Intergranular corrosion resistance of nanostructured austenitic stainless steel

Abstract

Nanostructured metals and alloys possess very high strength but exhibit limited plasticity. Enhancement of the strength/ductility balance is of prime importance to achieve wide industrial applications. However, postdeformation heat treatment, which is usually used to improve plasticity, can lead to a decrease in other properties. In the case of austenitic stainless steels, heat treatment in the range from 480 to 815°C can increase their susceptibility to intergranular corrosion. The aim of the work reported in this paper was to determine if nanostructured austenitic stainless steel is susceptible to intergranular corrosion if heat treated for 1 h at 700°C. Samples of 316LVM austenitic stainless steel were hydrostatically extruded, in a multi-step process with the total true strain of 1.84 to produce a uniform microstructure consisting of nanotwins. These nanotwins averaged 21 nm in width and 197 nm in length. Subsequent annealing at 700°C produced a recrystallised structure of 68-nm-diameter nanograins. The heat treatment improved the ductility from 7.8 to 9.2 % while maintaining the ultimate tensile strength at the high level of 1485 MPa. Corrosion tests were performed in an aqueous solution consisting of 450 ml concentrated HNO 3 and 9 g NaF/dm 3 (according to ASTM A262-77a). The evaluation of the corrosion resistance was based on transmission and scanning electron microscopic observation of the microstructure and chemical analyses. The results revealed that both the as-received and HE-processed samples are slightly susceptible to the intergranular corrosion after annealing at 700°C for 1 h.

Corrosion of Ultrafine Grained Materials by Severe Plastic Deformation, an Overview

“…[108][109][110]112,127,155,[184][185][186] Recently, other SPD processing emerged such as hydraulic extrusion (HE), 111) severe-or cryo-cold rolling. 45,75,76) These SPD processing generates UFG metals in bulk form, but in other processing, UFG or nanocrytallization can be achieved in the surface layer using high power shot blast, 78) ultrasonic peening, 77,79,80) surface mechanical attrition treatment (SMAT), [72][73][74] burnishing/brushing, [82][83][84] and friction stir processing (FSP).…”

Effects of Strain Energy and Grain Size on Corrosion Resistance of Ultrafine Grained Fe-20%Cr Steels with Extremely low C and N Fabricated by ECAP

“…They observed a rather smooth surface with a smaller penetration rate at grain boundaries and thus considerable improvement in intergranular corrosion. For SPD materials, corrosion behavior such as general [10][11][12][13][14][15][16][17][18][19][20], intergranular [21][22][23] and pitting corrosion [21,[24][25][26][27][28][29][30][31][32] of UFG aluminum and aluminum alloy [17,21,22,24,25,[29][30][31][32], copper and copper alloy [11,15,19,28] as well as stainless steels [10,12,18,23,27] and magnesium [13,14,16,20] processed by SPD, and corrosive environment dependence [33][34]…”

Roles of Inclusion, Texture and Grain Boundary in Corrosion Resistance of Low-Nickel Austenite Stainless Steel Containing Ce

“…A twin relationship (60°< 111 > ) of {111} < 110 > and {111} < 112 > orientations constitutes twin boundaries, endowed with high migration rate due to low energy, which is beneficial to the nucleation of {111} < 110 > and {111} < 112 > components. 25) As such, improving the whole intensities of α-fiber and γ-fiber textures is conducive to high proportion of ∑3 n boundaries. 26)…”