The Effect of ECAP Process on the Microstructure and Mechanical Properties of AISI 1020 Plain Carbon Steel

In the present study, the equal channel angular pressing (ECAP) was applied on AISI 1020 plain carbon steel to refine the grain size down to the sub-micrometer range. ECAP was conducted up to 10 passes at 300 ^°C in a die with a channel angle of 105^°. The microstructure before and after ECAP was observed in two different scales using a light microscope and a transmission electron microscope (TEM). Evaluation of mechanical properties was carried out by tensile tests and microhardness measurements. The results indicate that by applying 10 passes of ECAP, an ultrafine-grained microstructure with a mixture of equiaxed and elongated grains with an average grain size and width of 320 and 270 nm, respectively, is formed in the steel. In addition, the analysis of the X-ray peak profiles of the ECAP-ed samples shows that inside the grains, there are finer microstructural components such as dislocation cells/subgrains. The average size of these components was measured at ~143 nm. In terms of mechanical properties, it was proven that ECAP is very effective in improving the strength and hardness of the steel. It causes a three times growth in yield strength from 280 MPa to 1100 MPa and a 1.67 times increase in hardness from 125 to 395 Vickers. At the same time, the studied material showed an acceptable ductility of ε_f = 14.8% at these high strength levels. These promising mechanical properties was discussed in terms of characteristics of the ECAP-produced microstructure: extremely fine grains/subgrains, and increased dislocation density.