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

SECURITIES EXCHANGE ACT OF 1934

Dated September 20, 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

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

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: September 20, 2021

	GERDAU S.A.

	By:	/s/ Harley Lorentz Scardoelli
	Name:	Harley Lorentz Scardoelli
	Title:	Investor Relations Director

EXHIBIT INDEX

Exhibit		Description of Exhibit
99.1		Material Fact, September 13, 2021

Exhibit 99.1

GERDAU S.A.

CNPJ/MF nº 33.611.500/0001-19

NIRE: 35300520696

METALÚRGICA GERDAU S.A.

CNPJ/MF nº 92.690.783/0001-09

NIRE: 35300520751

SEIVA S.A. – FLORESTAS E INDÚSTRIAS

CNPJ/MF nº 87.043.832/0001-73

NIRE: 35300521781

material fact

Gerdau S.A., Metalúrgica Gerdau S.A. and Seiva S.A. - Florestas e Indústrias (collectively, “the Company”), in accordance with CVM resolution number 44/2021, hereby informs its shareholders and the capital markets that the Company, within the scope of lawsuit number 0023102-98.1990.8.19.0001, which is under judgment by the 14^th civil court in the District of Rio de Janeiro (“14^th civil court”), claiming the compensation of the losses caused by the Compulsory Electric Power Loan (ECE), had the following case development:

On December 16, 2019, the judicial expert designated by the 14^th civil court concluded the expert report;

On November 25, 2020, the decision from the expert report was accepted in favor of the Company, establishing the amount of approximately R$ 1.5 billion to be received by the Company;

On August 10, 2021, the judgment of interlocutory appeal filed by Centrais Elétricas Brasileiras S/A (“Eletrobras”) was concluded and the decision issued by 14^th civil court was maintained by the 8^th Civil Chamber of the Court of state of Rio de Janeiro;

On September 10, 2021 the Company became aware that Eletrobras made the deposit/payment in court of the amount established by the judicial system of the state of Rio de Janeiro, including the accrued charges of late interests and defeat fees;

The decision that established the amount in favor of Gerdau group was maintained by all instances of the judicial system of the state of Rio de Janeiro, and its suspension was rejected by the Superior Court of Justice (STJ); and

The final decision was reached, based on a judicial enforcement instrument, not subject to review of any nature by the Court, being possible only the appeals and other measures with remote possibilities of reception, due to its motivation being only delaying the solution.

In that sense, considering the current stage of the case, the Company concluded that the referred asset, until then considered as contingent asset, as disclosed in footnote 15 of the Financials Statements of Gerdau S.A. and Metalúrgica Gerdau S.A. as of June 30, 2021, due to uncertainties regarding the term, form and amount that would be effectively paid, conditions that are now defined, and these assets reached the accounting characteristics to provide the economic benefits, according to paragraph 35 of IAS 37 (CPC 25), which demands the recognition by the Company, in the 3^rd quarter of 2021, of a gain in the income statement and assets, which together total approximately R$ 1.5 billion, gross of taxes and related costs/fees.

The Company clarifies that is undertaking the necessary measures at the 14^th civil court to withdraw the amounts deposited in court.

The Company will keep its shareholders and the general public informed about the development of this case.

São Paulo, September 13, 2021.

Harley Lorentz Scardoelli

Executive Vice President

Investor Relations Officer