Sometimes, your chosen steel grade requires a slight performance bump, and, in this case, a refining process like electroslag remelting (ESR) may be a budget-friendly option for enhancing the metal’s purity.
What is Electroslag Remelting (ESR)?
Electroslag remelting (ESR) is a secondary refining process that removes impurities, improving the performance characteristics of a metal. ESR takes a previously melted steel, such as an air-melted ingot, and remelts it.
The key actions of the electroslag remelting process are as follows:
- A steel ingot is slowly dipped into a pool of molten slag, with an electric current maintaining the temperature of the slag well above the melting point of the ingot.
- The tip of the ingot melts, and its molten drops pass through the slag. The reactive nature of the slag removes impurities from the molten steel.
- The drops solidify, resulting in a purer ESR steel.
Naturally, this is a simplified explanation; the process is complex and can take hours to days. Each step is meticulously controlled with the aid of computers to produce alloys with a high degree of cleanliness. Modern-day ESR processing may also occur in bespoke inert gas atmospheres, under pressurization, or in a vacuum.
ESR vs. Vacuum Arc Remelting (VAR)
The specifications for fabricating critical parts—aircraft components, for example—may require high-performance steels. In this case, a designer could turn to an Aerospace Material Specification (AMS) that calls for either Type 1 or Type 2 metals (VAR or ESR, respectively).
Type 1 VAR (vacuum arc remelting) is typically used in North America, and Type 2 ESR steel is typically used in Europe. The two approaches are functionally similar, and the purity improvements are almost identical. The major difference is that VAR furnaces limit atmospheric interference to control purity, while ESR lets the mill tweak the chemistry of the produced steel via slag composition.
Is one remelt cheaper than the other? It depends on the mills, the size of their furnaces, the market, and so forth. Sullivan’s team can help you get the right material for your budget and project.
Why Use ESR Steel?
Consider an air-melted steel component that nearly meets target performance but falls short due to fatigue or wear. In this situation, we might recommend keeping the same grade but choosing the remelted version of it. That’s because VAR and ESR improve steel properties by about 20% relative to air-melts, as the metal becomes cleaner and less prone to subsurface cracks.
At Sullivan Steel, we stock the following ESR grades:
It’s worth noting that one remelted grade isn’t always better than another air-melted grade. One of the best examples is XD16N, a specialty air-melt from Aubert & Duval used for non-flight critical applications. It is often far less costly than a remelt yet has superior corrosion and fatigue resistance.
In the end, consulting with a knowledgeable supplier will help you choose the best option for your application. If you have any questions about choosing the right grade, ESR or otherwise, contact the experts at Sullivan Steel.