采用扫描电镜、透射电镜等方法研究了不同热处理工艺对700L汽车大梁钢冲击性能的影响。结果表明:低温退火处理对700L钢的冲击性能影响明显。在低于400℃退火时,钢板组织变化不明显,但冲击性能相较原板有所提高,在高于550℃退火时,钢板组织发生细微变化,冲击性能有所恶化。其中在200℃退火后,抗拉强度降低了约2.6 MPa,但-40℃冲击吸收功提高了28 J,伸长率提高了1.28%。奥氏体化热处理对700L钢的冲击性能有明显影响。原板经奥氏体化不同冷却工艺热处理之后,空冷后的钢板拥有最佳的冲击性能,其-40℃冲击吸收功相较原板提高了约202 J,组织主要由铁素体与少量的贝氏体与M/A岛组成,透射电镜表征表明,铁素体区几乎没有位错,而位错主要集中在少量的贝氏体与M/A岛中,这可能是空冷后钢板冲击韧性最好的一个原因。 The effects of different heat treatment processes on the impact properties of 700L automobile girder steel were studied by scanning electron microscopy and transmission electron microscopy. The results show that the impact of low temperature annealing on the impact properties of 700L steel is obvious. When annealed below 400 ℃, the microstructure of the steel plate is not obvious, but the impact performance is improved compared with the original plate. When annealed above 550 ℃, the microstructure of the steel plate changes slightly and the impact performance deteriorates. After annealing at 200 ℃, the tensile strength decreased by about 2.6 MPa, but the impact energy absorption at -40 ℃ increased by 28 J and the elongation increased by 1.28%. Austenitic heat treatment has a significant impact on the impact properties of 700L steel. The original plate after austenitizing the different cooling process heat treatment, the air-cooled steel plate has the best impact performance, its -40 ℃ impact absorption power compared to the original board increased by about 202 J, the organization mainly by ferrite and a small amount of Bayesian Body and M / A island. Transmission electron microscopy showed that there were almost no dislocations in the ferrite zone and dislocations mainly concentrated in a small amount of bainite and M / A islands, which may be the best impact toughness of the steel after air cooling One of the reasons