Investigation of Electroplastic Effect on Four Grades of Duplex Stainless Steels

Abstract

Since the late 1950s, an effect of electrical current in addition to joule heating on the deformation of metals called the Electroplastic Effect (EPE) has been known. It is used nowadays in the so-called Electrically Assisted Forming (EAF) processes, but the understanding of the phenomenon is not very clear yet. It has been found that EPE increases the formability of high stacking fault energy (SFE) materials, while low SFE materials reach fracture prematurely. Since Duplex Stainless Steels (DSSs) possess a microstructure consisting of two phases with very different SFE (low SFE austenite and high SFE ferrite) and they are widely used in industry, we investigated EPE on those alloys. Tensile tests at 5 A/mm2, 10 A/mm2 and 15 A/mm2 current densities along with thermal counterparts were conducted on UNS S32101, UNS S32205, UNS S32304 and UNS S32750. The DSS grades were characterized by means of optical microscopy, X-ray diffraction and their mechanical properties (ultimate tensile strength, total elongation, uniform elongation and yield stress). An increase in uniform elongation for the electrical tests compared to the thermal counterparts as well as an increase in total elongation was found. No differences were observed on the yield stress and on the ultimate tensile strength. Un uneven distribution of the current because of the different resistivity and work hardening of the two phases has been hypothesized as the explanation for the positive effect of EPE.

Investigation of Electrically-Assisted Rolling Process of Corrugated Surface Microstructure with T2 Copper Foil

“…They believed that the increase of the stability of retained austenite inhibited the effect of mechanically induced martensite transformation with the increase of temperature. In the investigation of Gennari et al [18], the uniform elongation and total elongation were improved greatly in the EA tensile test, while the changes of the yield stress and ultimate tensile stress were inapparent, compared to the thermal test. Perkins et al [19] conducted a series of studies by the EA compression of different metals, and found that there was a threshold current density in EA compression.…”

Substructure Formation, Texture, and Mechanical Behavior of Warm Rolled 2205-Type Duplex Stainless Steel

“…However, no evidence was found in warm-rolled DSS specimens because of the high temperature employed for the latter. The increase in deformation temperature increases the SFE, reducing the probability of mechanical twinning formation [46]. The dislocation substructures in the austenite appear as very dense irregular parts with rather thick diffuse sub-boundaries, presenting a wide spectrum of low-to high-angle misorientations (Figs.…”

Influence of Electropulsing Treatments on Mechanical Properties of UNS S32750 Duplex Stainless Steel

“…Investigations of the effect of both EAM and EPT on DSSs are still quite limited except for the work carried out by some of the authors [24] and a scientific report on duplex steel by Rahnama et al [39]. The aim of the present work is to examine the effect on the mechanical properties of electropulsing treatments on a material that possesses two phases with different crystal structure, composition, electrical resistivity, work hardening rate etc.…”

“…The discovery of such phenomenon led to the development of new approaches to material forming known as electrically assisted manufacturing (EAM) in which electrical current increases the formability of various metallic alloy exploiting the electroplastic effect (EPE). The electroplastic effect has shown to improve the formability on a wide variety of metallic materials such as aluminum [15][16][17], titanium [18][19][20], magnesium [21][22][23], stainless steels [24,25] and on a variety of forming processes as well. Some of the authors observed a relationship of the onset of EPE on FCC materials with respect the stacking fault energy (SFE), which drives dislocation's motion within the material [26].…”