Electrochemical and corrosion behaviour of work-hardened commercial austenitic stainless steels in acid solutions

This paper describes the results of a study concerning the electrochemical and corrosion behaviour of AISI Types 304L and 316L stainless steels, cold worked under various conditions, in 1M H₂SO₄ and in 0.1M HCl de-aerated solutions. Anisotropic behaviour of specimen surfaces with different orientations to the direction of deformation has been observed. Stress corrosion cracking of the deformed steels can occur at room temperature in the 0.1M HCl solution both in the active and transition regions of the polarization curves.     

Influence of chromium content on corrosion resistance of low alloyed chromium steels in hydrofluoric acid and in other acid environments

Abstract

The influence of chromium content on the corrosion resistance of low alloyed chromium steels is studied in 1·7M (3%) HF, 1·4M (5%) HCl, 0·75M H₂S0₄, and 1·5M HClO₄ at 45°C. The presence of chromium in the steels decreases their corrosion resistance in HF solutions, and to a lesser extent in H₂SO₄ and HClO₄ acid solutions. There was little effect in the HCl solution.     

The influence of alloying elements on the corrosion behaviour of ferritic steels in simulated combustion atmospheres

The low‐chromium steels (Cr content 0.7–1.4 wt.%) are usually being used in low temperature boiler applications where the environments are not so aggressive as in waste‐fire boilers. To improve their mechanical properties and corrosion resistance several alloying elements have been used. In the present study the new low‐chromium steels modified with Si, Ni and Ce have been investigated. These steels were compared with the common boiler steel – 2.25Cr1M. The multi‐sample exposure tests were made in moist air (8% O₂ + 15% H₂O) with and without 200 ppm SO₂ or 2000 ppm HCl addition at the isothermal temperature of 500°C. Corrosion products were analysed by Scanning Electron Microscope with Energy Dispersive Spectrometer (SEM/EDS) and XRD techniques. The results of the study show that addition of Ni and Si to the steels studied could improve their corrosion resistance, but only in moist air atmospheres. In SO₂‐containing atmospheres the corrosion resistance seems to remain the same, when in HCl‐containing atmospheres Ni and Si additions seem to have a negative effect on the corrosion behaviour. As could by seen from SEM analysis, the scales formed, on the steels with above elements, are more adherent to the metallic core. The cerium was added to the studied materials mainly to improve their mechanical properties. This alloying element seems to increase the corrosion rate of materials, especially in atmospheres containing Cl.     

Potentiodynamic polarization behaviour of two 17Cr13Ni2·5 Mo austenitic steels with different N contents

Potentiodynamic polarization measurements have been made on two 17Cr13Ni2·5Mo austenitic steels differing from each other in the content of N. The electrolyte solutions have been 1·0M H₂SO₄, mixtures of HCl and H₂SO₄ and 1·0M HCl at 20°C. In 0·9 and 1·0M HCl the polarization curves of the two austenitic steels possess two peaks which are difficult to explain. Experiments indicate that the steel containing N is less corrosion resistant than the steel without N.     

Influence of heat flux on localised corrosion of stainless steel under boiling conditions

The article deals with the influence of heat flux on localised forms of corrosion of stainless steels under the conditions of phase transition on a metal surface. The observations focused on the influence of the initiation and propagation of pitting corrosion and stress corrosion cracking. Pitting corrosion was tested in the environment of 0.6% FeCl₃ + 0.3% EDTA + 0.1% HCl, the susceptibility to stress corrosion cracking was verified in 35% MgCl₂. The tests proved a negative influence of heat flux on the initiation and propagation of non‐uniform corrosion.     

Influence of different heat treatments on corrosion resistance of martensitic stainless steels

The changes in microstructure, caused by different heat treatments, have considerable influence on the corrosion resistance of stainless steels. The heat treatment causes an alteration of carbide contained in steels. Changes in the constant B for these steels, (B = Rp · i_COR) have been observed in quenched, tempered and annealed conditions. Pitting corrosion resistance of martensitic stainless steels in quenched and tempered conditions in 0.1M H₂SO₄ by adding Cl^? ions has been investigated.     

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.     

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.     

Investigation of corrosion behavior of silver coated brass in acidic solutions

The corrosion behavior of uncoated brass and electrolytically silver coated brass in cyanide solutions such as 0.1 M HCl, 0.1 M H₂SO₄ and 0.1 M H₃PO₄ was investigated by Tafel polarization curves and cyclic voltammetry curves at 1., 24., 48., 72., 96. and 168. hours. The coating efficiency was calculated by current density of corrosion determined from Tafel polarization curves. Surface analysis of coated brass immersed into acidic solution by 168 hours was done. It is concluded that silver coating is very effective to protect the corrosion of brass for a long time.     

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.     

Corrosion resistances and passivation of powder metallurgical and conventionally cast 316L and 2205 stainless steels

The corrosion resistances and passivation of austenitic 316L and duplex 2205 powder metallurgical (P/M) steels, produced by gas atomizing and hot isostatic pressing (HIP), have been compared with those of their conventional cast counterparts. P/M 316L steel is shown to have significantly higher pitting corrosion resistance than conventional 316L steel in 0.5 M HCl. This effect is ascribed to the fine grained microstructure of the P/M 316L steel yielding an improved passive layer. The latter hypothesis is supported by photoelectron spectroscopy data demonstrating differences between the thickness and composition of the passive layers for the 316L steels.     

Electrochemical Evaluation of Corrosion on Borided and Non-borided Steels Immersed in 1 M HCl Solution

In this study the corrosion resistances of AISI 1018 and AISI 304 borided and non-borided steels were estimated using polarization resistance and electrochemical impedance spectroscopy (EIS) techniques. Boriding of the steel samples was conducted using the powder-pack method at 1223 K with 6 h of exposure. Structural examinations of the surfaces of the borided steels showed the presence of a Fe₂B layer with isolated FeB teeth on the AISI 1018 steel, whereas a compact layer of FeB/Fe₂B was formed on the AISI 304 steel. Polarization resistance and EIS of the borided and non-borided steels surfaces were performed in a corrosive solution of 1 M HCl. The EIS data were analyzed during 43 days of exposure to the acid solution. Impedance curves obtained during this period for the borided and non-borided steels were modeled using equivalent electrical circuits. The results of both electrochemical techniques indicated that boride layers formed at the steel surfaces effectively protect the samples from the corrosive effects of HCl. The main corrosion processes observed on the boride layers were pitting and crevice corrosion.     

Corrosion of low-temperature nitrided molybdenum-bearing stainless steels

Austenitic stainless steels with up to 6.1 wt.% Mo were nitrided at 425 °C and examined in 0.1 M Na₂SO₄ without and with chlorides at pH 3.0 and 6.5. Nitrided steels exhibited an increased resistance to pitting, but at pH 3.0 they had a decreased resistance to general corrosion. After corrosion at pH 3.0 surface films contained chromium nitrides and oxides of Mo, Cr and Fe. It is proposed that the improved pitting resistance of nitrided steels is associated with the initially accelerated dissolution which leads to the accumulation of corrosion resistant CrN and of oxidised steel components.     

Microstructure and Corrosion Behavior of Hot-Deformed and Cold-Strained High-Mn Steels

The electrochemical corrosion properties of 26Mn-3Si-3Al and 27Mn-4Si-2Al austenitic steels in two different states were studied in 0.1 M H₂SO₄ and 3.5% NaCl using potentiodynamic polarization tests. The effect of cold deformation on the microstructure and corrosion behavior of steels was analyzed. In acid solution, both steels exhibited lower corrosion resistance than in chloride solution independently on the steel state (hot-rolled, cold-worked). Cold deformation decreases the corrosion resistance, though this effect is smaller than the effect of chemical composition related to the combined Al + Si addition. All steels showed the evidence of pitting corrosion. The intensive dissolution of Fe and Mn takes place in the acid medium.     

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.     

Effect of Geobacter sulfurreducens on the microbial corrosion of mild steel, ferritic and austenitic stainless steels

The influence of Geobacter sulfurreducens was tested on the anaerobic corrosion of four different steels: mild steel 1145, ferritic steel 403 and austenitic steels 304L and 316L. Within a few hours, the presence of cells induced a free potential (E_oc) ennoblement around +0.3 V on 1145 mild steel, 403 ferritic steel and 304L austenitic steels and slightly less on 316L. The kinetics of E_oc ennoblement depended on the amount of bacteria in the inoculum, but the final potential value depended essentially on the nature of the material. This effect was due to the capacity of G. sulfurreducens to create a direct cathodic reaction on steel surfaces, extracting the electrons directly from material. The presence of bacterial cells modified the corrosion features of mild steel and ferritic steel, so that corrosion attacks were gathered in determined zones of the surface. Local corrosion was significantly enhanced on ferritic steel. Potential ennoblement was not sufficient to induce corrosion on austenitic steels. In contrast G. sulfurreducens delayed the occurrence of pitting on 304L steel because of its capability to oxidize acetate at high potential values. The electrochemical behaviour of 304L steel was not affected by the concentration of soluble electron donor (acetate, 1–10 mM) or the amount of planktonic cells; it was directly linked to the biofilm coverage. After polarization pitting curves had been recorded, microscopic observations showed that pits propagated only in the surface zones where cell settlement was the densest. The study evidenced that Geobacter sulfurreducens can control the electrochemical behaviour of steels in complex ways that can lead to severe corrosion. As Geobacteraceae are ubiquitous species in sediments and soils they should now be considered as possible crucial actors in the microbial corrosion of buried equipment.     

Corrosion and deposition of magnetite in ferritic steel steam generator tubes under acid chloride conditions

Abstract

Corrosion of a tube made up of 9Cr–1Mo, 2·25Cr–1Mo, and 2·25Cr–1Mo–Nb ferritic steels and containing artificial defects has been investigated under realistic steam generator conditions (355°C, 17·6 MPa) with acid chloride fault water chemistry (2 mg/kg HCl). Four regions of corrosion and magnetite deposition behaviour were observed on the tube surface. In non-heat flux regions, magnetite deposition was affected by mass transfer and probably also by surface potential. In low heatflux regions (<660 kW m^?2) observed increases in the rates of magnetite deposition and corrosion wereprobably due to rises in the degree of iron supersaturation and HCl concentration, brought about by boiling. Enhanced HCl concentrations in the normal heat flux region (660 kW m^?2) prevented magnetite deposition and caused an increase in corrosion of the three steels. Increases in corrosion and magnetite deposition were also observed at the weld between the 9Cr–1Mo and 2·25Cr–1Mo steels. In defects, accelerated corrosion was seen only in the 9Cr–1Mo steel and was confined to the top 0·15 mm. It is concluded that the corrosion behaviour observed in this work is determined by the residence time and concentration of solutions of HCl on tube and defect surfaces.     

Zur Korrosionsprüfung von Schweißverbindungen hochlegierter CrNiMo-Stähle und NiCrMo-Legierungen

On the corrosion testing of weldments of high alloyed CrNiMo-stainless steels and NiCrMo-alloys Weluments of high-alloyed CrNiMo stainless steels and Nicro alloys can he more susceptible to localized corrosion than the solution annealed basic material owing to segregations and precipitations in the heat affected zone, the high temperature zone and/or in the weld. To investigate these differences the FeCl₃-test (10% FeCl₃ · 6aq), the test “green death” (11.5% H₂SO₄, 1.2% HCl, 1% CuCl₂, 1% FeCl₃) as well as chronopotentiostatic tests in artificial sea water or in 3% NaCl-solution are used. In particular for testing the highest alloyed materials a CaCl₂ test was developed (4.5M CaCl₂, chronopotentiostatic test in duration of 8 to 10 hours at + 200 mV (SCE)), which can be carried out to a temperature of 115°C at atmospheric pressure. The aggressivity increases in the range FeCl₃-test, “green death”-test, CaCl₂-test. Matching and graduated over-alloyed weldments (TIG, heat input of 7 and 15.5 kJ/cm) of materials 1.4529, 1.4562, 2.4856, 2.4819 (german materials No.) are comparingly examined in various tests, of materials 1.4406, 1.4539, 1.4439 and 1.4563 (german materials No.) only matching weldments in the FeCl₃-test. In strongly oxidizing media only a highly over-alloyed performed weldment (filler material 2.4607, german material No.) produces the best corrosion behaviour, measured as the critical temperatures of localized corrosion. Measurements of critical current densities of passivation can be used for investigations of corrosion behaviour of weldments, too. Critical current densities of passivation are showing a tendency to inverse proportion to the critical temperatures of localized corrosion. Suitable electrolytes are among others 0.2M H₂SO₄ + 1M NaCl + 10^?3% KSCN, N₂-bubbled, 25 to 60°C and xM H₂SO₄ + 4M NaCl + 10^?3% KSCN (x = 0.05 to 1), 25°C, in contact with air. An influence of heat input at the welding is indicated in the test of localized corrosion, but it is only small. It is sometimes more clearly shown at measurements of passivation.     

Corrosion resistance of HVOF-sprayed coatings for hard chrome replacement

HVOF-sprayed coatings (WC-17Co, WC-10Co-4Cr, Co-28Mo-17Cr-3Si) and electrolytic hard chrome (EHC) coatings corrosion resistances have been compared through electrochemical polarization tests (0.1 N HCl, 0.1 N HNO₃) and Corrodkote test. EHC coatings passivate in HNO₃, but undergo pitting corrosion in HCl and in Corrodkote test too. HVOF coatings do not passivate, but possess more noble corrosion potentials. Both in HNO₃ and HCl, they undergo more generalized corrosion, with similar i_corr; crevice corrosion along splat boundaries is sometimes detected after the HCl test. Their i_corr in 0.1 N HCl solution is lower than in several of EHC coatings. No visible damage in the HVOF coatings has occurred after the Corrodkote test.     

The protective effect of polypyrrole coating on the corrosion of steel electrode in acidic media

In this study, the corrosion parameters of stainless steel containing 12% Cr, have been determined by Tafel extrapolation method in 1 M HCl, H₂SO₄ and H₃PO₄ media. Later, steel was coated with polypyrrole in 0.1 M Pyrrole + 0.3 M Oxalic acid solution by cyclic voltametric method. The corrosion parameters and percentage inhibition efficiencies of coated electrodes were investigated according to immersion times in the same media. In all acidic media studied, increases in immersion time, produced increased corrosion densities and a decrease in percentage inhibition efficiencies were determined.