducing conditions
Authors: Morita Kazuki , Mori Mamiko , Guo Muxing , Ikagawa Toru , Sano Nobuo
Published: December 2016

In order to optimize the slag composition operated in the decarburization process of stainless steel production, activity of chromium oxide, aCrOX, and phase relations for the CaO‐SiO2‐CrOX system have been investigated under moderately reducing conditions, PO2 = 7.04•10− 6Pa at 1873 K. Activity coefficients of chromium oxides show strong dependencies on XCaO/XSiO2, an index of basicity, and chromium content of the slag. Solubility of chromium oxide in the slag system drastically decreases with increasing XcaO/XSiO2, which is consistent with increase in activity coefficients of chromium oxides. The optimal CaO‐SiO2‐CrOX slag for a practical decarburization process has been recommended to be doubly saturated with CrO1.5 and CaCr2O4, namely XCaO/XsiO2 = 1.47 at 1873 K, which may not be significantly affected by operating temperatures.
Investigation of solidification and microsegregation of near‐net‐shape cast carbon steel
Authors: Senk Dieter , Engl Bernhard , Siemon Olaf , Stebner Guido
Published: December 2016

Different near‐net‐shape casting techniques are investigated in terms of solidification parameters, microstructure, and microsegregation of manganese in carbon steels based on experimental simulation methods: ingot casting of thick and thin slab samples, strip samples, and thin strip. The as‐cast thicknesses were between 1.9 and 150 mm. By calculations and measurements data have been determined which lead to the solidification structure like solidification‐ and cooling‐rate, secondary dendrite arm spacings, and the concentrations of microsegregations. Finally, some literature data of material properties of steel strip produced by the investigated methods are given.
Inclusions in continuously cast steel slabs ‐ numerical model and validation
Authors: Grimm Bernd , Andrzejewski Peter , Müller Klaus , Tacke Karl‐Hermann
Published: December 2016

A numerical model for liquid steel flow and inclusion transport and separation in continuous casting moulds is presented, which covers several features simultaneously. The free surface at the meniscus is computed; the submerged entry nozzle is discretised in detail to resolve the outlet geometry; gas injection through the SEN and its effect on liquid steel flow are considered; capture of inclusions within gas bubbles is covered in a simplified approach; the solidifying shell and the process of inclusion entrapment by the growing shell are simulated. Computed flow profiles are compared to experimental results on water and to measurements on liquid steel in a slab caster. Predicted inclusion profiles in solid slabs are compared to empirical findings from literature. Results of the model for various cases will be presented in a subsequent publication.
TRIP steel with reduced silicon content
Authors: Pichler Andreas , Stiaszny Peter
Published: December 2016

At present high strength thin sheet steel grades are gaining considerable market shares due to the intensified application in the automotive industry. Although several new high strength steels for cold forming have been developed and continuously improved for some decades there is still a necessity to increase the formability at a given high strength level. TRIP steels are a consistent further step to meet these requirements. Most of the published work concentrates on compositions with high C, Mn and Si contents which causes problems during production. Therefore in this work TRIP steels with reduced C and Si contents were produced and the influence of the annealing parameters on the microstructure and mechanical properties was investigated in detail for production via continuous annealing lines. Based on these investigations optimized heat cycles were proposed.
Experimental determination of the stability of retained austenite in low alloy TRIP steels
Authors: Vasilakos Apostolos N. , Papamantellos Kostas , Haidemenopoulos Gregory N. , Bleck Wolfgang
Published: December 2016

The stability of retained austenite is the most important parameter controlling the transformation plasticity effects in multiphase low alloy TRIP steels. In this work the thermodynamic stability of the retained austenite has been determined experimentally by measuring the Mσs temperature as a function of bainite isothermal transformation (BIT) temperature and time in two low alloy TRIP steels. A single‐specimen temperature‐variable tension test technique (SS‐TV‐TT) has been employed, which allowed to link the appearance of yield points in the stress‐strain curve with the mechanically‐induced martensitic transformation of the retained austenite. The results indicated that the MσS temperature varies with BIT temperature and time. Higher austenite stability is associated with a BIT temperature of 400°C rather than 375°C. In addition, the chemical stabilization of the retained austenite associated with carbon enrichment from the growing bainite is lowered at short BIT times. This stability drop is due to carbide precipitation and comes earlier in the Nb‐containing steel. At longer BIT times the retained austenite dispersion becomes finer and its stability rises due to size stabilization. The experimental results are in good agreement with model predictions within the range of anticipated carbon enrichment of the retained austenite and measured austenite particle size.
About the foamability of iron ‐ carbon alloys
Authors: Kunze Hans‐Dieter , Knüwer Matthias
Published: December 2016

The foamability of iron‐carbon alloys using the powder metallurgical process route was investigated. Pure iron and carbon powder with an addition of foaming agent were mixed and compacted. The foaming process started during heating the sample as soon as a temperature above the solidus temperature of the iron‐carbon alloy was reached. Result of the process is an iron foam with a porosity of up to 60%. It was investigated, how the foaming behaviour is influenced by the parameters of alloy composition and compaction process. Different foaming agents (alkaline earth metal carbonates and metal nitrides) as well as different carbon additions and compacting processes were tested.

It can be seen that sort and amount of foaming agent have an unexpected low influence on the expansion process whereas an increasing carbon content supports the expansion significantly. The use of different compacting processes has only little influence on the expansion itself, but highly effects both the pore distribution and homogeneity. The poor effect of the foaming agent cannot be satisfactorily explained. Investigations of a possibly premature gas emission or of a not gas‐tight inclusion of the foaming agent do not show clear results. The support of the expansion by carbon additions can be attributed to the formation of CO‐gas by the Vacher‐Hamilton law during simultaneous formation of the liquid Fe‐FeC‐eutectic phase. The more inhomogeneous pore structure of iron foams caused by the use of hot‐or hot isostatically pressed semi‐finished products can be traced back to a higher internal gas pressure in the sample which results in a burst of the microstructure of the semi‐finished product.
Optimisation of the electric arc furnace lancing strategy by physical and numerical simulation
Authors: Boemer Andreas , Rödl Sigurd
Published: December 2016

Due to a partial lack of detailed knowledge of the relevant physical processes, the operational proceeding of oxygen and solid material injection in the electric arc furnace is often still based on experience. Therefore, the influence of important operational parameters on the fluid dynamics of the DC electric arc furnace have been investigated to find optimised lancing conditions. Therefore, physical model trials and additional numerical simulation were performed. Based on a defined standard operation condition, oxygen‐ and particle flowrate, lance inclination and distance of the nozzle from melt surface were varied. Furthermore, different geometrical nozzle arrangements and the influence of the electric arc were investigated. The resulting mixing of the melt, particle dispersion, surface fluctuations, and foaming behaviour were compared. Suggestions have been made for improved lancing strategy and lance design.
Physical and mathematical modelling of tundish flows using digital particle image velocimetry and CFD‐methods
Authors: Odenthal Hans‐Jürgen , Pfeifer Herbert , Klaas Michael
Published: December 2016

The flow in continuous casting tundishes is considerably responsible for the flotation of non‐metallic inclusions and the quality of steel. Because tests in liquid steel can hardly be performed, water model testing considering the geometric and dynamic similarity laws is often used. Here, quantitative investigations with time and cost expensive laser measurement techniques are possible. The digital particle image velocimetry (DPIV) can be seen as a completion and is an effective method to obtain reliable results.
Dependence of the hydrogen permeation in stainless steel on carbon content, heat treatment and cold work
Authors: Dayal Ravin Kumar , Grabke Hans Jürgen
Published: December 2016

The hydrogen permeation behaviour in austenitic stainless steel (1.4301, AISI 304) was studied between 25 to 85 °C using the electrochemical double cell permeation technique. Influences of parameters like carbon content, grain size and cold work were investigated. Using the current transient plots from the permeation experiments, apparent diffusion coefficient,Dappvalues were calculated. Values ranging from 5.8•10−12to 2.7•10−10cm2/s were obtained for various conditions of the material. The increase in carbon mass content from 0.045 to 0.085 % resulted in a decrease inDappby a factor of 8. This was attributed to the increased blocking of interstitial sites by higher carbon in the latter steel. The annealing treatment, resulting in a slight grain growth caused a decrease inDappto about its half, in contrast to the reduced trapping effect of the grain boundaries. This was explained to be due to a longer hydrogen transport path required through the grain and less contribution of fast diffusion paths in the larger grain size material. A slight cold work (5% reduction in thickness) decreased theDappwhereas higher cold working (30 %) increased theDapp. The cold working results in an increase in dislocation density and the dislocations act as traps for hydrogen transport. This results in a decrease inDappvalues for 5 % cold work material. Strain induced martensite (α', bcc phase) formation in the matrix occurred in the higher cold worked material (10 and 30%). The presence of this bcc phase overcame the trapping effect of increased dislocation density resulting in an enhancement of hydrogen transport. From the activation energy calculated, it was concluded that the a' phase present did not provide a continuous medium for hydrogen transport, but added to the overall increase in the hydrogen transport process.
Quasi‐in‐situ observations of the sintering behaviour of molybdenum‐alloyed sintered steels
Authors: Schoeler Annett , Bleck Wolfgang , Link Rainer
Published: December 2016

The sintering behaviour of molybdenum pre‐alloyed sintered steels was investigated. A scanning electron microscope with a hot stage attachment was used, enabling quasi‐in‐situ observations of the sintering process. The material MSP 1.5Mo (Fe‐1.5% Mo) sinters in the austenitic phase, while MSP 3.5Mo (Fe‐3.5% Mo) sinters completely in the ferritic phase, due to the increased molybdenum mass content. The significantly higher self‐diffusion coefficient of iron in the ferritic phase leads to the accelerated sintering of MSP 3.5Mo, compared to MSP 1.5Mo. The effect on the sintering behaviour by adding the alloying elements chromium and phosphorus was also studied. While phosphorus accelerates sintering processes, chromium decreases the sintering rate. A pronounced shrinkage during non‐isothermal heating, due to cooperative particle movement, was detected for both sintered steels.
Melting and dissolution of high‐melting alloys in steel melts
Authors: Zhang Liuyi , Oeters Franz
Published: December 2016

About one year ago a booklet by Liuyi Zhang and Franz Oeters titled Melting and mixing of alloying agents in steel melts. Methods of mathematical modelling was published [1]. On pages 45, 46‐48, 49‐51 of this booklet numerical calculations are presented, inter alia, for the simultaneous melting and dissolution of high‐melting alloys in steel melts, and from these calculations certain conclusions are drawn. Caused by a programming error, these calculations and in consequence, also the conclusions are wrong. Meanwhile, the error has been eliminated, and new calculations were done. Because the results are considerably different from those before, we would like to publish the altered results in this communication. In the report, a short introduction into the problem is presented first, then some mathematical equations are explained, and finally, the new calculation results and their discussion are given. Reference is made in detail to the publication [1].
Local potentials under electrolyte droplets on steel
Authors: Meijers Steven , Lauterbach Martijn , de Wit Hans , Droog John
Published: December 2016

The scanning Kelvin probe shows great potential for the study of localised corrosion phenomena on coated metals. However, it still is difficult to unravel the contributions of the different components of complex coating systems to the measured Volta potentials. Experiments on simple model systems are necessary to increase our knowledge. The classical Evans drop experiment was chosen as such a model system. Using the scanning Kelvin probe potential distributions in the drop were measured. It was found that within the droplet no separate anode and cathode can be distinguished in the potential profile. A cathodic region was found just outside the droplet, where a very thin electrolyte layer exists. Twin drop experiments however showed potential differences in electrolyte over short distances.
Viscosity estimation models for ternary slags
Authors: Sridhar S. , Sichen Du , Seetharaman Seshadri , Mills K. C.
Published: December 2016

Five models to estimate slag viscosity have been compared with the experimental data obtained using the rotating cylinder method. The comparison was made for four ternary silicate systems, viz. FeO‐MgO‐SiO2, CaO‐MnO‐SiO2, FeO‐MnO‐SiO2 and CaO‐FeO‐SiO2. The KTH model and the model using the Gibbs energy of mixing have been found successful in estimating the slag viscosity. On the other hand, the comparisons of the experimental results with the calculated viscosity using the Riboud, Urbain and NPL models have shown poor agreement. While the limited number of the data points used for parameter optimisation would be one of the reasons for the failure of the Riboud and NPL models when applied for these ternary systems, the description of the slag composition in Urbain's approach could probably explain the disagreement between the estimated and experimental viscosity. Further studies are needed for the KTH model to accommodate fluorides in the model structure.
Theoretical analysis of the interfacial phenomena during the injection of carbon particles into EAF slags
Authors: Rodriguez H. H. , Conejo A. N. , Morales Rodolfo D.
Published: December 2016

A theoretical analysis of FeO reduction through the injection of carbon fines in electric arc furnace slags, involving the interfacial phenomena at the liquid‐gas‐solid interface, has been performed using basic principles of transport phenomena and physical chemistry of steelmaking. It was found that small angle contacts between slag and carbon favour FeO reduction. Moreover, FeO in basic slags are more prone to be reduced because the interfacial liquid‐gas interface has more free reaction places. In acid slags FeO reduction is difficult because the gas‐liquid interface is partially filled by polymeric silicates. When the particle size is smaller than 100 μm the influence of slag basicity is considerably decreased. Practical applications of these results can be found in electric arc furnace shops aiming at the mastering of slag foaming practices and energy saving.
Effect of carbon and sulphur on the surface tension of molten iron
Authors: Lee Joonho , Morita Kazuki
Published: December 2016

Surface tensions of Fe‐4%C‐S alloys were measured at 1623 and 1823 K using the sessile drop technique. Thermodynamic models based on Butler's equation for surface tension of liquid alloys have been compared with experimental results. Calculated values are found to be in good agreement with those of the experimental data of the system. At the same sulphur activity, the effect of carbon on the surface tension of Fe‐C‐S alloys was found to extrude only when the sulphur content was less than 0.005 %.
Bottom blowing investigations on a cold model reactor to optimise mixing behaviour in metallurgical processes
Authors: Stišovic Tatjana , Koch Klaus
Published: December 2016

Cold model investigations for discontinuous operating, metallurgical reactors are conducted with bottom blowing. Parameters are the bottom blowing rate, the h/d‐ratio and different bottom nozzle configurations, like a centric single nozzle, nozzle rings and screen bottoms. The main influence on the mixture behaviour is given by the h/d‐ratio. Furthermore, the mixing times are improved with increase of bottom blowing rate, nozzle diameter and eccentricity of the nozzle positions.
Microstructure and properties of hot‐rolled high strength multiphase steels for automotive application
Authors: Pyshmintsev Igor Y. , Mesplont Christophe , Jacobs Sigrid , De Cooman Bruno C.
Published: December 2016

Effects of alloying with combinations of the elements Mo, Cr and B on the bainite transformation behaviour and microstructure of hot‐rolled high strength sheet steels microalloyed with mass contents of Ti and Nb, 0.05 or 0.15 % C and 1.5 % Mn have been studied. The relationships between microstructures formed in the steels coiled at various temperatures and their mechanical properties have been investigated. The 0.15 % C microalloyed steel alloyed with Mo,Cr and B with a complex bainitic microstructure was found to have distinctive high performance behaviour combining continuous yielding, high tensile strength and plasticity after coiling in a wide temperature region. The strain hardening of the micro‐constituents typical for the investigated steels has been analysed to have a better understanding of the mechanical properties of complex phase microstructures in low alloy ferrous alloys. It was found that bainitic ferrite with austenitemartensite islands as a second phase leads to high strength and adequate elongation. The features of the bainite formation in the Mo, Cr and B alloyed CMn steel microalloyed with Ti and Nb during slow cooling from temperatures between 650 and 550 °C was studied by dilatometry.
Residual stress relaxation of welded steel components under cyclic load
Authors: Han Seungho , Lee Takkee , Shin Byungchun
Published: December 2016

It is a well known fact that the fatigue strength and the life of welded steel components are affected, to a considerable extent, by residual stresses distributed around their weldments. When externally applied load is superimposed on residual stresses, unexpected deformations and failure of the components can occur. These residual stresses are not constant, but are relaxed or redistributed during in‐service. Under monotonic load relaxation takes place when the sum of external and residual stress locally exceeds the yield stress of material used. It is noteworthy that under cyclic load the residual stress is considerably relieved by the first or the early cycles of load, and then is gradually relaxed with increasing loading cycles. Although many investigations in this field have been carried out, the phenomenon of and mechanism of stress relaxation are still not clear, and only a few comprehensive models have been proposed to predict amount of relaxed residual stress. In this study, the characteristics of residual stress relaxation under monotonic and cyclic load were investigated, and a model for quantitatively predicting the amount of residual stress relaxation is proposed.
The role of niobium as microalloying element in electrical sheet
Authors: Hulka Klaus , Vlad Constantin , Doniga Ana
Published: December 2016

The processing route of grain oriented electrical sheet was simulated by laboratory trials. Besides MnS, the effect of AIN and NbC as an inhibitor phase in 3 % silicon steel was also investigated. In the hot strip material the niobium microalloyed steel showed the highest volume fraction of the {110}<001> Goss texture at 0.3 to 0.4 mm below the surface. This superiority was maintained after cold rolling and annealing after both, one step or two step cold reduction schedules. A volume fraction of the Goss texture of more than 80 % is typical for this steel concept. It can be explained by the solubility product of NbC, which guarantees grain size control during the primary recrystallisation processes and allows the Goss texture component to grow during secondary recrystallisation, which usually follows a steel decarburisation. Consistent with the highest volume fraction of Goss texture, the core losses are lowest in the sheet using NbC as an inhibitor phase.
A novel approach in the estimation of splashing in the BOF
Authors: Luomala Matti J. , Virtanen Esa O. , Mure Petri T. , Siivola Tero P. , Fabritius Timo M.J. , Härkki Jouko J.
Published: December 2016

A new physical model has been developed to represent the splashing behaviour in the BOF. By this technique, which is performed by a relatively simple experimental set‐up, determination of splashing distribution on the walls of the model is possible. The method enables quite fast definition of the effect of different blowing parameters on the location and quantity of liquid splashed. The main advantage of this novel method is the fact that splashes are collected from the whole model wall circumference which is very important when interaction between lance jet cavities and bottom blowing plumes results in irregular splashing distribution. Preliminary results show that the method is excellently suited for investigation of splashing in the BOF.
Theory, experiments and numerical modelling of phase transformations with emphasis on TRIP
Authors: Antretter Thomas , Fischer Franz Dieter , Tanaka Kikuaki , Cailletaud Georges
Published: December 2016

This paper presents an overview of the co‐operative efforts aiming at the correct characterisation of the thermo‐mechanical behaviour of materials during the process of a phase change. In the first section the physical conditions for the onset of transformation processes, either diffusive or massive or displacive, expressed in terms of the chemical driving forces in a multi‐component system are derived on a very general basis. Introducing appropriate expressions for the chemical as well as the mechanical dissipation based on jump conditions of quantities such as the deformation rate and the diffusive fluxes at the moving interface allows to formulate proper transformation criteria. No fluxes will occur in the case of displacive, i.e. martensitic transformation which is responsible for the TRIP phenomenon. The mechanism governing the selection of a particular martensitic variant of the product phase out of a discrete number of possible variants is described in the paper. The underlying ideas and tools supplied by continuum mechanics eventually leading to a transformation condition for martensitic transformation are summarised in the appendix.

The second section of the paper shows some aspects of a comprehensive experimental program investigating the thermo‐mechanical behaviour of a maraging steel with very advantageous properties in the transformation regime. It allows to filter out the TRIP strain evolution during transformation from the total strain measured by means of a multiaxial tension torsion dilatometer equipment. The focus is put on finding a material law that is valid also for non‐proportional loading paths. Unlike the predictions of traditional constitutive relationships the TRIP strain rate exhibits a significant drop if the external load is removed during the progress of transformation suggesting the existence of a transformation related backstress.

Finally a method is demonstrated how to validate the experimental findings by means of a numerical algorithm. Based on the physical principles explained in the first part of the paper a subroutine can be devised and implemented into a commercial finite element code that allows to simulate the behaviour of the material represented by a unit cell. The simulations yield realistic results for the transformation kinetics, the load‐displacement curves as well as the material response for non‐proportional loading paths.
Improvement of weldability of TRIP steels by use of in‐situ pre‐ and post‐heat treatments
Authors: Cretteur Laurent , Koruk Ali Ihsan , Tosal‐Martínez Lucía
Published: December 2016

Low alloy TRIP‐aided steels are very interesting for the automotive industry as they combine both a high strength and an excellent formability. Though the actually developed TRIP steels can be considered as low alloyed when compared to the first generations of steels exhibiting TRIP effect, due to their chemical composition, they still exhibit a quite high carbon equivalent. This is particularly detrimental for the weldability of those materials. After solidification, welds are very hard and can show a brittle behaviour. The hardness of the heat affected zone of the welds can even exceed 500HV and cold cracking phenomena is prone to occur.

In the automotive industry, spot welding is the main joining process. During spot welding of TRIP steels, the interface between the plates can act like a notch and promote fracture of the weld. This is particularly dangerous when brittle welds are submitted to peel stresses. The aim of the paper is to demonstrate that a careful choice of the process parameters can significantly improve the resistance of the welds. The selection of the welding cycle parameters is far from being an easy task as many different parameters are involved. Therefore, a design of experiment methodology (DOE) was chosen to optimise the welding cycle for a cold‐rolled TRIP steel with a tensile strength above 700 MPa. Mechanical properties of the welds were significantly improved by use of pre‐ and post‐heat treatments. Those improved welding cycles were realised without excessive extension of the total weld cycle on a conventional spot welding machine. This means that the optimised welds can be obtained in the existing production lines without any additional investment or significant decrease in productivity.
Slag Emulsification during Liquid Steel Desulphurisation by Gas Injection into the Ladle
Authors: Lachmund Helmut , Xie Yongkun , Buhles Thorsten , Pluschkell Wolfgang
Published: December 2016

According to current practice, the desulphurisation of steel melts is mainly performed in the ladle with lime saturated top slags. The injection of argon gas into liquid steel provides for intensive mixing and accelerated sulphur transfer. During gas stirring treatment, an emulsification of top slag takes place. A numerical model describing the course of the desulphurisation reaction has been developed, which takes all relevant process parameters into account, including those of the emulsification effect. To check the validity of the model, operational tests have been performed on 185‐t‐heats. Results obtained from model calculations and operational tests show an excellent agreement.
Slag‐Droplet Model: a Dynamic Tool to Simulate and Optimise the Refining Conditions in BOF
Authors: Graveland‐Gisolf E. , Mink P. , Overbosch A. , Boom R. , de Gendt G. , Deo B.
Published: December 2016

Prior knowledge and control of the path of slag evolution during the blow are crucial for the optimal performance of the BOF process. This is, however, not an easy task owing to the complexity of the multicomponent‐multiphase reactions at high temperatures and the fact that the on‐line data available to simulate the process during the blow are limited. A slag‐droplet model was developed in the nineties on the basis of multi‐component mixed transport control theory, the production of iron‐oxide through jet‐metal interaction and droplet formation, waste gas analysis, dissolution rate of scrap, lime, ore, etc., and slag foaming. Recently, when new blowing practices had to be developed to cope with the changes needed in lining life and converter availability, the slag droplet model was used as a dynamic tool to guide the process adjustments. Operating practices were evaluated for retained slag practice and increased burned dolomite addition. Audiometer signals were recorded during the blow. The results obtained during plant trials, as described in this work, supported the predictions of the model and resulted in improvement of the practice. Precipitation rate of second phase particles (2CaO.SiO2 and 3CaO.SiO2) in slag substantially influences slag foaming behaviour.
Carbon Pickup in Continuous Casting Processes
Authors: Valentin Peter , Bruch Christian , Harste Klaus , Lachmund Helmut , Hecht Michael , Pötschke Jürgen
Published: December 2016

The quality of the as‐cast strand is influenced by a recarburization reaction since mould powder contains carbon particles necessary for a controlled melting behaviour. Intensive testing reveals a carbon pickup in the surface of the as‐cast strand depending on content and type of the carbon in the mould powder. Using the combination of laboratory trials and numerical simulations the effect of carbon pickup from mould powder to the strand shell was investigated. Laboratory experiments show that the recarburization of the liquid steel through the mould powder can be explained by Marangoni convection. This can happen in the slag rim when the carbon is entrapped by the solidifying steel and starts to diffuse inwards the strand.