Effects of Tempering Process on Microstructure and Mechanical Properties of Q690 Low Alloy High Strength Steel for Construction

The effects of tempering treatment at different temperatures on the microstructure and mechanical properties of Q690 high strength steel were studied by means of metallographic microscope, scanning electron microscope, room temperature tensile test and low temperature impact test. The results show that the microstructure of quenched Q690 steel is composed of ferrite, lard martensite and bainite. With the increase of tempering temperature, the strip characteristics in the microstructure of Q690 steel become less and less obvious. The microstructure of Q690 steel tempered at 460 ℃ is tempered tortenite and tempered bainite. And the microstructure of Q690 steel tempered at 500 ℃ recovers obviously and the carbide precipitates increase. The comprehensive mechanical properties of Q690 steel tempered at 460 ℃ are the best, with yield strength of 737.4 MPa, tensile strength of 875.6 MPa, elongation of 14.1%, yield strength ratio of 0.84, and impact absorption energy of 124 J at -40 ℃. All the mechanical properties meet the requirements of GB/T 19879—2015.