Overview
ABSTRACT
This paper deals with Vacuum Arc Remelting (VAR), a secondary metallurgical process based on refining the liquid metal under vacuum and controlling its solidification within a cooled crucible. It applies to reactive Ti or Zr alloys, which are purified without any contact with refractories, and to steels and superalloys, whose inclusion cleanliness is improved. The principle of the VAR process and the technology of furnaces are discussed, with an emphasis on the process operation and safety aspects. The specificities of remelting are detailed for different grades. Finally, the interest of numerical simulation as a tool to help in the choice of operating parameters is illustrated.
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Read the articleAUTHORS
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Alain JARDY: CNRS Research Director, - Doctorate in Materials Science from the Institut National Polytechnique de Lorraine - Institut Jean Lamour, UMR 7198 Université de Lorraine/CNRS, Nancy, France
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Isabelle CRASSOUS: Research Engineer, - Doctorate in Electrochemistry from Pierre et Marie Curie University Framatome, Centre de Recherche des Composants, Ugine, France
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Sylvain CHARMOND: Research Engineer, - Doctorate in Materials and Processes Science and Engineering from Grenoble Polytechnic Institute - Aubert & Duval, Les Ancizes, France
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Vincent DESCOTES: Research Engineer, - Doctorate in Materials and Processes Science and Engineering from Lorraine University - Aperam Alloys Imphy, Centre de Recherche P. Chevenard, Imphy, France
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Stéphane HANS: Head of the Alloys Elaboration and Casting R&D Department, - Doctorate in Materials Science and Engineering from the Institut National Polytechnique de Lorraine - Aubert & Duval, Les Ancizes, France
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Yvon MILLET: R&D Manager Europe - Timet Savoie, Ugine, France
INTRODUCTION
The Vacuum Arc Remelting (VAR) process was developed in the 1940s to meet the needs of the aerospace, energy and nuclear industries for high-value materials for critical applications. The remelted ingots, with their cylindrical geometry, are compact and highly homogeneous, with a mass of several tons, and are characterized by their low content of undesirable elements and their inclusionary cleanliness. Vacuum arc remelting is mainly used to produce two types of metal alloys, with roughly equal yields:
reactive metals (titanium or zirconium alloys), previously assembled in the form of sponge compacts from vacuum distillation and additive elements, remelted to eliminate undesirable elements (chlorine in particular) and obtain defect-free ingots. VAR remelting is also the final stage in scrap recycling operations, after initial melting by electron bombardment or plasma torch;
ingots of steels (stainless steel, maraging, etc.) or nickel- or cobalt-based superalloys, from consumable electrodes obtained by traditional means (EAF, AOD, VIM, etc.).
Reflow furnace technology, with particular emphasis on operating conditions and process safety, as well as the specific features of vacuum reflow, are discussed in detail in this article, the final part of which is devoted to process modeling. Numerical tools have been developed to describe the complex physical mechanisms involved, and are used as an aid in selecting operating parameters. The aim of the article is to give the reader an overall view of this technology, while detailing each technical aspect and the particularity of each family of alloys produced.
A glossary of acronyms is provided at the end of the article.
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KEYWORDS
solidification | titanium | electrical arc | zirconium | superalloys | special steels | inclusion cleanliness
Vacuum arc remelting (VAR) process
Vacuum arc remelting principle
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