Selective corrosion of duplex stainless steel bars in acid. Part 2: Effect of the surface strain and numerical analysis

Abstract

In the second part of this study, the effect of the strain level on the selective corrosion of the phases comprised in four different heavily strained duplex stainless steel (DSS) bars is analyzed. The corrosion behavior of the surface of bars with variable strain levels is analyzed and compared to the results of the less strained core of the same bars. For lean DSS bars (UNS S32304 and S32001 grades), an increase on the corrosion rate caused by the strains has been detected for the surface. For these DSS without Mo, ferrite has proved to be more sensitive to decrease on the corrosion resistance caused by the strain than austenite. In these cases, the strains expand the region of active corrosion toward higher potentials. On the other hand, when the grains are heavily strained parallel to the surface, if the most corrosion resistant phase has good corrosion behavior in the medium (UNS S32205 grades), the corrosion rate can be effectively slowed down, in spite of the microstructural defects.

Corrugated stainless steels embedded in mortar for 9years: Corrosion results of non-carbonated, chloride-contaminated samples

“…The influ ence of the forming process in the corrosion behaviour of stainless steels has been demonstrated in simulated pore solutions tests [13). The cold working of the reinforcements cause microstructural changes that can affect the corrosion behaviour of the stainless steels [55) and these changes are much more pronounced in the corrugations than in other regions of the surface [40).…”

“…It could be considered reasonable bearing in mind the non homogeneity that the passive layer should exhibit when it is formed on the surfaces of the corrugated stainless steel bars. Those surfaces exhibit different stress levels, and, particularly, highly stressed areas [40), thus limiting the protective abilit y of the passive oxides [13). Other research groups have also chosen this equivalent circuit to simulate the electrochemical behaviour of active and passive stainless steel in solution and in mortar [6, 48,49).…”

“…The lower strain level of these bars in corn parison with the tested 530400 can easily explain this fact (the lower tensile strengths of the 531603 and 531635 bars in Table 1 correspond to a less heavy forming process). A heavy forming pro cess would cause high densities of defects and dislocations in the corrugations, so these regions of the bars would become much more prone to corrosion [40).…”

“…of acid, 50 s) in the laboratory, reproducing the process carried out on the corrugated surfaces of the bars in industry. Moreover, the cross section of the bars are much less prone to corrosion than strained surface [40], thus assuring that all electrochemical information is related to processes taking place on the surface of the bars. This procedure minimizes the risk of crevice that shielding the cross-sections with resin could seldom cause.…”

Welded, sandblasted, stainless steel corrugated bars in non-carbonated and carbonated mortars: A 9-year corrosion study

“…The typical forming process of corrugated bars causes microstructural transformations in the stainless steels [6,7). The microstructural characteristics of the reinforced bars explains the decrease of the corrosion resistance in simulated pore solutions that has been detected for stainless steels when they are corru gated (8).…”