Effect of Intercritical Annealing Temperature on Structure and Properties of Low-Carbon High-Strength Steel for Shipboard

Low-carbon high-strength steel was treated by austenitizing at 900 ℃ and quenching, intercritical annealing at different temperatures (770,790,810,830 ℃), and tempering at 500 ℃. The effects of intercritical annealing temperature on the microstructure and mechanical properties of the test steel were studied. The results show that with the increase of intercritical annealing temperature, the recovery of lath martensite and bainite formed after annealing occurred, the lath martensite and bainite tended to merge and show block characteristics. Under the amealing condition of 770 ℃, the strength of the test steel was lower, the impact energy at -20 ℃ was higher, and the impact fracture mode was ductile fracture. When the annealing temperoture rose to 790 ℃ or above, the strength of the test steel increased, the impact energy decreased, and the fracture mode changed to quasi-cleavage fracture. The impact energy decreased farther with increasing temperature, and the tensile properties changed little.