SÃO PAULO, 3 de abril de 2018 /PRNewswire/ -- GERDAU S.A. (NYSE: GGB, BM&Fbovespa: GGBR3, GGBR4) hereby announces that the Form 20-F related to the fiscal year ended December 31, 2017 was filed with the U.S. Securities and Exchange Commission (SEC) and the Securities and Exchange...