Abstract: Simulated normalizing treatment of the center material of a 300 mm×300 mm section Q355E steel forging was carried out by using a simulated program-controlled heat treatment furnace. Effect of simulated normalizing temperature on the microstructure and properties of Q355E steel forgms for thick section wind-electron flange was studied by optical microscope, scanning electron microscope, tensile and impact testing machines. The results show that with the increase of simulated normalizing temperature in range of 780-900 ℃ and then tempered at 580 ℃, the impact absorbed energy at -50 ℃ of the specimens increases first and then decreases, and the average size of ferrite decreases from 14.73 μm to 12.07 μm and then increases to 15.02 μm, and the average size of pearlite increases from 3.69 μm to 10.51 μm. When the simulated heat treatment temperature is 820 ℃ and 840 ℃, the microstructure of ferrite and pearlite is uniform and fine, and pearlite is distributed in strip and near equiaxed shape, the impact absorbed energy at -50 ℃ is 183.8 J to 211.1 J, and the shear section ratio of the specimens is more than 50%. For 300 mm×300 mm section Q355E steel forgings, normalizing treatment at 820-840 ℃ can be selected to obtain excellent and stable low temperature impact absorbed energy.

Key words: Q355E steel, simulated normalizing treatment, low temperature toughness, microstructure, large section forgings