Stress Corrosion Cracking Behavior Research Articles

Effect of surface grinding on chloride induced SCC of 304L

The effect of surface grinding on the stress corrosion cracking (SCC) behavior of 304L austenitic stainless steel in boiling magnesium chloride has been investigated. SCC tests were conducted both without external loading and with varied levels of four-point bend loading for as-delivered material and for specimens which had been ground parallel or perpendicular to the loading direction. Residual stresses due to the grinding operation were measured using the X-ray diffraction technique. In addition, surface stress measurements under applied load were performed before exposure to evaluate the deviation between actual applied loading and calculated values according to ASTM G39. Micro-cracks initiated by a high level of tensile residual stress in the surface layer were observed for all the ground specimens but not those in the as-delivered condition. Grinding along the loading direction increased the susceptibility to chloride induced SCC; while grinding perpendicular to the loading direction improved SCC resistance. Surface tensile residual stresses were largely relieved after the initiation of cracks.

Evolution of Microstructure and Stress Corrosion Cracking Behavior of AA2219 Plate to Ring Weld Joints in 3.5 Wt Pct NaCl Solution

AA2219 aluminum alloy plate (T87) and ring (T851) were joined by tungsten inert gas (TIG) welding using multi-pass welding. The mechanical properties and stress corrosion cracking (SCC) resistance of the above base metals (BMs) in different directions (L, LT, and ST) were examined. Similarly, the weld metal joined by plate to plate and plate to ring (PR) joints was evaluated. The results revealed that the mechanical properties of the ring were comparatively lower than the plate. This was found to be due to the extremely coarse grain size of the ring along with severe Cu-rich segregation along the grain boundaries when compared to the plate material. The SCC resistance of the base and weldments were found to be good and not susceptible to SCC. This was shown to be due to high values of SCC index (>0.9) and the typical ductile cracking morphology of the BM and the weld joints after SCC test in the environment (3.5 wt pct NaCl) when compared to test performed in the control environment (air). However, the corrosion resistance of the weld interface between the FZ and ring was inferior to the FZ–plate interface.

Environmentally Assisted Cracking of Alloy 7050-T7451 Exposed to Aqueous Chloride Solutions

The stress corrosion cracking (SCC) behavior of 7050-T7451 plate material was investigated in short-transverse direction performing constant load and constant extension rate tests. Smooth and notched tensile specimens were permanently immersed in substitute ocean water and in an aqueous solution of 0.6 M NaCl + 0.06 M (NH4)2SO4. Alloy 7050-T7451 exhibited high SCC resistance in both synthetic environments. However, conducting cyclic loading tests, environment-induced cracking was observed. Applying a sawtooth waveform, notched tensile specimens were strained under constant load amplitude conditions at constant displacement rates ranging from 2 × 10−6 to 2 × 10−4 mms−1. The stress ratio R = σ min/σ max was 0.1 with maximum stresses of 300 and 400 MPa. When cyclically loaded in substitute ocean water, notched specimens failed predominantly by transgranular environment-induced cracking. Striations were observed on the cleavage-like facets. The number of cycles-to-failure decreased with decreasing displacement rate. A slope of 0.5 was obtained by fitting the logarithmic plot of number of cycles-to-failure vs nominal loading frequency, indicating a hydrogen embrittlement mechanism controlled by diffusion.

Influence of AC waveforms on stress corrosion cracking behaviour of pipeline steel in high pH solution

The effect of various waveforms AC on stress corrosion cracking (SCC) behaviour and mechanism of X80 pipeline steel was investigated in high pH carbonate/bicarbonate solution by polarisation curves and slow strain rate tensile tests. Under various waveforms AC, the passivity of the steel degrades severely, and pitting corrosion easily forms on the electrode surface. With or without AC application, the SCC behaviour and mechanism of the steels in the solution are distinctly different. Without the presence of AC, the cracks propagation are intergranular, and the mechanism is anodic dissolution. AC significantly increases the SCC susceptibility of pipeline steel. The order of the SCC susceptibility of the steel at various waveforms AC is: sine wave < square wave < triangular wave. Under a long term AC interference, the fracture mode is transgranular, and the mechanism of the steel in high pH solution is controlled by anodic dissolution and hydrogen embrittlement.

Experimental study on the stress corrosion cracking behavior of AISI347 in acid chloride ion solution

The stress corrosion cracking (SCC) behavior of AISI347 austenitic stainless steel exposed to acid solution containing chloride ion at different temperature and pressure is studied through slow strain rate testing (SSRT) at different test condition. The result of SSRT shows, with the pressure increasing, the SCC resistance is getting worse and the trend of brittle fracture presented by the fracture surface is more obvious. With the temperature rising, the mechanical properties of AISI347 getting worse first and then getting better, it gets to be the worst when the temperature is 260°C. The result of significance effect analysis of temperature and pressure on SCC shows that the temperature has a greater effect on the resistance to SCC of AISI347 austenitic stainless steel than the pressure. The main component of passive film is analyzed and the mechanism of SCC is discussed. Chromium oxides soluble in the acidic chloride solution results in the forming of corrosion pits and the cracking of the passive film under stress.

Effect of Oxidation Chemistry of Supercritical Water on Stress Corrosion Cracking of Austenitic Steels

Austenitic steel is a candidate material for supercritical water-cooled reactor (SCWR). This study is to investigate the stress corrosion cracking (SCC) behavior of HR3C under the effect of supercritical water chemistry. A transition phenomenon of the water parameters was monitored during a pseudocritical region by water quality experiments at 650°C and 30 MPa. The stress–strain curves and fracture time of HR3C were obtained by slow strain rate tensile (SSRT) tests in the supercritical water at 620°C and 25 MPa. The concentration of the dissolved oxygen (DO) was 200–1000 μg/kg, and the strain rate was 7.5×10−7/s. The recent results showed that the failure mode was dominated by intergranular brittle fracture. The relations of the oxygen concentration and the fracture time were nonlinear. 200–500 μg/kg of oxygen accelerated the cracking, but a longer fracture time was measured when the oxygen concentration was increased to 1000 μg/kg. Chromium depletion occurred in the oxide layer at the tip of cracks. Grain size increased and chain-precipitated phases were observed in the fractured specimens. These characteristics were considered to contribute to the intergranular SCC.

Effects of long-term thermal aging on the stress corrosion cracking behavior of cast austenitic stainless steels in simulated PWR primary water

The stress corrosion cracking (SCC) behavior of cast austenitic stainless steels of unaged and thermally aged at 400 °C for as long as 20,000 h were studied by using a slow strain rate testing (SSRT) system. Spinodal decomposition in ferrite during thermal aging leads to hardening in ferrite and embrittlement of the SSRT specimen. Plastic deformation and thermal aging degree have a great influence on the oxidation rate of the studied material in simulated PWR primary water environments. In the SCC regions of the aged SSRT specimen, the surface cracks, formed by the brittle fracture of ferrite phases, are the possible locations for SCC. In the non-SCC regions, brittle fracture of ferrite phases also occurs because of the effect of thermal aging embrittlement.

Improved Stress Corrosion Cracking Resistance and Strength of a Two-Step Aged Al-Zn-Mg-Cu Alloy Using Taguchi Method

Multi-step heat treatment effectively enhances the stress corrosion cracking (SCC) resistance but usually degrades the mechanical properties of Al-Zn-Mg-Cu alloys. With the aim to enhance SCC resistance as well as strength of Al-Zn-Mg-Cu alloys, we have optimized the process parameters during two-step aging of Al-6.1Zn-2.8Mg-1.9Cu alloy by Taguchi’s L9 orthogonal array. In this work, analysis of variance (ANOVA) was performed to find out the significant heat treatment parameters. The slow strain rate testing combined with scanning electron microscope and transmission electron microscope was employed to study the SCC behaviors of Al-Zn-Mg-Cu alloy. Results showed that the contour map produced by ANOVA offered a reliable reference for selection of optimum heat treatment parameters. By using this method, a desired combination of mechanical performances and SCC resistance was obtained.

Influence of RRA Treatment on the Microstructure and Stress Corrosion Cracking Behavior of the Spray-Formed 7075 Alloy

The effects of retrogression under pre-aging on the microstructure, mechanical properties, and stress corrosion cracking behavior of spray-formed 7075 aluminum alloys were investigated by the transmission electron microscopy, tensile tests, and slow strain rate tests. The results show that as a result of aging at 120°C for 16 h (as pre-aging), the strength of the alloy can be preserved on a high level and the grainboundary precipitates are discrete after retrogression and re-aging treatment. However, the retrogression treatment is uncontrollable by the shortened retrogression period. After retrogression at 200°C for 8 min and re-aging, the ultimate tensile strength, elongation, and the stress corrosion cracking index of the alloy are 791 MPa, 8.5% and 0.155, respectively.

Effect of Pre-aging on Stress Corrosion Cracking of Spray-formed 7075 Alloy in Retrogression and Re-aging

The effects of pre-aging in retrogression and re-aging (RRA) treatment on microstructure, mechanical properties, and stress corrosion cracking (SCC) behavior of spray-formed 7075 aluminum alloy were investigated by tensile test, slow strain rate test, and transmission electron microscope. The results show that the under aging (120 °C for 16 h) as the pre-aging in RRA treatment can vastly improve the mechanical properties and the SCC resistance of the alloy, compared with early aging (120 °C for 8 h), peak aging (120 °C for 24 h), and over aging (120 °C for 32 h) treatments, the ultimate tensile strength of the alloy is 782 MPa, which is higher than that for peak aging or conventional RRA treatment; and the SCC resistance of the alloy is also excellent after RRA with under aging as pre-aging.

Effect of pH Value on the Electrochemical and Stress Corrosion Cracking Behavior of X70 Pipeline Steel in the Dilute Bicarbonate Solutions

In this work, effects of pH value on the electrochemical and stress corrosion cracking (SCC) behavior of X70 pipeline steel in the dilute bicarbonate solutions were investigated using electrochemical measurements, slow strain rate tensile tests and surface analysis techniques. Decrease of the solution pH from 6.8 to 6.0 promotes the anodic dissolution and cathodic reduction simultaneously. Further decrease of the pH value mainly accelerates the cathodic reduction of X70 pipeline steel. As a result, when the solution pH decreases form 6.8 to 5.5, SCC susceptibility decreases because of the enhancement of the anodic dissolution. When the solution pH decreases from 5.5 to 4.0, SCC susceptibility increases gradually because of the acceleration of cathodic reactions.

Comparative study of the SCC behavior of E690 steel and simulated HAZ microstructures in a SO2-polluted marine atmosphere

Simulated microstructures of the typical CGHAZ, FGHAZ, and ICHAZ of an E690 welded joint were prepared with heat treatment at peak temperatures of 1300, 850, and 750°C, respectively. Slow strain rate tensile (SSRT) tests were implemented to investigate the stress corrosion cracking (SCC) behavior of E690 steel and the simulated HAZ microstructures in a SO2-polluted marine atmosphere. Results revealed that E690 steel and its simulated HAZ microstructures all had a high SCC susceptibility in the simulated SO2-polluted marine atmosphere with a combined mechanism of AD and HE. The SCC susceptibility gradually increased in the following order: BM, CGHAZ, FGHAZ, and ICHAZ. The cracking mode of BM and CGHAZ was transgranular, whereas that of FGHAZ and ICHAZ was intergranular. The lower SCC susceptibility of BM and CGHAZ was probably due to the impeding effect of lath bainitic grain boundaries on SCC propagation, whereas the higher SCC susceptibility of FGHAZ and ICHAZ was attributed to the facilitating effect of M-A islands on crack initiation and propagation.

Effect of Micro Arc Oxidation Treatment on the Corrosion and Stress Corrosion Cracking (SCC) Behaviours of AA7020-T6 Aluminum Alloy in 3.5% NaCl Solution

Alumina coating was formed on AA7020 aluminum alloy by micro arc oxidation (MAO) method and its corrosion and stress corrosion cracking (SCC) behaviors were examined in 3.5 wt. % NaCl solution. Potentiodynamic polarization (PP) was used to evaluate the corrosion resistance of the coating and slow strain rate test (SSRT) was used for evaluating the environmental cracking resistance in 3.5% NaCl solution. Results indicated that MAO coating on AA7020 alloy significantly improved the corrosion resistance. However the environmental cracking resistance was found to be only marginal. Key words: aluminum, micro arc oxidation, x-ray diffraction, stress corrosion cracking

Stress corrosion cracking of E690 steel as a welded joint in a simulated marine atmosphere containing sulphur dioxide

Stress corrosion cracking (SCC) behavior and mechanism of E690 welded joint in simulated marine atmosphere containing SO2 were investigated using SSRT method and electrochemical measurements. Results showed that it had very high SCC susceptibility in this environment with a combined mechanism of anodic dissolution and hydrogen embrittlement (HE). The intercritical heat affected zone in the welded joint was the most vulnerable location to SCC because this zone has less strength, more negative potential, and higher corrosion current density. The M-A constituents had a detrimental effect on SCC behavior in the synergetic effect of stress concentration, micro-galvanic corrosion, and HE.

Stress corrosion cracking behavior of X80 steel in artificial seawater under controlled strain rate and applied potentials

The effect of applied potential on the stress corrosion cracking (SCC) behavior of X80 steel was examined in artificial seawater (ASW) at different strain rates of 1×10−4, 1×10−5 and 1×10−6/sec. The controlled potential of −650, −850, −950 and −1,050 mVSCE, respectively, was applied during strainig. It was found that X80 steel was susceptible to SCC in seawater environment under both anodic and cathodic applied potentials and the susceptibility was sensitive to strain rate. The SCC was initiated at the surface pits under an anodic applied potential of -650 mVSCE. The effect of cathodic applied potential on the SCC behavior of X80 steel in ASW was more complex, such that the combined effect of surface damage, including pits and hydrogeninduced cracking, and hydrogen concentration generated on the surface tended to determine the SCC susceptibility. The SCC behavior of X80 steel with different applied potentials in ASW was discussed based on the microstructural and the fractographic observations.

Quasi-static behavior of notched Ti-6Al-4V specimens in water-methanol solution

Abstract The adoption of Ti-6Al-4V titanium alloy is widespread in advanced engineering fields, such as the aerospace, automotive, and maritime sectors, due to its remarkable mechanical characteristics and proven corrosion resistance. However, literature studies and field failures have underlined that the Ti-6Al-4V is susceptible to the stress corrosion cracking (SCC) and the corrosion fatigue phenomena in methanol-water solutions. Although several studies focused on the SCC behavior of this particular titanium alloy, recent corrosion fatigue experiments (R=0.1) on Ti-6Al-4V specimens in a water-methanol environment have highlighted a sensible decrease in maximum applied stress of up to 50% and a high sensitivity even to low methanol concentrations. In the present work, an experimental quasi-static SCC test campaign in water-methanol mixture at different concentrations has been conducted on flat dogbone Ti-6Al-4V specimens. The results have been compared with recent corrosion fatigue experiments to characterize the different damage mechanisms at play and decouple mechanical and chemical driving forces. The micromechanical behavior of the material has been analyzed, highlighting the role of the microstructure in the SCC mechanism. Failure surfaces have been investigated with scanning electron and optical microscopy.

Effect of long term exposure and hydrogen effects on HSSCC behaviour of titanium alloy IMI 834

Abstract Hot salt stress corrosion cracking (HSSCC) behaviour of alloy IMI 834 was studied to examine the effect of long-term exposure and the role of hydrogen. Studies were conducted by exposing the salt-coated specimens at 300, 350 and 400 °C, at different stress levels for 1000 h, and in the unstressed condition; and the role of hydrogen in HSSCC was studied by using X-ray diffraction. Although the specimens passed 1000 h of hot salt exposure test at stress levels higher than their yield strength, at these temperatures, the post-exposure tensile tests showed a significant loss in ductility and the presence of micro cracks. The study shows the presence of hydrides, which are responsible for HSSCC.

Microstructure, mechanical properties and stress corrosion cracking of Al–Zn–Mg–Zr alloy sheet with trace amount of Sc

Microstructural and property evolution of the Al–Zn–Mg–0.10%Sc–0.10%Zr alloy sheet during its preparation were investigated in detail by means of optical microscopy (OM), scanning electron microscope (SEM), energy dispersive X-ray (EDX), transmission electron microscopy (TEM), Vickers micro-hardness test and room temperature tensile test. Stress corrosion cracking (SCC) behavior of the Al–Zn–Mg–0.10%Sc–0.10%Zr alloy under different heat treatments was studied using slow strain rate test. The results showed that serious dendritic segregation existed in as-cast condition. The suitable homogenization treatment for Al–Zn–Mg–0.10%Sc–0.10%Zr alloy was 470°C/24 h. After homogenization treatment, dissoluble Zn and Mg enriched non-equilibrium phases dissolved into α-Al matrix completely. The suitable solid solution-aging treatment for Al–Zn–Mg–0.10%Sc–0.10%Zr alloy was solution treated at 470 °C for 60 min, followed by water quenching and then aged at 120 °C for 24 h. Under this aging temper, the grain structures were composed of sub-grains, ηʹ phases and nanometer-sized, spherical Al3(Sc, Zr) particles. Grain boundary precipitates (GBPs) area fraction was found to be an important parameter to evaluate the SCC susceptibility. The improved corrosion resistance from increasing aging temperature or prolonging aging time was due to the discontinuous η precipitates along the grain boundary and the high area fraction of GBPs. The main strengthening mechanisms of Al–Zn–Mg–0.10%Sc–0.10%Zr alloy are precipitation strengthening derived from ηʹ precipitates, dispersion strengthening, sub-grain strengthening and grain refinement caused by coherent Al3(Sc, Zr) particles.

Stress corrosion cracking of a high-strength friction-stir-welded joint of an Al–Zn–Mg–Zr alloy containing 0.25 wt.% Sc

Stress corrosion cracking (SCC) behavior and mechanism of a friction stir welded Al–Zn–Mg–Zr alloy with 0.25wt.% Sc were investigated. Impurity intermetallics and primary Al3ScxZr1−x particles both crack perpendicular to tensile direction, whereas anodic dissolution only occurs around the former, initiating SCC. During cracking propagation, both anodic dissolution and hydrogen embrittlement operate. The thermo-mechanically affected zone on advancing side adjacent to weld nugget zone is most susceptible to SCC, which can be ascribed to the enrichment of impurity intermetallics, continuously distributed grain boundary precipitates and its stronger galvanic coupling with weld nugget zone from their greater microstructure and micro-chemistry differences.

STUDY OF MICROSTRUCTURE AND STRESS CORROSION CRACKING BEHAVIOR IN WELDING TRANSITION ZONE OF Ni–BASED ALLOYS

Welding technique is generally used in nuclear power plant for manufacturing and machining important components such as steam generator. The similar metal weld and dissimilar metal weld were commonly involved to connect and fixup tubings in steam generators. However, in recent years large amounts of cracking accidents have been observed in the welded joints. A concern has been raised about the integrity and reliability in the joint transition zone due to the high susceptibility of heat affected zone (HAZ) and fusion zone (FZ) to stress corrosion cracking (SCC). In this study, the similar metal and dissimilar metal joints were investigated and compared, focusing on the correlation between microstructure, residual strain and SCC behavior. The microstructures of transition zone in Ni-based Alloys 690 and 52 similar metal joint and Alloys 182 and A533B low alloy steel dissimilar metal joint were investigated comprehensively by SEM, EBSD, TEM. The residual strain distribution in the HAZ of 690-52 similar metal joint was quantitatively measured. The SCC behavior of 182-A533B dissimilar metal joint in high temperature oxygenated water were simulated by creviced bent beam specimen. The HAZ in the similar joint exhibits higher residual strain, sensitive microstructure and high susceptibility to SCC, therefore, the HAZ region deserve more attention during the inspection and examination of components. The FZ of the dissimilar metal joint exhibits complicated microstructure and chemical