Stress Corrosion Cracking Behavior Research Articles

Stress corrosion cracking susceptibility of a high strength Mg-7%Gd-5%Y-1%Nd-0.5%Zr alloy

Abstract Through performing the tensile tests with different strain rates in 3.5 wt.% NaCl solution, the stress corrosion cracking (SCC) behavior and the effect of strain rate on the SCC susceptibility of an extruded Mg-7%Gd-5%Y-1%Nd-0.5%Zr (EW75) alloy have been investigated. Results demonstrate that the alloy is susceptible to SCC when the strain rate is lower than 5 × 10 −6 s −1 . At the strain rate of 1 × 10 −6 s −1 , the SCC susceptibility index ( I SCC ) is 0.96 and the elongation-to-failure ( e f ) is only 0.11%. Fractography indicates that the brittle quasi-cleavage feature is very obvious and become more pronounced with decreasing the strain rate. Further analysis confirms that the cracking mode is predominantly transgranular, but the partial intergranular cracking at some localized area can also occur. Meanwhile, it seems that the crack propagation path is unrelated to the existing phase particles.

Effect of Temperature on the Stress Corrosion Cracking of 304L Austenitic Stainless Steels in Alkaline Solution

A slow strain rate tensile (SSRT) test was carried out to investigate the stress corrosion cracking (SCC) behavior of the sensitized 304L austenitic stainless steels (ASSs) in alkaline solution (0.5M NaOH). Mechanical properties and fracture morphology evolutions of the 304L ASSs were studied as a function of temperature through slow speed tensile tester and scanning electron microscopy (SEM). The results showed that the tensile strength and percentage elongation after fracture significantly reduced as the test temperature rose. Fractographic examination revealed both ductile and brittle fracture features for the specimens tested in different environments. However, the proportion of brittle fracture characteristics changed with the temperature.

Microstructure and corrosion behaviour of gas tungsten arc welds of maraging steel

Superior properties of maraging steels make them suitable for the fabrication of components used for military applications like missile covering, rocket motor casing and ship hulls. Welding is the main process for fabrication of these components, while the maraging steels can be fusion welded using gas tungsten arc welding (GTAW) process. All these fabricated components require longer storage life and a major problem in welds is susceptible to stress corrosion cracking (SCC). The present study is aimed at studying the SCC behaviour of MDN 250 (18% Ni) steel and its welds with respect to microstructural changes. In the present study, 5.2 mm thick sheets made of MDN 250 steel in the solution annealed condition was welded using GTAW process. Post-weld heat treatments of direct ageing (480 °C for 3 h), solutionizing (815 °C for 1 h) followed by ageing and homogenizing (1150 °C for 1 h) followed by ageing were carried out. A mixture of martensite and austenite was observed in the microstructure of the fusion zone of solutionized and direct aged welds and only martensite in as-welded condition. Homogenization and ageing treatment have eliminated reverted austenite and elemental segregation. Homogenized welds also exhibited a marginal improvement in the corrosion resistance compared to those in the as-welded, solutionized and aged condition. Constant load SCC test data clearly revealed that the failure time of homogenized weld is much longer compared to other post weld treatments, and the homogenization treatment is recommended to improve the SCC life of GTA welds of MDN 250 Maraging steel.

Effect of aging treatment on the exfoliation corrosion and stress corrosion cracking behaviors of 2195 Al–Li alloy

2195 Al–Li alloy was processed by solid solution heat treatment and then aged at different temperatures, and its microstructure, mechanical properties, inter-granular corrosion (IGC), exfoliation corrosion (EXCO) and stress corrosion cracking (SCC) behaviors were observed and determined by scanning electron microscopy (SEM), transmission electron microscopy (TEM), immersion test in IGC and EXCO solutions, electrochemical impedance spectroscopy (EIS) and slow strain rate tensile (SSRT) test. The results reveal that the size and density of T1 precipitates at grain boundary are increased with increasing aging temperature whereas the density of T1 phases in grain is increased firstly and then reduced slightly. The IGC and EXCO susceptibility of 2195 alloy is increased while its SCC susceptibility in 3.5% NaCl solution is low and hardly influenced by the aging temperature. The hardness and tensile strength are increased at first and then decreased, but the elongation and static toughness values are declined with aging temperature. The optimum heat treatment for the practical application of 2195 alloy is the aged at 155°C for 14h temper.

Effects of laser shock peening on SCC behavior of Alloy 600 in tetrathionate solution

In this study, the effects of laser shock peening (LSP) on stress corrosion cracking (SCC) behavior of nickel based Alloy 600 in tetrathionate solution were investigated. The LSP induced compressive residual stresses and changes in the near surface microstructure, hardness were characterized. The effects of LSP on SCC susceptibility of Alloy 600 in tetrathionate solution were evaluated by slow strain rate tests and constant load tests. The results indicate a significantly longer time to failure and decreased susceptibility to SCC. These improvements were attributed to LSP induced compressive residual stresses, increased yield strength and hardening caused by near-surface microstructural changes.

Influence of alloyed Sc and Zr, and heat treatment on microstructures and stress corrosion cracking of Al–Zn–Mg–Cu alloys

Abstract Stress corrosion cracking (SCC) behavior of Al–Zn–Mg–Cu alloys with different Sc, Zr contents and heat treatments was studied using slow strain rate test. Grain boundary microstructures were identified by transmission electron microscopy (TEM) and statistical analysis. It was found that the SCC resistance of alloys is improved by increasing Sc, Zr contents and aging degree. Grain boundary precipitates (GBPs) area fraction was found to be an important parameter to evaluate the SCC susceptibility. The results reveal that for Al–Zn–Mg–Cu–0.25Sc–0.10Zr (wt%) alloy with different aging degrees, hydrogen induced cracking dominates the SCC when the area fraction of GBPs is relatively low. For peak-aged Al–Zn–Mg–Cu alloy and Al–Zn–Mg–Cu–0.10Sc–0.10Zr (wt%) alloy, anodic dissolution dominates the SCC when the area fraction of GBPs is sufficiently high.

Stress Corrosion Cracking Behavior at Inconel and Low Alloy Steel Weld Interfaces

Three-dimensional microstructure observations, macro- to micro-scopic residual stress measurements by three methods and creviced bent beam SCC tests were performed for Inconel/low alloy steel (LAS) weld samples. The possible reasons for the suppression of SCC crack propagation near the weld interface found at a nuclear power plant were estimated to include the crack branching at the grain boundary (GB) parallel to the interface, i.e., Type II GB, compressive residual stresses in the LAS region and crack tip oxidation in the LAS at the interface. The formation mechanism of Type II GB and stress gradient in individual grains in the Inconel are also discussed.

Effect of Post Weld Heat Treatments on Mechanical and Stress Corrosion Cracking Behaviour of Aa7075 Friction Stir Welds

The high strength aluminium alloys exhibits low weldability due to poor solidification microstructure, porosity in the fusion zone and lose their mechanical properties when they are welded by fusion welding techniques. Friction stir welding (FSW) is a promising technique to retain the properties of the alloy as the joining take place in the solid state. Even though mechanical properties of the welds are better, corrosion resistance of welds gets affected by the microstructural changes that occur during welding. In the present work the effect of post weld treatments viz. peak ageing (T6), overaging (T73), retrogression and retrogression & reaging (RRA) on the mechanical properties and stress corrosion resistance is studied. It was observed that Retrogression and RRA treatments improved the resistance to stress corrosion cracking and maintained the mechanical properties. The resistance to stress corrosion is improved in RRA and Retrogression condition with the minimum loss of weld strength. This is attributed to the dissolution, re-precipitation and re-distribution of precipitates.

Mechanistic aspect of stress corrosion cracking of X80 pipeline steel under non-stable cathodic polarization

In this work, the square wave polarization (SWP) technique and slow strain rate tensile test were combined to investigate the influence of cathodic potential fluctuation, i.e. the non-stable cathodic polarization, on the electrochemical and stress corrosion cracking (SCC) behavior of X80 pipeline steel in an acidic soil solution. It was found that the non-stable cathodic polarization accelerated both the anodic dissolution and the cathodic hydrogen evolution, inducing the increase of SCC susceptibility compared with the potentiostatic cathodic polarization. This provides a novel and important concern and recommendation for controlling pipeline SCC under CP fluctuation.

Comparative study of stress corrosion cracking susceptibility of Fe18Cr10Mn- and Fe18Cr10Mn1Ni-based high nitrogen stainless steels

The stress corrosion cracking (SCC) behavior of Fe18Cr10Mn1Ni(0.3–0.8)N alloys was investigated in aqueous NaCl environment by using slow strain rate test method, and the results were compared to those of Ni-free counterparts. The addition of N tended to improve the SCC resistance of Fe18Cr10Mn- and Fe18Cr10Mn1Ni-based alloys. The alloying Ni magnified the beneficial effect of N on the SCC susceptibility and, eventually, the Fe18Cr10Mn0.8N alloy was immune to SCC in 2M NaCl solution at 50°C. The SCC behavior of the present alloys was found to be closely related to the repassivation tendency and the resistance to pitting corrosion.

Improvement of Stress Corrosion Cracking (SCC) Resistance of a 7150 Al-Zn-Mg-Cu Alloy by Retrogression and Reageing (RRA) Treatment

A 7150 Al-Zn-Mg-Cu alloy is artificially aged at 120 oC for varying time. The peak hardness (T6 temper) is obtained at about 24 h at that temperature. Further, the T6 temper is subjected to retrogression and reageing (RRA) treatment. Slow strain rate test (SSRT) has been carried out on the T6 and RRA tempers. SSRT results indicated that the RRA temper have higher resistance to SCC compared to that of T6 temper. SCC behaviour of the alloy tempers have been explained with the help of microstructural features studied by transmission electron microscope (TEM). The large, discrete and discontinuous grain boundary precipitates observed in the microstructure of the RRA temper are believed to be the responsible factor for achieving higher SCC resistance. Further, SEM fractographs and crack morphology have also been analyzed to evaluate the SCC behaviour of the alloy tempers.

Numerical investigation on stress corrosion cracking behavior of dissimilar weld joints in pressurized water reactor plants

There have been incidents recently where stress corrosion cracking (SCC) observed in the dissimilar metal weld (DMW) joints connecting the reactor pressure vessel (RPV) nozzle with the hot leg pipe. Due to the complex microstructure and mechanical heterogeneity in the weld region, dissimilar metal weld joints are more susceptible to SCC than the bulk steels in the simulated high temperature water environment of pressurized water reactor (PWR). Tensile residual stress (RS), in addition to operating loads, has a great contribution to SCC crack growth. Limited experimental conditions, varied influence factors and diverging experimental data make it difficult to accurately predict the SCC behavior of DMW joints with complex geometry, material configuration, operating loads and crack shape. Based on the film slip/dissolution oxidation model and elastic-plastic finite element method (EPFEM), an approach is developed to quantitatively predict the SCC growth rate of a RPV outlet nozzle DMW joint. Moreover, this approach is expected to be a pre-analytical tool for SCC experiment of DMW joints in PWR primary water environment.

Intergranular Stress Corrosion Cracking Growth Behavior of Ni-Cr-Fe Alloys in Pressurized Water Reactor Primary Water

The purpose of this research was to compare the stress corrosion cracking (SCC) resistance of materials used at the present time for steam generator (SG) tubing in pressurized water reactor (PWR) primary water. Our results in PWR primary water for 20% cold-worked (CW) Alloy 800 (UNS N08800) are compared with already published data for SCC growth from 20%CW Alloy thermally treated (TT)690 (UNS N06690), 20%CW Alloy mill-annealed (MA)600 (UNS N06600), and 20%CW austenitic stainless steels. The second purpose was to examine the dependence of SCC growth on nickel and chromium in PWR primary water; the objective was to obtain the basic knowledge to understand SCC behavior of SG tubing materials. The third objective was to understand whether accelerated testing at higher temperatures is appropriate for predicting SCC initiation and growth at lower temperatures. For these objectives, SCC growth was measured in PWR primary water at 290, 320, 330, 340, and 360°C under static load conditions. Tests were performed us...

Stress corrosion cracking behavior of quenched and tempered 2.25Cr 1Mo steel

For stress corrosion cracking (SCC) study of 2.25Cr-1Mo steel, specimens were initially austenitized at 925°C for 2 hours and quenched in ice brine solution. With this process of heat treatment martensite was formed and banded morphology in the microstructure developed during previous processing was also removed. Tempering at 575°C for 1h was employed to introduce ductility in the quenched martensite of the specimens. The effects of temperature variations on SCC behavior showed a successive decrease in strength and ductility of the steel. Theses variations in tensile properties were correlated with scanning electron microscopic (SEM) examinations. The SEM results clearly revealed that mostly transgranular cracks initiated at the edges of the tensile specimens grown perpendicular to loading axes, and their intensity is increased with the testing temperatures.

Effects of Soil Type of Shanghai and Electrode Potential on Near-Neutral pH Stress Corrosion Cracking of Pipeline Steel X60

The effects of soil type of Shanghai and electrode potential from cathodic protection point on near-neutral pH stress corrosion cracking (SCC) behavior of pipeline steel X60 has been investigated for structural integrity assessment. The SCC behavior was evaluated through slow strain rate tests (SSRT) at various electrode potentials in three solutions containing different typical soils. Results showed that the SCC susceptibility generally increased with decreasing electrode potential in all the three environments, with quick increase happening in the range from-1500 to-700mV(SCE). It is suggested that hydrogen induced cracking should dominate the SCC at low potentials. In cathodic potential range, the rank of the SCC susceptibility for soil type was Near-city soil > Cyan-purple soil > Cyan-yellow soil. In anodic potential range, SCC susceptibility curves mixed each other in the three solutions.

Effect of Electrochemical Potential and Chloride Concentration on Stress Corrosion Cracking Behavior of 23Co14Ni12Cr3Mo Ultra-High Strength Steel in NaCl Solution

Effect of Electrochemical Potential and Chloride Concentration on Stress Corrosion Cracking Behavior of 23Co14Ni12Cr3Mo Ultra-High Strength Steel in NaCl Solution

Effect of δ-Ferrite Content on the Stress Corrosion Cracking Behavior of Cast Austenitic Stainless Steel in High-Temperature Water Environment

The slow strain rate tests (SSRT) at a nominal strain rate 1× 10−6/s were conducted to evaluate the mechanical properties of CF8A cast austenitic stainless steel (CASS) in air and high-temperature water environments. CF8A CASS is mainly composed of a matrix of γ phase dispersed with δ ferrites and is affected slightly by aging heat treatment. The hardness value of γ phase did not change with aging time, while that of δ ferrite increased with increasing the aging time. The SSRT results showed that a loss in elongation of a high δ-ferrite specimen was more significant than that of the low δ-ferrite specimens. The SCC paths of the low δ-ferrite specimen were along the links between δ ferrites dispersed in the matrix. For the high δ-ferrite specimen, most of the cracks were observed to propagate through the chromium depletion regions in the ferrite grains, which were preferentially oxidized during the SSR test in water. However, the elongation did not decrease further after aging time was longer than 2,400 h,...

SCC investigation of low alloy ultra-high strength steel 30CrMnSiNi2A in 3.5wt% NaCl solution by slow strain rate technique

To evaluate stress corrosion cracking (SCC) mechanism of low alloy ultra-high strength steel 30CrMnSiNi2A in environment containing NaCl, SCC behavior of the steel in 3.5wt% NaCl solution is investigated by slow strain rate technique (SSRT) with various strain rates and applied potentials, surface analysis technique, and electrochemical measurements. SCC susceptibility of the steel increases rapidly with strain rate decreasing from 1×10−5s−1 to 5×10−7s−1, and becomes stable when strain rate is lower than 5×10−7s−1. SCC propagation of the steel in the solution at open circuit potential (OCP) needs sufficient hydrogen which is supplied at a certain strain rate. Fracture surface at OCP has similar characteristics with that at cathodic polarization −1000mVSCE, which presents characteristic fractography of hydrogen induced cracking (HIC). All of these indicate that SCC behavior of the steel in the solution at OCP is mainly controlled by HIC rather than anodic dissolution (AD).

Effect of H2S Partial Pressure on Stress Corrosion Cracking Behavior of 13Cr Stainless Steel in Annulus Environment Around CO2 Injection Well

Electrochemical characteristics and stress corrosion cracking (SCC) behavior of 13Cr stainless steel were investigated by electrochemical measurements, U-bent specimen immersion test and surface analysis technique in an artificial solution with an autoclave, which aimed to simu- late the annulus environment around CO2 injection well. The results showed that annulus solution around injection well was a complicated H2S-CO2-Cl

Effect of AC on corrosion behavior of X80 pipeline steel in high pH solution

Corrosion behavior of X80 pipeline steel under the application of various waveforms AC was investigated in concentrated carbonate/bicarbonate solution by electrochemical measurements, immersion tests, and slow strain rate tensile tests. Under the application of AC current of various waveforms, the corrosion potential shifts negatively and the passivity of the steel degrades severely. Superimposed AC current causes an increase of corrosion rate, and the corrosion rate of the steel under square wave is the highest, next the triangular wave, the least sine wave. The steel mainly experiences localized corrosion under various waveforms AC, in particular with the square wave AC current, the pitting occurs more apparently. AC superimposition enhances the stress corrosion cracking (SCC) susceptibility of the steel in carbonate/bicarbonate solution, especially at square wave. At a short term effect of AC interference, the fracture mode is intergranular, and the SCC behavior of steel in high pH solution is affected by the anodic dissolution for steel with or without AC application.