The Pressure Electroslag Remelting Process (PESR)

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Introduction to Electroslag Remelting Technology

Electroslag Remelting (ESR) stands as a fundamental metallurgical process designed for producing steel with exceptional purity and controlled solidification structures. This well-established refining method has become indispensable in the steel and superalloy industries, where its primary objectives include inclusion removal, desulfurization, and the development of uniform microstructures throughout the final product.

The significance of advanced melting technologies becomes apparent when considering the challenges faced in modern alloy production. Many high-performance alloys contain reactive elements such as aluminum and titanium, which readily form oxides when exposed to atmospheric conditions during heating. These oxide formations prove detrimental to premium-quality melted alloys, compromising their structural integrity and performance characteristics.

Advanced Melting Technologies for Premium Alloys

Premium-grade alloys required by aerospace, energy, medical, and automotive industries demand protection from atmospheric contamination and residual impurities. This protection is achieved through melting processes conducted within controlled environments, such as vacuum containers. This approach provides metals producers with enhanced control over alloy chemistry, resulting in cleaner, more uniform products with superior properties necessary for critical service applications.

The substantial investments in state-of-the-art technologies including Pressure Electroslag Remelting (PESR), Vacuum Induction Melting (VIM), and Vacuum Arc Remelting (VAR) reflect extensive research demonstrating the genuine need for a new generation of steels with enhanced capabilities.

The Evolution to Pressure Electroslag Remelting

Traditional Electroslag Remelting operates as a secondary refining process that further enhances many alloys using consumable electrodes produced through VIM or conventional air melting as feedstock. Conventional ESR improves both microstructure and cleanliness of VIM or arc-melted alloys by removing inclusions as metal passes through the slag while controlling solidification rates in the refined metal ingot to minimize chemical segregation. The melting process through slag enables precise compositional control throughout the procedure.

Figure 1: Schematic design of a pressure electro slag remelting furnace (PESR)

Pressurized ESR Technology and Capabilities

Pressurized ESR (P-ESR) furnaces represent a significant technological advancement, possessing the capability to melt alloys under nitrogen pressures reaching several atmospheres. This enhanced pressure environment enables the production of extremely high nitrogen steel compositions that remain unattainable through standard air melting techniques. This revolutionary capability facilitates the manufacture of innovative high-nitrogen alloys with unique mechanical properties previously impossible to achieve.

Pressure ESR (P-ESR) surpasses standard ESR processes through its ability to melt metals under elevated nitrogen pressure conditions, permitting the production of alloys containing exceptionally high nitrogen levels. In P-ESR systems, the standard ESR crucible becomes enclosed within a pressure vessel melt chamber. This design modification allows the pressure above the slag to increase to levels significantly exceeding normal atmospheric pressure, thereby enabling substantially higher nitrogen concentrations to be achieved.

Operational Flexibility and Enhanced Control

The P-ESR furnace demonstrates remarkable operational flexibility, capable of melting at atmospheric pressure in air atmospheres or under inert gas covers of argon positioned over the slag. The implementation of inert gas covers over the slag provides enhanced compositional control of reactive elements, including aluminum and titanium, during the melting process. The high-nitrogen compositions achievable through the P-ESR process cannot be replicated using either conventional ESR or VAR melting techniques.

Industrial Implementation and Current Capabilities

The world's largest PESR unit currently operates at Energietechnik Essen GmbH in Germany, featuring a maximum operating pressure of 40 bars and the capacity to produce ingots weighing up to 20 tons with diameters reaching 1030 mm. The PESR process fundamentally operates as a conventional remelting facility housed within a pressure tank environment.

Figure 2: View of the industrialized PESR process at Energietechnik Essen GmbH for ingot weight up to 20 t and ∅1030 mm

The process design successfully addresses both ESR refining requirements and nitrogen pickup objectives. The metallurgical approach mirrors standard ESR processes, incorporating refining capabilities, low segregation characteristics, elimination of porosity or shrinkage, and the development of defined microstructures and solidification patterns. This comprehensive approach ensures that PESR technology delivers the enhanced performance characteristics demanded by modern industrial applications while maintaining the proven benefits of traditional electroslag remelting processes.