Stress Corrosion Cracking Properties Research Articles

Effect of Sc and Zr additions on corrosion behaviour of Al–Zn–Mg–Cu alloys

In this paper, the relationship between recrystallization and corrosion behaviour of Al–Zn–Mg–Cu alloys has been investigated. The additions of Sc and Zr inhibited the recrystallization of Al–Zn–Mg–Cu alloys remarkably. Intergranular corrosion, exfoliation corrosion, stress corrosion cracking and electrochemical properties of Al–Zn–Mg–Cu alloy and Al–Zn–Mg–Cu–Sc–Zr alloy under peak-aged treatment have been studied. Results show that the additions of Sc and Zr to Al–Zn–Mg–Cu alloy can improve the corrosion resistance observably due to the inhibition of recrystallization behaviour. The spacing of grain boundary precipitates Al–Zn–Mg–Cu–Sc–Zr alloy was found to be larger than that in recrystallized Al–Zn–Mg–Cu alloy, the discontinuity of precipitates distribution along the grain boundary was enhanced by the introduction of Sc and Zr.

A Study on Stress Corrosion Crack of Thick-Walled Elbow in Manifold for Acid Fracturing

Acid fracturing, with a pumping pressure up to 140 MPa for fractural liquid injection, is commonly used in enhanced oil recovery. Subjected to severely high hoop stress, stress corrosion cracking (SCC) often occurs at cracks inside manifold elbows which are due to acid corrosion and fracturing propping agent erosion. To avoid the occurrence of SCC, it is necessary to establish a substantial understanding of the fracture strength of thick-walled elbow, including the stress state distribution in elbow and SCC properties of elbow material. Base on the hoop stress calculation for thin wall straight pipe, a formula for hoop stress of thick-walled elbow is derived and also verified with finite element method (FEM). This is accomplished by introduce curvature factor and wall thickness factor into the formula. Furthermore, the critical stress intensity factor, KISCC, is determined subsequently in simulated acid fracturing corrosion condition. However, part of the considerable contribution of this work is to scale the critical crack depth. A simplified hoop stress formula proposed in this paper can be used in design of elbow wall thickness and strength evaluation. The established critical crack depth calculation formula can be applied to safety assessment of elbows with initial erosion cracks. The proposed method has been proved to be a simple and useful method to calculate the stress and fractural strength of thick-walled elbow.

Microstructure and Stress Corrosion Cracking of Spray Forming 7075 Alloy after Retrogression and Re-ageing Treatment

A typical age-strengthening 7075 aluminum alloy with high tensile properties can be spray-formed through T6 treatment,but its stress corrosion cracking(SCC) property appears very poor after this treatment. On the other hand,the SCC property may be improved by T7 treatment but the tensile strength of the alloy then be seriously harmed. Therefore,the effects of four kinds of retrogression and re-ageing(RRA) treatments on the microstructure and mechanical properties of a spray forming 7075 alloy are investigated by using mechanical,electric and transmission electron microscope observation measures in this research. It is obtained that the tensile strength and electric conductivity of the alloy reaches up to 748 MPa and 22.8 MS/m respectively under the condition of retrogressed at 200 ℃ for 10 min,and re-aged at 120 ℃ for 24 h. During retrogression treatment,GP zone and η′ phase are dissolved in matrix,η′ phase is then re-precipitated at 200 ℃ retrogression treatment over 10 min,which leads to the slight increase of tensile strength of the alloy. Because of the precipitation of shaped-η′ phases during retrogression and the corresponding RRA treatment a lots of η′ phases re-precipitate and η phases at grain boundary may improve the SCC resistance of the alloy.

Study of the SCC Behavior of 7075 Aluminum Alloy After One-Step Aging at 163 °C

For the past many years, 7075 aluminum alloys have been widely used especially in those applications for which high mechanical performances are required. It is well known that the alloy in the T6 condition is characterized by the highest ultimate and yield strengths, but, at the same time, by poor stress corrosion cracking (SCC) resistance. For this reason, in the aeronautic applications, new heat treatments have been introduced to produce T7X conditions, which are characterized by lower mechanical strength, but very good SCC behavior, when compared with the T6 condition. The aim of this study is to study the tensile properties and the SCC behavior of 7075 thick plates when submitted to a single-step aging by varying the aging times. The tests were carried out according to the standards and the data obtained from the SCC tests were analyzed quantitatively using an image analysis software. The results show that, when compared with the T7X conditions, the single-step aging performed in the laboratory can produce acceptable tensile and SCC properties.

Stress-Corrosion Cracking Property of Aluminum-Magnesium Alloy Processed by Equal-Channel Angular Pressing

Stress-corrosion cracking property of an aluminum-magnesium alloy processed by equal-channel angular pressing (ECAP) was investigated by a slow strain-rate tensile technique in a 3% NaCl solution of pH 4.2 at 303 K. The maximum stress and elongation of the Al-Mg alloy were lower in the NaCl solution than in air. The stress-corrosion cracking property was evaluated by the decrease ratio of maximum stress and elongation of the Al-Mg alloy with NaCl solution, 𝐼(𝛿max) and 𝐼(𝛿), respectively. 𝐼(𝛿max) and 𝐼(𝛿) were lower with ECAP than without it, showing that the susceptibility of stress-corrosion cracking decreased with ECAP. The polarization curve and time dependence of the anodic current density at constant potential of the Al-Mg alloy in the NaCl solution revealed that the anodic current density was lower with ECAP than without it, or the corrosion resistance of the Al-Mg alloy was improved by ECAP. The decrease in stress-corrosion crack susceptibility of the Al-Mg alloy with ECAP is attributed to an improvement in corrosion resistance afforded by ECAP.

Study on stress corrosion crack of austenitic stainless steel in simulated ocean environment

Recent studies on stress corrosion cracking properties of 321 bend pipe and pipe with weld, 316NG austenitic stainless steel pipe in ocean environment in virtue of slow strain rate tensile stress corrosion crack test are performed in different concentration of NaCl solution. Elongation and max tensile stress are selected as parameters to evaluate the SCC susceptibility based on the phenomenon that elongation and max stress fall as samples being exposed to NaCl solution environment, the results show that 316NG has the best stress corrosion crack resistance and 321 bend pipe materials behavior oppositely. In addition, the influence of differing strain rate and concentration of NaCl solution on properties of materials are researched, elongation increases along with tensile strain rate enhancement, mechanical properties are immune to variety of Cl- concentration from 3.5% to 26.5%.

Role of Slip Mode on Stress Corrosion Cracking Behavior

In this article, we examine the effect of aging treatment and the role of planarity of slip on stress corrosion cracking (SCC) behavior in precipitation-hardened alloys. With aging, the slip mode can change from a planar slip in the underage (UA) to a wavy slip in the overage (OA) region. This, in turn, results in sharpening the crack tip in the UA compared to blunting in the OA condition. We propose that the planar slip enhances the stress concentration effects by making the alloys more susceptible to SCC. In addition, the planarity of slip enhances plateau velocities, reduces thresholds for SCC, and reduces component life. We show that the effect of slip planarity is somewhat similar to the effects of mechanically induced stress concentrations such as due to the presence of sharp notches. Aging treatment also causes variations in the matrix and grain boundary (GB) microstructures, along with typical mechanical and SCC properties. These properties include yield stress, work hardening rate, fracture toughness K IC , thresholds K Iscc, and steady-state plateau velocity (da/dt). The SCC data for a wide range of ductile alloys including 7050, 7075, 5083, 5456 Al, MAR M steels, and solid solution copper-base alloys are collected from the literature. Our assertion is that slip mode and the resulting stress concentration are important factors in SCC behavior. This is further supported by similar observations in many other systems including some steels, Al alloys, and Cu alloys.

Effect of pH and Temperature on Stress Corrosion Cracking of API X60 Pipeline Steel

Stress corrosion cracking (SCC) is the result of the combined influence of tensile stress and a corrosive environment on a susceptible material. This paper analyzes the understanding mechanisms of stress corrosion cracking (SCC) of API X60 pipeline steel. The susceptibility to SCC and mechanism was investigated using slow strain rate tests (SSRT). The SSRT were performed at strain rate of 25.4 × 10−6 mm/sec in a glass autoclave containing a soil solution called NS4 with pH of 3 and 10 at room temperature and 50°C. Cathodic polarization potentials of −200 mV referred to Ecorr was applied. SCC properties were evaluated by SSRT in simulated soil solution (NS4 solution) that is typical environment for SCC under cathodic charging. The results of ratio reduction area (RRA), time to failure ratio (TFR) and elongation plastic ratio (EPR) indicate that X60 pipeline steel was more susceptible to SCC at pH 3 independently of the temperature. At high pH the SCC susceptibility was higher at 50°C. Scanning electron microscopy (SEM) observations of these specimens showed a brittle type of fracture with transgranular appearance. The failure and SCC mechanism of X60 steel into NS4 solution was hydrogen based mechanism. Hydrogen absorption by X60 pipe steel may result in local corrosion (primarily, SCC) of underground pipeline steel. SEM observations revealed the presence of internal cracks in some of these specimens.

Influencing Factors of 1Cr13 SSCC for Oil & Gas Wellhead

With the exploration of oil-gas field developing, more and more oil-gas well contain H2S, hydrogen sulfide stress corrosion has serious effect on production and restrict oil field development. With the applications of 1Cr13 steel in oil & gas wellhead, it is urgent to research hydrogen sulfide stress corrosion cracking (SSCC) properties in high-strength under the simulation condition of production. The tensile test under constant load and slow strain rate test (SSRT) were adopted to analyze the behaviors of 1Cr13 steel with orthogonal test under saturated H2S solution which included carbon dioxide under a partial pressure and its sample fracture was observed with SEM (Scanning Electron Microscope). Constant load tensile test is one of the first recognized by NACE to assess the performance of metallic materials against SSC approach under tensile stress in the aqueous solution which was in low pH value and H2S was saturated. Through the research above the mechanism of stress corrosion and the environmental factors that influence stress corrosion were investigated. The experimental results shown that the effects of environmental factors on SCC (Stress Corrosion Cracking) sensitivity of materials are in the following order: temperature effect > solution pH effect > chloride ion concentration effect, and 1Cr13 material has a better corrosion resistance for H2S and CO2 conditions under a certain stress so it can be proposed as the material of value for oil & gas wellhead. Through SEM it can be seen that the fracture is belonged to brittle fracture. The lattice bonding force is destroyed by hydrogen into the material that gathered in the certain crystal face and the material transform from plastic to brittleness, the material is failed, and SCC occurred.

Reducing Residual Stress in 7050 Aluminum Alloy Die Forgings by Heat Treatment

Aerospace aluminum alloy forgings can have the residual stresses arising from heat treatment reduced by modification to the quench cooling rates and subsequent aging treatments. A series of propeller hubs usually made from the alloy 2014 have been closed die forged from the less quench sensitive alloy 7050. These forgings have been subjected to various quenching and aging treatments in an attempt to improve the balance of mechanical properties with the residual stress magnitudes. These forgings were not amenable to stress relieving by cold compression or stretching. Warm water (60°C) and boiling water quenches are investigated in addition to quenching into molten salt (200°C) and uphill quenching from −196°C. Various dual aging treatments including retrogression and reaging have been evaluated in an attempt to optimize low residual stress magnitudes with mechanical properties. Residual stresses determined by the center hole-drilling strain-gauge method are reported in addition to electrical conductivity, stress corrosion cracking, fracture toughness, initiation fatigue, and tensile mechanical property variations. It was found that quenching into boiling water and salt at 200°C did substantially reduce the residual stress but had only a small detrimental effect on the majority of the properties measured. However, the influence of quench rate on fracture toughness was much more significant. This is attributed to both coarse grain boundary precipitation and heterogeneous precipitation of η on Al3Zr dispersoids within the grains, which promotes easier crack propagation.

Improvements in mechanical and stress corrosion cracking properties in Al-alloy 7075 via retrogression and reaging

Aluminum alloy 7075 has been widely studied, due to its excellent mechanical properties developed by age hardening and their extensive uses in the aircraft structure. Tensile test specimens were tested in various preaging conditions (100, 120, 140 °C) and various retrogression temperatures T 7 (160, 180, 200 °C) in order to evaluate the effect of heating cycles on the mechanical as well as corrosion properties. The optimum condition was preaging at T 6 120 °C and retrogressing at T 7 200 °C, which gave the highest hardness and tensile properties. The corrosion behavior of three-point-loaded specimens after 7 days of immersion in 3.5% NaCl solution, using modified electrochemical cell, was studied. The most resisting condition for SCC was preaging at T 6 = 100 °C and retrogression at T 7 = 160 °C for 250 min. Specimens retrogressed at 200 °C for 8 min showed low resistance to stress corrosion cracking.

Reducing residual stress in 2014 aluminium alloy die forgings

Closed die forgings manufactured from 2014 aluminium alloys have been subject to both standard and non-standard heat treatments in order to reduce the as-quenched residual stress magnitudes. Warm water (60 °C) and boiling water quenches are investigated. The influence of changing the surface finish of the forgings during boiling water quenching on the mechanical properties and residual stress has also been determined. In addition, high temperature (200 °C) and dual aging treatments have been evaluated in an attempt to combine low residual stresses with the required levels of mechanical properties. Residual stress magnitudes determined by the centre hole-drilling strain-gauge method are reported in addition to stress corrosion cracking, fracture toughness, fatigue and tensile mechanical property variations. The results indicate that boiling water quenching leads to very low residual stress but unsatisfactory mechanical properties. However, the same quenching regime applied to forgings with a black oxide coating results in low residual stress in combination with mechanical properties very close to those achieved by warm water quenching.

Stress-corrosion crack initiation and propagation behavior of Zircaloy-4 cladding under an iodine environment

Iodine-induced stress-corrosion cracking (ISCC) properties and the associated ISCC process of Zircaloy-4 fuel cladding were evaluated. Cladding was heat-treated to have either stress-relieved (SR) or recrystallized (RX) microstructures, and then an internal pressurization with a smooth and pre-cracked specimen was performed at 350 °C, in an iodine environment. The results showed that the threshold stress-intensity factor ( K ISCC) of the SR and RX Zircaloy-4 claddings were 3.3 and 4.8 MPa m 0.5, respectively. The crack propagation rate of the RX Zircaloy-4 was 10 times lower than that of the SR one. Crack initiation and propagation mechanisms of Zircaloy-4 claddings, which had different microstructures, were proposed by a grain-boundary pitting model and a pitting-assisted slip cleavage model; they showed reasonable results.

Retrogression and re-aging treatment of Al-9.99%Zn-1.72%Cu-2.5%Mg-0.13%Zr aluminum alloy

The effect of retrogression and re-aging(RRA) heat treatment on the microstructure and mechanical properties of a low frequency electromagnetic casting alloy as Al-9.99%Zn-1.72%Cu-2.5%Mg-0.13%Zr was investigated by tensile properties test, Vickers hardness, electrical conductivity test, DSC analysis, SEM and TEM observation. The results show that RRA heat treatment can improve the stress corrosion cracking(SCC) properties with retention of the high strength of T6 level. After preaging at 100 °C for 24 h, retrogression at 200 °C for 7 min, and then re-aging at 100 °C for 24 h, the alloy obtains tensile strength up to 795 MPa, yield strength up to 767 MPa, maintains 9.1% elongation, and electric conductivity of 35.6%IACS. TEM observation shows that the re-dissolution of GP zone and η′ phase in the early stage of regression leads to the decrease of hardness, then the increase in the volume fraction of η′ and η phases leads to the increase again in the peak value, and finally the general coarsening of all particles results in a softening of the alloy. Meanwhile it is found that the conventional T6 heat treatment as the preaging and re-aging regime is not the optimum regime to the RRA treatment of the high-zinc content super-high strength aluminum alloy.

A Comparison Study of Stress Corrosion Crack Growth Rates for AA7XXX Alloys as a Function of Bulk Aqueous Chloride Concentrations

Abstract Alternative aluminum alloys are under consideration for drop-in replacement and refurbishment of corrosion and stress corrosion cracking prone AA7075-T6 (UNS A97075) components on aging military aircraft. An assessment of new materials for refurbishment and replacement of older generation, aging components is necessary for a viable life extension program. A quantitative database of stress corrosion cracking (SCC) properties of old generation materials compared to currently available materials is needed as a guideline/justification for part replacement. This effort evaluates AA7150-T7751 (UNS A97150) and AA7040-T7651 (UNS A97040), both which meet mechanical property requirements and are thought to be superior to AA7075-T6 in terms of corrosion performance. Specifically, stress corrosion crack growth rates for these plate alloys were documented and found to be similar in various bulk aqueous chloride environments and to represent a significant improvement over measured rates for AA7075-T651.

Effect of different Mn contents on tensile and corrosion behavior of CD4MCU cast duplex stainless steels

Despite the significant use in the industry, the effect of Mn on the tensile and corrosion behavior of cast duplex stainless steels has not been well established. In the present study, the tensile and corrosion behavior of CD4MCU cast duplex stainless steels with different Mn contents of 0, 0.8 and 2%, respectively, was therefore examined. The polarization and the in situ slow strain rate tests were conducted in 3.5% NaCl + 5% H 2SO 4 aqueous solution to quantify the resistances to pitting corrosion and stress corrosion cracking with different Mn contents. The addition of Mn, which stabilized ferrite in the present study, affected the microstructure of the present alloy, and eventually the tensile and corrosion behaviors in a complex manner. Tensile properties of CD4MCU cast duplex stainless steel, for example, was found to be determined by the volume fraction of hard ferritic phase and the shape of austenitic phase. The addition of 0.8% Mn was detrimental to both pitting corrosion and stress corrosion cracking properties of CD4MCU cast duplex stainless steel due to the significant increase in contact area between the less-noble ferritic and the noble austenitic phases. With the addition of 2% Mn, the resistance to pitting corrosion and stress corrosion cracking in 3.5% NaCl + 5% H 2SO 4 aqueous solution is recovered. The resistance to stress corrosion cracking of the specimen with 2% Mn was still greatly inferior to that of the 0% Mn counterpart. The relationship between the microstructural evolution and the tensile and corrosion behavior of CD4MCU cast duplex stainless steels with different Mn contents was discussed based on the micrographic and fractographic observations.

Effect of Tungsten and Nickel Addition on the Repassivation Behavior of Stainless Steel

Abstract This study examines the effect of alloying elements of Ni and W on the repassivation properties of stainless steel (SS) as evaluated by a rapid scratching electrode technique and stress corrosion cracking (SCC) test. The SS specimens were grouped into two different grades according to Ni content (22Cr-5Ni duplex, Type 317LMN [UNS S31726] austenitic SS). Major considerations regarding alloy design were Ni content and the substitution of W for Mo. However, a similar pitting resistance equivalent number (PREN) of 35 to 36 was maintained for all specimens. The main factors for evaluation of repassivation properties are the peak current for the scratched surface and repassivation rate. In 1 M magnesium chloride (MgCl2) and 1 N sulfuric acid containing chloride ions (H2SO4 + 3.5% Cl−) solution, repassivation test results showed that repassivation properties decreased as Ni content increased. However, W substitution was effective on the repassivation process and increased the resistance of SCC property ...

Effects of Silicon and Chromium on the SCC Properties of Al-Zn-Mg-Cu Cast Alloy

Effects of Si and Cr additions and aging treatment on the stress corrosion cracking(SCC) resistance of Al-Zn-Mg-Cu cast alloys were investigated by C-ring test and electrical conductivity measurement. The SCC resistance of Al-Zn-Mg-Cu cast alloys decreased in the order of Cr containing alloy, Si containing alloy and base alloy. The lowest electrical conductivity of Cr containing alloy exhibited the best SCC resistance and this is probably due to an improved corrosion resistance by forming a passive film on the surface. The over-aged alloys showed the better SCC resistance. This is due to the increased distance between coarse particles at grain boundary. The fracture mode of the alloy was confirmed as intergranular type and showed brittle fracture surface. The SCC mechanism of Al-Zn-Mg-Cu cast alloys was found to be the anodic dissolution model.

Stress corrosion cracking and hydrogen embrittlement cracking of welded weathering steel and carbon steel in a simulated acid rain environment

The stress corrosion cracking (SCC) and hydrogen embrittlement cracking (HEC) characteristics of welded weathering steel and carbon steel were investigated in aerated acid chloride solution. The electrochemical properties of welded steels were investigated by polarisation and galvanic corrosion tests. Neither weathering steel nor carbon steel showed passive behaviour in this acid chloride solution. The results indicated that weathering steel had better corrosion resistance than carbon steel. Galvanic corrosion between the weldment and the base metal was not observed in the case of weathering steel because the base metal was anodic to the weldment. However, the carbon steel was susceptible to galvanic corrosion because the weldment acts as an anode. Slow strain rate tests (SSRT) were conducted at a constant strain rate of 7.87 × 107 s-1 at corrosion potential, and at potentiostatically controlled anodic and cathodic potentials, to investigate the SCC and HEC properties in acid chloride solution. The welded weathering steel and carbon steel were susceptible to both anodic dissolution SCC and hydrogen evolution HEC. However, weathering steel showed less susceptibility of SCC and HEC than carbon steel at anodic potential because of Cr and Cu compounds in the rust layer, which retarded anodic dissolution, and at cathodic potential due to the presence of Cr, Cu, and Ni in alloy elements, which inhibit the reduction of hydrogen ions. SEM fractographs of both steels revealed a quasicleavage fracture in the embrittled region at applied anodic and cathodic potentials.

Improvements in Strength and Stress Corrosion Cracking Properties in Aluminum Alloy 7075 via Low-Temperature Retrogression and Re-Aging Heat Treatments

Abstract The susceptibility of aluminum alloy 7075 (AA7075 [UNS A97075]) to intergranular stress corrosion cracking (SCC) in the peak strength T6 temper is alleviated through the use of the T73, or over-aged temper, which provides improved SCC resistance with a 10% to 15% strength loss compared to the T6 temper. Previous research has indicated that retrogression and re-aging (RRA) heat treatments reduce the trade-off between T6 strength and T73 SCC resistance. The short-term heat treatment they used, however, limited the applicability of RRA to thin sections of material. The primary goals of this research effort were to determine if lower retrogression temperatures could be used in the RRA process to extend the applicability of this heat treatment to thick section aircraft components and to quantify any observed improvements. Alternate immersion (AI) and double-cantilever beam (DCB) tests were conducted in a 0.6-M sodium chloride (NaCl) solution to evaluate the SCC resistance of various tempers. Improveme...