Exhibit 99.1 Metallus Announces First-Quarter 2024 Results CANTON, Ohio: May 9, 2024 – Metallus (NYSE: MTUS), a leader in high-quality specialty metals, manufactured components and supply chain solutions, today reported first-quarter 2024 net sales of 321.6millionandnetincomeof24.0 million, or 0.52perdilutedshare.Onanadjustedbasis(1),thefirst−quarter2024netincomewas26.1 million, or 0.56perdilutedshare,andadjustedEBITDAwas43.4 million. This compares with the sequential fou ...