bluuebunny/crossref_metadata_2025_split 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.
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.
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.
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.
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.
An Analytical Model for Dependence of Force and Forward Slip on Speed in Cold Rolling
Authors: Pawelski Hartmut 
Published: December 2016

An explicit analytical method for determining approximations for roll force and forward slip for strip rolling is introduced. It reproduces all main predictions of classical strip theory, but is completely free of any numerical algorithms. Nevertheless, for extreme cases of cold rolling, like foil or skin pass rolling, more sophisticated algorithms are still needed.For the friction coefficient in the roll gap and its increase from the entry to the neutral point also explicit relations are proposed. In the framework of this analysis, they are sufficiently precise for cold rolling with one‐phase lubricants and stochastic surfaces. Only a single parameter of adaptation is needed, the microscopic friction coefficient μmicro.The quality of the total model is illustrated by means of the dependence of roll force and forward slip on railing speed. For this purpose measured process data (four different pass‐schedules, seven to ten coils each) for cold rolling of copper with rolling oil is analyzed.
Activities of Phosphorus in Copper‐Iron Liquid Alloys Saturated with Copper‐Iron Solid Solutions
Authors: Kaida Y. , Hasegawa M. , Kikuchi Y. , Wakimoto K. , Iwase M. 
Published: December 2016

In order to determine the activities of phosphorus and iron in liquid {Cu‐Fe‐P} alloys, the two coexisting phases of liquid {Cu‐Fe‐P} alloys + <Cu‐Fe‐P> solid solutions were brought into equilibrium with a mixture of Al2O3 + AlPO4 + FexAl2O4 at temperatures of 1416K and 1526K. The oxygen partial pressures were measured with the aid of a solid‐oxide galvanic cell of the type:(+)Mo / Mo + MoO2/ ZrO2(MgO) / {Cu‐Fe‐P} + <Cu‐Fe‐P> + <Al2O3> + <AlPO4> + <FeAl2O4> / Fe(‐)The equilibrium reactions underlying the experiments can be expressed by 2[P]cu + (5/2) (O2) + <Al2O3> = 2 <AlPO4> and x[Fe]Cu + (1/2) (O2) + <Al2O3> = <FexAl2O4>The Henrian activity coefficient referred to 1 wt pct solution in pure liquid copper could be well expressed by the formulalog fP° = (4.46±0.40) ‐ (8.67±0.59)/(T/K).The iron activities referred to pure solid iron could be formulated as log aFe =‐ (0.37 ± 0.12) + (500 ±200) /(T/K).
A Study of Some Elemental Distributions Between Slag and Hot Metal During Tapping of the Blast Furnace
Authors: Andersson Annika J. , Margareta T. Andersson A. , Jönsson Pär G. 
Published: December 2016

This paper investigates the distribution of elements between slag and hot metal from a blast furnace through calculation of distribution coefficients from actual production data. First, samples of slag and hot metal tapped from a commercial blast furnace were taken continually at 10‐minute intervals for a production period of 68 hours. Distribution coefficients of manganese, silicon, sulphur and vanadium were then calculated from the results of the sample analyses.A major conclusion drawn from examination of the results was that the behaviour of the studied elements was as could be expected when approaching the equilibrium reactions from thermodynamic theory. The distributions of the elements in the slag‐metal system showed clear tendencies which did not appear to be influenced by the operational conditions of the furnace. For example, for manganese, vanadium and sulphur, it was found that a higher basicity led to a decreased distribution coefficient LMnand LV, but an increased LS, which is according to theory. Another observed relationship was that slag basicity increased with an increased carbon content in the hot metal, which indicated that SiO2was reduced to [Si] when the oxygen potential decreased. Furthermore, it was found that sulphur and silica behaviour likened that of acidic slag components, while the manganese oxide and vanadium oxide behaviour was similar to that of basic slag components.
Laser‐Aided Flow Curve Determination in Hydraulic Bulging
Authors: Bleck Wolfgang , Blumbach Michael 
Published: December 2016

Hydraulic bulging can be used to characterise sheet material under biaxial stress conditions. A new measuring method applying laser light section for geometry analysis and a camera device for local strain determination enables a continuous on‐line calculation of flow curves. Effective stress and equivalent strain can be recorded until the failure of the material, thus providing extended information compared to the tensile test. The testing procedure is predestined for simulation purposes and for an application in the quality control sector, allowing for a quick and profound material characterisation.This work presents flow curves, strain hardening curves, and strain paths of several steel grades and one aluminium alloy. Some selected materials were also investigated with regard to different yield criteria and results from the tensile test.
A Study on the Buckling Behaviour of Strips and Plates with Residual Stresses
Authors: Fischer Franz Dieter , Friedl Nikolaus , Noé Andreas , Rammerstorfer Franz G. 
Published: December 2016

During and after rolling or flattening of metal strips and plates the permissible deviations from flatness are described by the permissible absolute wave height and the flatness index. Both values can be determined on a measuring table while the material is not subjected to global tension. Because this procedure is expensive, time‐consuming and allows measurement only at discrete positions along the strip length, on‐line flatness measuring systems are used which can detect the distribution of longitudinal tensile stresses distributed across the strip width allowing for the calculation of the flatness index. This value does not always agree with the value obtained directly by measuring on the table even when the measurement of the longitudinal tensile stress distribution operates perfectly. It can be shown that the measurement of the tensile stress distribution does not give a direct indication on the wave height in the tension‐free state determined on the measuring table.To explain the relationship between tensile stress distribution in the strip and the flatness measurement on the measuring table, the buckling behavior is analysed both with and without dead load for simple symmetrical residual stress distributions resulting, e.g., from the rolling process. Based on the knowledge of the distribution of the longitudinal residual stresses across the strip width, the flatness index and the wave height can be determined by using a specialized finite element model. If the direct measurement is performed under action of dead load, large differences between the directly and indirectly obtained flatness index are observed. Below a certain limit of the intensity of the residual stress distribution the strips and plates lie flat on the measuring table. Above this limit the strip lying on the table exhibits post‐bucking deformations. In the latter case, the wave height increases with strip thickness and intensity of residual stresses.
Low‐alloyed TRIP‐Steels with Optimized Strength, Forming and Welding Properties
Authors: Traint Sandra , Pichler Andreas , Sierlinger Robert , Pauli Heinrich , Werner Ewald A. 
Published: December 2016

To obtain the superior strength‐ductility‐balance of TRIP‐grades, a special chemical composition in combination with well adapted processing parameters are a prerequisite. Despite of their excellent formability performance in terms of drawability as characterized by high n‐ and elongation values, compared to mild steels TRIP‐grades are challenging in the press and the body shops. The high strength level in combination with the high work hardening of TRIP‐grades result in higher levels of spring back compared to mild steels and higher press forces are required. Furthermore, a higher sensitivity to failure for sharp bending radii and a deterioration of the formability of punched edges is reported for TRIP‐grades. While spring back can only be minimized by advanced forming processes supported by new simulation techniques with improved ability to predict spring back, the sensitivity to failure under special forming conditions can be influenced by optimizing microstructural features. Contrary to the forming behaviour, which is influenced significantly by the microstructure, the weldability is mainly governed by the chemical composition and the surface condition of the material. The high carbon content of TRIP‐grades compared to mild steels results in a higher hardening potential after welding. Additionally, a fracture behaviour untypical for mild steels after destructive testing of spot welds is sometimes observed for TRIP‐grades, which is assessed critically by some OEMs.In this work, after a discussion of the processing conditions, possibilities are demonstrated to improve the forming behaviour by an optimization of the microstructure and the spot weldability by adapting the chemical composition of low‐alloyed TRIP grades. First very promising results for TRIP‐grades with a minimum tensile strength level of 700 MPa are discussed.
Energy Absorption Behaviour of Austenitic and Duplex Stainless Steels in a Crash Box Geometry
Authors: Ratte Evelin , Leonhardt Sven , Bleck Wolfgang , Franzen Markus , Urban Peter 
Published: December 2016

The improvement of the passive safety plays an important role in the development of new steels for automotive parts. At the same time aspects of weight reduction as well as the industrial feasibility have to be considered. Powered by these objectives, the development and application of new steel concepts for various purposes is promoted. For the present investigation especially weight reduction combined with an improvement of the passive safety are emphasised. As example one representative part of the body structure, the crash box, is considered. At the moment different steel grades (dual phase‐, TRIP‐and HSLA‐steels) as well as fibre reinforced materials are applied. New materials for this special purpose have to exhibit outstanding formability, a high capacity to absorb energy during a possible crash and should be cost effective compared to already existing material concepts. During this project different grades of austenitic stainless steels with varying stability were compared to duplex stainless steels and a TRIP grade with regard to their possible application as crash‐box material. The austenitic grades show excellent gradual formability according to their strength level. All of them exhibit an extraordinary strain hardening behaviour. The duplex grades show a lower formability but on a much higher yield level.Besides the determination of classical material data such as uni‐ and multi‐axial flow curves, dynamic tensile tests and forming tests for the determination of forming limit curves were performed. The material data were used in the simulation of a drop tower test which is commonly used to evaluate the performance of different materials in car components. The results were then evaluated with regard to the absorbed energy, the folding behaviour and the resulting forces.
Modelling of Stress State, Centre Consolidation and Roll Force in Billet Rolling
Authors: Lundberg Sven‐Erik , Överstam Henrik 
Published: December 2016

Roll pressure models have been derived from theoretical studies, FEM simulations and experimental investigations. A model developed from slip line field theory has been shown to fit well to the experimental results. The Finite Element simulations overestimated the pressure function. This is a common problem in hot rolling experiments, since the problem of measuring the correct rolling temperature makes the estimation of the yield strength very difficult. The difference between the FE calculations and the experimental measurements is a measure for the error in the experimental temperature measurements rather than for the accuracy of the Finite Element Method.Traditional modelling has not been an appropriate tool to evaluate the material flow in the centre of the billet. In spite of the fact that the entire stress state can be modelled by slip line field theory, the slip lines which determine the stress state in the centre coincide for actual geometries only in one single point. Thus the strain increments are known only in that single point. Since a material element passes that point instantaneously, it is not possible to find any finite strains in the centre by integrating any incremental function. By FEM, strain modelling is simple and the possibility to consolidate a porous bloom or ingot core can be determined.FE modelling requires an entirely new approach to the modelling problem. It is not reasonable to use FEM to evaluate only the temperature distribution for the use in roll force models from the previous century. Instead, a fully thermomechanically coupled FE model is suggested. However, the calculation time is still far too long to be used for on‐line control purposes. For this application hybrid modelling can be a solution, where off‐line FE models are combined with empirical modelling, and simplified models can be used for the process control.