GGB Gerdau SA

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 June 18, 2015

Commission File Number 1-14878

GERDAU S.A.

(Exact Name as Specified in its Charter)

N/A

(Translation of Registrant’s Name)

Av. Farrapos 1811

Porto Alegre, Rio Grande do Sul - Brazil CEP 90220-005

(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  o

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): o

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): o

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 o   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:  June 18, 2015

2

EXHIBIT INDEX

3

Exhibit 99.1

NOTICE TO THE MARKET

Gerdau S.A. hereby informs its shareholders and the market that, consequent to the resignation of director André Pires de Oliveira Dias, as of July 15, 2015, the Board of Directors, at a meeting held on this date, resolved to elect Harley Lorentz Scardoelli as the Investor Relations Director of Gerdau S.A. The transition process of the executives will happen until July 15, 2015.

Harley Scardoelli joined Gerdau in May 1988, and has worked in the company’s operations in Canada, United States, Spain and Brazil. He currently serves as Corporate Director in charge of Treasury, Financial and Planning departments, and, as of July 15, will accumulate the Investor Relations, Accounting, Tax and Legal departments. Scardoelli received bachelor’s degrees in Civil Engineering from the Federal University of Rio Grande do Sul (UFRGS) and in Business Administration from Pontifical Catholic University of Rio Grande do Sul (PUC-RS) and is a CFA charterholder.

The Board of Directors thank Mr. André Pires de Oliveira Dias for his important contributions to improving the processes under his leadership at Gerdau.