Effect of Fire-Induced High-Temperature on Microstructure and Seismic Performance of Q460GJEZ35 Fire-Resistant Steel

The hot-rolled Q460GJEZ35 steel was held at temperatures ranging from 225 ℃ to 625 ℃ for 60 min to simulate the fire temperature environment. The effects of temperature on the microstructure and seismic performance of the test steel were studied. The results show that the microstructure of the test steel under different temperatures was composed of granular bainite and ferrite. With the increase of temperature, the decomposition degree of martensite/austenite island in bainite increased, and the area fraction of precipitated carbides increased from 9.00% at 225 ℃ to 67.18% at 625 ℃; the yield strength and tensile strength of the test steel increased first and then decreased, and the yield ratio increased; the internal friction at room temperature decreased, resulting in the deterioration of seismic performance. The yield ratio of the test steel was basically linearly negatively correlated with the internal friction at room temperature. When the temperature was not higher than 325 ℃, the yield ratio remained below 0.8. When the temperature was not lower than 425 ℃, the yield ratio was 0.818–0.887. When the holding time was not more than 60 min at the temperature not higher than 525 ℃, the internal friction at room temperature of the test steel was relatively high, and the yield ratio was not greater than 0.85, indicating good seismic performance. The test steel still met the usage requirement after existing in a fire environment whose temperature was not higher than 525 ℃ for 60 min.