Study of historical developments in the use of fire resistant steels

Abstract

This paper presents a review of the most relevant articles on fire-resistant (FR) steels, as part of a research project at the University of the Basque Country (UPV/EHU) on the FR properties of steelstructures. An important characteristic of FR steels is that they maintain their mechanical properties at high temperatures better than the more widely used structural steels, mainly due to their special chemical composition and the thermal treatment used in their manufacture. The available information on FR steel tests has been analysed. All the data allow us to study the evolution of mechanical properties at different temperatures. We have, in particular, conducted a comparative evolution of the yield stress (YE) and the yield stress ratio (Ra) at different temperatures. A summary is also presented of the most important elements in their composition and the different manufacturing treatments of these steels and their influence on the initial YE and RA at different temperatures. For example, molybdenum and niobium improve the YE considerably at elevated temperatures. The alloy Cr–Mo–V–Nb is considered effective in FR steels and the use of boron is recommended, if an FR steelstructure is required to withstand temperatures higher than 700°C and to decrease the percentage of carbon. In view of the temperatures associated with manufacturing treatments, it should be recalled that although accelerated cooling, such as quenching, increases YE at room temperature and at high temperatures, it reduces the Ra of these steels. The most effective thermal treatment is air cooling, although special attention should be paid to the influence of slab reheating and the finish rolling temperature.