Influence of fast cooling on mechanical property of 800 MPa grade steel with low carbon bainite structure

A kind of low carbon bainitic steel for construction machinery were designed, and the effects of cooling rate on microstructure, strength and toughness of Q800D steel with thickness of 12 mm were studied. The results show that, with the increase of cooling rate in the steel, the density of the low angle grain boundaries and high angle grain boundaries increases, and the strength and toughness of the steel can improve. When cooling rate is 80 /s, the steel conforms to national standard for Q800D steel. Besides, considering the influence of grain boundary and M/A islands on the toughness, toughness factors under different cooling rates are calculated and found to be consistent with impact energy, which indicates good correlation between toughness factors and impact energy. ©, 2015, Editorial Office of Transactions of Materials and Heat Treatment. All right reserved.