Effect of repetitive equal channel angular pressing on microstructural stability of low carbon steel

The microstructure of ultrafine grained low carbon steel processed with repetitive equal channel angular pressing was investigated. A submicron ferrite grain size of ∼0.2 μm was achieved by pressings of up to 12 passes. Microstructural examination by TEM with SAD pattern on the pressed samples revealed the presence of high density dislocations inside the ferrite grains and ill-defined grain boundaries. These features became more significant as the number of pressings increased. The static annealing of the pressed samples at 753 K up to 24 hrs resulted in a recovery which was associated with the absorption of the dislocations by the grain boundaries. However, the recovery was inhibited as the number of pressings increased. The annealing process also led to the precipitation of cementite particles in ferrite colonies. The presence of precipitated particles inside the ferrite grains enhanced the microstructural stability of the low carbon steel at elevated temperatures.