Vacuum induction melting and remelting

Fewer than fifteen nations on Earth can produce aerospace-grade melted superalloy stock. As of 2026, India is one of them — but only at the first of several steps.

Vacuum induction melting, or VIM, is the indispensable foundation of every jet engine. Nickel- and cobalt-based superalloys, the metals that survive the furnace-like conditions inside a turbine, react violently with atmospheric oxygen and nitrogen. They must be melted in a vacuum. VIM strips out oxygen, nitrogen and volatile impurities to reach the cleanliness a turbine blade demands, casting ingots of roughly 150 to 300 kilograms per heat. The process emerged as a critical technology in the 1950s, driven by the aerospace sector's hunger for jet-engine superalloys.

India has now demonstrated it. MIDHANI (Mishra Dhatu Nigam Limited) melts superalloy cast sticks at its Hyderabad facility using advanced VIM, achieving the ultra-high purity and precise composition control aero-engines require. In October 2025 it received CEMILAC airworthiness certification for series production of eight superalloy grades, two titanium alloy grades and four special steels. In March 2026 it delivered indigenously developed VIM-cast superalloy sticks to HAL for AL-31FP engines, which power the Su-30MKI. It is also supplying the Tejas Mk-2, the AMCA's 110–130 kN engine, and the Kaveri derivative. Sunflag Steel operates a VIM facility near Nagpur with technology from DAIDO of Japan, and PTC Industries inaugurated a ₹1,000 crore titanium and superalloy plant in Lucknow in October 2025.

The gap is downstream. VIM alone does not finish the job. Its ingots are scalped to remove surface defects, then remelted by vacuum arc remelting (VAR) or electroslag remelting (ESR) — sometimes both, in triple-melt configurations — to produce a homogeneous microstructure and control segregation. Wrought nickel-base superalloys for modern engines are typically produced this way. India's secondary metallurgy capability remains limited to specialty producers, and as of 2026 the country imports the majority of its aerospace-grade superalloy ingots. Directional solidification and single-crystal casting, needed for the highest-stressed turbine blades, remain emerging. The feedstock itself — nickel from Russia and Brazil, cobalt from the DRC's Katanga Province, which supplies about 65% of the world's — arrives from abroad.

Closing the gap means building out VAR, ESR and hot isostatic pressing to the certified, traceable standard the highest tier demands. MIDHANI has revamped its VIM furnaces to support larger remelt stock and master heats for single-crystal superalloys. Certification cycles run 12 to 24 months. The first step is proven; the climb continues.