Abstract: By real-time tracing of vacuum heat treatment temperature of FV520B steel, the heating time lag at different heating temperatures was analyzed and the effect of different holding time on the microstructure and mechanical properties aging at 600 ℃ for different time was studied. The results show that the time lag of vacuum heat treatment increases with the decrease of heating temperature. In the early stage of vacuum aging of the FV520B steel, due to the time lag, the temperature in the workpiece core does not reach the set heating temperature. With the extension of the holding time, the microstructure changes greatly, the content of retained austenite increases and the precipitated phase gradually precipitates. The yield strength decreases and the impact absorbed energy increases with the prolongation of holding time. The power consumption of vacuum furnace can be used to determine whether the workpiece temperature is uniform, which can be used to guide the design of heat treatment process parameters.

Key words: FV520 steel, vacuum aging, heating arrival time, microstructure, mechanical proprieties