Industrial applications of modelling tools to simulate the PAMCHR casting and VAR process for Ti64

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.

Ti and TiAl melting with a semi-industrial PAMCHR

Upscaling from laboratory trials to industrialization is a critical step in the development of new metallurgical processes and products. Pilot trials are an important way to provide data that can be used to better understand and model the industrial-scale process. MetaFensch has invested in a semi-industrial Plasma Arc Melter Cold Hearth Refiner (PAMCHR) in order to support the development of the recycling of titanium scraps into aeronautical grade titanium alloy ingots. This pilot supports the industrial scale PAMCHR of the company Ecotitanium in the frame of a collaborative project with Aubert & Duval and Safran as industrial partners. The work done on the pilot scale PAMCHR consists in studying the influence of various parameters like the type of melting feedstock, plasma arc parameters, operating pressure on the final quality of the cast ingot. The goal is to understand the physico-chemical mechanisms involved in the plasma arc interacting with the liquid metal in order to optimize the melting and refining parameters for the industrial scale furnace Ecotitanium (Ti64 alloy). Ti64 and TiAl ingots were cast in 150 mm and 100 mm diameter. Chemical composition and solidification structure were characterized. The effect of the different process parameters on the titanium melt and on the ingot quality are studied. Examples of exploitation of the thermograms obtained with the thermal camera situated above the refining cold hearth will also be presented in this paper.

Effect of B2O3 on the Crystallization Behavior of CaF2-Based Slag for Electroslag Remelting 9CrMoCoB Steel

The non-isothermal crystallization characteristics of the electroslag remelting (ESR)-type slag with varied B2O3 contents were investigated by non-isothermal differential scanning calorimetry (DSC), field emission scanning electron microscopy (SEM-EDS), and X-ray diffraction (XRD). The crystallization mechanism of the B2O3-bearing slag was also identified based on kinetics analysis. The results showed that the primary crystalline phase was CaF2, there was no change in the type of the primary crystal as B2O3 content increased, and the morphology of the CaF2 crystal was mainly dendritic. The sequence of crystal precipitation during the cooling process was CaF2 to Ca12Al14O32F2 and MgO/MgAl2O4, followed by Ca3B2O6. The activation energy of CaF2 crystallization increased firstly, then decreased and reached stability, while the activation energy of Ca3B2O6 crystallization increased continuously with the increasing B2O3 content. The crystallization behavior of CaF2 was three-dimensional growth with a constant nucleation rate. The proper B2O3 content added into the CaF2-based ESR slag should be around 1.0% to limit the precipitation of the CaF2 crystal to attain good surface ingot quality and stable ESR operation.