Butler, Pennsylvania holds the only mill in the western hemisphere still cold-rolling grain-oriented electrical steel at M3 grades and below. Cleveland-Cliffs acquired AK Steel's legacy line in 2020, and four years later the IRA's Section 45X credits made every kilogram of that production a balance-sheet asset rather than a cost line. This is the steel that determines no-load loss in every domestic-content GSU shipped after 2024.
The Ghost of ARMCO
There is a particular irony in America’s decades-long dependence on imported electrical steel. The material itself, grain-oriented electrical steel (GOES), was an American invention. In the 1930s, metallurgist Norman P. Goss, working for the American Rolling Mill Company (ARMCO), discovered that by carefully cold-rolling and annealing a silicon-steel alloy, he could align the crystalline grains of the metal. This alignment anistropy created a path of least resistance for magnetic flux, slashing the energy lost as heat (hysteresis losses) when the steel was magnetized and demagnetized 60 times a second.
This breakthrough, commercialized out of Butler, Pennsylvania, was foundational. It made transformers dramatically more efficient, enabling the modern electrical grid. For decades, ARMCO and its successor, AK Steel, dominated the market from its plants in Butler, PA, and Zanesville, OH. American transformer manufacturers, from massive power transformer shops to high-volume distribution transformer factories, had a robust domestic supply of world-class GOES.
By the late 1990s and early 2000s, the landscape had shifted. Aggressive industrial policies in Japan, Korea, and later China, fueled a massive expansion of their steelmaking capacity. They scaled production, invested in thinner-gauge and higher-permeability grades, and often sold into the U.S. market at prices domestic producers couldn't match. The U.S. industry, facing high legacy costs and a lack of equivalent state backing, withered. By 2020, AK Steel was the sole remaining domestic producer of GOES, operating the same two plants at Butler and Zanesville. For many critical grades of steel, the U.S. had become almost entirely import-dependent.
The Tariff, The Pandemic, and The President
Two events snapped the system out of its stupor: the 2018 Section 232 tariffs and the 2020 COVID-19 pandemic. The tariffs, which placed a 25% levy on imported steel, were a blunt instrument intended to protect national security. While their broader economic effects are still debated, they undeniably altered the calculus for GOES procurement. Suddenly, imported steel from Asia wasn't automatically the cheaper option.
Then came the pandemic. The subsequent supply chain implosion revealed just how fragile the long-distance, just-in-time model had become. Lead times for finished transformers stretched from months to years. The bottleneck wasn't just at the assembly plants; it ran all the way back to the steel mills in Asia. Utilities looking to replace aging assets or connect new renewable generation found themselves in a queue, waiting for steel to be melted, rolled, and shipped from halfway around the world. A vague concern about supply chain resilience became an acute operational crisis.
This crisis has triggered the first serious effort in a generation to reshore GOES production. Cleveland-Cliffs, which acquired AK Steel in 2020, is now at the center of this effort. The company has announced significant investments aimed at upgrading its Zanesville and Butler facilities. The goal is not just to produce more steel, but to produce the high-quality, thin-gauge materials required by modern transformer designs—the very grades for which the U.S. has been most reliant on imports. The challenge is that reversing forty years of industrial offshoring is not as simple as flipping a switch at a furnace.
A Winding Road to Self-Sufficiency
Even with fresh investment and favorable tariffs, the path to a self-sufficient U.S. supply chain for GOES is long and complex. Transformer manufacturers—the direct customers for this steel—are rightfully conservative. A new steel supplier, even a domestic one, represents a new risk variable. Before any new GOES from an upgraded mill can be used in a production transformer, it must pass a rigorous qualification process.
This process is not trivial. It involves more than just checking if the steel’s datasheet matches the specs. An OEM will typically:
1. Procure sample coils: Obtain several tons of the new steel for initial testing.
2. Lab-test core properties: Build sample cores and run them through a battery of tests to verify no-load losses, permeability, and magnetostriction (which causes audible hum) under real-world flux densities specified in standards like IEEE C57.12.00.
3. Build test transformers: Fabricate a small number of complete distribution or power transformers using the steel.
4. Perform full type tests: Subject the test units to a full suite of electrical tests, including heat runs and impulse tests, to ensure they meet performance and reliability guarantees.
5. Audit the mill: Send quality engineers to the steel mill itself to audit their production processes and quality controls.
This entire process can take 12-18 months and cost hundreds of thousands of dollars. Only after a successful qualification will an OEM approve the new steel for use in customer orders. With dozens of transformer manufacturers in the U.S., each with their own internal qualification process, it will take years for the output of these newly revived mills to be fully absorbed into the supply chain.
The technical challenge is also significant. For years, the workhorse of the industry was 0.27 mm (M-grade) steel. However, the U.S. Department of Energy’s 2016 efficiency standards pushed manufacturers toward thinner, more efficient grades, such as 0.23 mm steel, or even 0.18 mm for high-efficiency units. These high-permeability, low-loss grades have been the primary domain of Japanese and Korean steelmakers. Ramping up domestic production of this material is Cleveland-Cliffs' top priority, but mastering the complex rolling and annealing processes at scale is a formidable metallurgical challenge.
Beyond M-Grades: What Does the Future Hold?
As the U.S. races to catch up, the technology of magnetic steels isn't standing still. The next decade will likely see the commercialization of materials and techniques that could once again reshape transformer design. The key question for the reshoring effort is whether to focus on matching today’s best-in-class GOES or to aim for what comes next.
The most mature alternative is amorphous metal. Instead of a crystalline structure, amorphous ribbons have a random, glass-like atomic structure, which dramatically reduces no-load losses—by as much as 70-80% compared to conventional GOES. While amorphous core transformers have been available for decades, their higher material cost, specialized manufacturing requirements, and lower flux capacity have limited their widespread adoption, especially in larger power transformers.
Looking beyond the immediate horizon, several technologies are in development:
- Laser Scribing: Using a laser to etch the surface of finished GOES can refine magnetic domains, reducing losses by another 8-10%. This is an incremental improvement, but a significant one.
- Nanocrystalline Cores: These materials offer a combination of the high permeability of GOES and the low losses of amorphous metals, but are currently far too expensive for grid-scale applications.
- Improved Alloys: Researchers continue to experiment with the Silicon content and other micro-alloying elements to push the fundamental performance of GOES itself.
For utility planners and engineers, the resurgence of the domestic steel industry is welcome news, but it comes with a new set of variables to manage. Will domestic steel command a permanent "green lane" premium? How will lead times for domestic vs. imported materials stratify? For those drafting procurement specifications, it may be time to look beyond just the lowest bid and consider adding criteria for supply chain transparency and material origin. Feel free to browse our own library of technical articles at our resources page.
The Engineer's Takeaway
The transformer core is the technological heart of the grid, and for too long its pulse was sourced from thousands of miles away. The effort to reshore grain-oriented electrical steel is more than just a matter of industrial policy; it is a direct investment in the resilience and security of the North American power system. The transition will be measured in years, not months, but for the first time in a generation, the future of the American transformer core looks to be forged in American steel.
