Recycling of superalloy scrap through electro slag remelting

Abstract

Electro Slag Remelting (ESR) with a water cooled copper electrode has been used for recycling machined superalloy scrap. Careful electrode design and optimization of process parameters are necessary to achieve target composition and mechanical properties. The design criteria are discussed in detail. Coolant water flow rate and velocity need to be carefully chosen to ensure adequate cooling to the electrode. It is necessary to adopt liquid start technique while using the electrode. It is also essential to provide refractory metal (molybdenum) tips at the bottom of the electrode. These tips help in initiating and sustaining the ESR operation. The copper wall thickness should allow formation of a solid slag skin around the copper portion of the electrode to prevent electrode erosion as well as melt contamination. The superalloy scrap was charged through the annular gap between the mould and the electrode. Considering ingot chemistry, soundness and surface finish as the main criteria, ESR process parameters were optimized. Superalloy scrap of composition close to that of Nimonic 80A was remelted using the water cooled electrode. The process has potential for recycling a range of superalloy scrap and scaling up to produce large diameter ingots.