Corrosion behaviour of AISI type 304L stainless steel in nitric acid media containing oxidizing species

The corrosion behaviour of AISI type 304L stainless steel (SS) in different concentration of 0.01 M, 1 M and 5 M HNO₃ in presence of oxidizing ions at different temperatures has been evaluated. The main objective of this study is to assess the corrosion resistance of type 304L SS in non-radioactive conditions encountered during storage of liquid nuclear waste. Electrochemical impedance spectroscopy (EIS) and laser Raman spectroscopy (LRS) has clearly brought out the deleterious effect of oxidizing species on the passive film leading to increased corrosion along with increase in HNO₃ concentration and higher temperature.     

Soft X-ray absorption spectroscopy study of the effects of Si, Ce, and Mo ion implantation on the passive layer of AISI 304 stainless steel

The chemical modifications introduced in the passive layer of AISI 304 stainless steel after Si, Ce, and Mo ion implantation were investigated and compared with non-implanted steel by soft X-ray absorption spectroscopy. The influence of ion implantation on the passive properties was evaluated by measuring soft X-ray absorption spectra at the Cr, Fe, Ni, Mn and Si 2p in addition to oxygen 1s thresholds. All ion implanted samples show a relative Cr-enrichment at the surface as compared with non-implanted samples. Fe 2p as well as O 1s spectral changes reveal chemical differences in the passive layer as a function of the element ion-implanted.     

Electrochemical behaviour of high nitrogen stainless steel in acidic solutions

The electrochemical behaviour of high nitrogen stainless steel in acidic solutions was studied by potentiodynamic polarization, EIS, Mott-Schottky and XPS. The passive film formed in neutral NaCl solution was very stable, but the stability of the film decreased with the addition of H₂SO₄ into the solution. The passive film formed in acidic Na₂SO₄ has a superior protective ability than that in acidic NaCl solution. The stability of the film formed in tested solution decreased with increase of applied potentials. The film formed on steel surface was of n-type semiconductor. Chloride penetration mechanism was proposed for the observed passive film breakdown.     

Potentiodynamic polarization behaviour of AISI type 316 stainless steel in NaCl solution

Potentiodynamic polarization behaviour of AISI type 316 SS in NaCl solution was investigated in terms of the potential scan rate effect. The critical pitting potential, E_pit, of the stainless steel appeared to be strongly dependent on the potential scan rate. A cumulative anodic electric charge density of the steel was defined as the total charge density from the open circuit potential, E_ocp, and calculated using the potentiodynamic polarization curves. It was found that, plotted as a function of the polarization time, the values of the cumulative charge density consisted of two lines with different slopes. It was confirmed that the deflection of the cumulative charge density vs. time plots corresponded to E_pit and the values of the cumulative charge density at the deflection were little dependent on the applied scan rate. The cumulative charge density at the deflection was defined as a critical electric charge density for the stable pitting. Also, it was suggested that this electric charge density should be associated with the critical condition for the stable pitting and the critical electric charge for stable pitting should be a representative parameter for the pitting resistance of a material.     

Comparative study of structural and semiconducting properties of passive films and thermally grown oxides on AISI 304 stainless steel

A comparative study including structural characterization and semiconducting properties of passive and thermally grown oxides on AISI 304 stainless steel is performed by near field microscopy, Auger electron spectroscopy, capacitance measurements and photoelectrochemistry. This comparative investigation is performed on thermally grown oxides at different temperatures and passive films formed at different potentials. The results obtained by characterization techniques show that the thickness of both oxides increases with increasing formation temperature and potential and allow discussing grain size and surface roughness vs. formation temperature. Capacitance measurements reveal semiconducting behavior of both iron and chromium oxides constituting whole passive and thermal oxides. These results allow extracting and discussing space charge layer thickness and doping densities of iron and chromium oxides in relation with formation conditions. The photocurrent results show a variation of the quantum efficiency with formation temperature and potential and a constant band gap value whatever the nature of the considered film. The variation of the quantum efficiency with applied potential in accordance with Pool–Frenkel model allow extracting and comparing donor densities with those obtained by capacitance measurements.     

Effect of sulphide on the corrosion behaviour of AISI 316L stainless steel and its constituent elements in simulated Kraft digester conditions

The electrochemical behaviour of AISI 316L steel and its constituent metals in simulated Kraft digester white liquor at 170 °C has been studied by registering slow scan rate voltammograms and impedance spectra at the corrosion potential. Interpretation of the results in terms of two approaches - the Mixed-Conduction Model for passive films and a two-step dissolution reaction - allowed for the estimation of corrosion currents and polarisation resistances as depending on the material and electrolyte medium. Tentative conclusions on the effect of sulphur-containing species in the white liquor on the corrosion mechanism of the studied materials are drawn.     

Nanostructure and local properties of oxide layers grown on stainless steel in simulated pressurized water reactor environment

The morphology and local electrical resistance of duplex oxide films formed on 316L stainless steel at 325 °C in simulated primary coolant of pressurized water reactor have been investigated at the nanometre scale with Conductive Atomic Force Microscopy. The electrical resistance varies over ∼1 order of magnitude for most oxide grains and over 2–3 orders of magnitude locally at grains and grain boundaries. This is rationalized in terms of local variation of the composition and thus resistivity of the mixed Fe(II)–Cr(III) barrier inner layer of the oxide films with grain boundaries of the outer layer possibly promoting Cr(III) enrichment.     

Effects of dithionite ion on corrosion of type 304 stainless steel in sulphuric acid solution

Corrosion behaviour of type 304 stainless steel was investigated, with particular attention to additive effects of hydrosulphite (Na₂S₂O₄) on corrosion in 0.1 mol/l H₂SO₄ solution with various amounts of Na₂S₂O₄ up to 60 mmol/l.Corrosion of SUS304 occurred below pH 3.0 at 30 °C in a 0.1 mol/l H₂SO₄ solution in which Na₂S₂O₄ was added to 0.1-20 mmol/l. The maximum corrosion rate at 30 °C was measured as 7.2 g/m² h (7.9 mm/y) in 0.1 mol/l H₂SO₄-10 mmol/l Na₂S₂O₄ at pH 1.2. Microscopic surface observation revealed that active dissolution was accompanied by intergranular corrosion at the metal surface.The SUS304 was easily passivated in 0.1 mol/l H₂SO₄ solution with more than 30 mmol/l Na₂S₂O₄. NiS was detected in the passivated film.     

Corrosion behavior of TiC particle-reinforced 304 stainless steel

TiC particle-reinforced 304 stainless steels were prepared using a new developed in situ technology and their corrosion behavior was compared with that of 304SS in 5 wt.% HCl solution. As compared to 304SS, E_corr, E_pit and E_rp values had shifted to a more negative region in 304SS containing TiC, indicating faster corrosion rate by TiC addition. The addition of TiC particles to 304SS resulted in no rapid pit propagation but maintained a high corrosion rate in the whole immersion time investigated.     

Surface chemistry and corrosion behaviour of 304 stainless steel in simulated seawater containing inorganic sulphide and sulphate-reducing bacteria

Although many studies have been carried out regarding the role of sulphide anions in promoting microbial corrosion of various metal substrates, very little is known about the differences between inorganic sulphide and biogenically-derived sulphide by sulphate-reducing bacteria (SRB) and what the reasons for differing corrosion behaviour between the two types of sulphide may be towards common metals. In this study, various electrochemical and surface analytical techniques were employed to study the effect of the inorganic and biogenic sulphide (active SRB present) on the surface chemistry and corrosion behaviour of 304 stainless steels in a simulated seawater-based modified Baar’s (SSMB) medium. Clear differences in the surface chemistry of the sulphurised passive film by inorganic and biogenic sulphide (active SRB present) were quantified by X-ray photoelectron spectroscopy (XPS). The transformation of metal sulphides in abiotic and biotic sulphide solutions with the exposure time was correlated with different corrosion behaviour of 304 stainless steels.     

The semiconducting properties of passive films formed on AISI 316 L and AISI 321 stainless steels: A test of the point defect model (PDM)

The semiconductor properties of passive films formed on AISI 316L in 1 M H₂SO₄ in three temperatures and AISI 321 in 0.5 M H₂SO₄ were studied by employing Mott–Schottky analysis in conjunction with the point defect model (PDM). Based on the Mott–Schottky analysis in conjunction with PDM, it was shown that the calculated donor density decreases exponentially with increasing passive film formation potential. Also, the results indicated that donor densities increased with temperature. By assuming that the donors are oxygen ion vacancies and/or cation interstitials, the diffusion coefficients of the donors for two stainless steels are calculated.     

Atomic Force Microscopy, Scanning Kelvin Probe Force Microscopy and magnetic measurements on thermally oxidized AISI 304 and AISI 316 stainless steels

Thermally oxidized AISI304 and AISI316 stainless steels are studied by Atomic Force Microscopy, Scanning Kelvin Probe Force Microscopy (SKPFM) and Magneto-Optical Kerr effect as a function of their growth temperature. The surface roughness is a competition between the roughness of the bare substrate and the roughness resulting from the oxide layer growth. Cr oxide is present at some places on the surface at low growth temperature as shown by SKPFM. The observed decrease of surface potential with the oxide layer thickness indicates an effective protection against corrosion. Magnetic measurements demonstrate that the outer layer contains a magnetite phase (in-plane magnetization).     

Corrosion resistance of welds in type 304L stainless steel made with a nickel-copper-ruthenium welding consumable

Ni-Cu-Pd welding consumables have been recently developed for 300-series austenitic stainless steels such as Type 304L (SS304L) to reduce the amount of Cr(VI) in the welding fumes. In this study, a modified filler metal that replaces Pd with Ru was evaluated. Initial tests conducted on button-melted samples and bead-on-plate welds indicated that Ni-Cu-Ru exhibited good corrosion properties. Actual Ni-Cu-Ru arc welds made on SS304L were successfully produced and the corrosion performance was comparable to or better than that of Ni-Cu-Pd welds. These welds are a suitable replacement for welds made with standard 300-series welding consumables, such as SS308L.     

Corrosion and passivation of low-temperature nitrided AISI 304L and 316L stainless steels in acidified sodium sulphate solution

304L and 316L steels were nitrided at 425 °C for 30 h and examined at various depths in 0.1 M Na₂SO₄ acidified to pH 3.0. In the near-surface region with about 7-14 wt% N, at potentials of active state anodic currents were much higher than those for untreated steels, whereas in deeper regions with <7 wt% N the currents were only slightly increased in comparison with untreated steels or they were even lower in passive and transpassive states. Surface films were composed of oxygen-containing species on top and of Cr-N species in deeper layers. It is suggested that strong corrosion of near-surface regions is associated with nitride precipitates. Beneficial effect of low nitrogen concentrations can be due to initially accelerated corrosion which leads to larger amounts of passivating species and to the accumulation of corrosion resistant chromium nitrides.     

Hydrogen effects on stainless steel passive film fracture studied by nanoindentation

Hydrogen effects on the fracture stress of passive film formed on 316L stainless steel were studied by nanoindentation. Hydrogen accumulated primarily on the sample surface and in the passive film. Displacement excursion related to film fracture appeared in load-controlled load–displacement curves when electrochemically polished and anodically passivated samples were indented. The excursion disappeared after the passivation film was removed electrochemically or by nanowear. The critical load, excursion depth and length decreased with higher hydrogen concentration, along with Young’s modulus and fracture stress of the passive film.     

High corrosion resistance of austenitic stainless steel alloyed with nitrogen in an acid solution

Passivity of austenitic stainless steel containing nitrogen (ASS N25) was investigated in comparison with AISI 316L in deareated acid solution, pH 0.4. A peculiar nature of the passivation peak in a potentiodynamic curve and the kinetic parameters of formation and growth of the oxide film have been discussed. The electronic-semiconducting properties of the passive films have been correlated with their corrosion resistance. Alloying austenitic stainless steel with nitrogen increases its microstructure homogeneity and decreases the concentration of charge carriers, which beneficially affects the protecting and electronic properties of the passive oxide film.     

Corrosion of 304 stainless steel exposed to nitric acid-chloride environments

In an effort to examine the combined effect of HNO₃, NaCl, and temperature on the general corrosion behavior of 304 stainless steel (SS), electrochemical studies were performed. The corrosion response of 304 SS was bifurcated: materials were either continuously passive following immersion or spontaneously passivated following a period of active dissolution. Active dissolution was autocatalytic, with the corrosion rate increasing exponentially with time and potential. The period of active corrosion terminated following spontaneous passivation, resulting in a corrosion rate decrease of up to five orders of magnitude. The length of the active corrosion period was strongly dependent on the solution volume-to-surface area ratio. This finding, coupled with other results, suggested that spontaneous passivation arises solely from solution chemistry as opposed to changes in surface oxide composition. Increasing NaCl concentrations promoted pitting, active dissolution upon initial immersion, a smaller potential range for passivity, longer active corrosion periods, larger active anodic charge densities preceding spontaneous passivation, and larger corrosion current and peak current densities. In contrast, intermediate HNO₃ concentrations promoted active dissolution, with continuous passivity noted at HNO₃ concentration extremes. During active corrosion, increased HNO₃ concentrations increased the anodic charge density, corrosion current density, and peak current density. The time required for spontaneous passivation was greatest at intermediate HNO₃ concentrations. Susceptibility to pitting was also greatest at intermediate HNO₃ concentrations: the pit initiation and repassivation potentials decreased with increasing HNO₃ concentration until the HNO₃ concentration exceeded a critical concentration beyond which susceptibility to pitting was entirely eliminated. Increasing solution temperature increased the susceptibility to both pitting and active dissolution.     

Hydrogen-assisted fatigue crack growth of AISI 316L stainless steel weld

The fatigue crack growth behaviors of AISI 316L stainless steel (SS) welds in air and gaseous hydrogen were evaluated, and further compared with the base plate. In air, the fatigue crack growth rate (FCGR) of the weld after heat-treatment at 1050 ^oC/1 h was similar to that of the base metal. Furthermore, all specimens became susceptible to hydrogen-accelerated crack growth. Mainly quasi-cleavage fracture related with the strain-induced martensite accounted for the accelerated crack growth in hydrogen. A smaller amount of martensite in the weld was responsible for the decreased susceptibility to hydrogen-enhanced fatigue crack growth relative to the base metal.     

Corrosion characteristics of polyaniline-coated 316L stainless steel in sulphuric acid containing fluoride

The corrosion resistance of conducting polyaniline (PANi) coatings deposited on 316L stainless steel (316L SS) at various cycle numbers of cyclic voltammetry (2-, 3- and 4-cycles) by electro-polymerization in sulphuric acid solution containing fluoride was investigated by electrochemical techniques. The corrosion resistance of the 316L SS substrate was considerably improved by the PANi coating. The increase of the cycle number of cyclic voltammetry increased the thickness and enhanced the performance of the PANi coating due to low porosity.