Microstructural evolution in a commercial low carbon steel by equal channel angular pressing

In the present investigation, both macroscopic and microscopic microstructural changes in a plain low carbon steel with a mixed structure of ferrite and pearlite were examined during equal channel angular pressing. During equal channel angular pressing, the sample was rotated 180 degrees around its longitudinal axis between the passages. By repeating the pressing up to the accumulated effective strain of similar to 4, ferrite grains with a submicron size of 0.2-0.3 mu m were obtained. Optical observation revealed that hard pearlite phase deformed macroscopically in a similar manner to soft ferrite phase due to a considerable capability of pearlitic cementite for plastic deformation under the present equal channel angular pressing conditions. An examination of micrographs taken by transmission electron microscopy showed that the microstructural change in ferrite phase was similar to those in single phase Al solid solution alloys in that the nonequilibrium configurations of grain boundary were observed. In pearlite phase, the morphological change of cementite lamellar plates was represented by the existence of either severely necked fragments parallel to each other or curled wavy fragments. Microstructural evolution in a plain low carbon steel subjected to equal channel angular pressing was discussed by comparing it to that of equal channel angular pressed Al solid solution alloys and heavily cold drawn pearlitic steel wire, which exhibited similar microstructural change. (C) 2000 Published by Elsevier Science Ltd on behalf of Acta Metallurgica Inc. All rights reserved.