Building Performance And Organization Of Fire-resistant Steel

Steel structure is a representative of the modernistic constructure, but which have a fatal shortcoming of fireproofing. In steel-frame buildings, steel members should be protected by spraying fire-resistant coating so as to preventing from calamity of fire, insuring safety of life and wealth. The work of spraying fire-resistant materials, however, has an injurious effect on the workers' health, higher construction costs, a longer construction period. In addition, the usable space of the building is reduced by such fire-resistant coating. Therefore, there has an increasing demand for eliminating or restricting fire-resistant coating. The fire-resistant steel meets to the needing.Microstructure and alloyed elements are the major factors to determine material properties. In order to probe in the relationship of Microstructure and alloyed elements with the fire-resistant steels' properties, and offer to a reference to the fire-resistant steels development in Microstructure and alloyed elements design. This paper adopts to industrial trial-produced fire-resistant steels. The mechanical properties and microstructure of the industrial trial-produced fire-resistant steels was investigated. By tempering, the effects of tempering temperature and time on microstructure were investigated, the relationship of microstructure and properties of fire-resistant steels was discussed. Discussed high-temperature strengthening mechanism of fire-resistant steels by phase analysis. At the same time, alloyed elements: molybdenum, chroraium, niobium effect on microstructure and high-temperature strengthening mechanism of fire-resistant steels have been discussed by thermo-calc software. It has found that multiphase microstructure consisting of polygomal ferrite , pearlite, grain banite are the basic microstructure of fire-resistant steels. The fine distribution of M-A island is a mostly factor of keeping significant high-temperature properties and low yield ratio on fire-resistant steels for building. In high temperature, the stable microstructure is propitious to evaluate high-temperature properties of fire-resistant steels. Molybdenumcontribute to the increase the strength by solid-solution strengthening, niobium make it by precipitation strengthening, chromium have a little effect on the high temperature strength of fire-resistant steels, and TiN serves as nucleation sites of NbC. Between 500℃ to 600℃, the precipitation strengthening of NbC is a major factor to fire-resistant steels to keep significant high temperature strength, molybdenum precipitated MoC and Mo2C play the same role, the same time, the precipitation of molybdenum and niobium prevent NbC from coarsing.Optical microscopy,SEM,TEM, and phase analysis have been used to determine the physical characteristics.