Search

Populations of inclusions conditioned very early in the alloy production process metals, during the refining and liquid metal treatment stages, are likely to drastically impact mechanical performance, especially fatigue resistance. Control performance of these materials therefore requires control of the inclusion populations, requiring in particular a very good knowledge of the mechanisms which govern their evolution in number and size in refining reactors. Inclusive behaviors in supply chains steel and aluminum have already been the subject of numerical studies at the process scale (Bellot et al., 2014 ; Waz et al., 2016) in which the transport and agglomeration of inclusions are modelled. In order to improve the modelling of key phenomena such as the aggregation and capture of wall inclusions, local simulations, at the scale of an inclusion pair and a layer limit to the wall of a reactor, are carried out here using a lattice Boltzmann method (Sungkorn and Derksen, 2012).

Europe is a major provider of titanium scrap but until now there has been no european facility dedicated to the production of aeronautical quality titanium alloys by recycling. UKAD, a joint-venture between Aubert & Duval and UKTMP, ADEME and Crédit Agricole Center France, created the company EcoTitanium, where the recycling of machining scraps is achieved using the Plasma Arc Melting Cold Hearth Refining (PAMCHR) process with the aim of producing such alloy ingots. The determination of the heat flux transferred from the plasma column to the surface of the liquid bath is an important issue needed for the development of a future 3D process modeling based on Ansys-Fluent CFD software. With this preliminary aim of predicting the heat flux, a study coupling pilot furnace testing and numerical modeling has been performed. Melting tests were carried out in a pilot PAMCHR furnace in MetaFensch, with a stationary torch. In parallel, the different contributions of the heat flux transferred to the surface of the liquid bath were identified and implemented in a simple 2D axisymmetric heat transfer model. Numerical results are compared to the experimental measurements, in order to define the heat flux transferred from the plasma torch.

The PAMCHR (Plasma Arc Melting Cold Hearth Refining) process followed by a VAR (Vacuum Arc Remelting) melting is used to recycle Ti64 scrap for aeronautical applications. The produced ingot quality is linked to the quality of charging materials and to numerous operating parameters. Ecotitanium (a company created by UKAD, a joint-venture between Aubert & Duval and UKTMP, ADEME and Crédit Agricole Centre France) launched a program with the Institut Jean Lamour dedicated to the development of specific modelling tools in order to get a better understanding of operating parameters effect on the final ingot quality. A model of the PAMCHR casting was developed and used to describe the heat transfer, liquid metal flow and alloying elements behavior during mixing in the liquid pool followed by segregation during solidification. The effect of PAMCHR electrode composition on the final VAR ingot composition is also studied using the SOLAR VAR model. Model validation by comparison with industrial ingots is presented with some examples of operating parameters sensitivity study.

Parmi les techniques de purification ultime de métaux à hauts points de fusion, le procédé de refusion par bombardement électronique associe une puissance thermique garantissant la fusion du métal, et une refusion sous vide permettant l'élimination d'impuretés par distillation. Ce papier présente la technique et le potentiel d'élimination par distillation. Among the ultimate purification techniques applied to the high melting point metallic materials, the electron beam remelting process, combining a high thermal power and vacuum, is particularly conducive to volatilization. This paper describes the technique and its efficiency to remove impurities by distillation.

In order to clarify the evolution mechanism of inclusions in 95CrMo, the industrial experiments were conducted. The composition, morphology and size of inclusions during refining and solidifying processes were analyzed by SEM-EDS detection and thermodynamic calculations. The inclusion evolution during refining process in molten 95CrMo steel can be concluded as: Al2O3 → Al2O3-MgO-CaO/CaS → Al2O3-MgO-SiO2-CaO-CaS, which is affected by slag-metal reaction and corrosion of refractory. The change of inclusion size during refining was analyzed based on their collision and floatation behavior. The composition of inclusions in billets indicate that there were mainly five types of inclusions, including spinel with sharp angle, spherical oxide inclusion composed of Al2O3, MgO, SiO2 and CaO, oxide-sulfide inclusion with single phase, inclusion with duplex phase, and MnS inclusion. The type of inclusions affects their size. The thermodynamic results indicate that most complex oxides formed in molten steel and no spinel generated during cooling process. CaS formed in the molten steel after tundish metallurgy and there were still some CaS precipitated in solid steel. MnS precipitated after steel solidification. The calculated results based on FACTSAGE 7.1 are in agreement with experimental results on the whole. [ABSTRACT FROM AUTHOR]

The aim of the current study is to clarify the influence of steel cleanliness on the fracture during wet wire drawing of high strength high carbon very fine filaments. Methodologies for inclusion identification and for inclusion count were developed. Ninety percent of the fractured filaments were associated with an inclusion which was SiO2, or SiO2-CaO or SiO2-MgO. The fracture of the wires resulted from debonding of the inclusion from the matrix. Inclusion density assessed from total oxygen content in the wire was successfully and reliably obtained. Inclusions exhibited a wide range of sizes but mostly around 6 μm. The inclusion density did not appear as the only parameter that affects the fracture occurrence. An important effect of size and of chemical composition of the inclusions was found. A critical size of inclusions for fracture was observed but it depends on the chemical composition of inclusions. [ABSTRACT FROM AUTHOR]

In today's steel automotive industry, press hardened steels meet requirements of a lower CO2 consumption and of a better safety of drivers. These steels contain titanium nitrides which can downgrade the in-use properties. From this laboratory study, with a wide range of N (20–120 ppm) combined with high Ti variations (20–110.10−3 wt.%), clear conclusions can be highlighted. Titanium content is the key parameter to drive inclusions content, more than N, as there is a high segregation of Ti in the last liquid, due to a low partition coefficient combined with a low back-diffusion coefficient. Due to this supersaturation in Ti, TiC can be formed. It does not mean that N has no effect. It has to be noticed that the density of inclusions coarser than two microns is highly dependent of the product [Ti] × [N]. Carbon is a very important factor too to take into account as the surpersaturation in Ti in presence of austenite is higher than in presence of delta-ferrite. This gives a few guidelines in the design of inclusions controlled new grades. [ABSTRACT FROM AUTHOR]

Copyright of Metallurgical Research & Technology is the property of EDP Sciences and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This paper presents a process and its variants to prepare alumina particle suspension in liquid tin alloy. Complication may arise due to the non-wettability of alumina by tin alloy. For this purpose, prior to introduce the powder into the liquid metal, the particles of alumina are covered by a thin layer of tin metal by using a controlled milling process. The operating conditions leading to an optimal coverage without particle damage and to a good dispersibility in the liquid metal have been searched. [ABSTRACT FROM AUTHOR]

In order to find a method to characterize the inclusion distribution of high-cleanliness materials, complementary techniques were tested, such as high-frequency (80 MHz) ultrasonic testing, X-ray tomography or Extreme Value Analysis (EVA). The micro-cleanliness was also characterized by standard methods based on observations of polished surfaces by light optical or scanning electronic microscopy. The combination of all these techniques, enhanced by metiS software, allows us to determine the complete 3D distribution of oxides or to estimate the probability of largest inclusion size by modelling virtual samples. At the end, fatigue testing was performed in order to try to link fatigue results to previous characterization outcomes. [ABSTRACT FROM AUTHOR]

The mechanical and use properties of metal alloys depend on several factors, including the amount and the geometry of impurities (inclusions). In this context, image analysis enables these inclusions to be studied from digital images acquired by various systems such as optical/electron microscopy or X-ray tomography. This paper therefore aims to present some geometrical and morphometrical tools of image analysis, in order to characterize inclusions in metal alloys. To achieve this quantification, many geometrical and morphometrical features are traditionally used to quantitatively describe a population of objects (inclusions). Integral geometry, via Minkowski's functionals (in 2D: area, perimeter, Euler-Poincaré number), has been particularly investigated in image analysis. Nevertheless, they are sometimes insufficient for the characterization of complex microstructures (such as aggregates/agglomerates of objects). Other quantitative parameters are then necessary in order to discriminate or group different families of objects. In particular, shape diagrams are mathematical representations in the Euclidean plane for studying the morphology (shape) of objects, regardless of their size. In addition, this representation also makes it possible to analyze the evolution from one shape to another. In conclusion, image analysis using integral geometry and shape diagrams provide efficient tools with known mathematical properties to quantitatively describe inclusions (providing separate information on size and shape). The geometrical characteristics of these inclusions could thereafter be related to the mechanical properties of the metal alloys. [ABSTRACT FROM AUTHOR]

Vacuum metallurgical processes such as the electron beam melting are highly conducive to volatilization. In titanium processing, it concerns the alloying elements which show a high vapor pressure with respect to titanium matrix, such as Al. Two different experimental approaches using a laboratory electron beam furnace have been developed for the estimation of volatilization rate and activity coefficient of Al in Ti64. The first innovative method is based on the deposition rate of Al on Si wafers located at different angles θ above the liquid bath. We found that a deposition according to a cos2(π/2−θ) lawdescribes well the experimental distribution of the weight of the deposition layer. The second approach relies on the depletion of aluminum in the liquid pool at two separate times of the volatilization process. Both approaches provide values of the Al activity coefficient at T = 1, 860 °C in a fairly narrow range [0.044-0.0495], in good agreement with the range reported in the literature. Furthermore numerical simulation of the Al behavior in the liquid pool reveals (in the specific case of electron beam button melting) a weak transport resistance in the surface boundary layer. [ABSTRACT FROM AUTHOR]