Effect of tempering on the microstructure and properties of a new multi-functional 460 MPa Grade construction structural steel

Abstract

A new generation of multi-functional construction structural steel with high yield strength of ∼545 MPa, excellent toughness of ∼170 J/cm2 at −20 °C, lower yield ratio smaller than 0.83, good fire resistance, and good corrosion resistance was successfully developed by thermo-mechanical controlled processing plus tempering. The effects of tempering on the microstructure and mechanical properties were investigated. The results show that although the bainite lath slightly coarsens and the dislocation density slightly decreases as the tempering temperature increases, the yield strength of the steel increases mainly due to the precipitation strengthening. The samples tempered at 300 °C show the best combination of strength, toughness, and yield ratio. In addition, the high-temperature strength of the newly developed Q460 steel is obviously higher than the conventional one, which is mainly attributed to the bainitic strengthening and precipitation strengthening. Moreover, a denser rust layer forms on the surface of new Q460 steel during corrosion because of the addition of Cr and Cu, which increases the corrosion resistance of the steel.