Tensile and Low-Cycle Fatigue Properties of HTRB630 High-Strength Steel Bars after Exposure to High Temperatures

Heat-treated ribbed bar 630 (HTRB630) is a new type of reinforcing steel produced in China. The tensile properties and low-cycle fatigue properties of HTRB630 high-strength steel bars after exposure to high temperature are crucial for the seismic performance of reinforced concrete structures potentially subjected to fire. With this aim, HTRB630 high-strength steel bar specimens were heated to high temperatures (200 degrees C, 400 degrees C, 600 degrees C, and 800 degrees C), and cooled to the room temperature by water. The appearance and microstructures of the specimens with different exposure temperatures were observed. The tensile tests and different constant strain amplitude low-cycle fatigue tests were carried out. Test results indicated that the specimens exposed to high temperature below 600 degrees C had good tensile properties and low-cycle fatigue properties. Variations of the metallographic structures of the specimens resulted in different tensile properties and different low-cycle fatigue properties. After exposure to the same temperature, as the strain amplitude increased, the shape of the hysteresis curve of the specimen was fuller, its plastic strain amplitude and plastic strain range and elastic strain range ratio increased, its maximum stress per cycle increased slightly, its softening characteristic was more obvious, and its residual dissipated energy density decreased. All specimens performed ductile fracture failures. Therefore, HTRB630 high-strength steel bars have broad application prospects in antifire reinforced concrete structures.