X70管线钢在不同温度近中性pH溶液中的应力腐蚀破裂行为

采用慢应变速率实验(SSRT)研究了不同温度和电位下X70管线钢在近中性pH溶液中的应力腐蚀破裂(SCC)行为．结果表明，不同温度下，X70管线钢在近中性pH溶液中的开裂方式都是穿晶型的，具有准解理特征，并且随着外加阴极电位的降低，SCC敏感性增加，氢致开裂占主导．随温度的下降，溶液pH值略有降低，SCC敏感性增加。     

316Ti在含氯离子300℃高温水中的应力腐蚀开裂

采用慢应变速率拉伸(SSRT)试验方法研究了316Ti在300℃高温水中的应力腐蚀开裂(SCC)行为。结果表明,在空气饱和条件下,试样的断裂时间、延伸率以及断裂能的值随着Cl^-浓度的增大显著降低,应力腐蚀敏感指数随着Cl^-浓度的增大则显著递增,二者具有一定相关性。316Ti不锈钢在300℃空气饱和水中发生SCC的临界Cl^-质量浓度为5 mg/L,只有在Cl^-质量浓度高于或等于5 mg/L,试样才发生穿晶型和部分沿晶混合型SCC。SCC裂纹多萌生于滑移台阶或蚀坑,也可能萌生于接近表面的铁素体相处;裂纹在向基体扩展过程中,铁素体相的存在阻碍了其扩展过程,从而提高了316Ti的抗SCC能力。氧在SCC裂纹萌生和扩展过程中都起着非常重要的作用。     

颗粒增强SiCp／2024铝基复合材料的应力腐蚀断裂行为

通过双悬臂梁试样试验和慢应变速率拉伸试验，研究了ＳｉＣｐ／２０２４铝基复合材料在ＮａＣｌ水溶液中的庆力腐蚀断裂行为，并探讨了增强体的存在对材料ＳＣＣ行为的影响。发增强体的存在并未使材料的ＳＣＣ机理发生本质上的变化，但使复合材料的ＳＣＣ抗力明显高于普通铝合金的。     

Caustic stress corrosion cracking of alloys 600 and 690 with NaOH concentrations

In order to evaluate the stress corrosion cracking resistance for commercial alloys (C600MA, C600TT, C690TT) and Korean-made alloys (K600MA, K690TT), C-ring tests were performed in a caustic environment of 4, 10, 20, 30, and 50% NaOH solution at 315°C, for 480 h with an applied potential of 125 mV vs. OCP. Different stress corrosion cracking phenomena were observed according to the NaOH concentration. The rate of caustic IGSCC attack did not appear to increase monotonically with caustic concentrations, but peaked at a concentration between 4 and 50% caustic, or approximately 30% NaOH. Intergranular stress corrosion cracking was found for C600MA in 10, 20, and 30% NaOH solutions, while no cracking was observed in the 4 and 50% NaOH solutions. In 30% NaOH solution, transgrnular stress corrosion cracking was detected in C690TT, which may be related with the large amount of plastic strain (150% yield) and the applied potential (125 mV vs. OCP). The overall data clearly indicate that C600MA has the worst SCC resistance while K690TT offers the best resistance. There is also fairly good correlation between the caustic SCC susceptibility and some metallurgical parameters, particularly the grain size and the yield strength at room temperature. Specifically, materials having larger grain size and lower yield strength exhibited higher caustic SCC resistance.     

应变速率对管线钢近中性pH值环境敏感开裂的影响

以X-70管线钢近中性pH值溶液(NS4和实际土壤溶液)为研究对象,研究了恒载荷、慢应变速率拉伸(SSRT) 和循环蓑荷等不同条件下的环境开裂行为.结果表明,在该体系中局部应变速率是联系各种不同断裂过程的纽带,决定着断裂的模式.当该局部应变速率低于发生应力腐蚀开裂(SCC)敏感局部应变速率的上限(即5×10-5 s-1)时, SCC才能够发生;在循环载荷作用下,当该局部应变速率高于此上限时,将发生力学因素起主导作用的腐蚀疲劳(CF)开裂;该局部应变速率继续升高时,将发生机械断裂.对X-70管线钢在近中性pH值的环境开裂,不论开裂过程是溶解或(和)氨的作用占主导,均受局部应变速率控制.在通常遇到的现场服役条件下, X-70管线钢在近中性pH值溶液中的开裂模式是SCC,不是CF,应称之为“近中性pH值应变促进腐蚀开裂”,实质上这是一种由局部应变速率决定的环境开裂行为.     

Effect of Cl~- Concentration on the SCC Behavior of 13Cr Stainless Steel in High-Pressure CO_2 Environment

An effect of Cl-concentration on the stress corrosion cracking(SCC) behavior of 13 Cr stainless steel was investigated by employing electrochemical measurements and the slow strain rate tensile tests.These tests were conducted in various solutions with different concentrations of NaCl at 90℃under 3 MPa CO_2 with 3 MPa N_2.The results indicate that the passive film of the specimen formed in the 10% NaCl solution has the best protective effect on the matrix.The SCC susceptibility does not increase with increasing the chloride ion concentration,the lowest SCC susceptibility occurs when the NaCl concentration is 10%,and the specimens show higher SCC susceptibility in the 5% NaCl and 20% NaCl solutions.     

Environmentally assisted cracking resistance of Al–Cu–Li alloy AA2195 using slow strain rate test in 3.5% NaCl solution

The general corrosion and environmental cracking resistances of Al–Cu–Li alloy AA2195 were investigated in 3.5% NaCl environment and compared with those of another high strength alloy AA2219. The general corrosion resistance of these alloys was examined using immersion corrosion and potentiodynamic polarization tests, while the stress corrosion cracking (SCC) resistance was evaluated by slow strain rate test (SSRT) method. The tested samples were further characterized by SEM–EDS and optical profilometry to study the change in corrosion morphology, elemental content and depth of corrosion attack. The reduction in ductility was used as a parameter to evaluate the SCC susceptibility of the alloys. The results indicated that the corrosion resistance of AA2195 alloy was better than that of AA2219 alloy as it exhibited lower corrosion rate, along with lower pit depth and density. However, the SCC index (?_NaCl/?_air) measured was greater than 0.90, indicating good environmental cracking resistance of both the alloys. Detailed fractography of the failed samples under SEM–EDS, in general, revealed a typical ductile cracking morphology for both the alloys.     

Environmentally assisted cracking behaviour of plasma electrolytic oxidation coated AZ31 magnesium alloy

Abstract

A wrought AZ31 magnesium alloy was plasma electrolytic oxidation (PEO) coated in phosphate and silicate based alkaline electrolytes. The effect of these PEO coatings on the stress corrosion cracking (SCC) behaviour of the alloy was investigated by slow strain rate tensile (SSRT) tests in ASTM D1384 solution. The untreated and PEO coated AZ31 magnesium alloy specimens were found to be susceptible to SCC, despite the fact that the PEO coatings offered an excellent general corrosion resistance. The results of the polarisation tests on the untreated AZ31 alloy specimen after prolonged immersion in ASTM D1384 electrolyte suggested the formation of a film on the surface constituted by the corrosion products. The cracking of this film and the evolution/ingress of hydrogen at these defective sites during the SSRT tests in the corrosive environment was believed to be responsible for the SCC of the untreated alloy. Similarly, the cracking of the PEO coatings during the SSRT test, the consequent exposure of the underneath magnesium alloy substrate and the associated electrochemical reactions were attributed as reasons for the SCC of the PEO coated specimens. The transgranular mode of fracture in all the cases avowed that the hydrogen induced cracking was the mechanism of SCC.     

2219铝合金母材及搅拌摩擦焊接头应力腐蚀敏感性

利用慢应变速率拉伸试验,研究2219铝合金母材及搅拌摩擦焊接头在不同腐蚀介质环境中的应力腐蚀行为.运用性能损失率指标和应力腐蚀指数评价材料的应力腐蚀敏感性.结果表明,应变速率为10-6 s-1时,2219铝合金母材和FSW接头在3.5%Na Cl介质环境中SCC敏感性小,断口由韧窝塑性区和腐蚀区组成;在剥蚀介质环境中,母材和FSW接头SCC敏感性大,断口呈冰糖状,有较深的腐蚀坑和二次裂纹,为沿晶脆性断裂.FSW接头SCC敏感性较母材大.     

Corrosion resistance of a cast steel overpack for high-level radioactive waste disposal in Japan

The corrosion rate and stress corrosion cracking (SCC) susceptibility of a cast steel are studied for its application to metal containers (namely overpacks) for geological disposal of high-level radioactive waste. Specimens for corrosion tests are cut from a prototype overpack manufactured by full-scale casting. Casting defects are widely distributed in the prototype overpack; however, the flat-bottom hole equivalent diameters for all defects detected by an ultrasonic test are 3.6 mm or less, which is relatively small. Forged steels and rolled steels are also tested for comparison of their corrosion properties with the cast steel. The corrosion rates are obtained by immersion tests in bentonite saturated with synthetic seawater under anaerobic conditions at 80°C for up to 1 year. The corrosion rate for the cast steel calculated by the weight loss during the experiments is close to that for the forged steels and rolled steels. The SCC susceptibility is examined using slow strain rate tests in a 1.5-mol L⁻¹ carbonate–bicarbonate solution, in which the occurrence of high-pH SCC is often reported for carbon steels. The SCC susceptibility increased with the increase in the carbon content of the products; however, there are no clear differences between casting and forging.     

Amine corrosion and amine cracking of API 5L X52 carbon steel in the presence of hydrogen sulphide and carbon dioxide

In this research, stress corrosion cracking (SCC) and corrosion behaviour of API 5L X52 carbon steel in 25?wt-% diethanolamine solution, saturated/unsaturated with carbon dioxide and containing 0 and 200?ppm hydrogen sulphide at different temperatures were investigated using slow strain rate test, electrochemical measurement and microscopic analysis. In addition, the presence of heat stable amine salts (HSASs) in the test solution was studied using spectrophotometry and Fourier transform infra-red spectroscopy. Analysis of the results showed that the primary components to form HSASs exist in the solution. The results indicated that SCC is more likely in solutions without amine. Increase in corrosion rate of carbon steel by increase in temperature was clearly observed and concluded that the simultaneous presence of hydrogen sulphide and carbon dioxide in the solution can increase the corrosion rate of carbon steel more than having one of the gases in the solution.     

不同晶粒尺寸5083铝合金晶间腐蚀和应力腐蚀开裂的差异性

通过冷轧和退火获得具有不同晶粒尺寸(8.7～79.2μm)的5083铝合金板.研究其微观结构、晶间腐蚀(IGC)、应力腐蚀开裂(SCC)和裂纹扩展行为.结果表明,粗晶粒样品表现出更好的抗IGC性能,其腐蚀深度为15μm.慢应变速率测试结果表明,细晶粒样品表现出更好的抗SCC性能,敏感性指数ISSRT为11.2％.此外,...     

Influence of retrogression and reaging on microstructure,mechanical properties and susceptibility to stress corrosion cracking of an Al‐Zn‐Mg alloy

The aim of the present work was to determine the influence of the retrogression and reaging (RRA) heat treatment on the correlation between microstructure, mechanical properties and susceptibility to stress corrosion cracking (SCC) of the AlZn5Mg1 alloy in dry air and sea water. The alloy received in the T6 temper was subjected to 9 different heat treatments, including retrogression at temperature 453–513 K for 600–3600 s, and reaging at temperature 363 K or 403 K for 16 h, 24 h or 48 h. The susceptibility to SCC was investigated by slow strain rate tensile tests at 10^?6 s^?1 strain rate; change in time to failure, fracture energy and reduction in area were taken into account. Generally, the heat treatment improving mechanical properties increased susceptibility to SCC. The observed effects were discussed in terms of change in microstructure, especially size and distribution of phase precipitates. The role of change in dislocation network was the most likely of no importance.     

氧氯协同对304L不锈钢在高温高压硼锂水中应力腐蚀开裂的影响

采用高温高压慢应变速率拉伸试验方法(SSRT),研究了饱和氧环境下不同氯离子浓度对304 L不锈钢在高温高压硼锂水介质中氯致应力腐蚀开裂的影响。结果表明:在一定浓度范围内有氧无氯或者有氯无氧环境下,304L不发生应力腐蚀开裂。在空气饱和氧条件下,氯离子浓度在1 mg/L至10 mg/L之间变化时,应力腐蚀敏感性随浓度变化不大;而当氯离子浓度大于20 mg/L时,应力腐蚀敏感性随浓度的增加变化很大,当氯离子浓度为50 mg/L,304L几乎完全为脆性断裂。     

Stress corrosion cracking of A588 steel weldments in flue gas related environments

This study investigated stress corrosion cracking (SCC) of A588 steel welds as determined by U-bend immersion tests and slow strain rate tensile (SSRT) tests to evaluate the steel’s cracking susceptibility in various regions of the weldments. The immersion test results indicated that the fusion zone (FZ) had better corrosion resistance than the other regions in the weld. It was also demonstrated that the columnar grain boundaries exhibited a higher resistance to corrosion than the grain interior of the FZ. However, the coarse elongated ferrite in the FZ is susceptible to hydrogen embrittlement (HE), which results in the formation of microcracks. As a result, a severe degradation of the weld’s tensile properties in the saturated H₂S solution was observed. Scanning electron microscope (SEM) fractographs of tensile specimens reveal a cleavage fracture in the coarse-grained heat-affected zone (CGHAZ) and featherlike rupture in the FZ, both indicating a high sensitivity to HE.     

X70管线钢焊缝应力腐蚀破裂的研究

采用慢应变速率试验、扫描电镜试验研究了X70管线钢焊缝拉伸试样在通5％CO2 95％N2的NS4溶液中的应力腐蚀破裂(SCC)敏感性。结果表明断口和柱面SCC裂纹均发生在热影响区(HAZ)。施加阴极电位时，在试样断口观察到明显的准解理断裂特征，断口和柱面有穿晶SCC裂纹。在自腐蚀电位和阳极电位条件下，SCC敏感性很低。在所研究的电位区间，总体趋势是随电位正向增加，断面收缩率、断裂时间和延伸率增加，而断口部位SCC裂纹平均扩展速率减少、即SCC敏感性降低。并利用显微组织变化和电化学理论分析了焊缝试样HAZ的SCC机理。     

X70钢焊接接头在近中性溶液中应力腐蚀行为研究

采用慢应变速率试验(SSRT)、扫描电镜以及电化学测量技术研究了X70管线钢焊接接头在近中性模拟土壤溶液中的应力腐蚀开裂(SCC)行为。结果表明,断口和柱面SCC裂纹均发生在热影响区(HAZ)。在试验溶液中,随着外加极化电位降低管线钢SCC敏感性增强,电位负移到一定电位值后,SCC敏感性减弱;随着溶液pH值降低,腐蚀速率增大,敏感电位区间负移。施加阴极电位时,在试样断口观察到明显的准解理脆断特征,断口和柱面有穿晶SCC裂纹。分析了焊接接头试样HAZ的SCC机理,在试验介质中,管线钢应力腐蚀开裂主要受阳极溶解和氢致开裂两种机理的联合作用,适当的电位可以使阳极溶解和氢致开裂的联合作用达到最大,从而造成较严重的应力腐蚀开裂。     

Role of environmental variables on the stress corrosion cracking of sensitized AISI type 304 stainless steel (SS304) in thiosulfate solutions

The stress corrosion cracking (SCC) behavior of sensitized AISI type 304 stainless steel (SS304) has been studied in dilute thiosulfate solutions as a function of thiosulfate concentrations and applied potentials. The susceptibility to SCC was observed to increase with thiosulfate concentrations and applied potentials. The addition of boric acid produced the reverse effect. A critical potential was found to exist, below which no SCC took place. Potential fluctuations, as recorded in the tests under open circuit conditions, appeared to be correlated with crack initiation and propagation during SCC. Current fluctuations observed in the controlled potential tests also gave indications of crack nucleation; however, at higher applied potentials such fluctuations were absent. The formation and presence of martensite in the specimens seemed to have a minor role in the overall SCC process. The aggressiveness of the thiosulfate concentration was also an important factor in determining the degree of susceptibility to SCC. The results obtained in the slow strain rate tests under open circuit as well as under potential-controlled conditions suggested a film ruptureanodic dissolution type of mechanism operative during SCC of sensitized SS304 in thiosulfate solutions.     

BEHAVIOUR AND MECHANISM OF STRESS CORROSION CRACKING FOR Al-Li-Cu-Mg ALLOY

Studies were made of the influence of aging conditions and applied potentials on thestress corrosion carcking(SCC)susceptibility for an Al-Li-Cu-Mg alloy by slow strainrate technique.The relationship between the relative hydrogen content on specimensurface,the applied potentials and elapsed time has also been examined.The SCCsusceptibility was found to be dependent on aging conditions in which the peak agedcondition gave the worst SCC resistance and the natural aged condition had the best one.The SCC susceptibility and surface hydrogen content relates to the applied potentials.The anodic potentials increase SCC susceptibility,while the cathodic ones below thecritical potential accelerate SCC.It is considered that both the anodic dissolution and     

Comparison of the Stress Corrosion Cracking Behaviour of AISI 304 Pipes Welded by TIG and LBW

The stress corrosion cracking (SCC) behaviour of AISI 304 pipe girth welds which were welded by a single-pass laser beam welding (LBW) and a multi-pass tungsten inert gas welding (TIG),respectively,was studied by the slow strain rate tests combined with the electrochemical corrosion tests.The results show that fracture of both the TIG joint and LBW joint occurs in the heat-affected zone (HAZ).According to the electron-backscattered diffraction observation of the microstructures,comparison of potentiodynamic polarization curves and X-ray photoelectron spectroscopy analysis of corrosion products on HAZs of the two joints after the electrochemical tests,the LBW joint exhibits better SCC resistance than the TIG joint in corrosion environments,due to the synthetic effect of more Cr2O3 in corrosion products,finer grains,lower residual strain and higher δ-ferrite content in its HAZ.Although the TIG joint has better mechanical property,considering lower SCC susceptibility and higher production efficiency of the LBW joint,the LBW promisingly replaces the TIG for welding of AISI 304 pipes in the nuclear power industry.