Prof. Dr.-Ing. Senk (Chair for Metallurgy of Iron and Steel, Department of Ferrous Metallurgy, RWTH Aachen University)
In this project (TP) B1 the sample material is produced within the project-relevant alloy from the system Fe-Mn-C-Al; the material is ordered by the other projects with according specifications. Relevant parameters are the alloy composition including microelements, degree of purity, state of segregation and the size of the as-cast grains. Therefor there are corresponding vacuum induction furnaces with capacity up to 100 kg, specially developed ingot molds for macro-segregation-free solidification and a new slow solidification furnace to produce oligia-crystalline samples with a crystal diameter up to 10 mm and a crystal length up to 40 mm. The slow solidification furnace was planned and put into operation in the second phase of the SFB 761. In the third phase this furnace will be developed to control the parameters and conditions of solidification more exactly.
The basis for the continuation of TP B1 was the successful, execution of the two previous phases of the SFB 761 TP B1. In these previous phases the initial system Fe-Mn-C was continuously extended. In the third phase the system will be extended to the Fe-Mn-C-X (X=Al, Si, …). The extension to more complicated, multi-phase alloys leads to massive changes in the solidification and high temperature behavior.
Diverse experiments for the correlation of the chemical composition, structure, mechanical characteristics and mechanical bending stress in a temperature range between solidus temperature and 800 °C are planned. The high temperature brittleness is controlled by rough and fine segregations, precipitations, grain boundary assignment and inclusions; summarized as purity. Especially the elements [N], [O], [S], [P], [B] and [Se] are responsible for local decrease of purity in nonmetallic particles. The critical temperature, critical extension and rate of extension are identified with the high temperature tensile test and some bending stress investigation. Mostly unwanted elements act into the material from alloy additives and recycling. In some cases these elements are used to control some specific characteristics. The ductility-decreasing mechanism, especially in the background of the local alloy composition with peritectic or one-phase solidification (either d-Fe- or g-Fe-lattice), has to be researched. Furthermore the influence of solute [H] on the mechanical high temperature characteristics will be investigated. Essential knowledge and data from the experiments for combination of solidification and mechanical stress are necessary for understanding of material behavior.
Sub-project B1 within the project application of SFB 761 examinates and analysis the melting and solidification parameters for “ab initio” simulation as well as production of designed samples for validation of “ab initio” simulation and deformation experiments.
The identification of distribution, interfacial tensions, limited cooling rate, segregation and diffusion coefficients are important for the characterisation of solidification for Fe-Mn-C materials. For this purpose, experiments and analysis will be arranged.
Analysing the influencing factors on these parameters and their interaction as well as quantification of influence and interaction enables a accurate description and prediction of melting and solidification of Fe-Mn-C materials.
Therefore analysis methods have to be developed, for example for the determination of interfacial tensions at the solidus-liquidus interface, or approved but extensive analysis methods will be used for the indentification of diffusion coefficients, which are described by the method of Crank.
Segregation coefficients in the system Fe-Mn-C for Mn contents between 10 to 30 Mass.-% are not measured yet. Furthermore solidification- and coolingrate and the influence of the carbon content is important for micro segregation. The distribution of carbon segregation in correlation with homogenisation effects at temperature slightly below the solidification temperature have to be determined. The maximum cooling rate for the formation of Fe-Mn-C phases has to be investigated in correlation with solidification and technical relevant tramp elements.
On the one hand the calculated data and their influencing- and interaction factors should be used for the validation of “ab initio” models, on the other hand the data should be included in the development of a Rapid Ingot Model, with the intension of rapid determination for the production of new materials.
Test material, which is commercial not available, will be produced to reproduce the pure Fe-Mn-C system with physically low fractions of tramp elements, especially gases. Furthermore technical relevant amounts of these elements, like phosphor, sulfur, silicon, hydrogen and oxygen, have to be concidered. The reproducibility of the samples has to be guaranteed. For this purpose the furnace will be adapted for the requirements of the Fe-Mn-C system. For example the integration of a manganese steam separator and a hydrogen measurement will be installed, also the scientific determined data for process control in connection with structure and properties of the system are important.