Temperature and time effect of thermal aging treatment on microstructure and corrosion resistance of UNS S31803 duplex stainless steel

Abstract

Duplex stainless steels correspond to a class of steel in which the microstructure is composed basically by the phases ferrite and austenite. Given the metastable character of ferrite, associated phase transformations can occur during thermal treatments, which can lead to a reduction in corrosion resistance. Therefore, the aim of this work was to evaluate the influence of the solution-treated at 1100°C for 30min and aging at 500 and 600°C for 1, 3 and 12h, on the microstructure and corrosion resistance of DSS UNS S31803. The steels were characterized by SEM, EDS, XRD, hardness, microhardness and thermal analysis. The steels aged at 500°C for 1h presented the phase alpha line dispersed in the ferrite, and the steels aged at 600°C for 12h presented the phases alpha line, sigma and chi. In the assays of double cycle potentiodynamic reactivation in solution of 0.5M H2SO4 and 0.01M KSNC, it was observed that no sensitization occurred. Furthermore, in the tests of cyclic potentiodynamic polarization, in 3.5% NaCl solution, it was verified that the precipitation of the alpha line phase did not alter corrosion resistance; nevertheless, the sigma phase reduced corrosion resistance.

Effect of Rapid Solidification Processing on the Microstructure and Corrosion of 316L Austenitic Stainless Steel

“…The chemical composition is similar to the cold rolled condition, as shown in Figure 6 (b-e). In addition, regions enriched with Fe, Cr, Ni and Mo were observed within the dendritic structure, according to the results shown in Table 2 and the results obtained by 13,[17][18][19][20] .…”

Effect of Precipitation of Alpha Line and Sigma Phases on the Microstructure and Corrosion Resistance of the Duplex Stainless Steel SAF 2205

“…The precipitation of the α' phase introduces barriers capable of reducing the dislocation movements and, therefore, leads to an increase in yield strength, hardness, microhardness, the limit of mechanical resistance, decrease in tenacity, elongation and corrosion resistance [23][24][25][26] . Thus, the ferrite embrittled by the formation of the alpha line phase suffers a brittle cleavage-type fracture, by crack propagation at interfaces and grain boundaries, even at room temperature 26,27 .…”

“…The formation of the α' phase may occur by two mechanisms: nucleation and growth; and spinodal decomposition of ferrite, depending on the chemical composition of the DSS and the temperature to which it is exposed [23][24][25] .…”

“…The precipitation of the α' phase by the mechanism of nucleation and growth is characterized by a greater variation in the local chemical composition, leading to the formation of nuclei of the α' phase, which grow until they reach a critical radius, promoting a barrier to nucleation [23][24][25] .…”

“…In the mechanism by spinoidal decomposition, there is a gradual diffusion of chromium, resulting in regions rich and poor in chromium, until the phases α' (rich in chromium) and α (rich in iron) are formed as final products in the chemical compositions of equilibrium. In the spinoidal decomposition of ferrite, there is a loss in tenacity and the increase in microhardness, because of the formation of the alpha line phase, which impedes the movements of the dislocation planes 6,[23][24][25][26][27][28][29] .…”