Cracking Of Steel Research Articles

Prevention of Sharp Fracture Caused by Large Size Inclusion in Cold Heading Steel

The cracking of cold heading steel during drawing was researched in this paper. The defects were detected by scanning electron microscope and EDS energy spectrum analysis, the direct causes of cracking were discussed and analysed, and the corresponding improvement measures were put forward. Results showed that the large size inclusions with high alumina content in steel were the main cause of cracks in cold heading steel due to their poor deformation ability. The plasticity of inclusions could be controlled through optimization of refining slag to reduce both the CaO and Al2O3 content.

Stress Corrosion Cracking of 23Co14Ni12Cr3Mo Ultra-High Strength Steel in 3.5% NaCl Solution under Constant Load Condition

Stress Corrosion Cracking of 23Co14Ni12Cr3Mo Ultra-High Strength Steel in 3.5% NaCl Solution under Constant Load Condition

Analysis of crack causes and effects of the A333 low carbon pipeline steel after thermite welding

By thermite welding on steel pipelines with an anode material to protect the cathode, cathodic protection has been widely used to prevent steel base pipelines from erosion. In this paper, some cracks were found in an accidental magnetic particle examination by the workers after thermite welding on steel pipelines. Therefore, a series of characterizations were conducted on the macro/microscopic morphologies, mechanical properties of the cracked A333 low carbon pipeline steel to find out the causes and effects. The obtained results show that the coarse martensite with a certain thickness in HAZ come into being bringing about plasticity reducing, strength and hardness increasing. And large welding stress and uncoordinated deformation lead liquid copper to infiltrate into the prior austenite grain boundaries in HAZ of the pipeline causing the formation of the copper penetration cracks.

Fitness-For-Service Assessment and Failure Analysis of Hydrogen-Induced Cracking in a Pipeline Steel

Fitness-For-Service Assessment and Failure Analysis of Hydrogen-Induced Cracking in a Pipeline Steel

Nonlinear dynamic characteristics of a cracked steel pipe wound by carbon fiber reinforced composite

In this paper, the nonlinear dynamic characteristics of a cracked steel pipe wound by carbon fiber reinforced composite are studied. The time-dependent stiffness is introduced to describe the influence of cracks on the dynamic characteristics of the system. The natural frequency of the system is obtained on the improved multi-scale method, and the effect of cracks on the system's stability is discussed. The vibration experiment of the system under stochastic excitation shows that the crack will grow as the stochastic excitation increases. This article provides a basis for material parameter selection of steel pipe wound by carbon fiber reinforced composite.

Effect of Acidizing Process on the Stress Corrosion Cracking of HP-13Cr Stainless Steel in the Ultra-depth Well Environment

The effect of acidizing process on the stress corrosion cracking of HP-13Cr stainless steel in the ultra-depth well environment was studied by the slow strain rate test, the electrochemical measurement, the microstructure observation, and the finite element modeling. The results indicated that the acidizing process significantly increased the stress corrosion cracking susceptibility of HP-13Cr stainless steel and induced the fracture mode to the brittle characteristic in the high temperature and CO2 pressure environment. The stress corrosion cracking susceptibility also increased with the increase of temperature and CO2 pressure. There were dense defects including pits and cracks in the fracture section from the transverse view. After the acidizing process, under tensile stress condition, the increasing roughness will cause the stress concentration and promote the local anodic dissolution, which induces the initiation of stress corrosion cracking.

Sulfide stress cracking inhibition of a supermartensitic stainless steel by using an imidazol obtained from palm oil

PurposeThis paper aims to use an imidazole-based n-ionic Gemini surfactant derived from palm oil to inhibit the sulfide stress corrosion cracking of a supermartensitic stainless steel.Design/methodology/approachThe slow strain rate testing technique, hydrogen permeation tests and potentiodynamic polarization curves have been used.FindingsAddition of the inhibitor below the critical micelle concentration (CMC) decreased the corrosion current density (icorr), but not enough to avoid embrittlement due to the entry of hydrogen into the steel. Instead, the addition of the inhibitor close to the CMC decreased the icorr, suppressed the entry of hydrogen and inhibited the sulfide stress cracking of steel. Finally, the addition of inhibitor above the CMC led to a slight increase of icorr and promoted localized corrosion, however, the sulfide stress cracking of steel was inhibited.Originality/valueA green sulfide stress corrosion cracking inhibitor of a supermartensitic stainless steel has been obtained.

Numerical Analysis of Edge Cracking in High-Silicon Steel during Cold Rolling with 3D Fracture Locus

In this study, a 3D fracture locus of high-silicon steel strip was constructed through a series of fracture tests with specimens of various shapes and corresponding finite element (FE) simulations of the fracture tests. A series of FE analyses coupled with the developed fracture locus was conducted, and the effect of the secondary roll-bending ratio (defined as L2/R2, where L2 and R2, respectively, denote the secondary work roll barrel length and the radius of the convex curvature of the work roll surface profile emulating positive roll bending) and the initial notch length on edge cracking in the strip during cold rolling was investigated. The results reveal that the 2D fracture locus that does not include the Lode angle parameter (varying between −0.81 and 0.72 during cold rolling) overestimates the edge cracking in the range of 13.1–22.2%. The effect of the initial notch length on the length of crack grown in the transverse direction of the strip during cold rolling is greatest when the ratio L2/R2 is 0.12.

Stress corrosion cracking of A517 steel in marine environments

PurposeThe purpose of this study is to develop the existence and mechanism of stress corrosion cracking (SCC) for A517 steel in marine environments.Design/methodology/approachSlow strain rate test (SSRT) and constant load tests were used to investigate the SCC susceptibility of A517 steel. In addition, the additive stresses caused by the corrosion film and hydrogen entering into steel were applied to reveal the fundamental mechanism of the SCC.FindingsThe SCC susceptibility increased due to anodic dissolution and additive stress caused by the corrosion-produced film under anode polarization. Furthermore, the SCC susceptibility increased with increasing cathodic polarization, which is due to the increased additional stress caused by hydrogen entering into the steel. However, when the cathode polarization further increased, the additional stress remained due to the constant hydrogen content, thus the SCC susceptibility did not vary. Moreover, the SCC susceptibility of A517 steel under an alternate immersion environment (AIE) was lower than that under a full immersion environment and the steel under the AIE with 0.5 W/D had the lowest SCC susceptibility.Originality/valueThe stress corrosion behaviors of A517 in marine environments under various conditions were systematically analyzed.

Влияние напряженно-деформированного состояния на путь распространения трещин квазискола в низкоуглеродистой стали, охрупченной водородом

Сonflicting data on the effect of the stress-strain state on the shape and path of quasi-cleavage cracks in hydrogen-embrittled steels and iron have been reported in the literature recently. However, this issue is important for understanding the nature of hydrogen embrittlement (HE) and, particularly, the role of hydrogen in the mechanism of crack propagation. In this regard, in the present study, smooth and notched specimens of low-carbon steel were tensile tested with in-situ cathodic hydrogen charging. The side surface of the specimens fractured in this way was examined by scanning electron microscopy aiming at quantitative characterization of the length and curvature of secondary side surface cracks. In addition, fractographic analysis was performed. A great number of cracks having a characteristic S-shaped curved geometry are found on the side surface of the notched specimens. Moreover, the cracks can smoothly curve both on the scale of several grains as well as within the individual grain interior. In contrast, in the case of smooth specimens, the cracks generally exhibit relatively straight appearance. Quantitative analysis using a statistically-representative dataset has shown that, on average, the curvature of cracks in the notched specimens is significantly higher and is varied over a wider range of values than in the smooth specimens. Based on the data obtained, it is concluded that the path of quasi-cleavage cracks in hydrogen-embrittled ferritic and ferrite-pearlitic low-carbon steels is mainly determined by the characteristics of the stress-strain state, and not by the microstructure or crystallographic orientation of individual grains.

Effects of different cooling rates on the microstructure, crystallographic features, and hydrogen induced cracking of API X80 pipeline steel

Hydrogen-Induced Cracking (HIC) is a primary failure mechanism of pipeline-welded joints in the absence of external loading in the oil and gas exploration industries. Three different cooling rates after austenitization were used to simulate in the laboratory different regions of the heat-affected zone (HAZ) formed when welding an API X80 pipeline steel specially designed to enhance the HIC resistance. The samples were characterized with regard to microstructure and crystallography as well as HIC resistance. The HIC resistance test used NACE TM0284-2011 methodology. The microstructure and its homogeneity varied as a function of cooling rates. Samples containing inclusions and segregation zone from the segregation bands of specimens showed reduced HIC resistance, while specimens containing only acicular ferrite and granular bainite coupled with the absence of segregation zone showed significant improvement in HIC resistance. The best HIC resistance results came from samples presenting fine acicular ferrite consisting of fine interlocking plates, with divergent crystallographic orientations, preventing the formation of localized strain distribution inside the grain and at grain boundaries. It was also found that a large proportion of medium-angle boundaries prevent microcrack initiation and the transgranular mode of crack propagation.

Slow strain rate technique for studying hydrogen induced cracking in 34CrMo4 high strength steel

Alloy hardened steels offer excellent combination of mechanical properties, hardenability and corrosion resistance. 34CrMo4 is a medium carbon, low alloy steel widely used due to a good combination of high-strength, toughness and wear resistance. However, this steel experiences hydrogen embrittlement (HE), a complex phenomenon depending on the composition and microstructure. This work estimates de loss of the mechanical properties caused by hydrogen in electrochemically H-charged specimens in absence of mechanical stress but also, at low strain rate and constant load. H-charging for 2 and 6 h induce YS losses of about 40% and 71% and UTS losses of 39% and 59%, respectively. The synergistic effect of the stress and the H-charging process leads to a higher loss, 91%, and a faster brittle fracture even though hydrogen content is similar to those firstly H-charged and then tested in air.

Towards a general damage law for interior micro-defect induced fatigue cracking in martensitic steels

Axially loaded cyclic tests of a precipitation-hardened martensitic steel at different stress ratios in 3% NaCl solution and steam environment were conducted up to very high cycle fatigue regime. In-depth fracture surface observation, quantitative characterization of microstructural damage, and theoretical modeling were carried out to illustrate the physics and mechanics of micro-defect induced interior cracking. Results showed apparent environmental effect on fatigue strength and crack initiation morphology. The fine granular area was observed for the first time in environmental media, heterogeneously distributed around micro-defect, and was found dependent on local fracture mode with a less probability in the case of faceted failure. The formation of fine granular area was confirmed as a result of microstructural damage with significant contribution from cyclic stress amplitude, and could be assisted by hydrogen speeding up lath martensites breakdown. A chemo-mechanical model of interior cracking was finally established based on the concept of interaction of inclusion, matrix, and environment induced plasticity. All these underpin a general fatigue damage law in micro-defects assessment for long-life structural integrity.

A Combined Inductive and Capacitive Non-Destructive Evaluation Technique Using a Single Spiral Coil Sensor

“Insulator-conductor” hybrid structures, such as insulated pipe/vessel and metallic structures with composite repairs, have been widely used in industry in recent years. Due to the two distinct types of materials, the comprehensive Non-destructive Evaluation (NDE) of such hybrid structure is often achieved via complementary NDE techniques, which may cause efficiency and cost issues, i.e., the conducting layer is inspected by magnetic induction related technique and the insulation layer is inspected by capacitive technique. This paper proposes a combined inductive and capacitive non-destructive evaluation technique using sensor with a single spiral coil etched on a Printed Circuit Board (PCB). The proposed technique uses both the inductance and stray capacitance of the planar coil. By measuring the coil impedance at frequencies below and above the resonant frequency, the inductive and capacitive responses can be separated to some extent, offering a simple and efficient way to image and discriminate the defects in both layers of the hybrid. Equivalent circuit analysis, Finite Element simulations and experimental research are applied. A system to implement this technique has been constructed, and its feasibility in imaging defects in insulators, conductors and a hybrid structure has been verified. The developed system successfully detected surface and hidden slots in Perspex, a through hole in aluminium, and a surface crack in steel at various lift-offs (up to 7 mm). In addition, line scan results on a steel plate with a surface crack covered by a Glass-fibre Reinforce Plastic (GFRP) plate with a hidden flat-bottomed circular hole are presented and discussed to further demonstrate the feasibility of the proposed technique on the defect detection and discrimination for “insulator- conductor” hybrid structures.

<i>In-situ</i> Observation of Cracking and Healing Behavior of High-carbon Steel during Oxide Scale Growth

This study investigates cracking and healing behavior during the oxide scale formation on high-carbon steel. The steel was heated to 1000°C at a rate of 2°C/s in the air atmosphere. The surface morphology of the oxide scale was monitored in situ using Laser Scanning Confocal Microscopy (LSCM) and oxide phases in the scale were analyzed by X-ray diffraction (XRD). The microstructures of scale cross-sections were analyzed by Electron Probe Micro-analysis (EPMA). Based on the surface morphology of the oxide scale at different temperatures, we established a relationship between blistering and the “state” of the oxide scale. Blistering occurs during the scale growth due to the decarburization process, since evolved gaseous products cause swelling and eventual rupturing of the oxide scale, forming cracks on the surface. Thermal stress induced by the difference in FeO/Fe3O4 thermal expansion coefficients causes crack expansion. Subsequent crack healing consists of the following steps: (1) oxygen penetrates the oxide scale through the cracks and reacts with FeO to form Fe3O4. This reduces the difference in the thermal expansion coefficients and decreases the thermal stress, restraining the crack expansion; (2) at a certain temperature, the oxidation rate increases and oxygen reacts with the substrate to form new oxides, which fill in the formed blisters. The mechanism of crack expansion and healing was developed by monitoring the evolution of oxide scale morphologies during the blistering process.

The study of laser deep penetration processing on prefabricated cracks of high carbon steel

This paper describes the testing of laser deep penetration processing on controlled fragmentation of high carbon steel (50SiMnVB). The objective of this research is to make use of defects in deep penetration zones and optimize the quality of prefabricated cracks. The research shows that a deeper central crack appear in the deep penetration zone when the heat input is 60 J/mm, and the appeared crack is affected by martensite in microstructure, high microhardness and a high magnitude of tensile stress. Furthermore, the fracture mode of the deep penetration zones is mixed-mode (ductile and brittle fracture).

Comparison of interatomic potentials on crack propagation properties in bcc iron

Atomistic simulations with interatomic potentials can provide insights into the cracking and failure of structural ferritic steels. Unfortunately, the evaluation of the simulation results often suffers from the uncertainties due to the quality and behavior of the employed interatomic potential. In this work, the molecular dynamics (MD) method has been used to simulate and to analyze the deformation and propagation of crack tips in α-iron. The influence of different types of potentials that we adopt on the crack propagation simulation is discussed. State of art M07, M20, and B20 potentials are considered. Overall, the microscopic deformation mechanism by the MD simulation with different types of potentials are similar, which dislocations are emitted from the crack tip, and twinning or martensite transformation happen. However, with a careful contradistinction, different mechanical responses are investigated. The relationship between the cracking mechanism and the intrinsic properties of α-iron, such as stacking fault energies, has also been discussed.

Comparative study on the stress corrosion cracking of a new Ni-advanced high strength steel prepared by TMCP, direct quenching, and quenching & tempering

The stress corrosion cracking (SCC) behaviors of Ni-advanced steels prepared by thermo-mechanical control process (TMCP), direct quenching (DQ), and quenching & tempering (QT) are examined by microstructural characterization, electrochemical test, hydrogen permeation test, and slow strain rate tensile test under different applied potentials. The results show that the SCC susceptibility of these Ni-advanced steels is low at open circuit potential in the simulated environment, and the SCC mechanism is mainly controlled by the anodic dissolution process. However, the SCC sensitivity increases significantly at −1200 mV, and the SCC mechanism becomes hydrogen-induced cracking. The SCC sensitivity of the test steels decreases in the following order: TMCP steel > QT steel > DQ steel, which is primarily attributed to the microstructural difference.

PROPOSED SHM SYSTEM WITH ACOUSTIC EMISSION (AE) TECHNOLOGY FOR TRAN HOANG NA STEEL ARCH BRIDGE

Tran Hoang Na arch bridge connects the Tran Hoang Na Street and Can Tho Bridge's approach road. The arch bridge is a kind of arch structure with super-static, high deformation. For large steel, the arched bridge is essential to control stress, deformation, and temperature values in the bridge's main structure. It allows managing quality during bridge construction and operation stage. This kind of structure is also affected by environmental factors, especially temperature influence, temperature difference during the day and in the annual cycle, and the impact of wind on hanging cables. The main girder, arches, and arch support construction can be deformed due to the effect of creeping (CR), shrinkage (SH), temperature changes (TU), and temperature gradients (TG). This paper presented the proposed complete SHM system for this arch bridge integrated with acoustic emission (AE) technology to control destructive activities in the bridge and monitor cracks in steel and concrete structures

Behaviour of single bonded anchors in non-cracked and cracked steel fiber reinforced concrete under short-time tensile loading

Due to notch effect of the holes, the anchors installed in concrete are highly likely to be intercepted by cracks that may form due to thermal and/or mechanical loads on the structure. The presence of cracks, alters the behaviour of anchors by reducing their stiffness and load carrying capacity. The behaviour of anchors in steel fiber reinforced concrete (SFRC) is one of the prime focuses in anchor technology today. However, the current research lacks the knowledge on the behaviour of anchors in SFRC intercepted by a crack. This paper investigates the behaviour of single bonded anchors intercepted by a crack (cracked concrete) in SFRC undergoing concrete cone breakout failure. Experimental investigations are carried out on bonded anchors installed in SFRC with different concrete grades and different fiber content. The tests are performed on the anchors in uncracked concrete and corresponding tests in cracked concrete show that the enhancement of performance of the anchors due to SFRC in uncracked concrete and cracked concrete is rather similar and the relative reduction in stiffness and strength of the anchors in cracked compared to uncracked concrete is equivalent in SFRC and in normal concrete. Based on the tests, a new proposal for the concrete cone capacity of anchors in cracked SFRC is proposed.