Corrosion Pits Research Articles

A comparative study on the corrosion behavior of Q235 steel in saturated acidic red and yellow soils

Purpose The purpose of this paper is to study the corrosion behavior of Q235 steel in saturated acidic red and yellow soils. Design/methodology/approach The corrosion behavior of Q235 steel in saturated red and yellow soils was compared by weight-loss, SEM/EDS, 3D ultra-depth microscopy and electrochemical measurements. Findings Rp of the steel gradually increases and icorr gradually decreases in both the red and yellow soils with time. The Rp of the steel in the red soil is lower, but its icorr is higher than that in the yellow soil. The uniform corrosion rate, diameter and density of the corrosion pit on the steel surface in the red soil are greater than those in the yellow soil. Lower pH, higher contents of corrosive anions and high-valence Fe oxides in the red soil are responsible for its higher corrosion rates and local corrosion susceptibility. Originality/value This paper investigates the difference in corrosion behavior of carbon steel in saturated acidic red and yellow soils, which can help to understand the mechanism of soil corrosion.

Effects of different magnitudes of static stress on the in vitro corrosion behavior of biodegradable zinc

Cardiovascular stents are subjected to complex mechanical stresses in service, and local stress concentrations due to irregular stent shapes may lead to premature failure. This work investigated the corrosion behavior of pure zinc under different tensile stresses and found that stress accelerates corrosion and promotes the expansion of corrosion pits. A numerical model of the relationship between corrosion rate, corrosion current density, and tensile stress was established, and an exponential function relationship was found. This work can provide theoretical references for the investigation of the corrosion behavior of zinc-based biodegradable materials under physiological stress and possible clinical applications.

Effect of ultrasonic shot peening and intermediate cerium salt conversion bath treatment controlling corrosion of Mg-Y-Zn-based alloy in salt water

Ultrasonic shot peening (USP) is often regarded as beneficial in mitigating corrosion of Mg alloys. However, increasing surface roughness induced by USP promotes localized corrosion pitting. Herein, we show that an intermediate phosphate bath treatment (CePT) before USP can minimize the surface roughness and ameliorate corrosion resistance of Mg-4.0Y-4.0Zn-0.5Zr-0.2Ca alloy (wt.%) in 0.1 M NaClsolution. In this regard, WZ44 alloy was subjected to Ce(NO3)3 + NaH2PO4bath treatment followed by USP for 30 s using AISI52100 steel balls and vice versa. The sub-surface features ofspecimens analyzed using XRD, FESEM, surface topography, and Vickers hardness reveal that CePT coating before USP increases microhardness (∼142–149 HV0.05 vs ∼ 125–135 HV0.05) and decreases surface roughness (Ra = 1.91–2.38 μm vs Ra = 2.58–2.76 μm). Potentiodynamic polarizationand electrochemical impedance spectroscopy demonstrate that corrosion current decreased (Icorr ∼ 9.81–13.69 µA/cm2 vs. ∼ 23.82–26.22 µA/cm2), coating (R1), and polarization resistance (R2) increased to ∼ 1704–1907 Ω.cm2,and ∼ 1834–1902 Ω.cm2, respectively,for specimens subjected to USP + CePT treatment together indicating superior corrosion resistance.Overall, an intermediate CePT before USP can effectively minimize corrosion pitting phenomena of WZ44 alloy in chlorinated solution by developing a ceramic coating interlocked with surface acting as a barrier between the metal/solution interface.

Acidithiobacillus species drive the formation of ferric-silica cemented microstructure: Insights into early hardpan development for mine site rehabilitation

Hardpan-based profiles naturally formed under semi-arid climatic conditions have substantial potential in rehabilitating sulfidic tailings, resulting from their aggregation microstructure regulated by Fe-Si cements. Nevertheless, eco-engineered approaches for accelerating the formation of complex cementation structure remain unclear. The present study aims to investigate the microbial functions of extremophiles on mineral dissolution, oxidation, and aggregation (cementation) through a microcosm experiment containing pyrites and polysilicates, of which are dominant components in typical sulfidic tailings. Microspectroscopic analysis revealed that pyrite was rapidly dissolved and massive microbial corrosion pits were displayed on pyrite surfaces. Synchrotron-based X-ray absorption spectroscopy demonstrated that approximately 30 % pyrites were oxidized to jarosite-like (ca. 14 %) and ferrihydrite-like minerals (ca. 16 %) in talc group, leading to the formation of secondary Fe precipitates. The Si ions co-dissolved from polysilicates may be embedded into secondary Fe precipitates, while these clustered Fe-Si precipitates displayed distinct morphology (e.g., “circular” shaped in the talc group, “fine-grained” shaped in the chlorite group, and “donut” shaped in the muscovite group). Moreover, the precipitates could join together and act as cementing agents aggregating mineral particles together, forming macroaggregates in talc and chlorite groups. The present findings revealed critical microbial functions on accelerating mineral dissolution, oxidation, and aggregation of pyrite and various silicates, which provided the eco-engineered feasibility of hardpan-based technology for mine site rehabilitation.

Effects of corrosion on the fatigue fracture behavior of 4140 steel for offshore wind turbine bolts

The fatigue life of bolt directly affects the safety of offshore wind turbine. In this work 4140 steel was subjected to salt spray corrosion simulating the coastal atmospheric environment. After rust removal, the surface morphologies of specimens were examined using an optical profiler. Corroded specimens were also assessed by fatigue testing and the resulting fracture surfaces were examined by scanning electron microscopy. Irregular pits appeared on corroded specimen surfaces. The relationship between fatigue life and surface roughness was obtained. The fatigue cracking of 4140 steel initiated at corrosion pits in conjunction with cleavage-type fatigue zones and plastic-type final fracture zones. Increase in surface roughness provided more crack sources, thus rapidly decreasing the fatigue life.

Stress corrosion behavior of B+F dual-phase X80 pipeline steel in different soil environments

The stress corrosion behavior and immersion corrosion behavior of B+F dual-phase X80 pipeline steel in simulated near-neutral and alkaline soil solutions were studied by slow strain rate tensile (SSRT) test, immersion corrosion test and polarization test. The results show that the strength and ductility of the samples in alkaline soil solution are weaker than those in near-neutral soil solution, and the elongation loss (Iδ) and area shrinkage loss (Iψ) are 2.81 and 2.76 times of those in near-neutral soil solution. Bainite and ferrite (B+F) dual-phase X80 pipeline steel is more sensitive to stress corrosion in alkaline soil solution than in near-neutral soil solution. The protective properties of the passive film determine the corrosion dynamics, because the more complete and uniform the passive film formed, the better the corrosion resistance. In both soil solutions, the cracks are mainly transgranular. The results of polarization and immersion experiments are consistent. The linear corrosion rate in alkaline solution is higher than that in near-neutral solution in immersion test. The corrosion pit of the sample is concentrated in bainite area in near-neutral solution while weak part around inclusions is preferentially corroded and forms large corrosion holes in alkaline solution. Therefore B+F dual-phase X80 pipeline steel is easier to corrode in alkaline soil solution.

Effect and simulation of tensile stress on corrosion behavior of 7050 aluminum alloy in a simulated harsh marine environment

The corrosion behavior of the 7050 aluminum alloy was investigated in the presence of high concentrations of H+ and Cl- ions simulating the marine environment of high salinity and local acidification in tropical seas. The results highlight the significant influence of tensile stress on the corrosion rate of the aluminum alloy with higher stress levels resulting in faster corrosion. Under the influence of tensile stress, corrosion pits form on the alloy surface, and their depth increases with higher levels of applied stress. It is important to note that the presence of a corrosion defect leads to a pronounced stress concentration, resulting in a much faster rate of corrosion compared to other regions. However, when subjected to low tensile stress (≤174 MPa), the corrosion at the defect exhibits uniform characteristics similar to a uniform corrosion process. Moreover, the potential at the defect shifts positively with increasing stress level. Furthermore, stress has an effect on the diffusive behavior of the aluminum alloy, leading to a higher potential at the defect center compared to its surrounding region. Nevertheless, as the tensile stress is further increased, this behavior is disrupted and stress corrosion cracking becomes the dominant mode of corrosion.

Corrosion and passivation behavior of in-situ TiC reinforced Al0.1CrNbSi0.1TaTiV refractory high entropy alloy coatings via doping C

This work is aimed to explore ways to further improve corrosion properties of single-phase RHEA coating by introducing in-situ TiC phase. Results shown that C/Al0.1CrNbSi0.1TaTiV RHEA coatings exhibited better comprehensive resistance to pitting and general corrosion compared to most of reported HEAs and traditional alloys. The passive film was dominated by a muti-oxide crystalline structure with a thickness of ∼ 11.52 nm. The small-size and evenly distributed TiC phase with most thermodynamically stable could be obtained via doping C and retard the nearby pitting process, improving the pitting behavior and the dense of passive film in 1.0 wt% C coating.

Numerical and experimental failure analysis of wind turbine blade fastener

The objective of this study is to conduct a root cause failure analysis on wind turbine fasteners constructed from carbon steel Grade 10.9. The presence of corrosion pits at the thread root, as well as beach and ratchet marks on the fracture surface, suggests that the fastener failed due to a corrosion-fatigue mechanism. The microstructure of the failed fastener predominantly consisted of 98 % tempered martensite, with some bainite and a small amount of chromium carbides, which is characteristic of quenched and tempered low alloy steel. Magnetic particle testing revealed similar crack marks on other fasteners in similar locations, indicating the points of maximum stress in these fasteners. Furthermore, finite element analysis using Abaqus software demonstrated that for a corrosion pit to grow, it required a minimum pit length and depth of 0.5 mm and 0.6 mm, respectively.

Investigation of microstructure and corrosion resistance of an Al-Zn-Mg-Cu alloy under various ageing conditions

In this study, transmission electron microscopy and 3D optical profilometer were employed to investigate the effects of single-stage ageing and regression re-ageing treatments on the microstructure and corrosion resistance of Al-Zn-Mg-Cu alloy. The results indicate the intergranular corrosion resistance is increased by 36% with the regression re-ageing. Based on the semi-elliptical damage model, a 3D expansion model for pits is established. Meanwhile forms a systematic study of the formation mechanism, nucleation and growth of corrosion pits. This will contribute to the systematic and in-depth study of the corrosion resistance of Al-Zn-Mg-Cu alloy in aviation applications.

Fatigue crack propagation near a corrosion pit in a HSS specimen

Corrosion and fatigue are very common forms of metal degradation, and thus an aspect of the complex issues involved is analysed within this work. A rectangular specimen with a surface fatigue crack and a surface corrosion pit subjected to remote tensile loading was modelled via the finite element method in order to assess the crack behaviour for various configurations of both the crack and the pit. A perpendicular crack was considered along with an angled crack, and the basic fracture parameters have been determined and discussed regarding the influence of the corrosion pit on further crack propagation. Additionally, selected fracture criteria have been applied in their classical one-parameter as well as generalised multi-parameter form to estimate the angle of further crack propagation. The results obtained are discussed thoroughly, and it is proved that the larger the corrosion pit, and the closer it is to the crack, the higher its effect on the fatigue crack behaviour is.

Control of the Composition and Morphology of Non-Metallic Inclusions in Superduplex Stainless Steel

Duplex stainless steel is a unique material for cast products, the use of which is possible in various fields. With the same chemical composition, melting, casting and heat treatment technology, pitting and crevice corrosion were observed at the interphase boundaries of non-metallic inclusions and the steel matrix. To increase the cleanliness of steel, it is necessary to carefully select the technology for deoxidizing with titanium or aluminum, as the most common deoxidizers, and the technology for modifying with rare earth metals. In this work, a comprehensive analysis of the thermodynamic data in the literature on the behavior of oxides and sulfides in this highly alloyed system under consideration was performed. Based on this analysis, a thermodynamic model was developed to describe their behavior in liquid and solidified duplex stainless steels. The critical concentrations at which the existence of certain phases is possible during the deoxidation of DSS with titanium, aluminum and modification by rare earth metals, including the simultaneous contribution of lanthanum and cerium, was determined. Experimental ingots were produced, the cleanliness of experimental steels was assessed, and the key metric parameters of non-metallic inclusions were described. In steels deoxidized using titanium, clusters of inclusions with a diameter of 84 microns with a volume fraction of 0.066% were formed, the volume fraction of which was decreased to 0.01% with the subsequent addition of aluminum. The clusters completely disappeared when REMs were added. The reason for this behavior of inclusions was interpreted using thermodynamic modeling and explained by the difference in temperature at which specific types of NMIs begin to form. A comparison of experimental and calculated results showed that the proposed model adequately describes the process of formation of non-metallic inclusions in the steel under consideration and can be used for the development of industrial technology.

Coil Spring Failure Analysis Reviewed from Residual Stress, Crytal Orientation, and Texture

Crystal defects can be identified through the crystallographic characteristics of crystal orientation (lattice), microstrain, and texture. Identification of crystal defects on the atomic scale through crystallography is very important in analyzing the mechanism of material properties due to the influence of dislocations. The slip mechanism is analyzed to minimize coil spring failure. This study aims to analyze the causes of coil spring failure based on crystallography. XRD testing was carried out for analysis of residual stress, crystal orientation, and texture using MAUD 2.94 version software. Hardness testing was carried out on the surface of the coil spring with locations near and far from the fracture using micro Vickers. The macro fracture morphology was analyzed using a DSLR camera and the micro fracture morphology was analyzed using SEM. The XRD result shows that the coil spring material has a tensile residual stress value of "202.4 ± 15.9 MPa" with the resulting crystal orientation showing the hkl (100), (200), (211), (200) fields. The plane (200) has a texture characteristic that is oriented towards the Rolling direction along the spring axis. Texture oriented towards Rolling Direction can be shown with a maximum probability value of 1.191. A high probability will have an impact on the presence of material surface defects. Surface defects are indicated by the presence of pit corrosion on micro and macro fracture morphology observations. The pit corrosion defects that occur in the failed coil springs are the beginning of the formation of crack initiation and cause stress concentration. The stress concentration will increase with loading and cause crack propagation.

Fracture prediction of corroded ZG300-500H cast steel with micromechanical fracture model

The effects of corrosion on the fracture prediction of steel are investigated. The power function for cast steel ZG300-500H in the acetic acid salt spray corrosion environment is fitted to illustrate the acceleration of the acetic acid salt spray corrosion test, and the statistical characteristics of the pit depth and pit diameter-depth ratio are analyzed. The material parameters of micromechanical fracture model under monotonic load are calibrated by tensile test and finite element analysis on smooth-notch tensile specimens. The VGM model and SMCS model can also be applied to predict the fracture of corroded ZG300-500H cast steel based on the random distribution model of corrosion pits. The finding is that the crack of the non-corroded single-notch specimens always initiates from the centre of the critical cross section. Corroded specimen cracks initiate from the severe corrosion areas. Once a crack is initiated, it always extends along the thickness and forms a visible crack. The subsequent crack propagation along the width direction can be simulated accurately.

Behavior of stub SCFST columns with localized pitting corrosion damage

In this research, eleven square concrete-filled steel tubes (SCFSTs), including nine specimens with localized pitting corrosion damage and two intact specimens for the purpose of comparison, were tested under axial loading. The pitting corrosion damage was simulated by mechanically drilled cylindrical pits on the surfaces of the square steel tubes in the experimental study. The results from experiments suggested that the axial compression performance of the specimens with localized corrosion pits was different from that of the intact specimens. It was also revealed that pitting parameters, including the degree of volume loss, the number of rows and columns of pits, and the diameter-to-depth ratio of pits, have a significant effect on axial compression performance. Following the experimental investigation, the finite element models were established and validated by the experimental observations and curves, and extended to consider the random characteristic of pitting corrosion, to simulate true local corrosion cases. A parametric analysis was further conducted to explore the influence of random pitting corrosion damage on the ultimate strength of SCFST. Finally, a DoV-based method for considering localized pitting corrosion damage was proposed and applied in codified rules for predicting the ultimate strength of such damaged SCFSTs.

Improved heat and corrosion resistance of high electrical conductivity Al-Mg-Si alloys by multi-alloying of Ce, Sc and Y

In order to improve the corrosion and heat resistance of Al-Mg-Si alloy conductor materials, Ce, Sc, Y and Zr were added in Al-Mg-Si alloy to regulate the microstructure. The Al-Mg-Si-Ce-Sc-Y alloy was designed with excellent pitting and intergranular corrosion resistance by obtaining the micron-sized Fe-containing second phase with a lower potential difference to Al matrix, more dispersed grain boundary precipitates with a higher proportion of Si particles, narrower width of PFZ and ideal distribution of intergranular precipitates. The Al-Mg-Si-Ce-Sc-Y alloy also maintained higher hardness, strength and electrical conductivity after overaging and annealing and the corrosion/heat resistance mechanisms were proposed.

Degradation Adaptability Assessment of Semisolid Powder Molded Mg-Zn-Mn Alloys for Orthopedic Applications.

Semisolid powder molding was used to prepare the medical Mg-6Zn alloy; in order to further improve its degradation adaptability, 0.5 and 1 wt % Mn were added. Then, the effect of the forming temperature (540, 560, 580, and 600 °C) on the in vitro degradation behavior of the prepared Mg-6Zn-xMn (x = 0.5, 1 wt %) was analyzed, and the optimized alloy was obtained. Finally, the biocompatibility and in vivo degradation performance of the optimized and Mn-free alloys were evaluated. Importantly, single-photon emission tomographic imaging (SPECT/CT) was first applied to monitor the in vivo degradation process. The results show that the corrosion mechanism of the Mn-free alloy is microgalvanic corrosion control with corrosive pitting. After adding Mn, the in vitro degradation rate decreases by half (0.17 ± 0.01 mm/year) as the forming temperature increases to 600 °C, and Mg-6Zn-1Mn prepared at 600 °C is the optimized alloy. Mn addition improves the corrosion product film protection and discontinuous secondary phases, and thus, the corrosion mechanism is changed to corrosive pitting control. Additionally, semisolid powder molding is an easy method to prepare alloys with low average pore interconnectivity (<10%), which is helpful for slowing down the degradation rate. The Mn-containing alloy has better biocompatibility, with a cytotoxicity of grade 0-1, due to its lower degradation rate. The in vivo corrosion rate of the Mn-free alloy is 0.19 mm/year after 28 days of implantation, which was precisely detected by SPECT/CT in real-time. The long-term in vivo degradation adaptability of Mn-free and Mn-containing alloys was not correctly presented, which may be due to the unreasonable bone defect model causing implant displacement. However, both of these alloys cause no obvious inflammation and show good healing. In summary, semisolid powder molding is a potentially promising technique to prepare medical Mg alloys, and nuclear imaging is an effective in vivo degradation evaluation method.

Mitigating Stress Corrosion Cracking of 304L and 316L Laser Welds in a Salt Spray through Micro-Shot Peening

Two austenitic stainless steel (ASS) plates, 304L and 316L, were cold-rolled (304R and 316R) with a 10% reduction in thickness and then subjected to laser welding. Cold rolling caused slight surface hardening and introduced residual tensile stress into the ASS plates. The susceptibility to stress corrosion cracking (SCC) of the welds (304RW and 316RW) was determined using the U-bend test pieces in a salt spray. To highlight the stress concentration at the weld’s fusion boundary (FB), the top weld reinforcement was not ground off before bending. Moreover, micro-shot peening (MSP) was performed to mitigate the SCC of the welds by imposing high residual compressive stress and forming a fine-grained structure. Cold rolling increased the susceptibility of the 304R specimen to pitting corrosion and intergranular (IG) microcracking. Moreover, pitting corrosion and SCC were found more often at the FBs of the 304RW. The corrosion pits of the peened 304RW (304RWSP) were finer but greater in amount than the those of the un-peened one. The results also indicated that the 316L ASS welds with MSP were resistant to the incidence of pitting corrosion and SCC in a salt spray. The better reliability and longer service life of dry storage canisters could be achieved by using 316L ASS for the construction and application of MSP on it.

Corrosion Behavior and Mechanisms of Co-Cr-Mo Alloy Fabricated by Powder Metallurgy Route in Ringer's Solution

The current research is aimed to study the corrosion behavior and mechanism of Co-Cr-Mo alloy fabricated by powder metallurgy route in Ringer's solution with 7.4 and 37oC for pH and temperature values, respectively.The research was done by using a potentiostat to obtain the potentiodynamic and cyclic polarization to measure and calculate some significant parameters of the alloy corrosion. The cyclic polarization curve is indicated the resistance of the fabricated samples to the pitting and crevice corrosions. Optical, SEM and SEM-Mapping observations were revealed that the corrosion of the tested alloy was due to inter-particle and inter granular corrosion

Crack cause analysis of a third stage stator vane of the low-pressure compressor in an aeroengine

A cracked third stage stator vane of the low-pressure compressor was found during a major overhaul of an aeroengine. The crack originated from a corrosion pit located on the arc transition between the leading edge and the upper edge plate. The finite element analysis results demonstrated the arc transition was the region with the large von-Mises stress under the wake excitation. The cleavage-like fracture and fatigue striations predominated throughout the fracture surface, indicating it was a pit-related fatigue crack. Meanwhile, Metallographic examination discovered most of corrosion pits beneath the bulging or peeling of the paint layer were distributed on the leading edge and the concave side. Moreover, the composition and phase identification results showed that the corrosion products included sulfate and alumina. Considering the pitting corrosion products and outdoor environment of the aircraft downtime, it was inferred that the cracked stator vane suffered from atmospheric corrosion.