Nb-microalloyed fire-resistant construction steels recent progress

Fire-resistant constructional steels have been commercialized in some parts of the world and are now poised for application in the USA, as a specification has been issued recently by the American Society for Testing and Materials (ASTM) that defines testing and material requirements. Selected metallurgical studies are reviewed, to help understand the microstructure/property relationships that control fire resistant (FR) properties in Nb-containing steels. Specific examples are cited which illustrate the apparent benefit of Mo in suppressing precipitate coarsening rates at elevated temperature and beneficial effects of microstructure refinement, microalloy precipitation, and warm working of ferrite on the FR properties. The concept of “active” fire resistance is illustrated (confirmed with both Cu and Nb containing steels thus far), whereby alloying and processing are designed to allow strengthening precipitates to form in the microstructure as a consequence of the heating encountered during a fire. The requirements of the new ASTM specification A1077/A1077M-12 are also summarized. (AU) Copyright © 2015 Companhia Brasileira de Metalurgia e Mineração (CBMM) All rights reserved.