Abstract: Microstructure evolution of a cold-rolled medium-carbon Cr-Mo steel annealed at 600 ℃ for different time was investigated by means of SEM and EBSD. The results show that the distribution of cementite particles becomes more dispersive and the spheroidization becomes more and more obvious as the annealing time increases, and the deformed ferrite strips are transformed into equiaxed ferrite grains. The cementite particles inside the grains are relatively fine, while those at the grain boundaries are large and partially distributed continuously. The grain size increases continuously, but the grain growth is not obvious when the annealing time is less than 240 min, and the grain size growth becomes faster when the holding time is further extended. The average ferrite grain size increases from 0.670 μm to 0.732 μm and then 2.000 μm when the holding time is extended from 15 min to 120 min and then 480 min. The grain growth rates are 55.7%, 9.7%, 74.3%, and 42.9% respectively for the annealing periods of 0-120, 120-240, 240-360, and 360-480 min. Among them, the percentage of grain size growth from 0 to 15 min is as high as 42.6%. Considering that the grain growth rate is relatively larger in the annealing period of 0-120 min, and the annealing time can be set at 120 min from the viewpoint of energy saving.

Key words: medium carbon Cr-Mo steel, cold rolling, annealing, microstructure evolution