Processing of a duplex stainless steel by equal channel angular extrusion

Abstract

A UNS S32205 duplex stainless steel was processed by ECAE in three different velocities, at room temperature, and heat treated in different temperatures and times to evaluate recrystallization. Attrition forces promoted great deformation heterogeneity in the samples sections, with hardness increase, and morphology changes in the grains and changing orientation through the processed samples. In treated samples surface, two types of distinct structures was formed, with surfaces positioned in 90º and 120º angles, probably because the annihilation of pilled dislocations in ferrite based centered cubic structure and austenite face centered cubic structure, respectively. The induced martensite by cold deformation was also observed. Some samples demonstrate located points of recrystallization in grain boundaries for some treatment conditions, the number of recrystallization nuclei increased with the increase of treatment time.Keywords: Duplex, ECAP, stainless steel. INTRODUCTIONAlthough the physical and mechanical properties of metals are determined by several factors, the grain size of the material is generally very significant and frequently a dominant factor in determining the properties and final application of the materials [1].The fact of the mechanical resistance increases with the grain size reduction makes interesting the production of materials with an extremely small grain size. Commercial metallic alloys are generally produced for specific applications where the alloys are submitted to specific mechanical and thermal processes. However this procedures can't be used to produce sub micrometric grain sized materials, because they presents a lower limit fixed, in order of a few micrometers, which represents the minimum grain size that can be obtained by these processes [1].To produce ultrafine grained materials by a coarse grained material, the imposture of an extreme high strain is necessary, in order to introduce a high density of dislocations, then these dislocations can be rearranged and form ordered grain boundaries. However, in practice, this situation is restrict in conventional conformation process, like the extrusion or stretching, it happens cause of this two reasons: the total strain that can be imposed to the material is limited by the cross sectional reduction in the specimen, and, the total strain imposed is insufficient to introduce an ultrafine grain structure to the material, due the low workability of these materials at room temperature.Considering these limitations, several researches have been directed to the development of new techniques that can be used to produce ultrafine grained materials and provide the understanding of the behavior during the recrystallization process. Between these techniques, the ECAE (equal channel angular extrusion) was developed, or ECAP (equal channel angular pressing). The principle of ECAE is based on severe plastic deformation application, through the imposture of an extremely high strain in a relatively low temperature, without any significant change...

Two-parameter Rigid Block Approach to Upper Bound Analysis of Equal Channel Angular Extrusion Through a Segal 2θ-die

“…The results of the comparison of obtained two-parameter UBM values (3)- (4), (6) with published experimental data 30,34 for ECAE punching pressure p/2k are shown in Figure 10, where ECAE die angle is 2θ=90º:…”

“…The mechanics of metal flow during Equal Channel Angular Extrusion (ECAE) or Equal Channel Angular Pressing (ECAP) through the 2θ-dies of simple Segal geometry attracts a lot of research contributions from different fields of theoretical , experimental [28][29][30][31][32] and industrial 8,25,33 science. ECAE assumes one or several extrusion passes of a lubricated billet in a 2θ-die of Segal geometry with two intersecting channels of equal cross-section in Figures 1-2.…”

“…Perig et al 16 have applied the Navier-Stokes equations in the curl transfer form for the numeric finite-difference description of viscous material flow through the following dies: (I) ECAE die with channel intersection angle 2θ=90°[ 16] , (II) S-shaped multiple angle die with movable inlet wall 20 , and (III) ECAE die with channel intersection angle 2θ=90° and [28][29][30][31][32] . Berta et al 29 outline comparable experimental ECAE data on the structure of the treated metal blanks at various channel angles 2θ=90° and 2θ=120° [ 29] .…”

Strengthening of Duplex Stainless Steel Processed by Equal Channel Angular Pressing (Ecap)

“…These methods also predicted the microstructure heterogeneity and grain shape well, proving to be a powerful tool for analyzing the microstructure after SPD processing. Other authors, such as Farias et al [36], studied the effect of processing speed and subsequent heat treatments on a DSS processed by ECAP. They observed the formation of martensite induced by cold deformation, where the grain boundaries act as preferential sites for recrystallization.…”

Impacto do uso de substâncias psicoativas na ideação suicida em adolescentes

“…Entendida como ato de horror que o homem comete contra seu semelhante, para submetê-lo e garantir sua identidade de poder absoluto" (Farias, 2010). É uma endemia, padrão cultural em muitas sociedades modernas, sendo responsável por percentuais de mortalidade e perdas, mais altos do que epidemias e guerras.…”