Corrosion behaviour of nanocomposite TiSiN coatings on steel substrates

Nanocomposite TiSiN coatings were deposited on tool steels. Detailed mechanisms that govern the corrosion of these coated steels were revealed, following immersion tests in a 70% nitric acid solution. Pitting originated preferentially from coating defect sites and expanded with increasing immersion time. Both Young’s modulus and hardness measured by nanoindentation decreased as the corrosion damage intensified. A thin oxide layer formed from the thermal annealing of the as-deposited samples at 900 °C was found to be effective against corrosive attack. In addition, compressive residual stress was noted to suppress the propagation of corrosion-induced cracks. The role of residual stress in controlling the corrosion resistance of these ceramic-coated steels is clarified by finite element analysis.     

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.     

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.     

Weld oxide formation on lean duplex stainless steel

Weld oxides have a strong influence on corrosion resistance, but have hitherto only been studied to a limited extent for duplex stainless steels. X-ray photoelectron spectroscopy (XPS) has here been used to study heat tint formed on gas tungsten arc (GTA) welds on the commercial duplex grades LDX 2101 (EN 1.4162/UNS S32101) and 2304 (EN 1.4362/UNS S32304) welded with and without nitrogen additions to the shielding gas. The process of heat tint formation is discussed in terms of transport phenomena to explain the effect of atmosphere, temperature and composition. The oxides formed were found to be enriched in manganese and corrosion testing shows that nitrogen has a strong influence on the weld oxide. A mechanism is proposed including evaporation from the weld pool and subsequent redeposition.     

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.     

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.     

Fabrication of continuous mesoporous organic–inorganic nanocomposite films for corrosion protection of stainless steel in PEM fuel cells

The organic–inorganic composite film was deposited on the 304 stainless steel as bipolar plate material for proton exchange membrane fuel cells by spin-coating method. As shown by XRD, N₂ adsorption–desorption and TEM, the composite films exhibit ordered mesoporous structures. The corrosion tests in 0.5 M H₂SO₄ system displayed that, compared with 304SS, the composite films made corrosion potential shifted to positive direction by 250–1000 mV (SCE) and corrosion current decreased by 1–3 orders of magnitude. Wherein, the C-50–60% composite film showed the optimal protective performance, its corresponding potentiostatic polarization process was extremely stable in the simulated fuel cells environment.     

Corrosion behaviour of corrugated lean duplex stainless steels in simulated concrete pore solutions

This work studies the corrosion behaviour of two corrugated lean duplex stainless steels (SAF 2001 and 2304 grades) in eight alkaline solutions (carbonated and non-carbonated, saturated Ca(OH)₂ solutions with different chloride contents). 2001 stainless steel is a new grade in market because of its composition. 2304 is a grade previously studied under different conditions. However, its use as reinforcement in concrete is new. Studies are carried out by polarization curves following scanning electronic microscopy (SEM) and optical observations. Results are compared to those of carbon steel and austenitic AISI 304 and duplex SAF 2205 under similar conditions. After corrosion tests in alkaline media with chloride, ferrite tends to corrode selectively in 2304 duplex, while austenite corrodes selectively in 2001 under the same conditions. The influence of the duplex microstructure on attack development and morphology is analyzed. The electrochemical parameters obtained from the polarization curves suggest 2001 could replace 304 keeping the structure its corrosion performance (and with clear economical advantages). 2304 shows better corrosion behaviour than the more expensive 304, but somewhat lower than the excellent behaviour shown by 2205.     

The effect of large heat input on the microstructure and corrosion behaviour of simulated heat affected zone in 2205 duplex stainless steel

In the simulated heat affected zone of 2205 duplex stainless steels, effects of large welding heat inputs on the microstructure and corrosion behaviour were investigated. Reformed austenite content increased with the coarsening of grain boundary austenite (GBA) and the growth of intragranular austenite (IGA) and Widmanstatten austenite (WA), thus improving the low temperature toughness and affecting corrosion state. Reduction of chromium nitrides contributed to better resistance to pitting corrosion. Moreover, the pitting corrosion and intergranular corrosion were improved resulting from the formation of more GBA and WA. The specimen with a Δt_8/5 of 100 s presents better comprehensive performance.     

Anodic behaviour of stainless steel S43000 in concentrated solutions of sulphuric acid

Electrochemical, AES and XPS techniques were employed to characterize the anodic behaviour of S43000 stainless steel in concentrated sulphuric acid (90.0-96.4 wt.%). Electrochemical experiments showed that passivity is not spontaneous and requires anodic polarization in the acids studied. Rotating cylindrical electrode experiments showed that the corrosion rate is controlled by the mass transfer rate of FeSO₄ from a saturated surface salt. AES and XPS analyses provided evidence that passivity involves the formation of a chromium-rich oxide-hydroxide film. The passivation mechanism and passive state stability are considered to relate to the manner in which undissociated H₂SO₄ molecules participate in the corrosion process. The findings have meaningful implications regarding the development of more corrosion resistant stainless steels for acid service.     

IGSCC crack growth in simulated BWR environment – Effect of nitrogen content in non-sensitised and warm rolled austenitic stainless steel

Effect of nitrogen level in strain hardened stainless steel (SS) on crack growth rate (CGR) in simulated boiling water reactor conditions has been the focus of this study. Type 304 LN stainless steel has been used in a warm rolled condition containing two different levels of nitrogen. Clear intergranular (IG) fracture was observed in both the stainless steels. The CGR increased 3 times in the stainless steel with higher level of nitrogen at all levels of dissolved oxygen and this was related to the increase in yield strength due to rolling and dynamic strain aging (DSA).     

Corrosion behaviour of low temperature plasma carburised 316L stainless steel in chloride containing solutions

The electrochemical corrosion behaviour of the carburised (expanded austenite) layer on 316L austenitic stainless steel produced by low temperature plasma carburising has been studied in 0.5 M NaCl and 0.5 M HCl + 0.5 M NaCl solutions. The present work focuses on the variation of the corrosion behaviour of the carburised layer with depth from the surface and the effect of carbon concentration on electrochemical behaviour. The results show that the carburised layer has excellent resistance to localised corrosion. There exists a critical carbon concentration, above which the expanded austenite possesses excellent resistance to both metastable pit formation and pit growth.     

Corrosion potential oscillations of nickel-containing stainless steel in concentrated sulphuric acid: II Mechanism and kinetic modelling

In the current work, the mechanism for oscillations in mixed potential of UNS S30403 Stainless steel in concentrated sulphuric acid is refined to clarify the importance of the stability limit of nickel sulphide in relation to the passivation potential of the steel. It is rationalized that the oscillation of the corrosion potential can occur spontaneously only when the nickel sulphide stability limit lies within a specific potential range above the passivation potential of the steel and below the tangent for re-activation. Two possible kinetic models are proposed and contrasted to illustrate which better explains the potential-time behaviour for depassivation.     

Effects of inclusions on the precipitation of chi phases and intergranular corrosion resistance of hyper duplex stainless steel

During the initial stage of aging heat treatment at 850 °C, inclusions such as (Cr, Mn, Al) oxides and (Cr, Mn, Al, Fe) oxides of a hyper duplex stainless steel act as preferential precipitation sites for the chi phase like ferrite/austenite phase boundaries and ferrite/ferrite grain boundaries. The chi phase is precipitated around the inclusions due to the blocking and piling up the alloying elements such as Mo and W around the inclusions. The precipitation of Mo and W enriched chi phase around the inclusions decreases the intergranular corrosion resistance due to the formation of Mo and W depleted zones.     

Corrosion behaviour of vacuum induction-melted Ni-based alloy in sulphuric acid

A vacuum induction-melted (VIM) Ni-based alloy was immersed in 60% H₂SO₄ solution to investigate its corrosion behaviour and resistance. The results indicate that the microstructure contains a γ-Ni solid solution + Ni₃Si particles, dendrite Ni₃Si, Ni₃B, Cr₇C₃, and CrB. The corrosion started at the zones of the γ-Ni solid solution + Ni₃Si particles and dendrite Ni₃Si. These zones transformed to oxide films and protected the alloy from significant attack. However, the pitting corrosion created paths for acid solution and/or to further attack. Therefore, the corrosion rate decreased and then stabilised at a high value as the immersion time increased.     

Electrochemical behaviour of duplex stainless steels in caustic environment

Recent studies have shown that duplex stainless steels can be susceptible to general corrosion and stress corrosion cracking in high pH caustic environments. This difference in the corrosion resistance can be attributed to changes in the electrochemical behaviour of steels. The present study has shown that the corrosion rates of duplex stainless steels increase with an increase in temperature and sulphide addition to caustic environments. Moreover, alloying Fe with Cr and Ni helps to raise the corrosion potential and lower critical current density of DSS in an alkaline environment whereas Mo can be detrimental to the corrosion resistance of the steel.     

Corrosion behaviour of intermetallic aluminide coatings on nitrogen-containing austenitic stainless steels

The present work reports the effect of aluminide layers on the aqueous corrosion behaviour of four different 316L stainless steels containing various nitrogen contents (0.015%, 0.1%, 0.2% and 0.56% N). Diffusion annealed aluminide layers are generated over the surface by heat treatment of the aluminium precoated alloys at 750 °C for 25 h in nitrogen atmosphere. X-ray diffraction patterns of the surface modified samples showed the presence of AlN, Al₁₃Fe₄ and FeAl₂ phases. Diffusion of aluminum into the alloy, and the formation of AlN by the reaction of aluminium with matrix nitrogen, was identified using secondary ion mass spectrometry (SIMS). The nitrogen peak in the diffused layer was found to increase with increasing nitrogen content of the base alloy. SEM observation of cross-sectionally mounted alloys showed the presence of spherical AlN phase in addition to iron aluminide intermetallic phases. The role of such a composite surface layer containing intermetallic aluminides and nitride on the corrosion resistance of austenitic stainless steels in 0.5 M NaCl and 0.5 M sulphuric acid is discussed in greater detail based on open circuit potential (OCP)–time measurements, potentiodynamic polarisation studies and electrochemical impedance spectroscopy (EIS) investigations. The aluminide layered alloy with 0.1% N content showed better corrosion performance. The presence of nitrogen was found to have a positive effect in enhancing the hardness of the composite layer. Role of matrix nitrogen on the microstructure and microchemical distribution at the surface, and its role on corrosion resistance in acidic and chloride media are discussed in detail.     

Effect of niobium on the corrosion behaviour of low alloy steel in sulfuric acid solution

This study examines the effect of niobium (Nb) addition on the electrochemical properties of low alloy steel using electrochemical techniques in a 10 wt.% sulfuric acid solution as well as surface analysis techniques. The potentiodynamic test reveals the passive behaviour of all specimens and a decrease in the passive currents with increasing Nb content. Electrochemical impedance spectroscopy (EIS) shows that the Nb-containing steels have higher passive and charge transfer resistance than the control samples. These results suggest that the interaction of elements improves the corrosion resistance of low alloy steel due to the formation of Nb, C, S, P, and Fe products on the surface.     

Effect of annealing temperature on the corrosion behavior of duplex stainless steel studied by in situ techniques

The effects of the annealing temperature on the microstructure and the corrosion behavior of duplex stainless steel 2507 were investigated by means of magnetic force microscopy (MFM), scanning Kelvin probe force microscopy (SKPFM), atomic force microscopy (AFM) and scanning electron microscopy (SEM). The SEM results indicated that the volume fraction of the austenite phase decreased with the increased annealing temperature. SKPFM/MFM measurements conducted in air at the room temperature and an ambient relative humidity of about 25% showed a higher Volta potential of the paramagnetic austenite than that of the ferromagnetic ferrite. The in situ AFM observation in a hydrochloric acid solution provided solid evidence that corrosion preferentially occurred in the ferrite phase. The sample annealed at 1100 °C exhibited a greater Volta potential difference between the ferrite and austenite and a higher corrosion rate in the ferrite, while that annealed at 1150 °C had a smaller Volta potential difference and a lower corrosion rate. The relative nobility and microstructure change of two phases, as well as their corrosion behavior, can be explained by the effect of the composition of alloying elements.     

Investigation on carbon dioxide corrosion behaviour of HP13Cr110 stainless steel in simulated stratum water

The carbon dioxide corrosion behaviour of HP13Cr110 stainless steel in simulated stratum water is studied by potentiodynamic curve and electrochemical impedance spectroscopy (EIS); the micro-structure and composition of the corrosion scale formed at high-temperature and high-pressure are analyzed by scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The results show that 13Cr stainless steel is in passive state in the stratum water, the passive current density increases and the passive potential region decreases with increasing temperature. The corrosion scale formed at high-temperature and high-pressure is mainly composed of iron/chromium oxides and a little amount of FeCO₃.