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

SECURITIES EXCHANGE ACT OF 1934

Dated April 11, 2018

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  xForm 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 oNo 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:  April 11, 2018

GERDAU S.A.
By:	/s/ Harley Lorentz Scardoelli
Name:	Harley Lorentz Scardoelli
Title:	Investor Relations Director

2

EXHIBIT INDEX

Exhibit	Description of Exhibit
99.1	Notice to the Market, April 11, 2018

3

EX-99.1

Exhibit 99.1

GERDAU S.A. CNPJ/MF n.º 33.611.500/0001-19 NIRE: 33300032266 NOTICE TO THE MARKET Gerdau, jointly with Votorantim Cimentos and Grupo Tigre, announces the creation of a new company to manage and promote a loyalty program for Brazil’s retail construction industry, called Juntos Somos +. The initiative functions like a benefits program for stores and respective vendors, with the aim of improving service to end customers and to construction industry professionals. This means that each sale of products of the companies participating in the program (steel, cement, mortar and grout, pipes and fittings, etc.) generates points, which can be exchanged for goods or services by store owners, vendors and clerks, according to the results of interest and applicable regulations. For example, points can be exchanged for technical courses, management training programs, goods and equipment, software sales and more. Votorantim Cimentos, founder of the program in 2015, will have a 45% stake, while Gerdau and Grupo Tigre each had 27.5%. The operation of the new company is subject to approval from Brazil’s antitrust agency CADE (Conselho Administrativo de Defesa Econômica). São Paulo, April 11, 2018. Harley Lorentz Scardoelli Executive Vice-President Investor Relations Officer