Effect of Annealing Temperature on Microstructure and Mechanical Properties of Hot Rolled High Strength Steel After Quenching-Partitioning

The hot rolled high strength steel was heated to different temperatures (780, 810, 840, 870 ℃) and kept warm for 600 s to anneal, and then was subjected to 200 ℃×60 s quenching+410 ℃×300 s partitioning heat treatment. The effects of annealing temperature on microstructure and mechanical properties were studied. The results show that with the increase of annealing temperature, the content of ferrite and martensite-autensite island in test steel after quenching-partitioning decreased, while the content of tempered martensite, residual austenite and bainite increased. With the increase of annealing temperature, the tensile strength decreased first and then increased, and the yield strength, percentage elongation after fracture, ratio of yield to strength and impact absorption work increased first and then decreased. The strength, plasticity and toughness of the test steel after quenching-partitioning at annealing temperature of 840 ℃ were well matched, the tensile strength (830 MPa) was large, the yield strength (585 MPa), the percentage elongation after fracture (39.6%), the ratio of yield to strength (0.70) and the impact absorption work reached the maxium values (28.35, 27.69 kJ, respectively, at −20,−40 ℃).