Electrochemical and Microscopy Study of Localized Corrosion on a Sensitized Stainless Steel AISI 304

Abstract

Corrosion has been frequently recognized as failure's root cause for diverse engineering components like those associated to production lines, like in boiling water reactor piping systems (1). It is important that several electrochemical techniques help conjointly to elucidate some of the corrosion specificities, like localized corrosion of traditional materials. Pitting corrosion has been usually reported to affect stainless steels because it engages more frequent than not, second phase particles that precipitate out at the matrix and the grain boundary network, thereby consuming alloying elements that, for example, participate on sustaining passivity. Thermally-dependent fabrication operations such as welding bring about sensitization, particularly within the 450 to 700 ºC range. Exposure propitiates nucleation and growth of chromium carbide networks: this makes the boundaries and neighboring areas sensitive to depletion. Thus the precipitates are directly suspect of significant decrements in protective potential as the chromium has been chemically bound to carbon, thereby decreasing the surface passivating abilities. Therefore, the present work reports the electrochemical and microscopy results obtained after immersing the heat treated SS304 samples for diverse periods in a suitable electrolyte to studying their potentiodynamic polarization and EIS behaviors.

Electrochemical Corrosion Behaviour of Different Grades of WC-Co, High-Cr White Cast Irons and Hadfield Steel in 1 M Sulphuric Acid

“…The vertical black lines seen in Figure 11 c shows that the twin boundaries also suffered chemical attack during the polarisation test. The same mechanisms were reported by Garfias-Garcia et al [ 44 ] and Zhang and Zhu [ 45 ]. It is also noteworthy that there are large amounts of corrosion products that appeared as pits and craters after they were unintentionally delaminated during or after the electrochemical test.…”

“…It was reported by other researchers that the severely attacked surfaces were as a result of the protective passive layer being removed during the polarisation process, causing more damage to the exposed and unprotective surface [ 40 , 42 , 44 ].…”

“…The dark lines seen around the grain boundaries, metal-carbide inclusions and the non-metallic inclusion, such as sulphide inclusions, are regions that Garfias-Garcia et al [ 44 ] reported were caused by hydrogen penetrating deeper into the surface of the steel. Abreu et al [ 61 ] adds that areas such as grain boundaries, twin boundaries and non-metallic inclusions are regions where the accumulation of hydrogen is mostly seen during corrosion.…”

“…There are a few studies available on the corrosion behaviour of Hadfield steels in acidic media [ 40 , 41 , 42 , 43 ]. In their studies, Grajcar et al [ 40 ] reported that the substantial mass loss of high-manganese steel in 1 M H 2 SO 4 solution was due to the hydrogen depolarisation mechanism, which was subsequently accompanied by the local cracking of the previously formed product layer, resulting in the protective passive layer being removed during the polarisation process, causing further significant damage to the exposed and unprotected surface [ 42 , 44 , 45 ]. Moreover, MnS inclusions were reported to act as initiating sites of pitting corrosion in steels [ 41 ].…”

Electrochemical Impedance Spectroscopy (EIS): A Review Study of Basic Aspects of the Corrosion Mechanism Applied to Steels

“…An example of this outstanding property is the existence of several types of stainless steels that usually contains a significant proportion of chromium (12 to 25 wt.% Cr) with nickel and molybdenum to prevent the formation of ferrous hydroxide Fe 2þ þ 2OH À ! Fe OH ðÞ 2 rusting product ÀÁ by the presence of Cr in the Fe-base alloy, which reacts with oxygen from the environment to form a passive adherent oxide-layer (Cr 2 O 3 ), thus, given a remarkably resistance to corrosion attack of the underlying metal, additionally, this oxide layer, can be regenerated by itself in the presence of oxygen [4,[7][8][9]. Based on the fundamental concepts, one of the advantages of using stainless steel is its high corrosion resistance, but in combination with other alloying elements can provide good mechanical strength, making the steel an appropriate material to be used in diverse applications that, in many cases, offers the only alternative for its high durability in aggressive environments; its use can be seen in domestic (cutlery, blades, household appliances and electronics), architectural (structures, handrails, concrete reinforcing bars, building components, cables for bridges and coastal works), transport (automotive exhaust system, ship containers, waste trucks and tankers for chemicals), chemical (pressure vessels, chemical containers, pipes, chemical plants, waste-water treatment), oil/gas (platform structures, machinery, storage tanks and pipelines), medical (surgical instruments, implants, equipment, dental inserts, wire and brackets in orthodontics), and other common uses (food containers, beverage bottles, springs, fasteners, bolts, nuts, washers and wires) [10].…”