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16 pages, 8570 KiB

Open AccessArticle

Stress Corrosion Cracking of Friction Stir-Welded AA-2024 T3 Alloy

by Marina Cabrini, Sara Bocchi, Gianluca D'Urso, Claudio Giardini, Sergio Lorenzi, Cristian Testa and Tommaso Pastore

Materials 2020, 13(11), 2610; https://doi.org/10.3390/ma13112610 - 8 Jun 2020

Cited by 15 | Viewed by 2554

Abstract

The paper is devoted to the study of stress corrosion cracking phenomena in friction stir welding AA-2024 T3 joints. Constant load (CL) cell and slow strain rate (SSR) tests were carried out in aerated NaCl 35 g/L solution. During the tests, open circuit [...] Read more.

The paper is devoted to the study of stress corrosion cracking phenomena in friction stir welding AA-2024 T3 joints. Constant load (CL) cell and slow strain rate (SSR) tests were carried out in aerated NaCl 35 g/L solution. During the tests, open circuit potential (OCP) and electrochemical impedance spectroscopy (EIS) were measured in the different zones of the welding. The results evidenced initial practical nobilty of the nugget lower compared to both heat-affected zone and the base metal. This effect can be mainly ascribed to the aluminum matrix depletion in copper, which precipitates in form of copper-rich second phases. In this zones, no stress corrosion cracking was noticed, but well-evident stress-enhanced intergranular corrosion occurred. This is due to the uneven distribution of platic deformation during the slow strain rate tests. Higher strain values are localized at the heat affected zone, where softening occurs. On the contrary, stress values at the nugget are not sufficient to favor both the initiation and propagation of stress corrosion cracks. In the range of processing parameter studied in this experimental work, the stress corrosion cracking susceptibility of the friction stir welding (FSW)-ed alloy is then similar to that of the base metal. Full article

(This article belongs to the Special Issue Stress-Corrosion Cracking in Materials)

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15 pages, 2889 KiB

Open AccessFeature PaperArticle

Hydrogen Permeation in X65 Steel under Cyclic Loading

by Marina Cabrini, Luigi Coppola, Sergio Lorenzi, Cristian Testa, Francesco Carugo, Diego Pesenti Bucella and Tommaso Pastore

Materials 2020, 13(10), 2309; https://doi.org/10.3390/ma13102309 - 17 May 2020

Cited by 8 | Viewed by 2741

Abstract

This experimental work analyzes the hydrogen embrittlement mechanism in quenched and tempered low-alloyed steels. Experimental tests were performed to study hydrogen diffusion under applied cyclic loading. The permeation curves were fitted by considering literature models in order to evaluate the role of trapping—both [...] Read more.

This experimental work analyzes the hydrogen embrittlement mechanism in quenched and tempered low-alloyed steels. Experimental tests were performed to study hydrogen diffusion under applied cyclic loading. The permeation curves were fitted by considering literature models in order to evaluate the role of trapping—both reversible and irreversible—on the diffusion mechanism. Under loading conditions, a marked shift to the right of the permeation curves was noticed mainly at values exceeding the tensile yield stress. In the presence of a relevant plastic strain, the curve changes due to the presence of irreversible traps, which efficiently subtract diffusible atomic hydrogen. A significant reduction in the apparent diffusion coefficient and a considerable increase in the number of traps were noticed as the maximum load exceeded the yield strength. Cyclic loading at a tensile stress slightly higher than the yield strength of the material increases the hydrogen entrapment phenomena. The tensile stress causes a marked and instant reduction in the concentration of mobile hydrogen within the metal lattice from 55% of the yield strength, and it increases significantly in the plastic field. Full article

(This article belongs to the Special Issue Stress-Corrosion Cracking in Materials)

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30 pages, 15033 KiB

Open AccessArticle

Hydrogen Embrittlement and Oxide Layer Effect in the Cathodically Charged Zircaloy-2

by Grzegorz Gajowiec, Michał Bartmański, Beata Majkowska-Marzec, Andrzej Zieliński, Bartosz Chmiela and Marek Derezulko

Materials 2020, 13(8), 1913; https://doi.org/10.3390/ma13081913 - 18 Apr 2020

Cited by 5 | Viewed by 2424

Abstract

The present paper is aimed at determining the less investigated effects of hydrogen uptake on the microstructure and the mechanical behavior of the oxidized Zircaloy-2 alloy. The specimens were oxidized and charged with hydrogen. The different oxidation temperatures and cathodic current densities were [...] Read more.

The present paper is aimed at determining the less investigated effects of hydrogen uptake on the microstructure and the mechanical behavior of the oxidized Zircaloy-2 alloy. The specimens were oxidized and charged with hydrogen. The different oxidation temperatures and cathodic current densities were applied. The scanning electron microscopy, X-ray electron diffraction spectroscopy, hydrogen absorption assessment, tensile, and nanoindentation tests were performed. At low oxidation temperatures, an appearance of numerous hydrides and cracks, and a slight change of mechanical properties were noticed. At high-temperature oxidation, the oxide layer prevented the hydrogen deterioration of the alloy. For nonoxidized samples, charged at different current density, nanoindentation tests showed that both hardness and Young’s modulus revealed the minims at specific current value and the stepwise decrease in hardness during hydrogen desorption. The obtained results are explained by the barrier effect of the oxide layer against hydrogen uptake, softening due to the interaction of hydrogen and dislocations nucleated by indentation test, and hardening caused by the decomposition of hydrides. The last phenomena may appear together and result in hydrogen embrittlement in forms of simultaneous hydrogen-enhanced localized plasticity and delayed hydride cracking. Full article

(This article belongs to the Special Issue Stress-Corrosion Cracking in Materials)

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14 pages, 7642 KiB

Open AccessArticle

Influence of Thermal Treatment on SCC and HE Susceptibility of Supermartensitic Stainless Steel 16Cr5NiMo

by Linda Bacchi, Fabio Biagini, Serena Corsinovi, Marco Romanelli, Michele Villa and Renzo Valentini

Materials 2020, 13(7), 1643; https://doi.org/10.3390/ma13071643 - 2 Apr 2020

Cited by 12 | Viewed by 2312

Abstract

A 16Cr5NiMo supermartensitic stainless steel was subjected to different tempering treatments and analyzed by means of permeation tests and slow strain rate tests to investigate the effect of different amounts of retained austenite on its hydrogen embrittlement susceptibility. The 16Cr5NiMo steel class is [...] Read more.

A 16Cr5NiMo supermartensitic stainless steel was subjected to different tempering treatments and analyzed by means of permeation tests and slow strain rate tests to investigate the effect of different amounts of retained austenite on its hydrogen embrittlement susceptibility. The 16Cr5NiMo steel class is characterized by a very low carbon content. It is the new variant of 13Cr4Ni. These steels are used in many applications, for example, compressors for sour environments, offshore piping, naval propellers, aircraft components and subsea applications. The typical microstructure is a soft-tempered martensite very close to a body-centered cubic, with a retained austenite fraction and limited δ ferrite phase. Supermartensitic stainless steels have high mechanical properties, together with good weldability and corrosion resistance. The amount of retained austenite is useful to increase low temperature toughness and stress corrosion cracking resistance. Experimental techniques allowed us to evaluate diffusion coefficients and the mechanical behaviour of metals in stress corrosion cracking (SCC) conditions. Full article

(This article belongs to the Special Issue Stress-Corrosion Cracking in Materials)

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16 pages, 11733 KiB

Open AccessArticle

Effect of Relative Humidity on Mechanical Degradation of Medium Mn Steels

by Qingyang Liu, Juanping Xu, Liancheng Shen, Qingjun Zhou, Yanjing Su, Lijie Qiao and Yu Yan

Materials 2020, 13(6), 1304; https://doi.org/10.3390/ma13061304 - 13 Mar 2020

Cited by 3 | Viewed by 2141

Abstract

Medium Mn steels have been considered as the next-generation materials for use in the automotive industry due to their excellent strength and ductility balance. To reduce the total weight and improve the safety of vehicles, medium Mn steels look forward to a highly [...] Read more.

Medium Mn steels have been considered as the next-generation materials for use in the automotive industry due to their excellent strength and ductility balance. To reduce the total weight and improve the safety of vehicles, medium Mn steels look forward to a highly promising future. However, hydrogen-induced delayed cracking is a concern for the use of high strength steels. This work is focused on the service characteristics of two kinds of medium Mn steels under different relative humidity conditions (40%, 60%, 80% and 100%). Under normal relative humidity (about 40%) at 25 °C, the hydrogen concentration in steel is 0.4 ppm. When exposed to higher relative humidity, the hydrogen concentration in steel increases slowly and reaches a stable value, about 0.8 ppm. In slow strain rate tensile tests under different relative humidity conditions, the tensile strength changed, the hydrogen concentration increased and the elongation decreased as well, thereby increasing the hydrogen embrittlement sensitivity. In other words, the smaller the tensile rate applied, the greater the hydrogen embrittlement sensitivity. In constant load tests under different relative humidity conditions, the threshold value of the delayed cracking of M7B (‘M’ referring to Mn, ‘7’ meaning the content of Mn, ‘B’ denoting batch annealing) steel maintains a steady value of 0.82 σ_b (tensile strength). The threshold value of the delayed cracking of M10B significantly changed along with relative humidity. When relative humidity increased from 60% to 80%, the threshold dropped sharply from 0.63 σ_b to 0.52 σ_b. We define 80% relative humidity as the ‘threshold humidity’ for M10B. Full article

(This article belongs to the Special Issue Stress-Corrosion Cracking in Materials)

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16 pages, 7605 KiB

Open AccessArticle

Numerical Investigation on Lateral Confinement Effects on Concrete Cracking Induced by Rebar Corrosion

by Gyeongcheol Choe, Yasuji Shinohara, Gyuyong Kim and Jeongsoo Nam

Materials 2020, 13(5), 1156; https://doi.org/10.3390/ma13051156 - 5 Mar 2020

Cited by 9 | Viewed by 2724

Abstract

Accelerated corrosion tests of reinforced concrete (RC) specimens were conducted to estimate the corrosion expansion rate of reinforcing bars. Subsequently, finite element analysis was performed with the estimated expansion rate for RC beams to investigate concrete cracking induced by corrosion. The influence of [...] Read more.

Accelerated corrosion tests of reinforced concrete (RC) specimens were conducted to estimate the corrosion expansion rate of reinforcing bars. Subsequently, finite element analysis was performed with the estimated expansion rate for RC beams to investigate concrete cracking induced by corrosion. The influence of the different confinement levels on crack behavior was investigated using mainly the amount of transverse reinforcement. An expansion rate of 2 was found to be appropriate when using Lundgren’s expansion model. Confinement levels affected the cracking behavior of steel bars. Cracks did not significantly affect structural capacity although they exceeded the allowable crack width. Nevertheless, repair and reinforcement measures are necessary because degrading durability factors such as carbonation or salt diffusion can reach the reinforcing bars through connected cracks. Full article

(This article belongs to the Special Issue Stress-Corrosion Cracking in Materials)

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19 pages, 7770 KiB

Open AccessArticle

A Comparative Study of Localized Corrosion and Stress Corrosion Cracking of 13Cr Martensitic Stainless Steel Using Acoustic Emission and X-ray Computed Tomography

by Kaige Wu, Kaita Ito, Ippei Shinozaki, Pornthep Chivavibul and Manabu Enoki

Materials 2019, 12(16), 2569; https://doi.org/10.3390/ma12162569 - 12 Aug 2019

Cited by 14 | Viewed by 4539

Abstract

An accurate evaluation of stress corrosion cracking (SCC) in 13Cr martensitic stainless steel (MSS) is still missing due to the lack of an in-situ insight into the process evolution and full characterization of the corrosion morphology. In this work, two main regimes involved [...] Read more.

An accurate evaluation of stress corrosion cracking (SCC) in 13Cr martensitic stainless steel (MSS) is still missing due to the lack of an in-situ insight into the process evolution and full characterization of the corrosion morphology. In this work, two main regimes involved in the SCC progression, including localized corrosion and cracking, were comparatively studied using in-situ acoustic emission (AE) monitoring and three-dimensional (3D) X-ray computed tomography (XCT) scanning. The stress corrosion tests were conducted with u-bent smooth specimens subjected to a single droplet of 1 μL 1% neutral NaCl solution. Localized corrosion and cracking evolution were controlled in tempered and quenched steel specimens, respectively. From XCT scanning, localized corrosion was featured by an irregular corrosion pit with deposited corrosion products containing cracks. The single dominant SCC crack was observed to initiate from corrosion pit and propagate with a 3D tortuous and discontinuous morphology. AE signals were detected in both cases. Correlated with in-situ observations and clustering analysis, source identification of AE signals was proposed. AE signals during localized corrosion were assessed to be mainly from cracking within the deposited corrosion products. Comparatively, hydrogen-bubble evolution, plastic deformation, and crack-branches coalescence were proposed as the AE sources of cracking evolution. Full article

(This article belongs to the Special Issue Stress-Corrosion Cracking in Materials)

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16 pages, 5710 KiB

Open AccessArticle

Laboratory-Based Investigation into Stress Corrosion Cracking of Cable Bolts

by Saisai Wu, Jinping Guo, Guangbin Shi, Junping Li and Caiwu Lu

Materials 2019, 12(13), 2146; https://doi.org/10.3390/ma12132146 - 3 Jul 2019

Cited by 10 | Viewed by 3551

Abstract

Cable-bolt failures due to stress corrosion cracking (SCC) could significantly compromise the sustainability and long-term stability of underground constructions. To fully understand the SCC of cable bolts, a two-step methodology was implemented: (i) long-term cable-bolt coupon tests using mineralogical materials collected from underground [...] Read more.

Cable-bolt failures due to stress corrosion cracking (SCC) could significantly compromise the sustainability and long-term stability of underground constructions. To fully understand the SCC of cable bolts, a two-step methodology was implemented: (i) long-term cable-bolt coupon tests using mineralogical materials collected from underground mines; and (ii) accelerated full-scale cable-bolt tests using an acidified solution. In the long-term tests, a novel three-point bending coupon was designed. The effects of mineralogical materials on SCC were evaluated under the simulated underground bolting conditions through the application of “corrosion cells”. For accelerated tests, SCC resistance of different type of cable bolts was examined using the new designed tensile-loading apparatus under the periodically increasing strain-rate loading mechanism. It was identified that mineralogical materials and applied stress intensity accelerated the corrosion process of the cable bolts. The number of wires and wire surface conditions in different types of cable bolt directly affected SCC susceptibility. The cable bolts with a greater number of wires provided higher resistance to SCC. The developed experimental methodologies can be applied to study SCC in other reinforcement materials and the results can be used to design optimal support systems in different environmental and geotechnical conditions. Full article

(This article belongs to the Special Issue Stress-Corrosion Cracking in Materials)

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17 pages, 8546 KiB

Open AccessArticle

Hydrogen Embrittlement Evaluation of Micro Alloyed Steels by Means of J-Integral Curve

by Marina Cabrini, Ennio Sinigaglia, Carlo Spinelli, Marco Tarenzi, Cristian Testa and Fabio Maria Bolzoni

Materials 2019, 12(11), 1843; https://doi.org/10.3390/ma12111843 - 6 Jun 2019

Cited by 13 | Viewed by 3086

Abstract

The aim of this work is the evaluation of the hydrogen effect on the J-integral parameter. It is well-known that the micro alloyed steels are affected by Hydrogen Embrittlement phenomena only when they are subjected at the same time to plastic deformation [...] Read more.

The aim of this work is the evaluation of the hydrogen effect on the J-integral parameter. It is well-known that the micro alloyed steels are affected by Hydrogen Embrittlement phenomena only when they are subjected at the same time to plastic deformation and hydrogen evolution at their surface. Previous works have pointed out the absence of Hydrogen Embrittlement effects on pipeline steels cathodically protected under static load conditions. On the contrary, in slow strain rate tests it is possible to observe the effect of the imposed potential and the strain rate on the hydrogen embrittlement steel behavior only after the necking of the specimens. J vs. Δa curves were measured on different pipeline steels in air and in aerated NaCl 3.5 g/L solution at free corrosion potential or under cathodic polarization at −1.05 and −2 V vs. SCE. The area under the J vs. Δa curves and the maximum crack propagation rate were taken into account. These parameters were compared with the ratio between the reduction of area in environment and in air obtained by slow strain rate test in the same environmental conditions and used to rank the different steels. Full article

(This article belongs to the Special Issue Stress-Corrosion Cracking in Materials)

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