6-K

FORM 6-K

**U.S.**SECURITIES AND EXCHANGE COMMISSION

Washington**,D.C. 20549**

REPORT OF FOREIGN PRIVATE ISSUER

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

SECURITIESEXCHANGE ACT OF 1934

Dated December 1, 2021

Commission File Number 1-14878

GERDAU S.A.

(Exact Name as Specified in its Charter)

N/A

(Translation of Registrant’s Name)

Av. Dra. Ruth Cardoso, 8,501 – 8° andar

São Paulo, São Paulo - Brazil CEP 05425-070

(Address of principal executive offices)

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

Form 20-F x 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): ¨

Indicate by check mark whether by furnishing the information contained in this Form, the registrant is also thereby furnishing the information to the Commission pursuant to Rule 12g3-2(b) under the Securities Exchange Act of 1934.

Yes ¨ No x

If “Yes” is marked, indicate below the file number assigned to the registrant in connection with Rule 12g3-2(b): Not applicable.

SIGNATURES

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

Date:  December 1, 2021

EXHIBIT INDEX

Exhibit 99.1

NOTICETO THE MARKET

Gerdau S.A. and Metalúrgica Gerdau S.A. (jointly, “Companies”) hereby inform their shareholders and the market that, in connection with the Notice to the Market disclosed on August 19, 2021, the corporate restructuring involving their Mexican subsidiary Sidertúl, S.A. de C.V. (“Sidertúl”) and Aceros Corsa, S.A. de C.V. (“Aceros Corsa”) and Gerdau Corsa, S.A.P.I. de C.V. (“Gerdau Corsa”), both located in Mexico and subsidiaries of the Companies jointly with the group formed by Corcre, S.A.P.I. de C.V. and Juan Angel Cordova Creel (jointly, “Grupo Córdova”), has concluded.

The corporate restructuring was approved by shareholders of the companies involved and by the Comisión Federal de Competencia Económica – COFECE (Mexican antitrust agency), and will produce effects as from December 1, 2021.

The merger of Sidertúl and Aceros Corsa with Gerdau Corsa (“Merger”) is part of the process to reorganize and simplify the ownership structure in Mexico in order to (i) strengthen the financial structure of Gerdau Corsa by reducing leverage and financial expenses; (ii) centralize the core business activities, resulting in greater operational efficiency at the companies involved; and (iii) optimize internal processes to generate synergies and economies of scale by reducing administrative, operating and tax expenses.

As a result of the Merger, Gerdau S.A. will indirectly hold 75% interest in Gerdau Corsa, retaining its shared control of the latter with Grupo Córdova. The corporate restructuring will also underscore the Companies’ commitment to their operations in Mexico, an important and strategic region for their long-term vision.

São Paulo, November 30, 2021.

Harley Lorentz Scardoelli

Executive Vice President

Investor Relations Officer