Comparison Study on the Semiconductive and Dissolution Behaviour of 316L and Alloy 625 in Hydrochloric Acid Solution

Abstract

The corrosion behaviour of 316L and Alloy 625 was investigated using cyclic polarization, electrochemical impedance spectroscopy, X-ray photoelectron spectroscopy, Auger electron spectroscopy and induced coupled plasma-optical emission spectrometer. The results indicated that Alloy 625 showed better corrosion resistance than 316L and the prolonging immersion time could enhance corrosion resistance of the two alloys. The passive film formed on the surface of 316L exhibited an electronic structure of p-p heterojunction, with Fe 3 O 4 and Cr 2 O 3 enriched in the outer and inner layers, respectively. However, Alloy 625 presented the electronic structure of n-p heterojunction dominated by the outer Fe 2 O 3 /NiFe 2 O 4 and inner Cr 2 O 3 . This resulted in the opposite semiconductive properties of the passive films formed on the two materials. In the acid solutions, Fe and Mo suffered from selective dissolution while Cr and Ni were relatively stable. The corrosion rates were mainly dominated by the dissolution of iron. Alloy 625 presented better corrosion resistance than 316L due to the obviously lower content of Fe and the higher content of Cr and Ni in the passive film. The continuously selective dissolution of iron resulted in the increase in Cr/Fe ratio in the passive film, which was responsible for the enhancement in corrosion resistance.

Cavitation erosion-corrosion behaviour of Fe-19Cr-15Mn-0.66 N high nitrogen austenitic stainless steel in sodium chloride solution

“…The peaks of Cr 2p3/2 in figure 7(a) consist of three peaks, corresponding to metallic Cr (Cr-met, 574.2 eV), Cr 2 O 3 (576.6 eV) and Cr(OH) 3 (577.4 eV). Previous research has shown that the passive film on austenitic stainless steels in 3.5% solution is composed of Cr-met, Cr 2 O 3 and Cr(OH) 3 [4,38]. Feng et al [39] reported that Cr 2 O 3 has a lower point defect density and higher thermodynamic stability than Cr(OH) 3 , making it a more stable component of the passive film.…”

Modeling of the cathodic and anodic polarization curves of metals and alloys at an electronic level

“…This result is in good agreement with many results in the corrosion eld, i.e., a passive lm of stainless steel had a duallayer structure characterized by the inner layer enriched with Cr 2 O 3 and the outer layer enriched with Fe 2 O 3 . [42][43][44][45] For the cathode electron gain process, the main reaction is the hydrogen evolution reaction on the Cr-rich region. The total reaction formula is:…”

“…, a passive film of stainless steel had a dual-layer structure characterized by the inner layer enriched with Cr 2 O 3 and the outer layer enriched with Fe 2 O 3 . 42–45…”

Corrosion Behaviors of Fe-22Cr-16Mn-0.55N High-Nitrogen Austenitic Stainless Steel in 3.5% NaCl Solution

“…where Y 0 is a proportionality constant, j 2 = −1 and n is an empirical exponent between 0 and 1. When n = 1, CPE represents a pure capacitive element; when n = 0, CPE represents a resistor; and when n = 0.5, CPE represents Warburg impedance [38]. Figure 7 shows the equivalent circuit diagram used to fit the AC impedance spectrum.…”