Corrosion of aluminium,stainless steels and AISI 680 nickel alloy in nitrogen‐based fuels

Nitrogen‐based compounds can potentially be used as alternative non‐carbon or low‐carbon fuels. Nevertheless, the corrosion of construction materials at high temperatures and pressures in the presence of such fuel has not been reported yet. This work is focused on the corrosion of AISI Al 6061, 1005 carbon steel (CS), 304, 316L, 310 austenitic stainless steels (SS) and 680 nickel alloy in highly concentrated water solution of ammonium nitrate and urea (ANU). The corrosion at 50 °C and ambient pressure and at 350 °C and 20 bar was investigated to simulate storage and working conditions. Sodium chloride was added to the fuel (0–5 wt%) to simulate industrial fertilizers and accelerated corrosion environment. Heavy corrosion of CS was observed in ANU solution at 50 °C, while Al 6061, 304 and 316L SS showed high resistance both to uniform and pitting corrosion in ANU containing 1% of sodium chloride. Addition of 5% sodium chloride caused pitting of Al 6061 but had no influence on the corrosion of SS. Tests in ANU at 350 °C and 20 bar showed pitting on SS 304 and 316L and 680 nickel alloy. The highest corrosion resistance was found for SS 310 due to formation of stable oxide film on its surface.     

Uniform corrosion and intergranular corrosion behavior of nickel‐free and manganese alloyed high nitrogen stainless steels

The uniform and intergranular corrosion behavior of two kinds of nickel‐free and manganese alloyed high nitrogen stainless steels (HNSSs) were investigated. A type of 316L stainless steel (316L SS) was also included for comparison purpose. Both solution annealed (SA) and sensitization treated (ST) steels were examined. It was found that the SA HNSSs had much weaker resistance to uniform corrosion compared to the SA 316L SS. The addition of molybdenum, to some extent, improved the uniform corrosion resistance of the HNSSs. The sensitization treatment had little influence on the uniform corrosion resistance of all the steels. The HNSSs showed an obvious susceptibility to intergranular corrosion, in particular the ST HNSSs. The intergranular corrosion rates of the sensitized HNSSs were much higher than that of the sensitized 316L SS. The degree of interganular attack for the ST HNSSs was much more serious than that for the 316L SS. The addition of molybdenum obviously improved the resistance of the ST HNSSs to intergranular corrosion. The double loop electrochemical potentiokinetic reactivation tests also proved that the HNSSs were rather susceptible to the sensitization treatment compared to the 316L SS. The relatively weak resistance of the HNSSs to uniform and intergranular corrosion may be due to high manganese promoted anodic dissolution. The improvement of uniform and intergranular corrosion resistance caused by the addition of molybdenum could be attributed to the synergistic effects of molybdenum and nitrogen in the HNSSs on the formation and stability of passive film.     

Electrochemical characteristics and interfacial contact resistance of multi-layered Ti/TiN coating for metallic bipolar-plate of polymer electrolyte membrane fuel cells

Metallic bipolar-plates have advantages over non-porous graphite ones due to their higher mechanical strength and better electrical conductivity. However, corrosion resistance and interfacial contact resistance are major concerns that remain to be solved, since metals such as stainless steels may develop oxide layers that decrease electrical conductivity, thus lowering fuel cell efficiency. In this study, multi-layered nitride coatings consisting of Ti and TiN were deposited on 316L stainless steel (SS316L) by a D.C magnetron sputtering method to enhance the corrosion resistance and to lower the interfacial contact resistance (ICR) of metallic bipolarplates for a polymer electrolyte membrane fuel cell (PEMFC). Electrochemical methods were conducted and ICRs of the coated specimens were measured to investigate the potential of the coated metallic bipolar-plate for use in PEMFCs. The multi-layered Ti/TiN coating deposited on SS316 showed lower ICR values than the single-layered TiN coating, and improved corrosion resistance when the PEMFC was not in operation while the degradation of the coating layer was observed in both cathodic and anodic working environments.     

In vitro electrochemical investigations of advanced stainless steels for applications as orthopaedic implants

Potentiodynamic anodic polarization experiments on advanced stainless steels (SS), such as nitrogenbearing type 316L and 317L SS, were carried out in Hank’s solution (8 g NaCl, 0.14 g CaCl₂, 0.4 g KC1, 0.35 g NaHCO₃, 1 g glucose, 0.1 g NaH₂PO₄, 0.1 g MgCl₂, 0.06 g Na₂HPO₄ 2H₂O, 0.06 g MgSO₄ 7H₂O/1000 mL) in order to assess the pitting and crevice corrosion resistance. The results showed a significant improvement in the pitting and crevice corrosion resistance than the commonly used type 316L stainless steel implant material. The corrosion resistance was higher in austenitic stainless steels containing higher amounts of nitrogen. The pit-protection potential for nitrogen-bearing stainless steels was more noble than the corrosion potential indicating the higher repassivation tendency of actively growing pits in these alloys. The accelerated leaching study conducted for the above alloys showed very little tendency for leaching of metal ions, such as iron, chromium, and nickel, at different impressed potentials. This may be due to the enrichment of nitrogen and molybdenum at the passive film and metal interface, which could have impeded the releasing of metal ions through passive film.     

Corrosion phenomena of alloys and electrode materials in Molten Carbonate Fuel Cells

The corrosion behavior of different alloys and the electrical conductivity of the growing corrosion scales was investigated under simulated and real molten carbonate fuel cell conditions. The corrosion of the usually used NiO cathode material was also investigated. In several exposure tests in oxidizing atmospheres, the FeCrMnNi steel 1.3965 showed a higher corrosion resistance to the aggressive carbonate media than the FeCrNi alloy 1.4404 (SS316L). This superior corrosion resistance is explained by the formation of a mixed (Fe,Ni,Mn)_xCr_3‐xO₄ spinel layer, which reduces the outward diffusion of iron ions more than the mixed (Fe,Ni)Cr₂O₄ spinel formed on austenitic FeCrNi steels. Oxide debris, which spalls off the current collectors, was investigated by XRD. The corrosion scales spalled off mainly at the curved area of the current collector and not at the cathode/current collector interface. The debris was strongly magnetic and consisted of several, in some cases lithiated iron oxides, whereby α‐Fe₂O₃ (hematite), γ‐Fe₂O₃ (maghemite) and Fe₃O₄ (magnetite) formed most of the debris. The investigations of the electrical conductivity of the corrosion scales have shown that the electrical conductivity is limited by the inner, Cr‐containing oxide of the multi‐layered corrosion scale. Cr‐rich alloys which contain more that 20 wt.% Cr showed extremely high ohmic resistance of the corrosion scale, much higher than that of alloys containing less than 20 wt.% Cr due to the formation of highly conductive mixed spinel layers. Small additions of Al in the alloy increased the ohmic resistance of the corrosion scale by many orders of magnitude. Corrosion tests in the fuel environment showed, that common uncoated stainless steels are not suitable for the use as anodic current collectors. The corrosion resistance in the anodic gas atmosphere is determined by the Cr and the Ni contents of the alloy. Only the model alloy NKK which contains 45 wt.% Ni and 30 wt.% Cr showed an acceptable corrosion resistance. The NiO dissolution and the Ni precipitation was investigated by single cell tests. These tests showed, that the replacement of the metallic Ni by an Al support (which is necessary to avoid cracks inside the ceramic) decreases the amount of metallic Ni in the ceramic matrix significantly. Therefore shorting of a fuel cell having a NiO cathode and a LiAlO₂ matrix with an Al support for the mechanical support is not expected in the target lifetime of 40 000 h. The double layer LiCoO₂‐NiO cathode also showed a significant reduction in Ni precipitation after testing. Due to the improvements and development in materials the MCFC‐lifetime has been trebled in the last few years.     

Enhancing the localised corrosion resistance of 316L stainless steel via FBR-CVD chromising treatment

The resistance of stainless steels to localised corrosion can be adversely affected by environmental and metallurgical heterogeneities existed in complex industrial infrastructures such as seawater desalination plants exposed to aggressive evnironments. It is therefore critical to enhance the localised corrosion resistance and understand the corrosion behaviour of stainless steels in complex and aggressive industrial environmental conditions. In this work, the localised corrosion resistance of chromised stainless steel 316L (SS316L) in simulated seawater desalination systems has been investigated by electrochemical and surface analytical techniques. It has been found that chromising processes have improved the localised corrosion resistance of SS316L by reducing its susceptibility to pitting, crevice, and welding zone corrosion in simulated seawater desalination environments. This increased corrosion resistance has been explained by electrochemical polarisation studies and surface analysis showing that the chromising treatment at 1050°C resulted in a continuous and stable chromium-enriched layer on the SS316L surface.     

Electrochemical behavior of sintered oxide dispersion strengthened stainless steels

The electrochemical behavior of powder metallurgy (P/M) oxide dispersion strengthened stainless steels (SS) (316L and 434L) have been compared with standard 430 and 316 wrought samples in 0.05 mol/l sulfuric acid. The effects of sintering temperature and yttria addition on the electrochemical behavior have been studied. The behaviour of the dispersion strengthened SS was comparable to that of the straight P/M samples. The straight P/M samples sintered at 1400 °C exhibited better corrosion resistance compared to the samples sintered at 1250 °C and this has been correlated to sintered densities. The P/M austenitic SS were superior to the P/M ferritic SS. Pitting resistance, studied by cyclic polarization experiments in 3.56 wt.% NaCl, of the P/M samples were comparable to the wrought samples. The addition of Y₂O₃ did not affect the pitting resistance.     

Localized corrosion properties of low interstitial ferritic,high purity austenitic and high chromium duplex stainless steels

Within the framework of a research aimed at characterizing the behaviour of new materials to pitting and crevice corrosion, an investigation has been made, using electrochemical techniques, of the following materials: ELI ferritic stainless steels (18 Cr-2 Mo-Ti; 21 Cr-3 Mo-Ti; 26 Cr-1 Mo); high chromium duplex stainless steel (Z 5 CNDU 21-08) and high chromium-nickel austenitic stainless steel (Z 2 CNDU 25-20); commercial austenitic stainless steels (AISI 304 L and 316 L) and laboratory heats of austenitic stainless steels with low contents of interstitials (LTM/18 Cr- 12 Ni, LTM/16 Cr- 14 Ni-2 Mo). It was possible to graduate a scale of resistance to pitting and crevice corrosion in neutral chloride solutions at 40 C; in particular the two experimental austenitic stainless steels LTM/18 Cr- 12 Ni and LTM/16 Cr- 14 Ni-2 Mo are at the same level as the AISI 316 L and 18 Cr-2 Mo-Ti, respectively. An occluded cell was developed and used for determining the critical potential for crevice corrosion (E_{localized corrosion}). For the steels under investigation E_{localized corrosion} is less noble than E_pitting especially for ELI ferritic 18 Cr-2 Mo-Ti and 21 Cr–3 Mo-Ti.     

Investigation on Pitting Corrosion of Nickel-Free and Manganese-Alloyed High-Nitrogen Stainless Steels

Pitting corrosion behavior of three kinds of nickel-free and manganese-alloyed high-nitrogen (N) stainless steels (HNSSs) was investigated using electrochemical and immersion testing methods. Type 316L stainless steel (316L SS) was also included for comparison purpose. Both solution-annealed and sensitization-treated steels were examined. The solution-annealed HNSSs showed much better resistance to pitting corrosion than the 316L SS in both neutral and acidic sodium chloride solutions. The addition of molybdenum (Mo) had no further improvement on the pitting corrosion resistance of the solution-annealed HNSSs. The sensitization treatment resulted in significant degradation of the pitting corrosion resistance of the HNSSs, but not for the 316L SS. Typical large size of corrosion pits was observed on the surface of solution-annealed 316L SS, while small and dispersed corrosion pits on the surfaces of solution-annealed HNSSs. The sensitization-treated HNSSs suffered very severe pitting corrosion, accompanying the intergranular attack. The addition of Mo significantly improved the resistance of the sensitization-treated HNSSs to pitting corrosion, particularly in acidic solution. The good resistance of the solution-annealed HNSSs to pitting corrosion could be attributed to the passive film contributed by N, Cr, and Mo. The sensitization treatment degraded the passive film by decreasing anti-corrosion elements and Cr-bearing oxides in the passive film.     

奥氏体不锈钢在熔融碳酸盐中的腐蚀

研究了含稀土316S和310S型不锈钢在650℃下(Li,K)2CO 3共晶熔盐中的腐蚀行为.结果表明：稀土元素能够通过促进富Cr氧化膜的形成而提高310S不 锈钢的耐蚀性能.316L(RE)由于具有较低的Cr含量,其耐蚀性能劣于310S合金.讨论了不锈钢 在熔盐中的腐蚀机理.     

Corrosion behaviour of Lotus-type porous high nitrogen nickel-free stainless steels

Corrosion behaviour of three austenitic Lotus-type porous high nitrogen Ni-free stainless steels exposed to an acidic chloride solution has been investigated by electrochemical tests and weight loss measurements. Polarization resistance indicates that the corrosion rate of Lotus-type porous high nitrogen Ni-free stainless steels is an order of magnitude lower than that of Lotus-type porous 316L stainless steel in acidic environment. The localised corrosion resistance of the investigated high nitrogen Ni-free stainless steels, measured as pitting potential, E_b, also resulted to be higher than that of type 316L stainless steel. The influences of porous structure, surface finish and nitrogen addition on the corrosion behaviour were discussed.     

Galvanic series of different stainless steels and copper- and aluminium-based materials in acid solutions

Galvanic series of AISI 304, 316, 316L, and 316Ti austenitic stainless steels, AISI 410 and 420 martensitic stainless steels, 63Cu37Zn brass, Cu, Al, and AlMg1 were established for 10% (wt.) hydrochloric, phosphoric, sulphamic, sulphuric, nitric, citric, acetic, and methanesulphonic (MSA) acids used as cleaners in order to predict galvanic corrosion when coupling these materials. It was found that each acid has a distinctive order of metallic materials in a galvanic series. The largest corrosion potential difference in all acids exists between Al-based materials and stainless steels, as well as Cu-based materials indicating the use of Al-based materials as sacrificial electrodes.     

High-Temperature Oxidation Behaviour of SS 216L (Fe–16Cr–6Ni–6Mn–1.7Mo)

Oxidation behaviour of a 216L austenite stainless steel (Fe–16Cr–6Ni–6Mn–1.7Mo) was evaluated at temperature between 700 and 900?°C by thermogravimetric analysis and compared with that of SS 316L. Transmission electron microscopy in combination with energy dispersive X-ray analysis was used to study surface morphologies and chemical composition of the oxide scales formed. Replacement of Mn with Ni in SS 316L enhances its oxidation rate. SS 216L exhibits an anomalous temperature dependence of the oxidation behaviour. A kinetic inversion was observed at temperature 900?°C. Surface analysis reveals domination of Mn and iron mixed oxides in oxide scale.     

Application of LPR and EIS techniques for on-site corrosion monitoring at the geothermal plant in Central Poland

Corrosion monitoring station was installed at ‘Geotermia Mazowiecka’ geothermal plant in Poland. Linear polarisation resistance and electrochemical impedance spectroscopy techniques were applied to estimate the corrosion rate and the surface changes of K55 carbon steel, L80-13CR and 316 stainless steels directly in the geothermal water flux. The enhanced corrosion of K55 carbon steel and corrosion rate of L80-13CR and 316 stainless steels was observed. The formation of biofilm increased the resistivity of the surface.     

Mo含量对不锈钢在环烷酸介质中腐蚀与中蚀的影响

制备了以316L为基的不同Mo含量的不锈钢，在精制环烷酸和含环烷酸的油中分别进行了静态和冲蚀实验，结果表明，316L基不锈钢在高温环烷酸介质中具有很好的抗腐蚀和冲蚀性能，随Mo含量增加，不锈钢的环烷酸腐蚀速率和冲刷腐蚀速率均逐渐减小，流体冲刷明显加剧不锈钢的环烷酸腐蚀，综合考虑不锈钢的抗蚀性能及机械性能，在设计抗环烷酸腐蚀和冲蚀的新型不锈钢时，Mo含量应保持在5%（质量分数）左右。     

Effects of Rare Earth Metal addition on the cavitation erosion-corrosion resistance of super duplex stainless steels

Austenitic stainless steels such as AISI 316L have been used in equipment in which fluid flows at high speeds which can induce cavitation erosion on metallic surfaces due to the collapse of cavities, where the collapse is caused by the sudden change of local pressure within the liquid. Usually AISI 316L is susceptible to cavitation erosion. This research focuses on developing a better material to replace the AISI 316L used in equipment with high speed fluid flow, such as impellers. The effects of Rare Earth Metal (REM) additions on the cavitation erosion-corrosion resistance of duplex stainless steels were studied using metallographic examination, the potentiodynamic anodic polarization test, the tensile test, the X-ray diffraction test and the ultrasonic cavitation erosion test. The experimental alloys were found to have superior mechanical properties due to interstitial solid solution strengthening, by adding high nitrogen (0.4%), as well as by the refinement of phases and grains induced by fine REM oxides and oxy-sulfides. Corrosion resistance decreases in a gentle gradient as the REM content increases. However, REM containing alloys show superior corrosion resistance compared with that of other commercial alloys (SAF 2507, AISI 316L). Owing to their excellent mechanical properties and corrosion resistance, the alloys containing REM have high cavitation erosion-corrosion resistance.     

Electrochemical and XPS studies of AISI 316L stainless steel after electropolishing in a magnetic field

The thermodynamic stability and corrosion resistance of surface oxide layer are the most important features of stainless steels. Electrochemical polishing (EP) is the most extensively used surface technology for austenitic stainless steels. We have modified this surface technology by introducing a magnetic field to the system. With this new process called the magnetoelectropolishing (MEP) we can improve metal surface properties by making the stainless steel more resistant to halides encountered in a variety of environments.In this paper, the corrosion research results are presented on the behaviour of the most commonly used material - medical grade AISI 316L stainless steel. The corrosion investigations have been concerned on the open circuit potential (OCP), electrochemical impedance spectroscopy (EIS), and polarisation curves studies in the Ringer’s body fluid under room temperature (25 °C). The X-ray photoelectron spectroscopy (XPS) was performed on 316L samples after three treatments: MP - abrasive polishing (800 grit size), EP - conventional electrolytic polishing, and MEP - magnetoelectropolishing. The comparison of the corrosion behaviour of the stainless steel’s surface after these processes was also carried out. The purpose of XPS studies was to reveal the surface film composition and the reason of this modified corrosion behaviour. It has been found that the proposed MEP process modifies considerably the composition of the surface film and improves the corrosion resistance of the same 316L SS studied.     

2205和316L不锈钢在氢氟酸中的电化学腐蚀行为

通过动电位极化和电化学阻抗方法考察了2205双相不锈钢和316L不锈钢在5%(体积分数)HF溶液中的电化学行为,借助Mott-Schokkty曲线分析了两种不锈钢表面钝化膜的半导体特性。结果表明：两种不锈钢在氢氟酸溶液中都能发生钝化,且2205双相不锈钢的钝化区间范围更宽,维钝电流密度更低。2205双相不锈钢表面钝化膜表现出更高的钝化膜电阻和电荷转移电阻,其抗氢氟酸腐蚀性能优于316L不锈钢,这主要与2205双相不锈钢中的Mo和Cr含量高、表面钝化膜缺陷少、钝化膜易修复等因素有关。     

Pitting Potential of stainless steels in artificial sweat

The pitting potentials of 12/12, 316 PX, AISI 303, 304, 316F and 316L austenitic stainless steels were determined in artificial sweat (perspiration) at room temperature. Two compositions of sweat were used: the BAM composition which contains two malodorous organic acids and the composition proposed in an ISO standard which does not contain them. The quasi-potentiostatic method (10 mV potential steps per min), potentiodynamic technique (1 V/min linear sweep) and scratch test were used on mechanically polished and HNO₃-passivated surfaces. The aggressivity of the two artificial sweats with respect to stainless steels was found to be practically the same. The pitting potentials and the classification of the stainless steels according to their pitting potential values were found to depend on the surface preparation and, to a lesser extent, on the test method. The experimental techniques were often complementary and a combination of two or three methods in conjunction may increase the confidence with which the conclusions can be applied. The lowest pitting corrosion resistance was found for AISI 303 and the highest for AISI 316L. As expected stainless steels with the lowest concentration of nonmetallic inclusions (sulfides and oxides) exhibited the best pitting corrosion resistance.     

Accelerated corrosion of five commercial steels under a ZnCl2-KCl deposit in a reducing environment typical of waste gasification at 673-773 K

The corrosion of five Fe-Cr commercial steels containing 0-18 wt.% Cr at 673-773 K has been studied in a reducing H₂-HCl-CO₂ atmosphere under a ZnCl₂-KCl deposit typical of waste gasification environments. In comparison with the behavior of the same steels in a similar gas mixture without salt deposit, all steels suffered from accelerated corrosion induced by the salt and formed porous scales with poor adherence to the underlying steels. Some Cl was detected close to the steels/scale interface, indicating that Cl-containing species were able to go through the scale down to the metal matrix. Even though the corrosion rates generally decreased with increasing Cr content, the high-Cr stainless steel SS304 was still unable to provide a good corrosion resistance against the ZnCl₂-KCl deposit. The reaction mechanisms are discussed on the basis of thermodynamic considerations and of the “active oxidation” model.