TRIPLE MELTING AOD + VIM + VAR PROCESS FOR SUPERALLOY PRODUCTION
Triple melting AOD + VIM + VAR process for super alloy production consisting of the following plant and operating sequence:
- Charge melting by electric arc furnace followed by AOD (Argon Oxygen Decarburization) refining and pouring in round molds.
- Second melting of ingots produced as per point 1. by VIM (Vacuum Induction Melting) followed by pouring in round molds.
- Third melting of ingots produced as per point 2. by VAR (Vacuum Arc Re-melting) process.
The innovation of this process consists of using a charge amount of 50-60 t necessary to allow the fundamental reactions of the AOD process and removing impurities like S, Pb, Sn, etc… by AOD refining which, otherwise, should be removed by ESR (Electro Slag Re-melting) process.
The proposed process constitutes an advantageous alternative to the triple melted VIM + ESR + VAR process because of the following characteristics obtainable by the AOD process:
- High homogeneity of the alloy obtained by turbulent agitation of the liquid bath resulting from the gas blown during the AOD process.
- Thorough desulphurization (sulfur less than 5 ppm) and deoxidization, minimization of impurities (Bi, Pb and Se volatilized and reduced to less than 1 ppm) and very high cleanliness.
- Tight control and high reproducibility of chemical composition.
- Very high re-melt rate stability and minimization of gases, inclusions and segregations by VIM + VAR processing of ingots produced by the AOD process.