Development and study of high-strength low-Mo fire-resistant steel

Microstructures and properties of hot-rolled fire-resistant steels with two Mo addition levels (about 0.15 and 0.3 wt.%) have been investigated. The results show that a low-Mo (about 0.15 wt.%) fire-resistant steel with high strength (ultimate tensile strength: 770.3 MPa, yield strength: 488.7 MPa) and low yield ratio (0.634) has been successfully developed by microalloying Nb, V, and Ti and controlling cooling rate in combination. It is possible to obtain two-thirds of room-temperature yield strength at 600 °C in high-strength low-Mo (about 0.15 wt.%) fire-resistant steel. The analysis indicates that the bainite strengthening and precipitation strengthening are both important in improving the high-temperature strength of fire-resistant steel, and these strengthening effects effectively replace the strengthening effects of Mo. The present results also show that two different components in bainitic microstructure, discontinuous cementites or retained austenite, have similar effects on high-temperature strength of fire-resistant steel.