Role of alloyed copper on corrosion resistance of austenitic stainless steel in H2S–Cl− environment

Corrosion test, surface analysis and thermodynamic calculation were carried out in the H₂S–Cl⁻ environments to clarify the role of alloyed Cu on the corrosion resistance of austenitic alloys. The alloyed Cu improved pitting corrosion resistance in the H₂S–Cl⁻ environment. The surface film of Cu-containing alloy indicated double layer consists of copper sulfide and chromium oxide, and the copper sulfide was able to exist stably compared to iron sulfide and nickel sulfide. It is concluded that the copper sulfide would enhance the formation of chromium oxide film which improve the pitting corrosion resistance in the H₂S–Cl⁻ environment.     

The effects of metal binder content and carbide grain size on the aqueous corrosion behaviour of TiC–316L stainless steel cermets

The room temperature electrochemical response of TiC-based cermets, with 10 to 30 vol.% 316L stainless steel binder and either fine- or coarse-grained TiC, has been investigated in an aqueous 3.5 wt.% NaCl solution. The assessment methods included Tafel extrapolation, in combination with potentiodynamic and potentiostatic polarisation. Corroded samples were characterised using SEM, with post-corrosion solutions analysed using ICP-OES. The highest corrosion resistance was achieved at the lowest binder contents, while those with a more coarse-grained structure generally showed superior resistance, due to a reduced TiC–316L interfacial area. Preferential dissolution of the steel binder was observed, leaving the TiC essentially unaffected.     

Stress corrosion cracking at constant load of 304L stainless steel in molten NaCl-CaCl2 at 570°C

The incubation and propagation times of cracks in 304L in molten NaCl-CaCl₂ at 570°C were related to the applied stress value, from creep and creep rate curves. Rest potential versus time curves were recorded simultaneously. The results showed intergranular stress corrosion cracking. When the temperature was kept at 570°C, precipitation of chromium carbide M₂₃C₆ which promoted cracking propagation, was induced. Determination of the crack rate shows that anodic dissolution at the bottom of the cracks is the main process during the stress corrosion crack propagation of 304L stainless steel in the stress range used.     

Degradation behavior of stainless steel in PbO–CaO–SiO2 slag in the presence of sulphur

Five stainless steel grades are subjected to PbO–CaO–SiO₂–S slag at 1200 °C. The degradation phenomena are identified as liquid slag and liquid metal corrosion, oxidation and sulphidation. The relation between sulphidation and steel and slag composition is discussed. For the slag with the lowest PbO/SiO₂ ratio, sulphidation is mainly recognized through (Fe, Cr)_xS_1?x at the surface and in the subsurface of the steel, especially for the steel grades with the lowest Cr content. For the slag with the highest PbO/SiO₂ ratio, sulphidation is mostly pronounced in the steel grades with the highest Ni content through the formation of a liquid (Ni, Pb, S) phase.     

Electrodeposition of multi-layer Pd–Ni coatings on 316L stainless steel and their corrosion resistance in hot sulfuric acid solution

Pd–Ni coating shows good corrosion resistance in strong corrosion environments. However, in complex aggressive environments, the performance of the coatings is limited and further improvement is necessary. The effects of the applied plating current density on the composition, structure and properties of Pd–Ni coatings were studied. By changing the current density in the same bath, multi-layer Pd–Ni coatings were prepared on 316L stainless steel. Scanning electronic microscopy, weight loss tests, adhesion strength, porosity and electrochemical methods were used to study the corrosion resistance of the films prepared by different coating methods. Compared with the single layer Pd–Ni coating, the multi-layer coatings showed higher microhardness, lower internal stress, lower porosity and higher adhesive strength. The multi-layer Pd–Ni coating showed obviously better corrosion resistance in hot sulfuric acid solution containing Cl^?.     

Corrosion behaviour of Ti DLC deposition on prenitrided 316L stainless steel and Ti–6Al–4V alloy

Abstract

316L and Ti–6Al–4V are widely used as biomaterials and materials of various mechanical components. In biomedical applications, they are used to manufacture coronary and pulmonary stents, hip prosthesis, screws and external fixations. However, Cr, Al and V are released from the alloys to the body environment and these ions mix into the blood stream. Release of even small amounts of these ions may cause local irritation of the tissues surrounding the implant. This situation may be prevented by applying suitable surface treatments to the biomaterials. The overall objective of the present paper is to examine the corrosion properties of duplex treated (nitrided and with a diamond-like carbon coating) 316L stainless steel and Ti–6Al–4V alloy. Diamond-like carbon films were deposited on nitrided samples using closed field unbalanced magnetron sputtering system. The corrosion behaviour of duplex treated samples was tested using the potentiodynamic method in ringer’s solution at 37°C. The corrosion resistance of duplex treated samples was significantly improved in comparison with the uncoated and single treated samples. In addition, the corroded surfaces were investigated by SEM where small pits were observed on all samples.     

Study of the pitting corrosion of superduplex stainless steel and X-65 carbon steel during erosion–corrosion by cyclic polarisation technique

Erosion-enhanced corrosion behaviour of X-65 carbon steel and UNS S32750 superduplex stainless steel was investigated by electrochemical cyclic polarisation. The tests were performed using a jet slurry device coupled with a potentio-galvanostat at various jet velocities of 4, 6.5 and 9?m?s^?1 and impingement angles of 30 and 90? in a 3.5?wt-% NaCl water containing 6?wt-% silica sand particles. The results showed that increasing the jet velocity and impingement angle increased the corrosion rate of both alloys. Negative hysteresis and greater E_rp than OCP were observed for superduplex stainless steel in all erosion–corrosion conditions that indicated the pitting resistance of the alloy. However, the low resistance of carbon steel against pitting during erosion–corrosion was demonstrated by positive hysteresis in the cyclic polarisation curves as well as SEM images of the eroded surfaces.     

Preconditioning of AISI 304 stainless steel surfaces in the presence of flavins—Part I: Effect on surface chemistry and corrosion behavior

Stainless steel AISI 304 surfaces were studied after a mild anodic polarization for oxide growth in the presence and absence of two derivatives of vitamin B2 (riboflavin and flavin mononucleotide) that can be secreted by metal-reducing bacteria and act as a chelating agent for iron species. The alterations in oxide chemistry were studied by means of surface-sensitive techniques such as X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectrometry analysis. The complementary electrochemical characterization revealed a preferential growth of an oxide/hydroxide iron-rich film that is responsible for an altered pit initiation and nucleation behavior. These findings suggest that as the corrosion behavior is determined by the interplay of the chemical and electronic properties, only a mild anodic polarization in the presence of redox-active molecules is able to alter the chemical and electronic structure of the passive film formed on stainless steel AISI 304. This helps to achieve a profound understanding of the mechanisms of microbially influenced corrosion (MIC) and especially the possible effects of the redox-active biomolecules, as they may play an important role in the corrosion susceptibility of stainless steel surfaces.     

Enhanced high-temperature corrosion resistance of (Al2O3–Y2O3)/Pt micro-laminated coatings on 316L stainless steel alloy

A 7-layer (Al₂O₃–Y₂O₃)/Pt micro-laminated coating was successfully prepared on 316L stainless steel alloy by magnetron sputtering. High-temperature cyclic oxidation and hot corrosion tests were adopted to investigate the high-temperature corrosion resistance of the coating. It is revealed that the (Al₂O₃–Y₂O₃)/Pt micro-laminated coating which effectively suppressed the inward diffusion of oxygen and corrosive fused salt to an extremely low level can significantly improve the high-temperature corrosion resistance of alloy substrate. The great mechanical properties of such coating were attributed to the brittle/ductile laminated composite structure by means of multilayer toughening and release mechanisms.     

Electrical mapping of AISI 304 stainless steel subjected to intergranular corrosion performed by means of AFM–LIS in the contact mode

The paper presents results of the AFM-based approach to local impedance spectroscopy (LIS) measurements performed in a 20 × 20 μm grid within an austenite grain–grain boundary region for sensitized AISI 304 stainless steel (SS). Maps of electrical parameters obtained on the basis of localized impedance spectra were demonstrated, presenting their changes and correlation with the sample topography. Performed research revealed significant differences in the electrical distribution of the contact resistance considered as the passive layer resistance and contact capacitance considered as the passive layer capacitance determined for austenite grain interiors and austenite grain boundaries affected by intergranular corrosion.     

Effect of friction stir and activated-GTA welding processes on the 9Cr–1Mo steel to 316LN stainless steel dissimilar weld joints

ABSTRACT

The consequence of friction stir welding (FSW) and activated-gas tungsten arc welding (A-GTAW) processes on the evolution of microstructure and mechanical properties of 9Cr–1Mo (P9) steel to 316LN stainless steel dissimilar weld joint is investigated. The FSW specimen shows considerably higher tensile strength (～652?MPa) compared to A-GTAW specimen (～595?MPa) as well as its base metal of P9 (～642?MPa) and 316LN (～608?MPa) owing to the formation of tempered martensite and refined austenite in P9 and 316LN weld portion, respectively. The cross-weld tensile test revealed that the specimens failed in the base metal of 316LN SS for both FSW and A-GTAW process with ductile mode fracture. This study proves that FSW could be an alternate joining technique.     

Microstructure and corrosion behaviour of ferritic steel–Zr-based metal waste form alloys in simulated ground water

ABSTRACT

The microstructure and corrosion behaviour of the metal waste form (MWF) alloys based on ferritic steel with Zr content in the range of 3–15?wt-% were investigated. The MWF alloys are composed of α-Fe and Fe-Zr phases and with the increase of Zr content, α-Fe phase gradually decreases and the relative content of Fe–Zr intermetallic phase also increases. TEM and XRD confirmed the presence of Fe₂Zr and Fe₂₃Zr₆ intermetallics. Potentiodynamic polarisation curves showed The MWF alloys exhibited passivation behaviour in the simulated Kalpakkam (KGW) and Rajasthan ground water (RGW) media. Electrochemical impedance spectra revealed improved passive film stability in RGW than in KGW which is related to the formation of more stable adherent insoluble passive film in RGW. Higher Zr containing MWF alloy exhibited higher corrosion resistance than lower Zr containing MWF alloys. The relative content of Fe–Zr intermetallics is attributed for the corrosion resistance of The MWF alloys.     

The effect of nitrogen and carbon on the stress corrosion cracking performance of sensitized AISI 304 stainless steel in chloride and sulfate solutions at 250°C

Slow strain rate tests (SSRT) were conducted on sensitized AISI 304 stainless steels (SS) with varying nitrogen and carbon contents in order to study their susceptibility to stress corrosion cracking (SCC). The tests were performed in de-aerated 0.01 M NaCl at 250°C, at a strain rate of 2 × 10⁻⁶s⁻¹ and at various applied potentials in the range −0.4 to 0.1 V(NHE), after which scanning electron microscopy (SEM) was used to observe the fracture surfaces of the SSRT specimens. SSRT results show that SCC occurs above a certain critical potential (E_SCC) which depends on the carbon and nitrogen contents; E_SCC is in the range −0.3 to 0 V(NHE), with nitrogen additions up to 0.16 wt% increasing E_SCC and carbon additions decreasing E_SCC. This implies that the degree of sensitization (DOS) is the major factor which determines E_SCC. The DOS also determines the fracture mode obtained above E_SCC; at low DOS transgranular stress corrosion cracking (TGSCC) occurs, while at high DOS intergranular stress corrosion cracking (IGSCC) is the predominant mode. The potential ranges in which (1) IGSCC and (2) simultaneous IGSCC, TGSCC and shallow pitting occurred corresponded to (1) the passive range and (2) potentials above the breakdown of passivity on the polarization curves. The results of this investigation are compared with those obtained from similar tests in sulphate solutions [T. A. Mozhiet al., Corrosion42, 197 (1986)], and possible mechanisms discussed.     

Correlation between microstructure and corrosion behavior in an AISI 316L steel pipeline exposed for 100,700 h at 640°C in a petrochemical plant

The microstructure and electrochemical properties of 316L stainless steel were investigated after two conditions: aged at 640°C for 100,700 h and solution annealed at 1050°C for 2 h. While the aged samples were obtained from a pipe of a petrochemical reactor plant that was in service, the solution annealing was carried out in a conventional laboratory furnace. After aging, the precipitates present in decreasing order of quantity were sigma, Laves phase, and M₂₃C₆. After solution annealing, the microstructure was full austenitic. These results were in agreement with equilibria phase simulation with Thermo-Calc software. Intergranular corrosion susceptibility, evaluated by means of the single loop electrochemical potentiokinetic reactivation technique and Practice A of ASTM 262, indicated a preponderant role for the sigma precipitate. The pitting potential (E_pit) was evaluated through potentiodynamic polarization curves in 0.6 M NaCl and electrochemical impedance spectroscopy was performed at the corrosion potential to complement the information about the corrosion resistance.     

The a.c. corrosion of stainless steel—II. The polarization of ss304 and ss316 in acid sulfate solutions

An experimental study has been made to examine the effect of alternating current on the corrosion of Types 304 and 316 Stainless Steels in acidic aqueous sulfate solutions. The polarization curves were measured with an alternating voltage (AV) modulation technique and the pitting behavior of the stainless steels was examined with a constant potentiostatic coulometry and SEM photomicrography. The experiments were made with sinusoidal, square and triangular AV over a range of AV frequencies from 60 to 1000 Hz and AV magnitudes from 0 to 1000 mV rms. The results indicate that AV increased the critical current density for passivity and decreased the passive potential regime by shifting the transpassive potential toward the active direction and increasing the current density in the passive regime. The effect was similar to the addition of chloride ions to the corrosion environment. AV enhanced the pitting of the stainless steels at both the passive and transpassive potentials. Passivity was destroyed regardless of the AV waveforms; triangular wave caused the severest destruction, followed by sinusoidal and square waves.     

Preconditioning of AISI 304 stainless steel surfaces in the presence of flavins—Part II: Effect on biofilm formation and microbially influenced corrosion processes

Biofilm formation and microbially influenced corrosion of the iron-reducing microorganism Shewanella putrefaciens were investigated on stainless steel surfaces preconditioned in the absence and presence of flavin molecules by means of XANES (X-ray absorption near-edge structure) analysis and electrochemical methods. The results indicate that biofilm formation was promoted on samples preconditioned in electrolytes containing minute amounts of flavins. On the basis of the XANES results, the corrosion processes are controlled by the iron-rich outer layer of the passive film. Biofilm formation resulted in a cathodic shift of the open circuit potential and a protective effect in terms of pitting corrosion. The samples preconditioned in the absence of flavins have shown delayed pitting and the samples preconditioned in the presence of flavins did not show any pitting in a window of −0.3- to +0.0-V overpotential in the bacterial medium. The results indicate that changes in the passive film chemistry induced by the presence of minute amounts of flavins during a mild anodic polarization can change the susceptibility of stainless steel surfaces to microbially influenced corrosion.     

The corrosion of mild and stainless steel in alkaline anaerobic conditions representing the Belgian “supercontainer” concept and the Swiss L/ILW repository

Deep geological repositories for radioactive waste contain metallic materials, either used to construct disposal canisters or as low-/intermediate-level waste (L/ILW). The safety relevance of corrosion is linked to canister lifetime in the former case and gas generation in the latter. More specifically, the Belgian “supercontainer” concept envisages mild steel for the used fuel disposal canister, and in the case of the Swiss L/ILW repository, mild steels are the largest metallic waste component due to the decommissioning of civilian power-generating facilities. For these circumstances, the corrosion environment is dominated by the chemistry of cement, which is used as buffer or backfill material. The corrosion behaviour of mild steel in anoxic environments was studied through the analysis of the hydrogen end-product. Hydrogen analysis was conducted by periodically purging the cell head-space and analysing the gas using a solid-state hydrogen sensor. While this method is limited to providing only uniform corrosion rates averaged over periods of time, ranging from weeks to months, it provides excellent resolution and sensitivity. The test cell environments were matched against the anticipated Belgian high-level waste and Swiss L/ILW repository environments, and also against experiments that have been conducted by other researchers for comparative purposes. Samples were exposed to synthetic cement pore waters, representing fresh and degraded cement. In young cement waters, the formation of initial corrosion products resulted in steel wire corrosion rates of the order of µm/year, which, at 80°C rapidly declined to ∼10 nm/year. In contrast, SA516 grade 70 steel plate corroded much more slowly under similar conditions. In aged cement waters, initial corrosion rates were higher but declined faster towards a longer-term rate of ∼10 nm/year. 316L stainless steel, embedded in cementitious material, corroded at a rate of <1 nm/year at 50°C.