Mechanical properties of heat-treated high tensile structural steel at elevated temperatures

• Investigate mechanical properties of high tensile steel at elevated temperatures.
• Discuss change of microstructure of high tensile steel at elevated temperatures.
• Propose fitted stress–strain relations of high tensile steel at elevated temperatures.

This paper investigates experimentally the mechanical properties of heat-treated high tensile strength low alloy structural steel RQT 701 with proof strength of 740 MPa at elevated temperatures. Standard axial tensile tests at elevated temperatures were carried out by using both steady-state and transient-state methods. The test results were compared with those from mild steels of grades up to S460. The comparisons indicate that the RQT 701 steel has smaller relative thermal elongation, and higher reductions of effective yield strength and elastic modulus at elevated temperatures. The test results on proportional limit, effective yield strength and elastic modulus were fitted into Eurocode stress–strain models for numerical analysis and fire resistant design.