Case Study: Development of XM-19 stainless steel for a tokamak fusion reactor

Tokamak reactors are advanced devices designed to harness nuclear fusion, the same process that powers the sun. Although tokamak technology is still under development, it represents one of the most promising pathways toward safe, sustainable, and reliable energy for the future.

Challenge: Exceptional material properties, unconventional production route

A customer approached us as they were facing persistent issues with their existing steel supplier while working on a tokamak fusion reactor, one of the most demanding engineering environments.

The application required material with:

• Exceptional mechanical performance at cryogenic and elevated temperatures
• Low magnetic permeability to avoid interference with magnetic fields
• Internal quality must comply with a stringent ultrasonic testing level
• Stability and reliability under extreme thermal and mechanical loads

The customer required XM-19, a specialized austenitic stainless steel, produced under strict and extensive specification. SIJ Acroni had not previously manufactured XM-19 steel, meaning that the production route had to be developed from scratch.

Approach: Co-developing the material through close technical partnership

The customer approached SIJ Acroni not merely as a supplier, but as a development partner. From the outset, the collaboration was close and highly technical.

The customer provided us with requirements and application constraints. We then co-designed the technical specification, drawing on deep metallurgical expertise. A new production path was developed, including adapted chemical composition and optimized manufacturing parameters.

Close cooperation was a defining feature of the project. Regular technical meetings were held with the customer’s chief metallurgist, ultrasonic controller, and purchasing officer. During inspection of the first plates, the customer’s development engineer and ultrasonic controller worked on site with SIJ Acroni’s experts. Every square meter of material was jointly inspected.

The customer’s development engineer spent two separate one-month visits at SIJ Acroni, enabling rapid feedback and continuous improvement.

Once the first delivery was completed, SIJ Acroni further refined and improved the specification, enhancing consistency and performance for future production.

Solution: Tailored XM-19 steel for tokamak fusion applications

SIJ Acroni successfully developed and produced XM-19 stainless steel specifically tailored for fusion reactor applications.

Key achievements included:

• A customized alloy composition
• An improved manufacturing and quality-control process
• Reliable mechanical performance across extreme temperature ranges

The resulting steel delivers consistent performance from –269 °C (near absolute zero) up to 650 °C, making it suitable for the harsh operational conditions inside a tokamak reactor.

Key mechanical properties

The developed XM-19 steel meets or exceeds all critical requirements:

• High tensile strength
• Excellent impact toughness
• Low and stable magnetic permeability
• Mechanical and microstructural stability 
• Wide temperature ranges from cryogenic to elevated temperatures

These properties ensure structural integrity, operational safety, and long-term reliability in fusion environments.

Results 

• Successful supply of XM-19 steel for a tokamak fusion reactor
• Resolution of the customer’s previous supplier challenges
• Establishment of SIJ Acroni as a trusted development and production partner
• A validated production route for future XM-19 and fusion-related projects

The customer explicitly highlighted the value of direct access to our development, sales, and technical experts, noting that such a collaborative and responsive experience would not have been possible elsewhere.

This project demonstrates SIJ Acroni’s ability to go beyond standard steel production, developing new materials, processes, and partnerships to support our clients. By combining metallurgical expertise, flexibility, and close customer collaboration, SIJ Acroni enabled a critical step forward in fusion reactor development.