Estudo da solubilização do Nb em aços microligados durante reaquecimento de placas

• Ano de defesa: 2010
• Autor(a) principal: Camilla Pessanha Schiavo
• Tipo de documento: Dissertação
• Tipo de acesso: Acesso aberto
• Idioma: por
• Instituição de defesa: Universidade Federal de Minas Gerais; UFMG
• Palavras-chave em Português: Aços microligados; solubilização de precipitados; conformação a quente; Engenharia metalúrgica; Metalurgia física; Engenharia de minas
• Link de acesso: http://hdl.handle.net/1843/BUOS-8DPFAV

This study evaluate the reheating conditions effects on the dissolution of microalloyed steels, specially Nb and Ti, and the N influence in the dissolution of cabonitrides, nitrates and carbides. Samples of 3 industrially produced slabs of Nb-Ti-V microalloyed steel, which contain different amounts of N, due to the operational conditions, were evaluated. These samples were undergo different thermal cycles representing industrial reheating conditions, so as to allow the determination of the best conditions for the carbonitrides dissolution heat treatment. The microalloyed quantity present in solid solution were estimated with product solubility equations and the applicability of the software Themo-Calc for the prevision of precipitates dissolution was verified. It was also part of the scope of this project estimate the reheating conditions influence on Tnr evaluated by torsion tests. Product solubility equations indicated until soaking temperature equal 1100°C only VC, VN e NbN precipitates are going to dissolve. At soaking temperature equal 1200°C, TiC and NbC are going to dissolve. Only for soaking temperatures up to 1250°C we could affirm all the precipitates were being dissolved and the complex precipitate Nb(CN). Thermo-Calc software estimated VC, NbC, (Ti, Nb)(C, N), AlN and MnS precipitates for all compositions. For lowest and hightest N contents this software also estimate Ti4C2S2 precipitate. It was also verified VC dissolution until 800°C, NbC dissolution at 1200°C and (Nb, Ti)(C, N) dissolution at 1200°C. At 1200°C, equal the industrially temperature for this kind of steel, were estimated that 90% of Nb contents are going to be on solid solution. Dissolution temperatures estimated by product solubility equations and by Thermo-Calc software were near. Its important to remember that these methods dont use kinetics conditions on their calculous. The Tnr increases with reheating temperature and reheating time, therefore with Nb an Ti contents in solid solution.