Research

2058 KiB

Open AccessArticle

Hydrogen Assisted Cracking in Pearlitic Steel Rods: The Role of Residual Stresses Generated by Fatigue Precracking

by Jesús Toribio, Leticia Aguado, Miguel Lorenzo and Viktor Kharin

Materials 2017, 10(5), 485; https://doi.org/10.3390/ma10050485 - 02 May 2017

Cited by 3 | Viewed by 3929

Stress corrosion cracking (SCC) of metals is an issue of major concern in engineering since this phenomenon causes many catastrophic failures of structural components in aggressive environments. SCC is even more harmful under cathodic conditions promoting the phenomenon known as hydrogen assisted cracking [...] Read more.

Stress corrosion cracking (SCC) of metals is an issue of major concern in engineering since this phenomenon causes many catastrophic failures of structural components in aggressive environments. SCC is even more harmful under cathodic conditions promoting the phenomenon known as hydrogen assisted cracking (HAC), hydrogen assisted fracture (HAF) or hydrogen embrittlement (HE). A common way to assess the susceptibility of a given material to HAC, HAF or HE is to subject a cracked rod to a constant extension rate tension (CERT) test until it fractures in this harsh environment. This paper analyzes the influence of a residual stress field generated by fatigue precracking on the sample’s posterior susceptibility to HAC. To achieve this goal, numerical simulations were carried out of hydrogen diffusion assisted by the stress field. Firstly, a mechanical simulation of the fatigue precracking was developed for revealing the residual stress field after diverse cyclic loading scenarios and posterior stress field evolution during CERT loading. Afterwards, a simulation of hydrogen diffusion assisted by stress was carried out considering the residual stresses after fatigue and the superposed rising stresses caused by CERT loading. Results reveal the key role of the residual stress field after fatigue precracking in the HAC phenomena in cracked steel rods as well as the beneficial effect of compressive residual stress. Full article

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

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4014 KiB

Open AccessArticle

Corrosion-Fatigue Crack Growth in Plates: A Model Based on the Paris Law

by Jesús Toribio, Juan-Carlos Matos and Beatriz González

Materials 2017, 10(4), 439; https://doi.org/10.3390/ma10040439 - 22 Apr 2017

Cited by 12 | Viewed by 5282

Abstract

In this paper, a Paris law-based model is presented whereby crack propagation occurs under cyclic loading in air (fatigue) and in an aggressive environment (corrosion-fatigue) for the case of corner cracks (with a wide range of aspect ratios in [...] Read more.

In this paper, a Paris law-based model is presented whereby crack propagation occurs under cyclic loading in air (fatigue) and in an aggressive environment (corrosion-fatigue) for the case of corner cracks (with a wide range of aspect ratios in the matter of the initial cracks) in finite-thickness plates of 316L austenitic stainless steel subjected to tension, bending, or combined (tension + bending) loading. Results show that the cracks tend during their growth towards a preferential propagation path, exhibiting aspect ratios slightly lower than unity only for the case of very shallow cracks, and diminishing as the crack grows (increasing the relative crack depth)—more intensely in the case of bending than in the case of tension (the mixed loading tension/bending representing an intermediate case). In addition, the crack aspect ratios during fatigue propagation evolution are lower in fatigue (in air) than in corrosion-fatigue (in aggressive environment). Full article

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

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12935 KiB

Open AccessArticle

Interacting Effects Induced by Two Neighboring Pits Considering Relative Position Parameters and Pit Depth

by Yongfang Huang, Tieqiang Gang and Lijie Chen

Materials 2017, 10(4), 398; https://doi.org/10.3390/ma10040398 - 09 Apr 2017

Cited by 9 | Viewed by 3680

Abstract

For pre-corroded aluminum alloy 7075-T6, the interacting effects of two neighboring pits on the stress concentration are comprehensively analyzed by considering various relative position parameters (inclination angle θ and dimensionless spacing parameter λ) and pit depth (d) with the finite [...] Read more.

For pre-corroded aluminum alloy 7075-T6, the interacting effects of two neighboring pits on the stress concentration are comprehensively analyzed by considering various relative position parameters (inclination angle θ and dimensionless spacing parameter λ) and pit depth (d) with the finite element method. According to the severity of the stress concentration, the critical corrosion regions, bearing high susceptibility to fatigue damage, are determined for intersecting and adjacent pits, respectively. A straightforward approach is accordingly proposed to conservatively estimate the combined stress concentration factor induced by two neighboring pits, and a concrete application example is presented. It is found that for intersecting pits, the normalized stress concentration factor K_tnor increases with the increase of θ and λ and always reaches its maximum at θ = 90°, yet for adjacent pits, K_tnor decreases with the increase of λ and the maximum value appears at a slight asymmetric location. The simulations reveal that K_tnor follows a linear and an exponential relationship with the dimensionless depth parameter R_d for intersecting and adjacent cases, respectively. Full article

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

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12155 KiB

Open AccessArticle

Effects of Nitrogen and Tensile Direction on Stress Corrosion Cracking Susceptibility of Ni-Free FeCrMnC-Based Duplex Stainless Steels

by Heon-Young Ha, Chang-Hoon Lee, Tae-Ho Lee and Sangshik Kim

Materials 2017, 10(3), 294; https://doi.org/10.3390/ma10030294 - 15 Mar 2017

Cited by 17 | Viewed by 4985

Abstract

Stress corrosion cracking (SCC) behavior of Ni-free duplex stainless steels containing N and C (Fe_balance-19Cr-8Mn-0.25C-(0.03, 0.21)N, in wt %) was investigated by using a slow strain rate test (SSRT) in air and aqueous NaCl solution with different tensile directions, including parallel [...] Read more.

Stress corrosion cracking (SCC) behavior of Ni-free duplex stainless steels containing N and C (Fe_balance-19Cr-8Mn-0.25C-(0.03, 0.21)N, in wt %) was investigated by using a slow strain rate test (SSRT) in air and aqueous NaCl solution with different tensile directions, including parallel (longitudinal) and perpendicular (transverse) to the rolling direction. It was found that alloying N was effective in increasing the resistance to SCC, while it was higher along the longitudinal direction than the transverse direction. The SCC susceptibility of the two alloys was assessed based on the electrochemical resistance to pitting corrosion, the corrosion morphology, and the fractographic analysis. Full article

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

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3292 KiB

Open AccessFeature PaperArticle

Strain Effect on Electronic Structure and Work Function in α-Fe₂O₃ Films

by Li Chen, Changmin Shi, Xiaolong Li, Zhishan Mi, Dongchao Wang, Hongmei Liu and Lijie Qiao

Materials 2017, 10(3), 273; https://doi.org/10.3390/ma10030273 - 09 Mar 2017

Cited by 17 | Viewed by 6554

Abstract

We investigate the electronic structure and work function modulation of α-Fe₂O₃ films by strain based on the density functional method. We find that the band gap of clean α-Fe₂O₃ films is a function of the strain and [...] Read more.

We investigate the electronic structure and work function modulation of α-Fe₂O₃ films by strain based on the density functional method. We find that the band gap of clean α-Fe₂O₃ films is a function of the strain and is influenced significantly by the element termination on the surface. The p_x and p_y orbitals keep close to Fermi level and account for a pronounced narrowing band gap under compressive strain, while unoccupied d_z₂ orbitals from conduction band minimum draw nearer to Fermi level and are responsible for the pronounced narrowing band gap under tensile strain. The spin polarized surface state, arising from localized dangling-bond states, is insensitive to strain, while the bulk band, especially for p_z orbital, arising from extended Bloch states, is very sensitive to strain, which plays an important role for work function decreasing (increasing) under compressive (tensile) strain in Fe termination films. In particular, the work function in O terminated films is insensitive to strain because p_z orbitals are less sensitive to strain than that of Fe termination films. Our findings confirm that the strain is an effective means to manipulate electronic structures and corrosion potential. Full article

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

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10867 KiB

Open AccessArticle

SCC of 2304 Duplex Stainless Steel—Microstructure, Residual Stress and Surface Grinding Effects

by Nian Zhou, Ru Lin Peng, Mikael Schönning and Rachel Pettersson

Materials 2017, 10(3), 221; https://doi.org/10.3390/ma10030221 - 23 Feb 2017

Cited by 13 | Viewed by 5822

Abstract

The influence of surface grinding and microstructure on chloride induced stress corrosion cracking (SCC) behavior of 2304 duplex stainless steel has been investigated. Grinding operations were performed both parallel and perpendicular to the rolling direction of the material. SCC tests were conducted in [...] Read more.

The influence of surface grinding and microstructure on chloride induced stress corrosion cracking (SCC) behavior of 2304 duplex stainless steel has been investigated. Grinding operations were performed both parallel and perpendicular to the rolling direction of the material. SCC tests were conducted in boiling magnesium chloride according to ASTM G36; specimens were exposed both without external loading and with varied levels of four-point bend loading. Residual stresses were measured on selected specimens before and after exposure using the X-ray diffraction technique. In addition, in-situ surface stress measurements subjected to four-point bend loading were performed to evaluate the deviation between the actual applied loading and the calculated values according to ASTM G39. Micro-cracks, initiated by grinding induced surface tensile residual stresses, were observed for all the ground specimens but not on the as-delivered surfaces. Loading transverse to the rolling direction of the material increased the susceptibility to chloride induced SCC. Grinding induced tensile residual stresses and micro-notches in the as-ground surface topography were also detrimental. Full article

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

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11790 KiB

Open AccessArticle

Stress Corrosion Cracking Susceptibility of 304L Substrate and 308L Weld Metal Exposed to a Salt Spray

by Chia-Hao Hsu, Tai-Cheng Chen, Rong-Tan Huang and Leu-Wen Tsay

Materials 2017, 10(2), 187; https://doi.org/10.3390/ma10020187 - 15 Feb 2017

Cited by 22 | Viewed by 5904

Abstract

304 stainless steels (SS) were considered as the materials for a dry storage canister. In this study, ER (Electrode Rod) 308L was utilized as the filler metal for the groove and overlay welds of a 304L stainless steel substrate, which was prepared via [...] Read more.

304 stainless steels (SS) were considered as the materials for a dry storage canister. In this study, ER (Electrode Rod) 308L was utilized as the filler metal for the groove and overlay welds of a 304L stainless steel substrate, which was prepared via a gas tungsten arc-welding process in multiple passes. The electron backscatter diffraction (EBSD) map was used to identify the inherent microstructures in distinct specimens. U-bend and weight-loss tests were conducted by testing the 304L substrates and welds in a salt spray containing 5 wt % NaCl at 80 °C to evaluate their susceptibility to stress corrosion cracking (SCC). Generally, the weight loss of the ER 308L deposit was higher than that of the 304L substrate in a salt spray in the same sample-prepared condition. The dissolution of the skeletal structure in the fusion zone (FZ) was responsible for a greater weight loss of the 308L deposit, especially for the cold-rolled and sensitized specimen. Cold rolling was detrimental and sensitization after cold rolling was very harmful to the SCC resistance of the 304L substrate and 308L deposit. Overall, the SCC susceptibility of each specimen was correlated with its weight loss in each group. Full article

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

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15468 KiB

Open AccessArticle

A Study on the Susceptibility to SCC of 7050 Aluminum Alloy by DCB Specimens

by Xing Qi, Jirong Jin, Chunli Dai, Wenjuan Qi, Wangzhao He and Renguo Song

Materials 2016, 9(11), 884; https://doi.org/10.3390/ma9110884 - 01 Nov 2016

Cited by 18 | Viewed by 4038

Abstract

The stress corrosion cracking (SCC) of different aging states for 7050 aluminum alloy in 3.5% sodium chloride aqueous solution has been studied by means of double cantilever beam (DCB) specimens, cathodic polarization, scanning electron microscope (SEM), transmission electron microscope (TEM) and time-of-flying second [...] Read more.

The stress corrosion cracking (SCC) of different aging states for 7050 aluminum alloy in 3.5% sodium chloride aqueous solution has been studied by means of double cantilever beam (DCB) specimens, cathodic polarization, scanning electron microscope (SEM), transmission electron microscope (TEM) and time-of-flying second ion mass spectrometer (ToF-SIMS). The results showed that the susceptibility to SCC (Iscc) of 7050 aluminum alloy decreases with increasing the aging time. When a cathodic polarization potential of −1100 mV was applied to DCB specimens, the ion current intensity of hydrogen (I_H⁺) near the crack tip and Iscc increased obviously, thus the degree of the diffusion of hydrogen into the grain boundary become more serious. The observation of microstructure indicated that the precipitates on the grain boundary become coarse and are sparsely distributed with increasing the aging time of 7050 aluminum alloy. Full article

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

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4603 KiB

Open AccessArticle

A Modelling Study for Predicting Life of Downhole Tubes Considering Service Environmental Parameters and Stress

by Tianliang Zhao, Zhiyong Liu, Cuiwei Du, Jianpeng Hu and Xiaogang Li

Materials 2016, 9(9), 741; https://doi.org/10.3390/ma9090741 - 02 Sep 2016

Cited by 4 | Viewed by 4076

Abstract

A modelling effort was made to try to predict the life of downhole tubes or casings, synthetically considering the effect of service influencing factors on corrosion rate. Based on the discussed corrosion mechanism and corrosion processes of downhole tubes, a mathematic model was [...] Read more.

A modelling effort was made to try to predict the life of downhole tubes or casings, synthetically considering the effect of service influencing factors on corrosion rate. Based on the discussed corrosion mechanism and corrosion processes of downhole tubes, a mathematic model was established. For downhole tubes, the influencing factors are environmental parameters and stress, which vary with service duration. Stress and the environmental parameters including water content, partial pressure of H₂S and CO₂, pH value, total pressure and temperature, were considered to be time-dependent. Based on the model, life-span of an L80 downhole tube in oilfield Halfaya, an oilfield in Iraq, was predicted. The results show that life-span of the L80 downhole tube in Halfaya is 247 months (approximately 20 years) under initial stress of 0.1 yield strength and 641 months (approximately 53 years) under no initial stress, which indicates that an initial stress of 0.1 yield strength will reduce the life-span by more than half. Full article

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

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