6-K

U.S. 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

SECURITIESEXCHANGE ACT OF 1934

Dated August 9, 2023

Commission File Number 1-14878

GERDAU S.A.

(Translation of Registrant’s Name into English)

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 ¨

Exhibit Index

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.

Date:  August 9, 2023

Exhibit 99.1

GERDAUS.A.

Tax ID (CNPJ/ME) 33.611.500/0001-19

Registry (NIRE): 35300520696

materialfact

Gerdau announces certification of iron ore reserves in Minas Gerais

GerdauS.A. (B3: GGBR / NYSE: GGB) hereby informs its shareholders and the general market that the independent certifier SRK Consulting has prepared the certification report for the iron ore reserves at the mine located in Miguel Burnier District, municipality of Ouro Preto (MG - Brazil). The herein mentioned mining operations are integral part of Brazil Business Segment, with the main focus on supplying iron ore for it.

The certification is a significant milestone for the BRL 3.2 billion investment in Gerdau's sustainable mining platform, aimed to provide ore with high-quality and competitive cost for the Ouro Branco (MG) plant, while also playing an important role in its decarbonization process. Disbursements for the year 2023 are already included in the investment Plan announced on March 1, 2023.

According to the conclusions of the report, the Company started to have certified reserves of 476 million metric tons^1^ of iron ore, according to the table below:

Miguel Burnier Summary Mineral Reserves at January of 2023

The Report was prepared according to industry best practices and in accordance with subchapter 1300 of Regulation S-K issued by the U.S. Securities and Exchange Commission – SEC, considering the technical report standard established by said regulation.

Considering the expected annual production level of 5.5 million metric tons^2^ of iron ore from the sustainable mining platform, the certified reserves indicate a 40-year life-of-mine from the investment, reinforcing Gerdau's commitment to the socioeconomic development of the state of Minas Gerais today and in the future.

São Paulo, August 09, 2023.

Rafael Dorneles Japur

Executive Vice-President and Investor Relations Officer

^1^ Dry metric ton; ^2^Wet metric ton, assuming a humidity of 10%.