Exhibit 5.1

CONSENT OF INDEPENDENT REGISTERED PUBLIC ACCOUNTING FIRM

We consent to the incorporation by reference in this Registration Statement on Form F-10 of our reports dated March 12, 2025 relating to the financial statements of Algoma Steel Group Inc. (the “Company”) and the effectiveness of the Company’s internal control over financial reporting, appearing in the Annual Report on Form 40-F of Algoma Steel Group Inc. for the nine month period ended December 31, 2024.

/s/ Deloitte LLP

Chartered Professional Accountants

Licensed Public Accountants

Toronto, Canada

July 18, 2025