Deoxidation Limits of Titanium Alloys during Pressure Electro Slag Remelting

Abstract

Abstract. This paper focuses on deoxidation of titanium alloys produced by aluminothermic reduction (ATR) and subsequent homogenizing and alloying by vacuum induction melting (VIM). The main goal of the performed research work is to outline the deoxidation limit during pressure electro slag remelting (PESR) of the described material. To obtain electrodes for deoxidation, a Ti-24Al-16V masteralloy was produced by ATR and afterwards melted in a 0.5 litre calcium-zirconate (lab scale) or 14 litres high purity calcia (pilot scale) crucibles with continuous addition of Ti-sponge after reaching liquid state in order to obtain a final Ti-6Al-4V alloy. During melting, in both cases evaporation of calcium was noticed. The cast ingots were analysed for oxygen using inert gas fusion method, matrix and alloying elements were analysed by XRF. Results show oxygen levels between 0.5 and 0.95 wt.-% for the ingots which were melted in calcium-zirconate crucibles and approx. 1 -1.2 wt.-% for the material produced by utilization of calcia crucibles. The subsequent deoxidation was carried out in lab and pilot scale electroslag remelting furnaces using a commercially pure calcium fluoride slag and metallic calcium as deoxidation agent. It could be shown, that deoxidation of the highly contaminated material is possible applying this method to a certain limit. Pilot scale trials showed a reduction of oxygen contents by 1500 -3500 ppm. Oxygen levels in lab scale trials showed weaker deoxidation effects. In order to describe the achieved deoxidation effects in a quantitative way, the analyzed oxygen contents of the obtained ingots are compared with calculated data resulting from a mathematical kinetic model. The modelled datasets are in good agreement with experimental oxygen values.

Thermodynamic Considerations of Direct Oxygen Removal from Titanium by Utilizing the Deoxidation Capability of Rare Earth Metals

“…For example, there are many reports on the deoxidation of solid Ti using Ca as a deoxidant. [7][8][9][10][11][12][13][14][15]20,[24][25][26][27]29,[33][34][35]37] Oxygen removal during melting process using Ca, [31,32] Al, [28] and H 2 [30,36] as deoxidants was also studied. More recently, deoxidation with Mg under a H 2 atmosphere was reported and gained a significant amount of attention in the field.…”

Effects of Nitrogen Gas Pressure on the Solidification Parameters and As-cast Microstructure Revolution during Pressurized Electroslag Remelting AISI 304 Stainless Steel

“…Besides, they also studied the deoxidation during the production of titanium alloys using PESR. 6) A. Patel et al 1) investigated the effect of pressure and types of nitrides on nitrogen distribution in the stainless steel. F. Takahashi et al 7) studied the effect of nitrogen content on deformability of Mn-Cr-N steels manufactured using a lab-scale PESR.…”