A Study of Inhomogeneous Plastic Deformation of 1045 Steel

An experimental study was conducted on the inhomogeneous plastic deformation of 1045 steel subjected to monotonic tension and cyclic tension-compression. Small strain gages were used to characterize the local deformation and transmission electron microscopy (TEM) was used to study the microstructures associated with the observed deformation phenomenon. Under monotonic tension, the strain of the Lu¨ders front was lower than the full Lu¨ders strain. The local strains were inhomogeneous even at the work-hardening stage. Under stress-controlled cyclic loading with stress amplitudes below the lower yield stress, cyclic deformation consisted of an incubation stage, a significantly inhomogeneous cyclic softening stage, and a saturation stage. Inhomogeneous cyclic plasticity persisted at the saturation stage. A monotonic tension preload can eliminate the incubation stage in the subsequent cyclic loading. Under asymmetric cyclic loading with a mean stress, the cyclic plastic deformation was accompanied by noticeable inhomogeneous ratcheting deformation. TEM was used to analyze the distribution and evolution of the dislocation structures at different locations of the specimen. With increasing loading cycles, the dislocation substructures evolved in a sequence of loose tangles, thick veins, long walls, elongated cells, and equiaxial cells. Based upon the mechanical experiments and observations of dislocation arrangements, the mechanisms governing inhomogeneous cyclic plastic deformation were discussed.