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 April 27, 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.

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.

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:  April 27, 2015

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EXHIBIT INDEX

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Exhibit 99.1

NOTICE TO THE MARKET

The controlling shareholders of Metalúrgica Gerdau S.A. and Gerdau S.A., after assessing the statements made by market agents, informed the management of the Companies the intention to remain in the Level 1 corporate governance listing segment of the São Paulo Stock Exchange (BM&FBOVESPA) and expressed their intent to vote accordingly on the matters on the agenda involving the Level 1 segment at the Annual and Extraordinary Shareholders’ Meetings to be held on April 28 and 29, 2015, respectively.

Porto Alegre, April 24, 2015.

André Pires de Oliveira Dias

Executive Vice President

Investor Relations Director