bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence of constant and variable restraining force on springback of TRIP700 and stainless steel grades
Authors: Greisert Carsten , Wesemannm Jürgen
Published: December 2016

Newly developed high strength steels (HSS) like dual phase (DP) and transformation induced plasticity (TRIP) grades as well as austenitic grades like AISI 304 and AISI 301 show superior strength compared to the microalloyed grades with the same formability (e.g. HSLA340). However, due to the multiphase microstructure and the austenite martensite transformation during forming, a higher springback will appear.

In this paper the influence of different process parameters of six high strength steels on springback after stamping is investigated. The material properties were determined with uniaxial tensile tests. A modified Duncan Shabel test was used to draw U‐profiles with a controlled restraining force. To investigate different process parameters, constant restraining forces of 1 and 5kN and die radii of 3, 6, 9, and 12 mm were applied. In a second step, a shape set process was used. A constant restraining force of 1kN was used until a draw depth of 80 % was reached. Then the restraining was increased to 5.5 kN. The springback and the sidewall force were measured and analysed. An increased restraining force and a reduced die radius increases the sidewall force and reduces the springback. This resulted in a significant decrease in springback. The tests with variable restraining forces, also known as shape set process have shown that it combines a good formability with a reduced springback.
Gibbs Free Energy and Conditions of Spinel (MgO‐Al2O3) Formation in Liquid Steel
Authors: Itoh Hiroyasu , Fujii Katsumori , Nagasaka Tetsuya , Hino Mitsutaka
Published: December 2016

The formation conditions of spinel non‐metallic inclusion during deoxidation with aluminum in secondary refining furnace with MgO lining were discussed in the present work. The thermodynamic data of deoxidation equilibrium with magnesium, calcium and aluminum in liquid iron were determined by the authors. The activities of oxygen and dissolved deoxidizer were evaluated in the thermodynamic description by the first and second order interaction parameters including the cross product terms.
Trials for Reducing Depth of Oscillation Marks in Continuous Casting
Authors: Kudoh Masayuki , Itoh Yoichi
Published: December 2016

Improvement of surface defects in a continuously cast slab or billet is important for saving surface scarfing and for carrying out direct rolling. Deep oscillation marks, one type of the surface defects, sometimes cause surface cracking and positive segregation. In this study, the mechanism by which oscillation marks are formed was investigated by using a continuously cast simulator, which is a billet‐type machine. Then attempts were made to reduce the depth of oscillation marks by two methods in which electromagnetic force, which is the most effective means for reducing depth, was not used. The two methods were use of an adiabatic board for preventing solidification of a meniscus and the use of a board for suppressing the flow of flux.

Overlapping of a molten metal on a meniscus resulted in formation of oscillation marks in tin. On the other hand, bending of a solidified shell also resulted in formation of oscillation marks in a tin‐lead alloy. The depth of the oscillation marks formed by the overlapping mechanism was greater than that formed by the bending mechanism. Both mechanisms depended on the strength of the solidified shell. Therefore, two trials to reduce the depth of oscillation marks formed by the overlapping mechanism were carried out. In one trial, an adiabatic board was inserted into the molten metal. Reduction in depth of the oscillation marks reduced up to about 86% was achieved when high viscosity flux was used. However, the adiabatic board was not effective when low viscosity flux was used. In the other trial, a board was inserted into a molten flux layer with a depth of 10 mm in depth in order to suppress the flow of the flux and to change the direction of flux flow, and the depth of oscillation marks was reduced by about 33%. Therefore, both of these methods are effective for reducing the depth of oscillation marks in a continuously cast billet.
Conditions of Liquid Steel Treatment for Near Net‐Shape Casting Processes
Authors: Senk Dieter , Mavrommatis Konstantinos
Published: December 2016

Slab casting for hot rolled steel and strip casting using the twin roll casting (TRC) method are compared in terms of inclusions evolution. There are differences of the processes, mainly the use of casting flux in CC of slabs, or pool shapes and sizes in terms of TRC, particularly when roll diameters vary. The inclusion evolution of alumina in a low carbon steel grade was estimated. By modelling particle growth rate, coagulation and deposition, an ‘agglomeration index’ was created to describe the probability of clogging in the SEN. Similarly the growth of secondary alumina precipitation during cooling of the melt in the pool by Stokes collision and turbulent collision was estimated in terms of forming large particles which are able to float‐up. Influences of melt superheat or caster size were taken into account.
Tensile strains ahead of entry into the roll gap
Authors: Beynon John H. , Krzyzanowski Michal
Published: December 2016

Tensile strains ahead of entry into the roll gap were analysed using the finite element method and compared with results of the analytical approach developed by Pawelski [1]. The longitudinal tensile strains in the stock surface ahead of contact with the roll produced by frictional contact with the roll were calculated for the different roll gap aspect ratios, ho/L = 0.1,…1 and Coulombic friction coefficient 0.1,…0.5. The results have been analysed in terms of oxide failure resulting from this kind of deformation and compared with predictions using the advanced oxide scale model. A simple formula has been developed to evaluate the longitudinal strain component at entry into the roll gap for a given friction coefficient and aspect ratio. It was related to cracking of the oxide scale in tension at this area. Prediction of the scale behaviour at this area is a key to understanding the friction and heat transfer phenomena taking place at the roll/stock interface. It is also important for optimisation of descaling operations.
Design and Production of Thin and Small Micro Strips
Authors: Kopp Reiner , van Putten Koos
Published: December 2016

This article describes a recently started research project about the rolling of small and very thin strip, or in other words the production of micro strip using flat rolling processes. Main subject of the article is the finite element simulation of the production process and its validation. First the practical relevance of micro strip and its production process are presented. Furthermore the scaling effects which miniaturisation brings with it are introduced. Determination and consideration of the size effects are essentials in order to make optimisation possible. It is proposed to determine the size effects in the flow curve with a miniaturised multi‐layer plane strain compression test. The simulation will be done on a continuum base which includes the determined size effects out of the multi‐layer plane strain compression test. Finally a comparison of the FEM‐simulation results (rolling force, cross sectional geometry) with real processes validates the modified finite element simulation.
A Morphological Comparison between Inclusions in Aluminium Killed Steels and Deposits in Submerged Entry Nozzle
Authors: Dekkers Rob , Blanpain Bart , Wollants Partick , Haers Frank , Gommers Bart , Vercruyssen Carina
Published: December 2016

A study was carried out to compare the inclusions present in low carbon aluminium killed (LCAK) steel with oxide particles in a clogging deposit formed during casting of LCAK steel. Steel pin samples were taken in the ladle and in the tundish. It was observed that oxide particles in the clogging deposit are mainly coral‐shaped clusters, dendritic clusters and irregular plates. From the comparison with inclusions in LCAK steel, it is concluded that the particles in the clogging deposits are formed during reoxidation of the steel, at least after the ladle metallurgy process and most probably in the submerged entry nozzle. They are not the result of sintering of small preexisting inclusions.
Application of the FE‐Method to the Simulation of Fatigue Crack Growth in real Structures
Authors: Fulland Markus , Richard Hans A.
Published: December 2016

In the following paper at first general concepts which have to be considered for the accomplishment of a 3D fatigue crack propagation simulation by the FE‐method in real structures are introduced. In doing so numerical aspects concerning the necessary mesh generation as well as fracture mechanical issues will be discussed. Furthermore the 3D crack simulation program ADAPCRACK3D, which has been developed at the Institute of Applied Mechanics at University of Paderborn, is presented in its general functionality. The simulation example of the crack propagation in a shutter ring of a hydraulic press shows the practical relevance of both the implemented algorithms and fracture mechanical concepts.
DTA‐Measurements to Determine the Thixoformability of Steels
Authors: Püttgen Wolfgang , Bleck Wolfgang
Published: December 2016

Semi‐solid metallurgy (SSM), also known as “thixoforming” or “thixoprocessing”, is of special interest as a new potential manufacturing technology for components in the automobile, machine and electronic industries. The aim of this technology is to produce complex shapes which cannot be produced with conventional processing methods.

An important process step of semi‐solid processing (SSP) is the reheating and isothermal holding of the billet within the solid‐liquid range in order to obtain the required fraction liquid content and the desired globular microstructure. Aside from the investigation of billet heating and the development of a suitable tool design, the development and evaluation of adequate microstructures over a wide temperature area is very important. The focus of this paper is to determine the semi‐solid area of different steels through Differential Thermal Analysis (DTA) measurements. To determine a process window for handling the alloys in the semi‐solid state, the DTA‐results can be combined with microstructure parameters. Subsequent quenching experiments show the development of the microstructure parameters (e.g. grain size, phase distribution, volume fraction, shape factor, matrix character, contiguity, and particle density of the primary solid and liquid phases). A comparison of the slopes of the determined solid‐liquid areas for different steels show the width of the melting or freezing intervals to evaluate the possible process windows. DTA‐experiments performed at different heating rates show the influence of faster heating and cooling rates on the solidus‐liquidus interval. To evaluate the suitability for the thixoforming processes, this paper describes, and then compares, the semi‐solid intervals of different steel grades, which have been investigated in the Department of Ferrous Metallurgy at the RWTH Aachen University. The tool steel HS 6‐5‐3 and the cold work tool steel X210CrW12 have a wide semi‐solid area, which can be explained due to the dissolution of different carbides. In contrast to this, the steels C45, 42CrMo4, 16MnCr5, 34CrNiMo4, 100Cr6, X220CrVMo13‐4 and the Alloy 33 show a much smaller semi‐solid area.
Characterization of Steel Thixoforming Tool Materials by High Temperature Compression Tests
Authors: Kopp Reiner , Shimahara Hideki , Schneider Jochen M. , Kurapov Denis , Telle Rainer , Münstermann Simon , Lugscheider Erich , Bobzin Kirsten , Maes Michel
Published: December 2016

The experimental set‐up and the results of high temperature compression tests for the characterization of tool materials for steel thixoforming are presented. The scope of this test is to reproduce the load profile of steel thixoforming processes consisting of mechanical, thermal, tribological, and chemical components on the forming mould. Tool materials were chosen following a concept within the Collaborative Research Center ‐ SFB 289 ‐ “Forming of metals in the semi‐solid state and their properties”. Three materials groups are distinguished: thin film deposited by physical vapor deposition (PVD) and plasma assisted chemical vapour deposition (PACVD), thick coatings (thermal spraying), and bulk ceramic materials. Samples were characterized using scanning electron microscopy (SEM), electron‐dispersive spectroscopy (EDS) and X‐Ray diffraction analysis (XRD). The results show varying resistance of the tool materials concerning the load profile. In order to provide an appropriate tool solution for the thixoforming of steels, different load profiles within the forming moulds are identified and the corresponding tool part is made from that material with the best performance.
Effect of Residual Elements on Hot‐Crack Susceptibility of Austenitic Stainless Steel
Authors: Scheller Piotr R. , Bleck Wolfgang , Flesch Roman
Published: December 2016

After partial melting and solidification of cylindrical samples hot tensile tests were performed on austenitic stainless steels containing residual elements such as copper, tin and lead as well as calcium and magnesium. Using well controlled cooling conditions down to the testing temperature a radially solidified microstructure in the test zone of the samples was achieved. The testing material was prepared by remelting of base material from the industrial production and addition of single elements in the vacuum induction furnace. The maximum strength and the reduction of area were determined in the temperature range between liquidus and 1100°C.

With regard to the reheating and hot rolling process some samples were thermally treated under industrial conditions. The ductility of the material at temperatures down to 950°C was tested and the effect of annealing was evaluated. Recommendations for material processing by continuous casting and hot rolling were derived from the tests performed.
A Study of the Effect of Aluminium on the Mechanochemical Reduction of Hematite by Graphite
Authors: Khaki Jalil Vahdati , Panjehpour Masoud , Kashiwaya Yoshiaki , Ishii Kuniyoshi , Bafghi Mohammad Sheikh‐Shab
Published: December 2016

The effect of addition of small amounts of aluminium on mechano‐chemical reduction of hematite by graphite was studied. Various amounts of aluminium (0 to 10%) were added to a hematite‐graphite mixture, in which C/O ratio was 1:1. The hematite‐graphite‐aluminium mixtures were then subjected to ball milling followed by heating up reduction. The heating up reduction was carried out in Ar atmosphere, using TG‐DTA device. In TG‐DTA experiments, samples were heated by a constant heating rate of 10 °C/min from room temperature up to 1100 °C and maintained for 30 minutes at this temperature. To clarify the reactions which took place during milling and heating up reduction, the samples were subjected to XRD examinations. It was found that the heat generated during exothermic reaction of aluminothermic reduction of hematite promoted the endothermic reaction of carbothermic reduction. In the course of heating up reduction, the carbothermic reaction occurred just after aluminothermic reaction. Increasing of aluminum content from 0 to 10% in 2 hours ball milled samples decreased the temperature of carbothermic reaction from 1020 °C to about 860 °C. The further ball milling of the samples up to 5 and 10 hours, for the samples containing 10 and 5% aluminium respectively, caused the decrease of the temperature of aluminothermic and carbothermic reactions to around the melting point of aluminium.
In‐Situ Observation of the Formation of MnS during Solidification of High Sulphur Steels
Authors: Valdez Martin Emiliano , Wang Yan , Sridhar Seetharaman
Published: December 2016

A Confocal Scanning Laser Microscope equipped with a gold image furnace was used to directly observe the precipitation of MnS during solidification of high sulphur steels under isothermal conditions in the temperature region 1440 to 1480°C on the free surface of the steel melt. For the case of Al‐killed steels, below 1480°C MnS particles were found to precipitate with Fe forming simultaneously around them. This MnS containing structure continued to grow rapidly (264 μm/s) as a surface film. The film gradually changed, as the level of S in the melt decreased, into a eutectic structure (with lamella spacing of 2 μm) as predicted by thermodynamics. In Si‐ killed steels there was significantly lower tendency to form MnS both in terms of time until precipitation occurred and growth rate.
A Newly Developed Upper‐Bound Approach for Calculating the Width Flow in Hot Rolling
Authors: Rasp Wolfgang , Yusupov Artem
Published: December 2016

This paper presents an investigation of the 3D metal‐forming process during hot flat rolling by an upper‐bound approach. The general aspects of this limit analysis refer to the volume deformation taking into account a polynomial propagation of the free side surfaces. In this approach the deformation region is limited by the roll‐gap entrance and exit with parallel planes. It is characterized by a non‐linear velocity field. A mathematical model of an upper‐bound calculation for the symmetrical flat rolling is developed in order to examine the influence of the most relevant functions, namely the velocity field together with the boundary conditions. A comparison of reasonable onsets is proposed. Therefore, the study can offer useful knowledge for better prediction of lateral flow.
Identification of Rheological Parameters on the Basis of Various Types of Compression and Tension Tests
Authors: Gawad Jerzy , Kuziak Roman , Madej Lukasz , Szeliga Danuta , Pietrzyk Maciej
Published: December 2016

The objective of the project was to determine flow stress on the basis of various plastometric tests. The experiments used uniaxial compression, ring compression, and plane strain compression for two sizes of samples and tensile tests. The material was carbon‐manganese steel, and all the tests were performed at three temperatures (900, 1000, and 1100°C) and at three strain rates for each temperature (0.1, 1, and 10 s−1). Inverse analysis was applied to the interpretation of the results of all compression tests. The flow stresses obtained from various compression tests were compared resulting in the following observations: consistent results between the tests were observed for low values of the Zener‐Hollomon parameter, but some discrepancies appeared for larger values of this parameter. The sensitivity of the results of inverse analysis with respect to the friction factor was investigated next, and it was concluded that the flow stress determined from ring compression showed the largest sensitivity to friction. This sensitivity was lower for uniaxial compression and plane strain compression of small samples, and no sensitivity was observed for plane strain compression of large samples. Finally, the simulations of the tensile tests were performed using the rheological models determined in compression, and reasonably good results were obtained.
Simulation of the Process Influencing Behaviour of Forming Machines
Authors: Großmann Knut , Wiemer Hajo
Published: December 2016

In the design of sheet metal components and associated tools the use of forming process simulation based on finite element method is state of the art. The modelling of the forming process, however, neglects fundamental influences of the forming machine. But today, the machine behaviour influencing the process can be described with simulation tools sufficiently.

The article presented here describes the current state of simulation for forming machines in regard to static and dynamic influences on the forming process. Furthermore, two examples and a proposal for enhancing the model are given.
Selected Problems of Die‐Forging of PM Steel Products
Authors: Szczepanik Stefan
Published: December 2016

The paper discusses the selected technological and material problems of closed‐die forging of PM steel preforms. The first part presents technological variants of hot forging routs of PM materials. In the second part the influence of hot forging parameters on the density, mechanical properties and structure are discussed. The influence of the size of powder particles, powder manufacturing method, chemical composition and heat treatment conditions on mechanical properties after forging is shown. The research on thermomechanical forging of PM preforms has resulted in potential possibilities of shortening of the manufacturing route to obtain products with high density and good mechanical properties from one heating before forming.
Reoxidation on the Surface of Molten Low‐Carbon Aluminum‐Killed Steel
Authors: Wang Yan , Sridhar Seethamaran
Published: December 2016

The unwanted formation of oxide on the surface of molten steel is a process that plagues virtually all grades of steel and often results in unacceptable defect distributions in the finished product. The kinetic rates of the reaction remain largely unknown due to the difficulties in experimental measurements at high temperature involving reactive molten melts. This paper presents recent experimental work and analysis of oxide evolution on the surface of Al‐killed steel melts at oxygen partial pressures of Po2= 1~5×10−5atm, by using a Confocal Scanning Laser Microscope (CSLM) equipped with a gold image furnace. The effects of gas flow rate (170~300 cm3/min) and temperature (1580~1630°C) were investigated. The oxide phase formed on the melt surface was in all cases Al2O3 but not the thermodynamically stable FeAl2O4. It was found, under the range of experimental conditions in this study, that the rate controlling mechanism for oxide nucleation and growth was gas phase mass transfer of oxygen to the melt surface. The morphology of the oxide changed gradually from distinctly dendritic at low gas flow rates to aggregates as the flow rate was increased.
Technology Progress and Strategy in Blast Furnace Ironmaking in China
Authors: Shen Fengman , Yang Tianjun , Gao Bin
Published: December 2016

In recent years, a rapid technology progress in blast furnace ironmaking has been achieved in China. Both the production capacity and the output have been growing sharply. In this paper, some production indexes and technology development in blast furnace ironmaking in China are reviewed briefly and the strategy development of a new process for pulverized coal injection and the technology of long campaign are introduced and discussed in details.
Zero Inclusion Steel and its Oxide Inclusions Characteristics
Authors: Xue Zhengliang , Weng Yuqing , Li Zhengbang
Published: December 2016

Vacuum induction melting and electron beam melting have been used to produce a steel with a composition of 4×10−6 T[O], 5×10−6 [S], 3×10−6 [N]. Examining the samples of the steel with original position analysis and SEM showed that the non‐metallic inclusions in the steel were mainly alumina particles with a size ranging from 1 to 4 microns. The morphology and composition of the inclusions extracted electrolytically from the steel were analysed using SEM and EDS. It was found that some deoxidization products and lining materials with a size ranging from 10 to 20 microns, and some flux inclusions with a size around 40 microns existed in the steel. Most of these bigger inclusions originated from raw materials. Finally this paper also proposed an effective method to remove these bigger inclusion particles from zero inclusion steel.
Mathematical Model for Growth and Removal of Inclusions in Molten Steel under Gas‐stirring Conditions
Authors: WANG Li Tao , PENG Shi Heng , ZHANG Qiao Ying , LI Zheng Bang
Published: December 2016

A three‐dimensional mathematical model has been developed to predict growth and removal of inclusions during gas stirring through eccentric tuyeres in a ladle. In the model, the efficiency of inclusion removal is investigated under three different collision mechanisms: Brownian, turbulent and Stokes collision. The Importance of the three approaches of wall adhesion, Stokes flotation and bubble adhesion on inclusion removal is analysed and the efficiency of inclusion removal through three types of tuyeres in central, eccentric and multi‐tuyere form is studied. The results indicate that inclusion growth resulting from turbulent collision is most important and the effect of Stokes collision is remarkable with increased inclusion size, while inclusion growth resulting from Brownian collision is negligible. Removal by Stokes flotation is the main mechanism for large inclusions, while inclusion removal by wall adhesion is negligible. The smaller the bubbles are, the higher the efficiency of inclusion removal is. The type of tuyere arrangement has a great effect on inclusion removal. Inclusion removal in a 135t ladle with one eccentric tuyere is more efficient than in a ladle with central tuyere or multi‐tuyere design.
Studies on Dephosphorisation of Steel in Induction Furnace
Authors: Sen Niladri
Published: December 2016

Steel melters who use recycled steel scrap in small induction furnaces have no control on phosphorus input from scrap. For furnaces of capacity less than 2T, dephosphorisation in external ladle is not possible owing to excessive heat loss. Studies on dephosphorisation were thus carried out in the induction furnace itself using lime based fluxes with and without addition of fluxing agents like CaF2 and Na2O. The fluxes were added directly and also added through injection. The effects of individual components of fluxes on dephosphorisation were estimated. Correlation were developed between dephosphorisation and different expressions of basicity values. An operator can easily use these correlation to predict dephosphorisation levels depending on type of flux used and mode of addition.
Mathematical Modelling of Magnesia Carbon Refractories Reactions with Steel
Authors: Cirilli Filippo , Tonelli Mario
Published: December 2016

The production of super clean steel has put in clear evidence the importance of the refractory in influencing the degree on internal cleanliness of steel. In fact chemical species transfer from the refractory to the steel bath. To reduce the steel contamination caused by the refractory it is necessary to know the interaction between the refractory and the steel. A mathematical model of the modifications of the refractory surface in contact with the steel has been developed. The work is focused on magnesia‐carbon refractory (taking into account the presence of reducing agents too, as Al, Si and Mg) and carbon steel. The model calculates the new phases formed when liquid steel and refractory are in contact. The model is based on the following mechanism of reactions: (i) Magnesia reacts with graphite forming gaseous CO and Mg. (ii) The other oxides present in the refractory (mainly CaO and SiO2 which constitutes a glassy phase) pass into the steel, giving dissolved elements and dispersed oxides. (iii) Gaseous Mg reacts at the interface refractory/steel with oxygen dissolved in the steel forming solid MgO. (iv) The MgO generated and the oxides originating from the glassy phase form the new oxide system. The newly formed phase can potentially be transferred to the bath through the steel flow against the refractory walls. The results of the model simulations have been validated by experimental tests.
Multi‐Layer Compression Tests under Hot Forming Conditions
Authors: Bernrath Gottfried , Volles Ralf , Kopp Reiner
Published: December 2016

Exact simulation of forming processes using the finite element method requires as precise specification as possible of the prevailing material data and physical boundary conditions. The article presents a method of determining the flow‐stress for sheet metals under hot‐forming conditions. The value is determined in a cylindrical multi‐layer compression test which up to now has been underestimated even for cold testing conditions. This article presents some special adaptations which are necessary for testing under high temperature conditions. The method is able to supply reliable data for FEM simulation, as is demonstrated in some examples.
Grain Refinement of TRIP‐Assisted Multiphase Steels through Strain‐Induced Phase Transformation
Authors: Godet Stéphane , Harlet Philippe , Jacques Pascal J.
Published: December 2016

To develop high performance steels for automotive applications, enhanced strengthening mechanisms are required. This study aims at assessing the critical parameters leading to the refinement of the strain‐induced ferrite matrix of thermomechanically processed multiphase steels. Hot rolling simulations allowed the definition of the temperature, strain and cooling rate conditions bringing about the formation of strain‐induced ferrite with a reduced grain size. The relationship between the deformation and the concurrent or subsequent phase transformations is highlighted thanks to a thorough characterisation of the generated microstructures. It is also shown that the prior austenite grain size influences the distribution of the second phases within the finely grained ferrite matrix.
The Structure And Properties of a Thermo‐mechanically Processed Low Carbon High Strength Steel
Authors: Ghosh Arindam , Shukla Rabindra , Das Samar , Chatterjee Subrata
Published: December 2016

Research efforts were given towards development of low carbon high strength steels since recent past. The present study deals with the development of a low carbon high strength steel alloyed with Mn, Ni, Mo, Cu and microalloyed with Ti and Nb. The steel was subjected to three stage controlled rolling operation followed by accelerated cooling. The structure and properties of the steel at various processing conditions were evaluated. Microstructural observation reveals predominantly lath martensite along with twinned martensite structure at all processing conditions. High strength values at higher finish rolling temperatures have been obtained due to fine martensitic structure along with tiny precipitates of microalloying carbide and carbonitride. The strength value increases marginally at lower finishing temperature due to comparatively finer lath size of martensite and increased precipitation density of carbides, carbonitrides along with Cu particles. The variation in impact toughness properties at different finish rolling temperatures is found to be negligible at ambient and subambient temperatures. The formation of stable and large TiN/TiCN particles during casting have impaired the impact toughness values at ambient and at ‐40°C temperatures.
A Thermodynamic Model of the EAF Process for Stainless Steel
Authors: Arnout Sander , Verhaeghe Frederik , Blanpain Bart , Wollants Patrick , Hendrickx Roel , Heylen Gert
Published: December 2016

A time‐dependent thermochemical model has been developed for the electric arc furnace (EAF) process for stainless steel production. Time dependency is implemented by a stepwise input of energy and matter into an equilibrium reactor. The equilibrium calculations are performed using data from FACT‐databases and implemented using the programming library ChemApp. The material input for the model was generated by reconciliation of industrial data and the energy input is approximated from the industrial data and scaled through an efficiency factor. The model is used to calculate the evolution of temperature and composition of gas, slag and metal phases with time. Agreement of the end composition in the metal phase with industrial data is good. In the slag phase, however, Cr, Fe, Mn and Si are oxidized significantly less than expected due to excess formation of CO‐gas. The dynamics of the slag composition are examined in more detail. Here a fair agreement is reached for the main slag components. However, for Cr, Fe and Mn the model cannot predict the dynamics, which seem to be strongly kinetically controlled. The results of the equilibrium model can thus provide some insight into the kinetics of the process.
Selection of Suitable Tool Materials and Development of Tool Concepts for the Thixoforging of Steels
Authors: Püttgen Wolfgang , Pant Martin , Bleck Wolfgang , Seidl Ingold , Rabitsch Roland , Testani Claudio
Published: December 2016

This paper describes the results of the European project “THIXOCOMP” within the 5th framework programme concerning the material selection and development of tools for the thixoforging of steels. Due to high process temperatures, special requirements are necessary regarding the tool material and the tool concept. Special tool coatings (High Velocity Oxi Fuel, HVOF and Plasma Spray, CAPS) with high strength, high corrosion and oxidation resistance were deposited on substrate materials 1.2367, 1.4841 and 2.4631 to improve the properties of the tool materials. Different laboratory tests were performed to investigate the suitability of the tool systems. Pull tests, micro‐hardness measurements, high temperature corrosion tests and spelling resistance tests were performed to investigate the adhesion of the coatings. The investigation of the thermal shock loading on the coated samples indicated a clear dependence on the base material. Both coatings on the base materials 1.2367 and 1.4841 were removed completely in the spelling resistance tests, so that even in the coated state, they are not suitable as tool materials for the thixoforming of steel. The combination of 2.4631+HVOF provided the best results. Afterwards, thixoforging trials were performed with the nickel‐based alloy, 2.4631. After 30 trials at 1290°C (HS6‐5‐3), the tool showed no macroscopic damages, whereas a deformation of the press channel was already visible after eight forming trials at 1430°C (100Cr6).
Constitutive Equation for AISI4140 Steel Applicable to a Wide Range of Strain Rates at Elevated Temperatures
Authors: Kim S.I. , Byon S.M. , Seo S. W. , Min O. , Lee Y.
Published: December 2016

This paper presents a method to determine a constitutive equation of AISI4140 steel when it deforms at a wide range of strain rates (0.05~1900s−1) under high temperatures. The fundamental idea considered here is that the dependency of flow stress upon strain rate and temperature is described by the power law model of the Arrhenius equation. Strengthening coefficient and work hardening exponent are introduced to take a simplified treatment to the flow stress behaviour characteristics without losing accuracy of the model. The validity of the proposed constitutive equation has been examined using results obtained from the hot compression test (GLEEBLE® 3500C) and Split Hopkinson‐Pressure Bar test at high temperature. Results revealed the proposed constitutive equation could predict flow stress‐strain curve of the steel with an acceptable amount of error at the ranges of strain rates.
Modelling of the High‐temperature Ductility Properties during Solidification of Austenitic Stainless Steel
Authors: Diederichs Roman , Trute Sebastian , Bleck Wolfgang
Published: December 2016

Knowledge of the high‐temperature ductility properties of steel grades is essential for the processing of steel products due to the existence of critical temperature regions. Embrittlement in the liquid/solid two‐phase region and in the precipitation region can be distinguished. In these regions, material failure can occur due to cracking as soon as the appearing strains and stresses exceed the formability of the material at a given temperature. Therefore, the temperature ranges where reduced ductility occurs have to be identified to ensure appropriate processing of the materials in continuous casting or welding. These temperature regions are usually investigated by means of hot tensile testing after melting of the specimen in situ. As these experiments are time‐consuming and expensive, a mathematical estimation of the results would be a great advance.

The presented research work outlines the possibility of a mathematical description of the most important characteristics in the relationship reduction of area versus testing temperature. Especially the zero ductility temperature and zero strength temperature, the critical solidification interval, the maximum ductility range and the region of the secondary ductility drop, including the beginning of the ductility drop and the minimum ductility, are investigated. Furthermore, the reduction of area values for given testing temperatures can be estimated on the base of the chemical composition and the parameters of the hot tensile tests. For this purpose, a model formulated by means of multiple regression analysis on the basis of published experimental data is proposed for the description of the high‐temperature ductility properties of austenitic stainless steel grades of the Cr‐Ni‐ and the Cr‐Ni‐Mo‐type.
Fatigue Crack Propagation in Friction Stir Welded and Parent AA6082
Authors: Ericsson Mats , Sandström Rolf
Published: December 2016

The fatigue crack propagation characteristics of a friction stir welded Al‐Mg‐Si alloy, 6082, have been investigated. The electrical potential drop method was used for measurements. A low and a high load ratio (R) level were tested. At low load ratio (R=0.1) and a low stress intensity δK the propagation rate in the weld was higher than in the parent material by a factor of 3 to 5. However, the propagation rates were approaching each other close to fracture. At high load ratio (R=0.8) the propagation rate was similar in the parent material and weld. The weld crack growth rate was about the same at low and high R (except close to fracture), while the parent material growth rate increased at high R. Paris law was used to describe the measured crack propagation rates in the weld. In the case of the parent material, showing an R‐dependence, Forman's law was used.
Transformation Textures in As‐hot rolled TRIP Steels
Authors: Jonas John J. , He Youliang , Godet Stéphane
Published: December 2016

The microstructures of TRIP steels finish‐rolled above and below the recrystallization‐stop temperature (Tnr) are compared. Here, the retained austenite grains are equiaxed or elongated, respectively, according to whether final rolling was carried out above or below the Tnr. The recrystallized austenite did not contain a sharp texture, the best defined component of which was the cube. The bainite that formed in this case was characterized by weak concentrations of the Goss and rotated Goss and a fairly strong concentration of the rotated cube. It also displayed the transformation products of a retained rolling fibre in the prior austenite. The deformed austenite contained the typical fcc rolling texture, where the copper is considerably more intense than the brass under these conditions. After transformation to bainite, the presence of a strong transformed copper component is evident, together with somewhat less intense contributions from the three transformed brass components. The data indicate that strong variant selection took place in the deformed austenite and that it was also present in the recrystallized material, but to a lesser extent. The latter displayed evidence of incomplete recrystallization in that the transformation texture included components obtained from both “recrystallized” and “deformed” austenite.
Influence of Residual Elements on Mechanical Properties of Two Carbon Steel Grades
Authors: Xu Su , Brown Jim R. , Tyson William R.
Published: December 2016

Experiments were carried out to study the influence of residual elements on microstructure and mechanical properties of two carbon steel grades (i.e. 0.04% C and 0.20% C). The effect of residuals on the microstructure of the carbon steels was mainly to decrease ferrite grain sizes. The effect of residuals on tensile properties was mainly to increase yield and tensile strengths and to slightly decrease ductility, which reflected a combination of solid solution hardening by residuals and grain refinement. The 40 J notch toughness transition temperature (TT) was determined by fitting Charpy absorbed energies to a hyperbolic function and by finding the temperature corresponding to 40 J in the fitted curve; a statistical analysis was performed to ensure the repeatability of TTs defined by this procedure. After the step‐cooling heat treatment to maximize segregation, the 40 J TT of a 0.04% C steel with high Mn and Si contents increased by 28K and the 40 J TT of 0.20 % C steels with the highest residual level (0.085% Sn, 0.4% Cu and 0.4% Ni) increased by 24K, indicating that the upward shift of TT is small even for high levels of residuals. Grain boundary segregation was semi‐quantitatively analysed by Auger electron spectroscopy. Small amounts of Sn segregation were observed, most notably in the low‐C grade.
Rheological Model for Simulation of Hot rolling of New Generation Steel Strips for Automotive Applications
Authors: Hadasik Eugeniusz , Kuziak Roman , Kawalla Rudolf , Adamczyk Mariusz , Pietrzyk Maciej
Published: December 2016

The main objective of this paper is the development of a rheological model for automotive steels for the conditions of hot strip rolling and implementation of this model in a finite element program is. Three types of steels were investigated, IF, dual phase and TRIP steel. Plastometric tests were performed on a Gleeble 3800 simulator for the temperature range 850‐1200°C and strain rates 3‐150 s−1. Inverse analysis was applied to eliminate the influence of disturbances occurring in the plastometric tests and to determine the real flow stress of the material. The coefficients in the flow stress equation were evaluated and this equation was implemented in the FEM code as the constitutive law. The model was validated by comparison of measured and calculated loads in the compression tests and by strip rolling experiments conducted in the laboratory mill. Validation confirmed a good predictive capability of the rheological model.
Transient Heat Transfer Analysis of Blast Furnace Cooling Staves
Authors: Qian Zhong , Du Zhaohui , Wu Lijun
Published: December 2016

The capability of cooling staves is crucial for a long campaign life of blast furnaces (BF). Transient heat transfer analysis of blast furnace cooling staves made of copper, cast steel, and ductile cast iron are performed. Moreover, the temperature field variations of cooling staves according to different distributions of gas flow temperature are studied. A discussion of cooling staves made of the three different materials is given based on their performance during the transient heat transfer process. The results indicate that copper staves are suited for a long campaign life, as their performance is much better compared to cast steel and ductile cast iron staves especially during unsteady heat transfer. Moreover, the capacity of staves made of cast steel is better than that of ductile cast iron.
Mixing and Oxide Cleanness in Sequence Casting of Heats of Differing Compositions
Authors: Bolender Thorsten , Jacobi Hatto , Weinberg Matthias , Wünnenberg Klaus
Published: December 2016

For a two‐strand slab caster and a tundish capacity of 50 t the transition zone between two heats of different chemical composition was experimentally defined. The distribution of various elements was measured. The transition curves also show the penetration depth of the casting stream using a bifurcated submerged nozzle. This is basic information for the calculation of the mixing zone. Knowledge of the permissible composition ranges permits optimisation of the usable length of the strand. The impact of ladle change on oxide cleanness is analysed as well.
Investigation of Orientation Gradients in Pearlite in Hypoeutectoid Steel by use of Orientation Imaging Microscopy
Authors: Takahashi Tetsuya , Ponge Dirk , Raabe Dierk
Published: December 2016

The microstructure of pearlite in hypoeutectoid steel was investigated using high resolution orientation imaging microscopy. Systematic orientation gradients were observed along the longitudinal direction within the pearlitic ferrite lamellae. Corresponding orientation gradients seemed to occur also in the cementite within the same pearlite colony. The orientation gradients in the ferrite strongly correlated with the local topographical curvature of the pearlitic colony. The orientation relationship between the ferrite and the cementite lamellae was constant even in areas with strong orientation gradients.
Preliminary Investigation of Mathematical Modeling of Stainless Steelmaking in an AOD Converter: Application of the Model and Results
Authors: Shi Guo‐Min , Wei Ji‐He , Zhu Hong‐Li , Shu Jie‐Hui , Jiang Qing‐Yuan , Chi He‐Bing
Published: December 2016

The changes in the contents of C, Cr, Si, and Mn in molten steel and the bath temperature during the refining of 304‐grade stainless steel, including both the oxidation (decarburization) and reduction processes, in a side and top combined blowing AOD converter of 120 t capacity have been predicted. The calculations were performed using the mathematical model proposed and presented in Part I of the present work [1] and were based on the designed operational mode of the AOD converter. The model predictions were compared to the referenced values given by the technological design. The results demonstrate that the predictions by the model are in good agreement with the reference values. Not only the competition of oxidation among the elements dissolved in the steel during the oxidative refining process and the corresponding distribution ratios of oxygen, but also the competition of reduction among the oxides during the argon stirring and reductive refining process and the relevant supplied oxygen ratios of the oxides, can all be characterized more comprehensively and determined more reasonably by using the Gibbs free energies of the oxidation and reduction reactions. Corresponding to the top, side, and side and top combined (overall) refining processes of 304‐grade stainless steel in a 120 t AOD converter, the carbon concentrations at the critical rates, i.e. the critical carbon concentrations, after which the decarburization changes to be controlled by the mass transfer of carbon in molten steel, are 1.20, 0.37 and 0.53 mass%, respectively, under the given designed operational mode. The model can offer some useful information for determining the technology of the side and top combined blowing AOD refining process of stainless steel.
Effects of Strain Rate and Identification of Material Constants for Three Automotive Steels
Authors: Larour Patrick , Rusinek Alexis , Klepaczko Janusz R. , Bleck Wolfgang
Published: December 2016

The main topic of this paper is an analysis of experimental results for three kinds of sheet steel: DP600, TRIP700 and H340LAD, which are used in the automotive industry. Such results were partly reported earlier in [1]. For comparison purposes the experimental results obtained at LPMM for an ES (DC05) mild steel have also been integrated in this paper. The tension tests were performed at room temperature in a relatively wide range of strain rates, that is from ~3.0·10−4 s−1 up to ~103 s−1. Since at low and high strain rates two different specimen geometries were applied, detailed numerical analyses have been performed in order to estimate the geometry effects on the final true stress versus true strain characteristics at different strain rates. A relatively new constitutive relation of the form = 0 is applied. This constitutive relation in the form of the Mechanical Equation of State (MES), called also the RK relation, has been developed by Rusinek and Klepaczko [2]. The main advantage introduced in the RK approach is the rate and temperature sensitivity of the strain hardening exponent, n , a very important improvement in comparison to other constitutive formulations. It appears that introduction of the rate and temperature sensitivity of strain hardening is very important in all BCC and FCC micro‐structures. In BCC structures the tangent modulus of may substantially decrease when strain rate increases. A special procedure was applied, according to Rusinek and Klepaczko [2], to determine the material constants for those three steels. An excellent fit to experimental data was obtained. Some FE calculations performed earlier on the energy absorbing profiles under impact with the RK constitutive relation have shown very good confirmation of experiment. In addition, two specimen geometries were analysed via an FE method.