* Contribuição técnica ao 69º Congresso Anual da ABM – Internacional e ao 14º ENEMET - Encontro Nacional de Estudantes de Engenharia Metalúrgica, de Materiais e de Minas, 21 a 25 de julho de 2014, São Paulo, SP, Brasil. Tema: Metalurgia física e comportamento de materiais em temperaturas elevadas CHARACTERIZATION OF A NEW LOW MANGANESE, NIOBIUM MICROALLOYED STEEL FOR SOUR SERVICE* Mario González Ramírez 1 Neusa Alonso Falleiros 2 Hélio Goldenstein 3 Frank Barbaro 4 Abstract The safe transport of sour gas requires steels with enhanced hydrogen induced cracking (HIC) resistance. Centerline segregation bands of high hardness microconstituents and non-metallic inclusions are the heterogeneities usually linked to HIC failures in pipeline steels. Full-scale production heats of a new low Mn, Nb microalloyed steel were produced by different steel mills aiming at the application in sour gas environments. The new alloy design provides both effective strengthening and control of sulphide inclusions. Coil microstructure consisted of fine grained ferrite with a small volume fraction of uniformly dispersed eutectoid aggregates. Most importantly the microstructure was uniform in both the longitudinal and transverse directions and exhibited exceptional consistency. Samples from this steel were submitted to HIC testing according to NACE standards TM0284-2003 without any sign of cracking. The results, so far, confirm that this new alloy design provides the unique opportunity to economically produce a high strength pipe steel grade with improved sour service resistance for the linepipe industry. Keywords: HIC; API 5L; Sour service; H2S; Nb microalloy; Low Mn. 1 Doutor em Engenharia, Departamento de Engenharia Metalúrgica e de Materiais, EPUSP, São Paulo, SP, Brasil. 2 Professora Doutora, Departamento de Engenharia Metalúrgica e de Materiais, EPUSP, São Paulo, SP, Brasil. 3 Professor Titular, Departamento de Engenharia Metalúrgica e de Materiais, EPUSP, São Paulo, SP, Brasil. 4 Doutor em Engenharia, Professor da Universidade de Wollongong, Consultor da Companhia Brasileira de Metalurgia e Mineração (CBMM), Austrália. ISSN 1516-392X 2077