Cracking Of Steel Research Articles

Effect of nanosized NbC precipitates on hydrogen-induced cracking of high-strength low-alloy steel

We investigated the effect of nanosized NbC precipitates on hydrogen-induced cracking (HIC) of high-strength low-alloy steel by conducting slow-strain-rate tensile tests (SSRT) and performing continuous hydrogen charging and fracture analysis. The results reveal that the HIC resistance of Nb-bearing steel is obviously superior to that of Nb-free steel, with the fractured Nb-bearing steel in the SSRT exhibiting a smaller ratio of elongation reduction (Iδ). However, as the hydrogen traps induced by NbC precipitates approach hydrogen saturation, the effect of the precipitates on the HIC resistance attenuate. We speculate that the highly dispersed nanosized NbC precipitates act as irreversible hydrogen traps that hinder the accumulation of hydrogen at potential crack nucleation sites. In addition, much like Nb-free steel, the Nb-bearing steel exhibits both H-solution strengthening and the resistance to HIC.

Stress concentration affecting hydrogen-assisted crack in API X70 pipeline base and weld steel under hydrogen/natural gas mixture

A sudden change in the geometrical parameters of a material, such as bends, T-branches, and welded joints may increase the stress concentration, which in turn may enhance the diffusible hydrogen concentration. In this study, quantitative evaluations of the effect of stress concentration factors on hydrogen environmental embrittlement (HEE) will be studied based on the mechanical performance of notched tensile specimens with variations in the stress concentration factors (Kt) of the X70 pipeline base and weld metal. To highlight the role of stress concentration, the tests are performed under a 10 MPa gas mixture condition with a low partial hydrogen pressure. The maximum strengths of the notched specimens were nearly consistent across all Kt values. The degree of HEE susceptibility of the base metal increased with increasing Kt value. However, in the weld metal, prominent reductions in the RA occurred at all Kt values. The complex HEE susceptibility of the weld metal can be attributed to the synergistic action of the microstructure heterogeneity and Kt values.

Mechanical criterion for nucleation of intergranular stress corrosion cracking in austenitic stainless steel

This study investigated mechanical criteria for the nucleation of intergranular stress corrosion cracking (IGSCC) in thermally-sensitized type 304 austenitic stainless steel. Constant load testing was conducted on a stainless-steel specimen in a tetrathionate solution, and the cracking behavior, including crack initiation, coalescence, and growth at grain boundaries (GBs) on the specimen surface, was observed in situ. Local normal strains along GBs were measured on the smooth surface via the digital image correlation (DIC) technique. Local normal stresses at GBs were estimated using the Schmid-modified grain boundary stress (SMGBS) model, which has been widely used for evaluating the stress state of GBs, considering the effect of the GB plane geometry and grain orientations of grains adjacent to the GBs. The relationship between IGSCC nucleation sites, strains, and stresses was discussed. As a result, there was a slight correlation between local normal stress obtained via the SMGBS model and local normal strain via DIC measurement. The use of experimentally measured local normal strain was found to be suitable to characterize IGSCC nucleation sites.

Analysis of the early stage of stress corrosion cracking in austenitic stainless steel by EBSD and XRD

This study examined nucleation behavior during the early stage of stress corrosion cracking (SCC) in sensitized austenitic stainless steel based on microstructural assessments, using X-ray diffraction (XRD) and electron back-scattered diffraction (EBSD). The SCC experiment was conducted while applying a constant load corresponding to an initial strain of 2% in a tetrathionate solution. The crystal orientations on the smooth surface of a thermally sensitized specimen were determined via EBSD before and after testing, and diffraction spots were intermittently examined using XRD. Some grains having a high Schmid factor were found to be locally deformed near grain boundaries (GBs) due to constant tensile loading in the corrosive solution, such that intergranular stress corrosion cracks occurred at these GBs. The results of this work demonstrate that the passivation film on the metal first fractures due to localized deformation, after which newly created surfaces near GBs are exposed to the corrosive solution. Localized crack-like corrosion subsequently proceeds in chromium-depleted zones near GBs to generate intergranular SCC.

Behaviour of steel beams retrofitted with anchored carbon-fibre-reinforced polymer strips

Steel bridge beams can be damaged due to increased traffic loads and environmental impacts. An experimental study on the use of bonded and mechanically anchored carbon-fibre-reinforced polymer (CFRP) strips was undertaken to assess the retrofitting of such steel beams. The number of mechanical anchors used in the ends of the bonded strips was varied from zero to eight. The steel beam samples were tested under four-point loading. Loading was applied as an increasingly high static load and a low repetitive fatigue load. The load–displacement behaviour under the effects of static and fatigue loading and the strain distributions along the strips were measured and interpreted. The results showed that retrofitting cracked steel beams with CFRP strips is an effective method. In addition, retrofitting with anchored strips increased the performance of cracked beams under the effects of both static and fatigue loading.

Кинетика процесса накопления повреждений и разрушения в зонах концентраторов при испытаниях образцов на разрыв

The paper considers the effect of various stress concentrators on processes of damage accumulation, initiation and propagation of crack in steel (steel 3) samples during uniaxial tensile. In the middle of the samples there was a transverse welded joint or a hole with a diameter of 5 mm. The acoustic-emission testing results showed that weight content of location impulses (Wi) in the clusters of low, middle and high energy level and criteria parameters value Wi at the stages of the samples destruction have similar pattern of change despite the various types of concentrators, stress-strain material diagrams, pattern of damage accumulation, number of registered acoustic emission (AE) events and its registration activity.

Damage Behavior of 30CrMnSiA Steel under Coupling action of Marine Atmospheric Environment and Tensile-compressive Load

The coupling test of marine atmospheric environment and tensile-compressive load for 30CrMnSiA steel was carried out with the coupling test equipment of marine atmospheric environment and tension, compression and bending load. The damage behavior of 30CrMnSiA steel on the coupling action of marine atmospheric environment and tensile-compressive fatigue load was discussed. The metallographic results showed that the damage behavior characteristics of static test and coupling test were consistent. The decrease of tensile strength, proof strength plastic extension and percentage elongation after fracture of 30CrMnSiA steel were accelerated by the coupling action of marine atmospheric corrosion and tensile-compressive fatigue load. And the accelerated ratio of the coupling test was more than 10 times that of the static exposure test. The fracture morphology results showed that the fracture of the coupling test was corrosion fatigue fracture, and the cracks of 30CrMnSiA steel in the coupling test extended from the fatigue source to the core, forming directional corrosion fatigue damage.

Corrosion-Electrochemical Properties of 17G1SU Steel in Chloride-Acetate Solutions with Different Concentrations of Hydrogen Sulfide

We investigate the corrosion-electrochemical properties of 17G1SU steel in chloride-acetate solutions for different concentrations of hydrogen sulfide. It is shown that, if this concentration increases, then the corrosion potential of steel shifts to the side of more negative values and the corrosion rate increases almost linearly. The presence of hydrogen sulfide does not affect the values of Tafel constants of the cathodic and anodic reactions. It is shown that the rate of cathodic reactions may become higher as a result of the direct reduction of hydrogen from H2S molecules. For hydrogen-sulfide concentrations > 1500 mg/dm3, the rate of cathodic processes decreases due to the complications of diffusion, which may be caused by the adsorption of hydrogen-sulfide molecules and a decrease in the rate of catalytic recombination of adsorbed hydrogen atoms. Hydrogen-induced cracking of stress-free steel is revealed for hydrogen-sulfide concentrations ≥ 500 mg/dm3.

Influence of edge and corner cracks on the impact and bending behavior of spring steel

During the course of production of the spring steels, depending on the production process, the ductility drop and decrease in strength will lead to crack formation in the spring steel. Also some of the strength enhancing heat treatment process directly influences the service performance of spring steel by the emanating edge and corner cracks, which is an important scientific issue. The present experimental investigation focuses of the impact and bending behavior of spring steel with varied edge and corner crack configurations. The behavior of the material has also been investigated to ascertain its satisfactory service temperature. The specimen preparation and the experimentations have been carried out according to the ASTM standards. The results have revealed that the corner cracked spring steel can give effective service till 100 °C, beyond which it will decrease drastically. It is also determined that the double corner cracked samples have highest impact energy and lowest is noted for triple corner notched samples. In case bending loads the, the double edge notched sample loaded in the thickness direction has shown maximum strength and the lowest in noted for the triple sided notched samples. Finally it can be stated that the presence of edge and corner cracks in the spring steel will reduce the strength, service life and will lead to the most dangerous catastrophic failure.

Effect of Titanium and Boron Microalloying on Sulfide Stress Cracking in C110 Casing Steel.

The effect of Ti and B microalloying on the hardenability, prior austenite grain size (PAGS), mechanical properties, and sulfide stress cracking (SSC) of C110 grade steel was studied by Jominy testing, static tensile testing, an optical microscope (OM), scanning electron microscopy (SEM) and double cantilever beam (DCB) testing. The results show that the addition of 0.015% Ti and 0.002% B into a medium-carbon Fe-Cr-Mo-Nb-V steel increased the hardenability and refined the PAGS and quenched martensite packets, and the size of carbides was reduced. It is believed that these behaviors are responsible for the improvement in the threshold stress intensity factor KISSC.

The Influence of Alternating Current on Stress Corrosion Cracking of Grade X70 Pipe Steel

The Influence of Alternating Current on Stress Corrosion Cracking of Grade X70 Pipe Steel

Observation of Stress Corrosion Cracking of Stainless Steel Using Real-Time In-Situ High-Speed Atomic Force Microscopy and Correlative Techniques

Observation of Stress Corrosion Cracking of Stainless Steel Using Real-Time In-Situ High-Speed Atomic Force Microscopy and Correlative Techniques

Phase-Field Simulation of Stress Corrosion Cracking in Stainless Steel

Stress corrosion cracking (SCC) sometimes occurs in stainless steels, which are used for steam turbines of geothermal power plants. In order to prevent SCC that causes serious accidents in the plants, understanding the SCC behavior through experiments and numerical simulations is essential. Phase-field (PF) method is one of the widely used numerical simulation methods to analyze various microscale-material phenomena including electrochemical reactions such as corrosion. In this study, we have developed a new PF model for simulating a SCC behavior in a stainless steel, which includes the stress concentration at the propagating crack tip, diffusion and electrophoresis of ions in the liquid solution. The PF model is based on the PF model for general and pitting corrosion in a pure iron [C. Tsuyuki et al., Scientific Reports, Vol. 8 (2018), 12777.], which incorporates the Butler-Volmer equation. The stress evolution during the SCC is calculated by solving the mechanical equilibrium equation by means of fast Fourier transform. The diffusion and electrophoresis of ions are analyzed by solving the Nernst-Planck equation. Through the numerical simulations of SCC in a polycrystalline stainless steel which have a notch, we revealed that the crack growth rate increase in accordance with the stress intensity factor. The results have proved the crack proceeds through the grain when the elastic strain energy at the crack tip is high, and it propagate through the grain boundary when the low energy.

Early identification of stress corrosion cracking of P110 low alloy steel in downhole fluid by electrochemical noise measurement

ABSTRACT Electrochemical noise (EN) measurements were applied to detect the stress corrosion cracking (SCC) of API P110 low alloy steel in simulating CO2-containing downhole fluid during the slow strain rate test (SSRT). Several statistical parameters of potential and current transients were defined, and they were proven to be indicative of the metastable and stable pitting, as well as the initiation and propagation processes of microcracks. The EN results showed that the amplitude and lifespan of current transients increase with the CO2 concentration. The increasing SCC susceptibility of P110 steel is mainly attributed to the decreasing pH at the crack tip, which not only accelerated the rupture of passive film on crack walls but also prolonged the lifespan of cracks advance. EN measurement may be a promising technique for the early diagnosis of SCC.

A micromechanical analysis of intergranular stress corrosion cracking of an irradiated austenitic stainless steel

Irradiation Assisted Stress Corrosion Cracking (IASCC) is a material degradation phenomenon affecting austenitic stainless steels used in nuclear Pressurized Water Reactors (PWR), leading to the initiation and propagation of intergranular cracks. Such phenomenon belongs to the broader class of InterGranular Stress Corrosion Cracking (IGSCC). A micromechanical analysis of IGSCC of an irradiated austenitic stainless steel is performed in this study to assess local cracking conditions. A 304L proton irradiated sample tested in PWR environment and showing intergranular cracking is investigated. Serial sectioning, Electron BackScatter Diffraction (EBSD) and a two-step misalignment procedure are performed to reconstruct the 3D microstructure over an extended volume, to assess statistically cracking criteria. A methodology is also developed to compute Grain Boundary (GB) normal orientations based on the EBSD measurements. The statistical analysis shows that cracking occurs preferentially for GB normals aligned with the mechanical loading axis, but also for low values of the Luster-Morris slip transmission parameter. Micromechanical simulations based on the reconstructed 3D microstructure, FFT-based solver and crystal plasticity constitutive equations modified to account for slip transmission at grain boundaries are finally performed. These simulations rationalize the correlation obtained experimentally into a single stress-based criterion. The actual strengths and weaknesses of such micromechanical approach are discussed.

Fiber optic sensing of concrete cracking and rebar deformation using several types of cable

Distributed fiber optic sensing (DFOS) is increasingly being applied in civil engineering. One recently emerging type of DFOS, Optical Frequency Domain Reflectometry (OFDR), offers improved accuracy and resolution. This paper presents an experimental study that investigates the ability of OFDR, implemented using several types of fiber optic cable, to detect concrete cracking and large strain steel deformation. More specifically, the experimental investigation involved six reinforced concrete specimens with different types of optical fiber embedded in both the concrete and rebar. OFDR successfully detected continuous rebar deformation and bond stress through the post yielding range, as well as strain localization indicative of concrete cracking. The type of optical fiber is shown to have a substantial influence on the measured strain response after the onset of nonlinear behavior (i.e., cracking and yielding) and into the large deformation regime where measurement survivability becomes an issue. The higher performing fibers reveal unprecedented detail regarding the interaction between concrete and rebar and demonstrate potential for application in RC structures. Based on these findings, the paper gives practical recommendations for cables with different size and structure.

Mechanical and metallurgical considerations on the effects of ppb-level chloride on stress corrosion cracking of low alloy steels in high-temperature water

This paper studies the effects of very low-level chloride (< 5 ppb) on the stress corrosion cracking (SCC) growth of low-alloy pressure vessel steel in oxygenated high-temperature water. Chloride levels as low as 3 ppb increase SCC susceptibility. Besides the chemical reason, this paper provides perspectives on the underlying mechanical and metallurgical contributions. A substantial variation was observed from three high-sulphur steels. Sulphur is not the only contributor to SCC. The synergy of material, environmental, and mechanical parameters controlled the crack-tip strain rate and crevice chemistry that govern the SCC response in the high-purity high-temperature water environments at intermediate K.

A New General Paradigm for Understanding and Preventing Li Metal Penetration through Solid Electrolytes

Summary The use of lithium (Li) or sodium (Na) metal anodes together with highly ion-conductive solid electrolytes (SEs) could provide batteries with a step improvement in volumetric and gravimetric energy densities. Unfortunately, these SEs face significant technical challenges, in large part because Li and Na dendrites can penetrate through SEs, leading to short circuits. The ability of such a soft material (Li or Na metal) to penetrate through ceramic is surprising from the point of view of models widely used in the Li-battery field. We introduce a concept, new to the battery field, for preventing penetration of lithium dendrites through SEs by putting the SE surfaces into a state of residual compressive stress. For a sufficiently high compressive stress, cracks have difficulty forming, and cracks that do form are forced to close, inhibiting dendrite penetration. This approach is widely used to solve commercially important stress corrosion cracking problems in metals and static fatigue problems in ceramics and glasses (e.g., Gorilla Glass). However, the technique will not be useful for SEs if the Li-ion transport rate through a SE is substantially reduced when the SE is under compression. Our molecular dynamics calculations for Li-ion transport through a common SE demonstrate that the introduction of even very high residual compressive stresses (∼10 GPa) has only a modest effect on Li-ion transport kinetics, suggesting that this approach is viable and capable of providing a new paradigm for developing high-performance and mechanically stable SEs.

Hydrogen embrittlement of API 5L X65 pipeline steel in CO2 containing low H2S concentration environment

The basic corrosion mechanisms in CO2 environments are widely investigated and reported by scientific community. However, cracking failure mechanisms in CO2 environment or in environments where CO2 coexist with other gases need a better understanding. Cracking susceptibility of API 5L X65 in pure CO2 was recently reported and the basic mechanism was attributed to hydrogen embrittlement. The influence of hydrogen permeation and the detrimental effect of cathodic polarisation support the assumption of hydrogen embrittlement as the determining factor for the loss of plasticity and strength. The loss of strength of an API 5L X65 steel when CO2 and H2S coexist in the same environment is the focus of the present work. Hydrogen embrittlement (HE) and hydrogen induced cracking (HIC) of pipeline steels are failures modes expected to occur in CO2 with traces of H2S environments. The present work aims to approach the performance in laboratory of an API 5L X65 steel in CO2 with traces of H2S environment (slightly sour), using as baseline the performance of the material in pure CO2 environment (sweet), already reported. Hydrogen permeation and Slow Strain Rate Tests (SSRT) were carried out in CO2 environment containing low concentration of H2S. It was observed that traces of H2S in CO2 environment promote much more intense hydrogen permeation, much higher than in purely CO2 environment. Loss of ductility was also much more severe than in CO2 environment, with and without the influence of cathodic polarisation. Hydrogen generation enhancement promoted by traces of H2S in solution, corresponding to an average content of 21 ppm in solution, had a heavy effect on hydrogen embrittlement of the steel, confirmed by the lower ratio of reduction in area (RRA) and time to fracture in comparison with sweet service conditions.

Angle expanding fracture analysis of Q420B angle steel

The cracking angle steel is analyzed by chemical composition analysis, tensile test, impact strength, bending test, metallographic structure and other physical and chemical test methods and all indicators meet the requirements of the standard, so material quality is not the cause of crack of angle steel. The stress distribution of Q420B angle steel in the process of expanding angle in cold working is analyzed by numerical simulation. Three dimensional simulation results show that when the angle of expansion reaches 92° and the maximum principal stress exceeds the tensile strength of the material, the angle steel breaks; The results of plane strain calculation show that when the angle of expansion reaches 92.6° and the maximum principal stress exceeds the tensile strength of the material, the angle steel breaks.