Research On Microstructure And Performance Of High-strength Fire-resistant Steel

With the rapid development of high rise building, the demand for construction steel is increased greatly. Meanwhile, higher performance of construction steel is required, such as strength, quake resistance and fire resistance. Fire resistance of steel can be achieved mainly through adding appropriate alloy element (Mo, V, Nb, Ti, etc). Mo is one of the most effective elements which improve the high temperature strength of steel. However, with the increase of Mo content, the cost of construction steel increases largely. Therefore, it is significant to develop fire resistance steel which is characterized by less alloy element adding and low Mo content.In this paper, high strength fire resistance steel590FR of Ansteel was studied. Based on thermal simulation and mechanical testing and by means of optical microscope, SEM and TEM, the microstructures of tested steel under high temperature and hot rolling status were studied; the effect of alloy elements on microstructure and performance under high temperature and ambient temperature were discussed respectively; and the fire resistance mechanism was analyzed. The results show that:1) The mechanical property of tested steel rolled and tempered met the requirement of fire resistance. Addition of Mo was effectively reduced in the tested steel. Thereby, the production cost was greatly reduced.2) The tested steel tempered after rolling. Its best mechanical property is at600℃3) The microstructure of tested steel was PF+GB, and M/A in GB was mainly martensite. The grain size of ferrite in tested steels did not coarsen with the tempering temperature increasing. Pearlite spheroidizing and M/A decomposing under high temperature=were the main factors for high temperature performance degradation. Therefore, to reduce the formation of pearlite and to improve the high temperature stability of the martensite were the main approaches to improve high temperature property of fire resistance steels.4) Small and diffused NbTi (C, N) in the tested steel played the role of precipitation strengthening. At600℃, the amount of tempering precipitated phase increased and there was no obvious coarsening, which was the major factor to high temperature performance of fire resistance steel.