Effect of equal channel angular pressing on structure and mechanical properties of a low carbon steel

Experiments were conducted on a plain low carbon steel with an initial grain size of similar to 30 mum to investigate the changes of microstructure and mechanical properties by repetitive equal channel angular pressings. Under the pressing conditions of giving a strain of similar to 1 and rotating samples 180 degrees between each pass, the yield strength significantly increases from 310 to 750 MPa after single pass, and it reaches 1050 MPa after 12 passes. The increment of yield strength gradually decreases as the number of passes increases. The examination of microstructure by transmission electron microscopy shows that ferrite consists of parallel bands of elongated subgrains having a width of 0.3 mum and a length of 2 mum after a single pass. The subgrains are further divided by boundaries with low angle misorientation on subsequent passages. Low angle boundaries turn to high angle boundaries without noticeable grain refinement as the number of pass increases. In addition, lamellar cementites in pearlite are broken up into fragments within a pearlite colony. Analyses of structural and mechanical changes in a plain low carbon steel by equal channel angular pressing indicate that the strength enhancement is mainly due to the grain refinement of ferrite.