Strengthening of duplex stainless steel processed by equal channel angular pressing (ECAP)

Abstract

This manuscript presents the study of the microstructural evolution, plastic anisotropy, and mechanical behavior of a duplex stainless steel (DSS) processed by the equal channel angular pressing (ECAP) technique. The ECAP process produced shear bands affecting both phases, austenite and ferrite, which in turns act as preferential sites for the appearance of the new ultrafine grains. Microstructural observations indicated grain sizes smaller than 300 nm in both phases. However, marked differences in the grain boundary misorientations were observed. Most ferrite grain boundaries showed low misorientations (average misorientation of 30°). In contrast, the austenite grain boundaries were mainly dominated by high-angle grain boundaries (average misorientation of 39°). The ECAP processing allowed to reach a yield strength over 1.1 GPa after one ECAP pass. Dislocations formed walls in the ferrite, while they were distributed evenly in the austenite grains creating plastic gradients between the two phases. Through the visco-plastic self-consistent model, it was found that austenite and ferrite strain hardening at different rates, generating plastic instabilities at different strain magnitudes. In this way, it was shown that austenite is the phase that provides more hardening while ferrite provides ductility. Regarding the anisotropy of the steel, crystal plasticity simulations showed that during the first passes of ECAP, the Lankford coefficients increase notably due to the heterogeneous microstructure of sheared grains with a higher density of defects forming subgrains in ferrite than austenite. Moreover, the austenite was more responsible for the larger planar anisotropy ($$\Delta r$$ Δ r = 2.18) values than ferrite ($$\Delta r$$ Δ r = 1.67) after two ECAP passes.

An Overview on the Corrosion Behavior of Steels Processed by Severe Plastic Deformation

“…In duplex steels processed by ECAP, it has been shown that the appearance of shear bands is favored because the two phases store different magnitudes of deformation, creating a heterogeneous state. In addition, during ECAP, the fraction of austenite declines gradually, and it tends to refine ferrite faster, which is attributed to the twinning deformation mechanism that favors grain fragmentation (31,61) .…”

Microstructural Heterogeneity and Mechanical Properties of a Welded Joint of an Austenitic Stainless Steel

“…On the other hand, metallic materials with two phases, such as duplex, dual phase, and austenitic stainless steels, present different dislocation densities due to their different capacities to distribute deformation. According to several authors [38,44,45], deformation distribution must also be heterogenous between the two phases leading to additional material hardening. It also demonstrates the creation of plastic gradients around the weld seam and between the phases of each zone.…”

Investigation of the Efficiency of Roll Profiles and Technological Schemes of Deformation of Asymmetric Rolling in Relief Rolls of C11000 Copper Alloy by FEM Simulation

“…The SPD implementation due to the intensification of shear and alternating strains makes it possible to achieve the refinement of the initial structure to an ultrafine-grained state and obtain unique mechanical characteristics, which are sometimes par-adoxical [4,5]. At the same time, the most well-known SPD methods-high-pressure torsion (HPT) and equal-channel angular pressing (ECAP)-allow deforming samples of limited geometric dimensions, which significantly reduces the possibility of using these methods on an industrial scale [6][7][8][9].…”