Initiation Mechanism of Localized Corrosion Induced by Al2O3-MnS Composite Inclusion in Low-Alloy Structural Steel

Abstract

The present work systematically investigated the initiation mechanism of localized corrosion induced by Al2O3-MnS composite inclusion in E690 steel under a simulated marine environment. The results showed that a micro-gap exists between the Al2O3-MnS inclusion and the matrix, and electron backscattered diffraction (EBSD) analysis revealed significant lattice dislocation zones around the Al2O3-MnS composite inclusion. The presence of the micro-gap and the lattice dislocation both promoted the localized corrosion initiation. The Volta potential of Al2O3 detected by scanning Kelvin probe force microscopy (SKPFM) was approximately 149.33 mV higher than that of the steel matrix, and the Volta potential of MnS was 10 mV lower than that of the steel matrix. The current-sensing atomic force microscopy (CSAFM) results showed that the Al2O3 was not conductive, while the MnS had good conductive properties. Therefore, it was not possible for a galvanic couple to be formed between Al2O3 and the adjacent steel matrix. A galvanic couple effect between the MnS and the adjacent steel matrix was directly demonstrated for the first time. The MnS acted as the anode phase for preferential dissolution in the corrosion process. The in situ immersion experiments and the Pourbaix diagram results confirmed that the dissolution of MnS was an electrochemical reaction process and the dissolution of Al2O3 was a chemical reaction.

Effect of Ca and Sb on the Corrosion Resistance of E690 Steel in Marine Atmosphere Environment

“…The slatted bainite organization of the E690 alloy fine-tuned steel, which consists of fine M/A island particles arranged in an orderly manner, may have contributed to its superior corrosion resistance compared to the traditional ferrite + pearlite organization found in weathering steel [41]. The results also suggest that the corrosion activity of 2# steel is initially slightly higher than that of 1# steel but becomes significantly lower with prolonged immersion time.…”

A critical review of the recent advances in inclusion-triggered localized corrosion in steel

“…After a series of immersion tests and characterizations, it was found that MnS did preferentially dissolve (the signals of Mn and S elements cannot be detected after 15 min immersion in an aggressive solution). Nevertheless, the localized corrosion triggered by inclusions did not terminate, especially the detection signals of Al and O elements were weak after immersion for 30 min, which fully 16,21 .…”

“…As depicted in Fig. 14, a Al 2 O 3 -MnS complex inclusion-triggered localized corrosion system involved in some investigations is a representative case in terms of the above situation 16,21 . Volta potential measurement and conductivity test determine the insulating properties of Al 2 O 3 , and also confirm the illustration in Section 3.2 that conductive MnS inclusions often act as an anode in stainless steel (Fig.…”

“…1 15 , since it is widely perceived that miniature galvanic cells are prone to be formed in these places due in large part to potential difference between defects and adjacent metal matrix thanks to the heterogeneity in element composition or the discontinuity of surrounding passive film [16][17][18][19][20] . Controversies still exist, though, doubts regarding the applicability of traditional galvanic coupling theory on deciphering localized corrosion triggered by internal defects in metallic materials, particularly the inclusion-induced selective dissolution in steel, was recently raised again by scholars based on some unexpected evidence, which evinces that overwhelmingly used traditional mechanism can sometimes fail in practice and reminds us that our mechanistic understanding for some inherent phenomena is still rudimentary [21][22][23][24][25][26] .…”

Effect of addition of alumina and rare-earth oxide particles on the corrosion resistance and mechanism of low carbon low alloy steel

“…For the Al 2 O 3 and RE oxide particles that participate in the initial pitting corrosion, although micro acidic region can be generated [4,35], Cu is not enriched or less enriched due to their small number and immovable Cu atoms, as shown in figures 13(a) and (b). For Al 2 O 3 particles that do not participate in the initial pitting corrosion, a micro acid region cannot be formed around them owing to their high stability [4,33,40]; thus, Cu is not enriched (figure 13(c)). However, RE oxide particles that do not participate in the initial pitting corrosion can decompose and a micro acid region is formed [35]; therefore, Cu is enriched (figure 13(d)).…”