Corrosion Of Austenitic Stainless Steel Research Articles

Corrosion of austenitic stainless steel at 90 °C under highly saline and anoxic conditions: A microspectroscopic study

The stainless steel AISI 309 S used for containers for vitrified high-level radioactive waste was exposed to 90 °C under highly saline and anoxic conditions for different exposure times up to 294 days. The surface damage was limited and no pitting could be detected. The corrosion layer is made of an inner-layer mostly of chromium (hydr)oxides and an outer-layer made of Fe- and Ni-based spinel compounds with admixed nickel (hydr)oxides. Minor contributions of magnetite and layered double hydroxide could be identified. Dissolved amounts of metal ions were very low, the pH increased only slightly and the redox potential decrease was limited.

Influence of Realistic, Cyclic Atmospheric Cycles on the Pitting Corrosion of Austenitic Stainless Steels

Pitting corrosion was evaluated on stainless steels 304H, 304, and 316L the surfaces of which had ASTM seawater printed on them as a function of surface roughness after exposure to an exemplar realistic atmospheric diurnal cycle for up to one year. Methods to evaluate pitting damage included optical imaging, scanning electron microscopy imaging, profilometry analysis, and polarization scans. The developed cyclic exposure environment did not significantly influence pitting morphology nor depth in comparison to prior static exposure environments. Cross-hatching was observed in a majority of pits for all material compositions with the roughest surface finish (#4 finish) and in all surface finishes for the 304H composition. Evidence is provided that cross-hatched pit morphologies are caused by slip bands produced during the grinding process for the #4 finish or by material processing. Additionally, micro-cracking was observed in pits formed on samples with the #4 surface finish and was greatly reduced or absent for pits formed on samples with smooth surface finishes. This suggests that both a low RH leading to an MgCl2-dominated environment and a rough surface containing significant residual stress are necessary for micro-cracking. Finally, the use of various characterization techniques and cross sectioning was employed to both qualitatively and quantitatively assess pitting damage across all SS compositions and surface finishes.

The mechanoelectrochemical effect on the electrochemical corrosion of austenitic stainless steel

In this paper, the mechanoelectrochemical effect on the electrochemical corrosion of 316 L austenitic stainless steel was investigated by theoretical, experimental and simulated methods. The modified piecewise formula φa,eq=φa,eq0−ΔPmVmzF−TRzFln(KN0εp+1) for calculating the strain on anode equilibrium potential of austenitic stainless steel was proposed. It is demonstrated that the corrosion current increases from 8.03×10−6A⋅cm−2 to 28.38×10−6A⋅cm−2 within 20% strain, especially within 10%, which is in better agreement with the experimental results. This modification not only made the physical meaning of parameters clearer, simplified the formula, but also made the calculation results more accurate. Moreover, the localized galvanic corrosion caused by non-uniform deformation had been verified by finite element model. The results revealed that the non-uniform strain at the initial stage of strain (εp<0.05) has a greater influence on the corrosion resistance.

Inhibition of Intergranular Corrosion in Austenitic Stainless Steels Through Critical Near-Surface Plastic Deformation and Aging

Inhibition of Intergranular Corrosion in Austenitic Stainless Steels Through Critical Near-Surface Plastic Deformation and Aging

Sensitization to Corrosion of Austenitic Stainless Steels: Watch Straps Intended to Come into Direct and Prolonged Contact with Skin

Nine grades of steel from different European steelmakers, namely 304L, 316L, and 904L, were evaluated. The austenitic steels studied are used in the manufacture of watch straps. The evaluations have been carried out in accordance with the ASTM standards which specifically concern the forms of corrosion, pitting (G48-11, FeCl3), intergranular (A262-15, Strauss method) test and Tuccillo–Nielsen test. The polarization electrochemical test on link watch straps was implemented by the microelectrode technique. Stress corrosion has also been investigated in the assembly of laser welded pin and link. It should be noted that, despite the fact that the grade of steel is in conformity with the classification standards, we note that the corrosion behavior is very different from one steelmaker to another. There are parameters that can change the quality of steel such as the technology process, casting volume, deoxidizers’ addition, remelted steel process and traces of pollutants. In consequence, we observe an extensive dispersion of results concerning nickel release, according to the EN 1811 European legislation regarding the protection of the population’s health, specifically relating to skin contact. In conclusion, steels DIN 1.4441 (316L Med) and DIN 1.4539 (904L) present a very good resistance to the morphologies of pitting and crevice corrosion. The 316L and 304L steel grades, also known as DIN 1.4435, DIN 1.4404 and DIN 1.4306, display a major difference in pitting and crevice corrosion behavior.

Physical and chemical properties of sea salt deliquescent brines as a function of temperature and relative humidity

Thermodynamic modeling has been used to predict chemical compositions of brines formed by the deliquescence of sea salt aerosols. Representative brines have been mixed, and physical and chemical properties have been measured over a range of temperatures. Brine properties are discussed in terms of atmospheric corrosion of austenitic stainless steel, using spent nuclear fuel dry storage canisters as an example. After initial loading with spent fuel, during dry storage, the canisters cool over time, leading to increased surface relative humidities and evolving brine chemistries and properties. These parameters affect corrosion kinetics and damage distributions, and may offer important constraints on the expected timing, rate, and long-term impacts of canister corrosion.

Inhibition of Intergranular Corrosion in Austenitic Stainless Steels Through Critical Near-Surface Plastic Deformation and Ageing

Inhibition of Intergranular Corrosion in Austenitic Stainless Steels Through Critical Near-Surface Plastic Deformation and Ageing

Corrosion of austenitic stainless steels and nickel-based alloys in concentrated phosphoric acid at elevated temperatures

The corrosion sensitivity of several austenitic stainless steels (316L, 316Ti, Sanicro28, Sanicro35) and nickel-based alloys (Hastelloy G30 and Hastelloy G35) was determined at elevated temperatures in food grade phosphoric acid (FGPA). The materials were submerged in a harsh environment of >85 wt% FGPA at temperatures ranging from 80 to 160°C. The main aim was to understand the corrosion phenomena occurring in such environment and define the temperature range for which corrosion is within acceptable limits for these materials. Moreover, the role of a material's chemical composition on the corrosion resistance in phosphoric acid was experimentally elucidated. The corrosion sensitivity was determined by weight loss measurements, scanning electron microscopy and energy dispersive X-ray spectroscopy. The high concentrations of alloying elements in the selected metals allow them to form a protective passive surface film, which inhibits further oxidation. Depending on the stability of the passive film, materials will be corrosion resistant up to higher temperatures. Alloys with an increased molybdenum content showed a higher general and pitting corrosion resistance up to 140°C. Moreover, copper alloying resulted in an improved corrosion resistance at higher temperatures.

Influence of Chloride Concentration on Stress Corrosion Cracking and Crevice Corrosion of Austenitic Stainless Steel in Saline Environments.

Stainless steels are used as canister materials for interim storage of spent fuel. Crevice corrosion has proved to be a safety concern of 304L stainless steel spent fuel canisters, when exposed to the saline environments of coastal sites. To study the effects of chloride concentration and test duration on the crevice corrosion behavior, and the effect of relative humidity on the initiation of discrete SCC cracks, a test program was conducted on the 304L steel specimens sprayed with synthetic sea water of 3.5 wt.%. The salt-deposited specimens, wrapped up with a crevice former to form a crevice configuration, were then exposed to an environment at 45 °C with a pre-set 45%, 55%, and 70% relative humidity (RH), for 400 h and 10,000 h, respectively. The surface features and crack morphology of the tested 304L stainless-steel specimens were examined by energy-dispersive spectrometry (EDS) and electron back scatter diffraction (EBSD). For the specimens deposited with a chloride concentration of 1 g/m2, no cracks were found in the corroded regions after 400-h exposure, whereas SCC cracks were observed with the specimens tested for 10,000 h at all three pre-set relative humidity. The specimens tested at the pre-set relative humidity 45% are characterized with discrete SCC cracks, but, on the other hand, those exposed to the environments of 55% and 70% relative humidity show SCC cracks of distinct features. From the results of 10,000-h tests, it is inferred that the chloride concentration threshold for SCC initiation of 304L stainless steel at 45 °C is between 0.1 g/m2 and 1 g/m2.

Susceptibilidade à corrosão intergranular e por pites do aço inoxidável austenítico AISI 347 soldado e solubilizado

A susceptibilidade ao ataque intergranular e por pites nos aços inoxidáveis austeníticos é resultado do fenômeno de sensitização, que ocorre quando esses aços são utilizados em temperaturas entre 480-815 °C. Neste trabalho foi avaliada a susceptibilidade à corrosão intergranular e por pites de amostras de aço inoxidável austenítico AISI 347 nas condições: soldado sem tratamento térmico, soldado e solubilizado a 1060 °C por 27 min e a 950°C por 5h. Para avaliar a resistência à corrosão, foram realizados: ensaio de susceptibilidade a corrosão intergranular (de acordo com a norma ASTM 262 – 02A) e teste de resistência a corrosão por pites (de acordo com a norma ASTM G48). A caracterização microestrutural consistiu de análises por microscopia ótica confocal (MO) e, a partir das micrografias obtidas, foi quantificada a fração volumétrica dos constituíntes presentes de acordo com a norma ASTM E 562-02. Os ensaios mostraram que as amostras solubilizadas após a soldagem apresentaram uma redução de 34% p. na fração de ferrita delta presente na ZF. Na análise da susceptibilidade a corrosão intergranular, observou-se que o material soldado solubilizado a 1060°C foi o mais susceptível. Na análise da susceptibilidade à corrosão por pites, a amostra soldada solubilizada a 1060°C apresentou maior quantidade de pites profundos na face polida (concentrados principalmente na ZTA e no MB). Também foi observada a relação entre o acabamento superficial das amostras e a perda de massa: a amostra soldada solubilizada a 950°C apresentou a maior perda de massa pois possuía as piores condições de acabamento superficial.

Investigation of Inhibitive Effects of 2-Mercaptobenzimidazole (2-MBI) and Polyethyleneimine (PEI) on Pitting Corrosion of Austenitic Stainless Steel

In the present study, pitting corrosion of 316 austenitic stainless steel has been investigated in 3.5% NaCl solution at temperatures of 25, 40 and 60 °C using electrochemical methods (Cyclic potentiodynamic polarization (CPP) and Electrochemical impedance spectroscopy (EIS)). Then, inhibitive effects of 2-Mercaptobenzimidazole and Polyethylenimine with different concentrations on pitting corrosion of this alloy were analyzed. Adsorption behavior of the inhibitors on the substrate surface was also investigated using Fourier-transform infrared spectroscopy (FT-IR) and atomic force microscopy (AFM). Finally, microstructural studies were used by optical microscopy (OM) and scanning electron microscopy (SEM). The results showed that pitting corrosion of this alloy was well prevented by both inhibitors. However, corrosion resistance of 2-MBI was better than corrosion resistance of PEI and the results of OM and SEM showed better adsorption of 2-MBI compared to PEI. The highest pitting potential (626 mV vs. saturated calomel electrode (SCE)) was obtained in the presence of 2-MBI, while for PEI was 410 mV vs SCE. Also, it is found that desorption of inhibitors occurred at 60 °C and the effect of good inhibition did not occur at temperatures above 60 °C (inhibition efficiency for optimum concentration of PEI at 25 and 60 °C is 90.23 and 49, respectively). EIS and cyclic polarization tests showed that thickness of the passive layer increases with increasing the inhibitor concentration, which increases alloy corrosion resistance. The result showed that 2-MBI and PEI inhibition mechanism is deposition of single protective layer and double-layer adsorption, respectively.

Crystallographic Evaluation of Susceptibility to Intergranular Corrosion in Austenitic Stainless Steel with Various Degrees of Sensitization.

This study investigated the susceptibility to intergranular corrosion (IGC) in austenitic stainless steel with various degrees of sensitization (DOSs) from a microstructural viewpoint based on the coincidence site lattice (CSL) model. IGC testing was conducted using oxalic acid and type 304 stainless steel specimens with electrochemical potentiokinetic reactivation (EPR) ratios that varied from 3 to 30%. As a measure of IGC susceptibility, the width of the corroded groove was used. The relationship between IGC susceptibility, grain boundaries (GB) structure, and EPR ratio of the specimens was evaluated. As a result, the IGC susceptibility cannot be characterized using the Σ value, irrespective of the DOS of the specimen. The IGC susceptibility increases with increasing unit cell area of CSL boundaries, which is a measure of the stability of the CSL boundaries, and then levels off. The relationship between the IGC susceptibility and unit cell area is sigmoidal, irrespective of the DOS of the specimen. The sigmoid curve shifts rightward and the upper bound of IGC susceptibility decreases with decreasing DOS of the specimen.

Effect of Thermomechanical Parameters on Grain Growth and Recrystallization during Grain Boundary Engineering of Austenitic Stainless Steel

Grain boundary engineering has been attracting attention as an effective method to prevent intergranular corrosion of austenitic stainless steel and Ni based alloys. It has been considered that grain growth and recrystallization play important role in evolution of grain boundary character distribution during thermomechanical process. However, systematic researches to examine the effect of thermomechanical process parameters on grain growth and recrystallization have not been performed. In this study, grain boundary character distribution of 304 austenitic stainless steel after thermomechanical process with various parameters was analysed by electron backscatter diffraction (EBSD). Grain boundary character distribution was mainly affected by the reduction ratio of cold rolling. Abnormal grain growth was observed in the specimen with small reduction ratio (3%). Length ratio of coincident site lattice (CSL) boundaries was drastically increased to 86% in the 3% cold rolled and annealed specimens from 67% in the base material. On the other hand, normal grain growth was observed in thermomechanical processed specimens with slightly higher reduction of cold rolling (5%). In these specimens length ratio of CSL boundaries did not exceed 80%, which is required to disconnect the random boundary networks and to improve intergranular corrosion resistance effectively. Detailed analysis of grain boundary character distribution has shown that disconnection of random boundary networks was achieved by formation of annealing twins during abnormal grain growth.

Chemical and Physical Effects of Fluoride on the Corrosion of Austenitic Stainless Steel in Polluted Phosphoric Acid

The effect of fluoride ions was investigated on the austenitic stainless steel in a typical solution of phosphoric acid that is used in industrial process, for clear understanding the damage that caused by corrosion to special alloying material Uranus B6 at temperature of 80 °C. For that the electrochemical and spectroscopy methods were used like potentiodynamic and electrochemical impedance spectroscopy, X-ray diffraction and UV–visible–IR reflection, Scanning electron microscopy and energy-dispersive spectroscopy analysis (SEM–EDX). The electrochemical methods show the drastic effect of fluoride on the passivation parameters, especially icrit, ipass and Epit caused by decreasing the alloy elements in the surface alloy, specially the molybdenum. Moreover, the spectroscopy results reflect that fluoride has two axes of interaction with the surface alloy; chemical interaction that was appeared by the dissolution mechanism, which it increases the dissolution of the base alloy atom and the alloying elements and this result was improved by the UV–visible–IR and EDX analysis. And the physical effect was demonstrated by X-ray diffraction, which is showing a deformation of the crystalline structure of surface alloy; and different pit types were detected by SEM. And the suggestion of the effect of fluoride on the nickel percent in the passive film and also on the molybdenum and copper has been proposed as a mechanism to explain these results.

The Role of Pitting at Mns Inclusions in Intergranular Corrosion of Sensitized Type 304 Stainless Steel in NaCl Solution

The degree of sensitization and susceptibility of intergranular corrosion of austenitic stainless steels are properly evaluated from immersion testing in acidic solutions as rapid screening methods. However, most of stainless steels are used in near-neutral pH environments, and the typical corrosion morphology in these environments is pitting. Acidification is known to occur inside pits due to the hydrolysis reaction of dissolving metal ions. Under practical service conditions around neutral pH such as seawater and river water, pitting is assumed to be closely related to the initiation of intergranular corrosion. It is well-known that non-metallic inclusions, such as MnS, act as the initiation sites for pitting of stainless steels. Chiba et al. demonstrated that a small inclusion-free area on Type 304 indicated superior pitting corrosion resistance even in 3 M NaCl. 1) It would appear that MnS inclusions strongly affect pitting and intergranular corrosion of sensitized stainless steels. To clarify the role of pitting at MnS inclusions in intergranular corrosion of sensitized Type 304 stainless steel (sensitized at 923 K), in situ observations were carried out during micro-scale anodic polarization in 1 M NaCl (pH 5.4). Micro-scale potentiodynamic anodic polarization was performed for a small area with a MnS inclusion at a sensitized grain boundary. Intergranular corrosion was initiated from the pit that was generated at the MnS inclusion located at the sensitized grain boundary. Acidification inside the pit probably caused intergranular corrosion due to the transition from passive to active state. In 1 M NaCl, the depassivation pH values at the sensitized grain boundary with and without MnS inclusions were 1.0 and 0.4, respectively. It is likely that the dissolution of MnS accelerates the depassivation and promote the initiation pf intergranular corrosion. The dissolution products from MnS are supposed to accelerate depassivation of Cr-depleted regions. 1) A. Chiba, I. Muto, Y. Sugawara, N. Hara, J. Electrochem. Soc., 160, C511-C520 (2013).

Studies on pitting corrosion in austenitic stainless steel interfered by square-wave alternating voltage with different parameters using multi-potential steps method

Studies on pitting corrosion in austenitic stainless steel interfered by square-wave alternating voltage with different parameters using multi-potential steps method

Application of a modified bi-polar electrochemistry approach to determine pitting corrosion characteristics

The application of bi-polar electrochemistry produces a linear potential gradient between two feeder electrodes, allowing the full spectrum of anodic to cathodic reaction kinetics to be controlled. A modified bi-polar approach is introduced, by superimposing a constant electrochemical potential on the potential gradient, thereby controlling the location and spatial distribution of anodic to cathodic reactions along the exposed sample surface. Application of this approach is demonstrated by controlling the extent of pitting corrosion in austenitic stainless steel as a function of the applied potential.

Digital holographic microscopy as a new technique for quantitative measurement of microstructural corrosion in austenitic stainless steel

The aim of this paper is to introduce reflective digital holographic microscopy (rDHM) as a new method for quantitative evaluation of corrosion. Despite the commonly-used evaluation methods, rDHM does not require scanning, while it measures the microstructural height profile of the corroded sample surface within a macroscale area. Based on the height profile across the corroded grain boundaries, a quantitative criterion is suggested to distinguish between intergranular and transgranular corrosion. The experimental results show the capability of rDHM to analyse the microstructural corrosion in AISI 304 stainless steel. The presented method can also be applied as a surface characterization method for analysis of a variety of metallurgic effects such as crystal elasticity and crystal orientation.

Plastic deformation and corrosion in austenitic stainless steel: A novel approach through microtexture and infrared spectroscopy

The anodic potentiodynamic polarization behaviors of austenitic stainless steels, with varying Cu (copper) and/or Mo (molybdenum) additions, were explored after plane strain compression. Though all the alloys showed developments in deformed microstructures, the presence of Cu+Mo did not result in strain induced martensite formation (SIMF). However, the presence of Cu+Mo revealed the highest degradation in corrosion performance. A combination of microtexture measurements and fourier transform infrared spectroscopy (FTIR)-imaging revealed that the presence of SIMF promoted post-passivation stability or retention of a protective Cr2O3 film.

Application of Ultrasonic Methods for Early Detection of Intergranular Corrosion in Austenitic Stainless Steel

ABSTRACTIntergranular corrosion (IGC) is one of the major localized corrosion problems faced by austenitic stainless steel components in ultra-supercritical power plants, which occurs along the grain boundaries of material and results in loss of engineering properties. Ultrasonic technique was applied to the early detection of IGC in austenitic stainless steel super304H. Acoustic attenuation and nonlinear parameter were measured at multiple excitation frequencies, and an equivalent attenuation factor and an equivalent nonlinear factor were defined to evaluate the IGC damage. Results indicated that both factors increased monotonously as the degree of IGC developed, and the equivalent nonlinear factor is more sensitive to IGC at early stage. Thus they can be utilized for early detection of IGC in austenitic stainless steel.