Caracterização microestrutural e mecânica de aços resisitentes ao fogo a base de MO-Si-P

• Ano de defesa: 2004
• Autor(a) principal: Odair Jose dos Santos
• Tipo de documento: Tese
• Tipo de acesso: Acesso aberto
• Idioma: por
• Instituição de defesa: Universidade Federal de Minas Gerais; UFMG
• Palavras-chave em Português: aços estruturais; aços para construção civil; Aços resistentes ao fogo; Engenharia metalúrgica; Metalurgia física; Aço Corrosão; Ligas de aço; Resistencia de materias; Aço de alta resistencia
• Link de acesso: http://hdl.handle.net/1843/BMGZ-69WNXF

Cracking problems during continuous casting of USI SAC structural steels produced by USIMINAS has led to development of a new steel design based on the substitution of Si and P for this former alloy base (Cr and Cu). The new design reduced significantly production costs associated with slab scarfing, without altering the original mechanicaland physical characteristics of the product. Similar changes in chemical composition were considered for USI FIRE, fire resistant steels, which, apart from the addition of Mo, have a composition similar to that of USISAC steels. Therefore, the present work aimed to develop a new USI FIRE steel based on the Mo-Si-P-Nb alloy system which presents a performance similar to the usual Mo- Cu-Cr steel and a lower production cost. Six runs of the new USI FIRE steel were produced Si and P contents similar to those of USI SAC 350 and different C, Mo and Nb contents. Tension properties (in the 25 to 600°C interval), microstructure, hardenability and toughness of the six alloys were evaluated. Only the alloy contained Nb and higher Mo and C contents was considered to be fire resistant. Its performance was attributed mainly to its higher amount of Mo. This composition increased the volume fraction of martensite and bainite in the microstructure, displaced dynamic strain aging manifestations to higher temperatures and slowed down coarsening of NbC particles by segregation to the precipitate/matrix interface. However, the toughness of this alloy did not meet its specified value. This was linked to its higher hardenability causes by the presence a higher amount of Mo and Nb in solid solution.