Vacuum Arc Remelting: A Look at Using VAR to Achieve Performance Characteristics

Component designers who push the performance boundaries of their materials soon approach — and even exceed — the physical limits of their default “go-to” metal grades. This is often the case for conventional air-melted steels. Specifying a more controlled melting technique like vacuum arc remelting (VAR) enhances a metal’s purity and may be an economical way to improve component performance without having to use a completely different grade.

In this post, we’ll look at what happens during the VAR process, how it improves performance characteristics, and the situations that should trigger remelting as a consideration.

How Does Vacuum Arc Remelting Work?

U.S. aerospace designers typically specify VAR steels for their most demanding applications. Why is that?

Vacuum arc remelting is a secondary process in the production of metals; it purifies a steel to produce ingots with fewer flaws and inclusions than air-melt alone. VAR uses a previously melted steel and remelts it again inside a vacuum chamber. The entire process is computer-controlled with basic steps that look like this:

• An electrode (instead of an ingot) is cast via an initial melting technique
• The electrode is then grounded inside a vacuum chamber
• A powerful arc is struck, melting the electrode
• Molten metal drips into a temperature-controlled crucible
• Ingots are cast, then reheated and hot worked to produce bar stock

Of course, this is an oversimplification of vacuum arc remelting; it’s an intricate process that takes hours to days, with every step painstakingly managed to produce alloys with a refined microstructure and reduced amount of inclusions.

Also commonplace in the aerospace industry are extremely pure (and typically more expensive) double vacuum-melted steels like VIM-VAR, where the initial ingot is vacuum induction melted, followed by VAR as a secondary process as described above.

Using VAR for Better Metal Performance

When it comes to selecting a steel, the goal is usually more about achieving performance parameters than it is about insisting on a melt practice. Knowing a process like vacuum arc remelting can imbue steels with impressive characteristics, how do you use this knowledge?

As an example, say an air-melted steel component has been found to fail earlier than expected due to fatigue, wear, or crack initiation. It comes close to the target performance, but it’s just not quite there. We’d likely recommend keeping the same steel grade but jumping to vacuum arc remelt for a cleaner metal that’s less prone to subsurface cracks.

See our related post, Exploring the Fatigue Life of Metals: An Interview with Sullivan’s Experts

As a general guidepost for designers, remelting can bump up performance characteristics, such as fatigue resistance, by about 20 percent compared to air-melts. And there’s an additional 10 percent increase if you go extra-pure by specifying VIM-VAR. 

However, just because one grade is only air-melted and an entirely different grade is remelted does not necessarily mean the remelted grade is better than the air-melted grade. As such, it is wise to talk to a supplier who supports their steels with technical expertise to help guide you in the best choice for your application.

VAR and VIM-VAR Options at Sullivan Steel

Looking for steel with high cleanliness? We currently stock the following grades in VAR or VIM-VAR:

• 52100 (VAR and VIM-VAR)
• BG42^® (VIM-VAR)
• Nitriding 135M™ (VAR)
• NC310YW^® (VIM-VAR)
• M50 (VAR and VIM-VAR)
• 9310 (VAR)
• 440C (VAR)
• M50NiL (VIM-VAR)
• 4340 (4340)
• A-21^® (VIM-VAR)

In addition to VAR and VIM-VAR-produced materials, we also offer specialty, cost-effective performance grade steel alternatives like XD16N for non-flight critical applications. This alloy is a designer air-melt steel for Aubert & Duval that boasts the cleanliness of VAR alloys for exceptional corrosion resistance and high hardness at an economical price.

Remember, using VAR to improve steel performance depends on the grade. Our team can help you select the right grade and melt practice for your application, so contact Sullivan today!