Supplemental Prospectus - Form 424B3

Filed Pursuant to Rule 424(b)(3)

Registration No. 333-260534

PROSPECTUS SUPPLEMENT NO. 9

(to prospectus dated June 30, 2022)

ALGOMA STEEL GROUP INC.

129,836,439 Common Shares

604,000 Warrants to Purchase Common Shares

24,179,000 Common Shares Underlying Warrants

This prospectus supplement amends and supplements the prospectus dated June 30, 2022, as supplemented or amended from time to time (the "Prospectus"), which forms a part of our Registration Statement on Form F-1 (Registration Statement No. 333-260534). This prospectus supplement is being filed to update and supplement the information included or incorporated by reference in the Prospectus with the information contained in our Report on Form 6-K, furnished to the Securities and Exchange Commission on August 15, 2022 (the "Form 6-K"). Accordingly, we have attached the Form 6-K to this prospectus supplement.

This prospectus supplement updates and supplements the information in the Prospectus and is not complete without, and may not be delivered or utilized except in combination with, the Prospectus, including any amendments or supplements thereto. This prospectus supplement should be read in conjunction with the Prospectus and if there is any inconsistency between the information in the Prospectus and this prospectus supplement, you should rely on the information in this prospectus supplement.

Our Common Shares and Warrants are listed on The Nasdaq Stock Market ("Nasdaq") under the symbols "ASTL" and "ASTLW", respectively, and on the Toronto Stock Exchange (the "TSX") under the symbols "ASTL" and "ASTL.WT," respectively. On August 12, 2022, the last reported sales prices of the Common Shares on Nasdaq and the TSX were $9.48 and C$12.11, respectively, and the last reported sales prices of the Warrants were $1.90 and C$2.54, respectively.

We are a "foreign private issuer" as defined in the U.S. Securities Exchange Act of 1934, as amended (the "Exchange Act"), and are exempt from certain rules under the Exchange Act that impose certain disclosure obligations and procedural requirements for proxy solicitations under Section 14 of the Exchange Act. In addition, our officers, directors and principal shareholders are exempt from the reporting and "short-swing" profit recovery provisions under Section 16 of the Exchange Act. Moreover, we are not required to file periodic reports and financial statements with the U.S. Securities and Exchange Commission as frequently or as promptly as U.S. companies whose securities are registered under the Exchange Act. Additionally, Nasdaq rules allow foreign private issuers to follow home country practices in lieu of certain of Nasdaq's corporate governance rules. As a result, our shareholders may not have the same protections afforded to shareholders of companies that are subject to all Nasdaq corporate governance requirements.

Investing in our securities involves a high degree of risk. You should review carefully the risks and uncertainties described under the heading "Risk Factors" beginning on page 6 of the Prospectus, and under similar headings in any amendment or supplements to the Prospectus.

None of the Securities and Exchange Commission, any state securities commission or the securities commission of any Canadian province or territory has approved or disapproved of the securities offered by this prospectus supplement or the Prospectus or determined if the Prospectus or this prospectus supplement is truthful or complete. Any representation to the contrary is a criminal offense.

The date of this prospectus supplement is August 15, 2022.

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 6-K

REPORT OF FOREIGN PRIVATE ISSUER

PURSUANT TO RULE 13a-16 OR 15d-16

UNDER THE SECURITIES EXCHANGE ACT OF 1934

For the month of August 2022

Commission File Number 001-40924

ALGOMA STEEL GROUP INC.

(Exact name of Registrant as specified in its charter)

N/A

(Translation of Registrant's name)

105 West Street

Sault Ste. Marie, Ontario

P6A 7B4, Canada

(705) 945-2351

(Address and telephone number of registrant's principal executive offices)

Indicate by check mark whether the registrant files or will file annual reports under cover of Form 20-F orForm 40-F:

Form 20-F ☒ Form 40-F ☐

Indicate by check mark if the registrant is submitting the Form 6-K in paper as permitted by Regulation S-T Rule 101(b)(1): ☐

Indicate by check mark if the registrant is submitting the Form 6-K in paper as permitted by Regulation S-T Rule 101(b)(7): ☐

INCORPORATION BY REFERENCE

Exhibit 99.1 of this Form 6-K is incorporated by reference into the Registration Statement on Form S-8 (Commission File No. 333-264063) of the Registrant, Algoma Steel Group Inc.

2

DOCUMENTS INCLUDED AS PART OF THIS REPORT

Exhibit
99.1		Press Release dated August 12, 2022

3

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned, thereunto duly authorized.

		Algoma Steel Group Inc.
Date: August 15, 2022			By:		/s/ John Naccarato
			Name: John Naccarato
			Title: Vice President Strategy and General Counsel

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Exhibit 99.1

Algoma Steel Confirms USW Local 2251 Agree to Take Offer to Employees for a Vote

August 12, 2022

Operations Continue in Ordinary Course during Voting Process

SAULT STE. MARIE, Ontario, Aug. 12, 2022 (GLOBE NEWSWIRE) - Algoma Steel Group Inc. (NASDAQ: ASTL; TSX: ASTL) ("Algoma" or the "Company") announced today that United Steelworkers Local 2251 ("2251" or the "Union") have agreed to take the Company's last offer to a vote by employees in the affected bargaining unit. Operations will continue in the ordinary course during the voting process, and the Union has agreed to provide advance notice to the Company to allow for a safe and orderly shutdown of operations in the event the Union instructs employees to go on strike.

Algoma President and Chief Executive Officer Michael Garcia commented. "We respect the collective bargaining process and are pleased that our employees will have their say on a matter of such critical importance to their livelihoods, the lives of their families, and fellow community members. The Company has offered a non-concessionary,top-of-market wage and benefit package which includes a 5.5% wage increase, continuation of COLA, significant improvements in pensions and benefits for employees, and enhanced retiree benefits over a four-year term that delivers the stability needed to ensure a successful transition to electric arc steelmaking. A signing bonus is also included contingent upon no disruption to operations and uninterrupted shipments to our customers."

He went on to say, "If ratified, this agreement will help to secure our collective future, provide for sustained profitability even at the bottom of the steel cycle, and allow us to maintain the phenomenal momentum we have generated together since emerging from CCAA."

Cautionary Statement Regarding Forward-Looking Statements

This news release contains "forward-looking information" under applicable Canadian securities legislation and "forward-looking statements" within the meaning of the U.S. Private Securities Litigation Reform Act of 1995 (collectively, "forward-looking statements), including statements regarding the anticipated impact of the coal conveyor fire. These forward-looking statements generally are identified by the words "believe," "project," "expect," "anticipate," "estimate," "intend," "strategy," "future," "opportunity," "plan," "provide," "pipeline," "may," "should," "will," "would," "will be," "will continue," "will likely result," and similar expressions. Forward-looking statements are predictions, projections, and other statements about future events that are based on current expectations and assumptions, including with respect to the risk of a work stoppage and whether (and to what degree) such stoppage could adversely impact the Company's operations and financial position. Many factors could cause actual future events to differ materially from the forward-looking statements in this document, including timely access to necessary components, fabrications and other products or services required to complete repairs, which may increase costs and negatively impact our business and results of operations. Readers should consider the risks and uncertainties set forth in the section entitled "Risk Factors" and "Cautionary Note Regarding Forward-Looking Statements" in Algoma's Annual Report on Form 20-F, filed by Algoma with the Ontario Securities Commission (the "OSC") (available under the company's SEDAR profile at www.sedar.com) and with the Securities and Exchange Commission (the "SEC") (available at www.sec.gov), as well as in Algoma's current reports with the OSC and SEC. Forward-looking statements speak only as of the date they are made. Readers are cautioned not to put undue reliance on forward-looking statements, and Algoma assumes no obligation and does not intend to update or revise these forward-looking statements, whether as a result of new information, future events, or otherwise.

About Algoma Steel Group Inc.

Based in Sault Ste. Marie, Ontario, Canada, Algoma is a fully integrated producer of hot and cold rolled steel products including sheet and plate. With a current raw steel production capacity of an estimated 2.8 million tons per year, Algoma's size and diverse capabilities enable it to deliver responsive, customer-driven product solutions straight from the ladle to direct applications in the automotive, construction, energy, defense, and manufacturing sectors. Algoma is a key supplier of steel products to customers in Canada and Midwest USA and is the only producer of plate steel products in Canada. The Company's mill is one of the lowest cost producers of hot rolled sheet steel (HRC) in North America owing in part to its state-of-the-art Direct Strip Production Complex ("DSPC"), which is the newest thin slab caster in North America with direct coupling to a basic oxygen furnace (BOF) melt shop.

Algoma has achieved several meaningful improvements over the last several years that are expected to result in enhanced long-term profitability for the business. Algoma has upgraded its DSPC facility and recently installed its No. 2 Ladle Metallurgy Furnace. Additionally, the Company has cost-cutting initiatives underway and is in the process of modernizing its plate mill facilities.

Today Algoma is on a transformation journey. Algoma is investing in its people and processes, optimizing and modernizing to secure a sustainable future. Our customer focus, growing capability and courage to meet the industry's challenges head-on, position us firmly as your partner in steel.

For more information contact:

Brenda Stenta

Manager Communications & Branding

Algoma Steel Group Inc.

Phone: 705.206.1022

E-mail: [email protected]