ESR Refining Potential for Titanium Alloys using a CaF₂‐based Active Slag

Abstract

Since the end of the Cold War and due to the needs to produce titanium more cost‐efficient and thus more attractive for its civilian use, the electroslag remelting (ESR) process has become an increasingly important topic of international research programmes, because titanium and titanium aluminides can be chemically refined by ESR in some degree. Using ESR, titanium turnings from machining steps and scrap from foundries can be remelted, refined and provided as secondary titanium for the market at relatively favourable prices. This article investigates the removability of the main impurities out of titanium and titanium‐aluminium alloys by electroslag remelting using the active slag system CaF2‐Ca‐(CaO). Thermochemical and kinetic aspects of the ESR process are considered.

Deoxidation Limits of Titanium Alloys during Pressure Electro Slag Remelting

“…Extending Tsukihashis work, Okabe et al [6] equiblirated Ti melts with CaO and Ca (a Ca = a CaO = 1) and calculated the activity coeffictient f TiO . Based on this work, Stoephasius et al [5] calculated the deoxidation limits of Ti and TiAl melts with metallic calcium as deoxidant. Since during electroslag remelting, instead of pure CaO a CaF 2 -(CaO) slag (with metallic Ca as deoxidant) is used, the CaO activity is decreased.…”

“…Thus, because of the high vapour pressure of Ca, this results into difficult handling of high Ti containing melts. Figure 1: Necessary Ca content in the slag in order to achieve specification conform oxygen contents in titanium and titanium aluminide [5] 3. Experimental…”

Experimental investigation and thermodynamic assessment of the Al–Ca–Ti system

“…Several routes of using calcium as a deoxidation agent were already studied. Calcium is usually used in a mixture, so-called fluxes such as Ca-CaO-CaF 2 that reduce the high vapor pressure of pure calcium in electroslag remelting processes (ESR) [4]. Another way how to remove oxygen from the Ti-Al alloy is remelting in a CaO crucible.…”

A Novel Method to Remove Iron Impurity from Aluminum

“…Stoephasius and Reitz have investigated the removal of the main impurties out of titanium and titanium-aluminum alloys by electroslag refining using a CaF 2 -based active slag. 16) In the present work, electroslag refining was applied to commercial aluminum for removal of iron impurity. The effect of electroslag refining on the iron removal using KClNaCl-Na 3 AlF 6 flux containing P and the reaction mechanism between the melt and the molten slag were investigated.…”

“…[14][15][16] In the process, high current is applied through a resistive slag layer, and the heat generated within the slag melts a consumable electrode. Metal droplets formed at the tip of the electrode, drop through the molten slag, and solidify in a mould to form the ingot.…”