Low temperature stress corrosion cracking of Inconel 600 under two different conditions of sensitization

The low temperature stress corrosion cracking (SCC) of Inconel 600 under two different conditions of sensitization was studied in sulfur-bearing environments. In one case the material was sensitized directly from the mill annealed condition (MAS) and in the other, solution annealing followed by water quenching was used prior to sensitization (SAS). The propensity to SCC increased significantly by the SAS treatment, as revealed by dynamic tests in very dilute sodium thiosulfate or sodium tetrathionate solutions, and U-bend tests in a concentrated thiosulfate solution which failed to crack the MAS material. The implications of these observations are discussed in terms of the microstructures of the materials.     

Stress corrosion cracking study of microalloyed pipeline steels in dilute NaHCO3 solutions

Studies were carried out to evaluate the stress corrosion cracking (SCC) behavior of a X-70 microalloyed pipeline steel, with different microstructures by using the slow strain rate testing (SSRT) technique at 50 °C, in NaHCO₃ solutions. Both anodic and cathodic potentials were applied. Additionally, experiments using the SSRT technique but with pre-charged hydrogen samples and potentiodynamic polarization curves at different sweep rates were also carried out to elucidate hydrogen effects. The results showed that the different microstructures in conjunction with the anodic applied potentials shift the cracking susceptibility of the steel. In diluted NaHCO₃ solutions cathodic potentials close to their rest potential values decreased the SCC susceptibility regardless the microstructure, whereas higher cathodic potentials promote SCC in all steel conditions. Certain microstructures are more susceptible to present anodic dissolution corrosion mechanism. Meanwhile concentrated solution did not promotes brittle fracture.     

Corrosion and stress corrosion cracking of amorphous FeNiMoxB alloys in several neutral and acidic media

Corrosion and stress corrosion cracking behaviour of a series of amorphous iron alloys FeNiMo_xB (x = 0, 2, 4, 8.5) has been investigated in several neutral and acidic media. In particular in aqueous solutions of ferric chloride, potassium tetrathionate and sulphuric acid containing chlorides stress corrosion cracking (SCC) has been studied by means of constant strain tests and corrosion rates have been evaluated by means of weight loss measurements. In several cases polarization curves have been recorded in order to clarify the electrochemical behaviour of the amorphous alloys. SEM observations of the fracture surfaces have been performed. It has been observed that the glassy alloys under investigation are susceptible to SCC at free corrosion potential in all the environments. SCC has been observed on specimens cathodically and anodically polarized in sulphuric acid containing chlorides. Hydrogen embrittlement can reasonably be considered responsible of the SCC phenomenon, except in sulphuric acid solution on specimens anodically polarized and in iron chloride solution. A deleterious effect of molybdenum has been noted on the corrosion rates of unstressed specimens and on the time to failures of stressed samples.     

氢对LC4高强铝合金应力腐蚀断裂的影响

采用慢应变速率拉伸试验研究了氢在LC4高强铝合金应力腐蚀断裂过程中的作用。结果表明，LC4合金在干燥空气中不发生应力腐蚀断裂，而在潮温空气中发生应力腐蚀断裂，在潮湿空气和阳极极化条件下，铝合金的应力腐蚀断裂机理是以阳极溶解为主，氢几乎不起作用，在预渗氢或阴极极化条件下，氢脆起主要作用，预渗氢时间延长可加速LC4合金的应力腐蚀断裂。     

Relationship between electrochemical characteristics and SCC of X70 pipeline steel in an acidic soil simulated solution

Stress corrosion cracking (SCC) of X70 pipeline steel in simulated solution of the acidic soil in Yingtan in China was investigated using slow strain rate test (SSRT), SEM and potentiodynamic polarization technique. Experiment results indicate that X70 steel is highly susceptible to SCC as applied potential reduces, which is manifested in loss of toughness and brittle fracture. Constant polarization current can detect the occurrence of SCC. The lower the polarization current is the sooner stress corrosion cracking occurs. The SCC mechanisms are different at varying potentials. When potential is higher than open circuit potential, anodic process controls SCC, whereas when potential is far lower than open circuit potential, cathodic process controls SCC, and between these two potential regions, a combined electrochemical process controls the SCC. Stress or strain has a synergistic effect with electrochemical reactions to accelerate the cathodic hydrogen evolution process, which makes the X70 pipeline steel to be more susceptible to SCC.     

Al—Li—Cu—Mg合金应力腐蚀性能及机理研究

利用恒应变速率方法研究了Al—Li—Cu—Mg合金的应力腐蚀开裂,包括时效条件及外加电位对应力腐蚀的影响,同时研究了试样表面相对氢浓度与外加电位及应力腐蚀时间的关系,实验结果表明,合金的应力腐蚀性能取决于时效条件,其中峰时效条件下最差,自然时效条件下最好,应力腐蚀敏感性及试样表面氢浓度与外加电位有关,阳极电位增加应力腐蚀敏感性,阴极电位低于临界电位时加速应力腐蚀,认为合金在应力腐蚀过程中阳极溶解与氢脆机制联合作用。     

Constant strain-rate testing of AISI type 304 stainless steel in 0.5 M H2SO4 + 0.1 M NaCl solution at room temperature with controlled potential

The constant strain-rate (CSR) test method has been applied to investigate the stress corrosion cracking (SCC) susceptibility of AISI Type 304 stainless steel in 0.5 M H₂SO₄ + 0.1 M NaCl at 25°C within a range of controlled potentials. Cracks were found to form in two distinct potential regions: in the cathodic range, and in the passive potential region. A clear differentiation between the two observed types of cracks was attempted. Crack morphology, the measured current during straining and the reduction of area were used as criteria. SCC was found to occur essentially in the passive potential region; in the cathodic range the cracks were due to hydrogen embrittlement.     

外加电位对X70管线钢在库尔勒土壤模拟溶液中应力腐蚀开裂敏感性的影响

采用慢应变速率拉仲试验(SSRT)研究了不同外加电位下X70管线钢在库尔勒土壤模拟溶液中的应力腐蚀开裂(SCC)行为,并用扫描电镜分析了不同电位下的断面形貌.结果表明,X70管线钢在库尔勒土壤模拟溶液中具有SCC敏感性;在Ecorr附近施加弱极化时,应力腐蚀开裂敏感性增加;施加强阳极电位时,发生强烈阳极溶解,导致阳极溶解断裂;施加强阴极电位时,析氢过程加强,导致氢致应力腐蚀断裂.     

X100管线钢在酸性土壤模拟溶液中的应力腐蚀行为

采用慢拉伸(SSRT)、动电位极化和SEM观察等方法,研究了在不同的阴极保护电位条件下X100钢在酸性土壤模拟溶液中的应力腐蚀行为.结果表明,X100钢发生穿晶裂纹的应力腐蚀,裂纹的萌生和发展与阴极保护电位有关.完全阳极过程控制时,X100钢无裂纹出现,但出现晶间腐蚀;在混合过程控制时,应力腐蚀敏感性较低,裂纹发展缓慢;在完全阴极过程控制时,氢脆机制起主要作用,裂纹扩展迅速.     

Stress corrosion cracking and hydrogen embrittlement susceptibility studies on modified 9Cr-1Mo steel weldments in acidic and neutral media

Abstract

There is much scope for the development of new engineering materials for high temperature applications such as for tubing used in steam generation in fossil fuel and nuclear power plants and in petrochemical cracking units. The materials for such applications are often manufactured from mild steel and low alloy ferritic steels containing up to 9%Cr. Modified 9Cr-1Mo ferritic steel, prepared by incorporating vanadium and niobium, is one of the newer materials extensively used for high temperature applications. A study of weldments of this alloy and its susceptibility to stress corrosion cracking (SCC) and hydrogen embrittlement was carried out in acidic and neutral media. The anodic behaviour of modified 9Cr-1Mo under 90% proof stress was also examined. Mechanical properties of the material were assessed before and after SCC and hydrogen embrittlement tests. The SCC tests were made at various anodic potentials in 1M H₂SO₄ and showed that the welded alloy is not susceptible to SCC in all three critical zones. The alloy was, however, susceptible to SCC in chloride environments, namely a solution containing equal volumes of 1M NaCl and 1M MgCl₂. Fractographic analysis was carried out to determine the reasons for the failure of this alloy. The hydrogen embrittlement studies in 1M H₂SO₄ showed that the alloy is prone to delayed hydrogen cracking at more negative potentials. The fractographic examination using scanning electron microscopy revealed the presence of adsorbed hydrogen in microvoids which were responsible for the failure of the alloy. Other possible reasons for the failure of the alloy are also discussed.     

船用5052-O铝合金在海水中的力学和电化学性能(英文)

采用电化学实验和SEM表面形貌观察,对船用5052-O铝合金在海水中的腐蚀保护电位进行优化,以克服诸如点蚀、腐蚀、应力腐蚀开裂和氢脆等行为的发生。在外加电流阴极保护的条件下,最优的保护电位范围为-1.3V～-0.7V。在此电位下,试样的腐蚀电流密度较低,经恒电位实验后,试样表面形貌保持得较好。     

Effect of Travel Speed on the Stress Corrosion Behavior of Friction Stir Welded 2024-T4 Aluminum Alloy

The effect of travel speed on stress corrosion cracking (SCC) behavior of friction stir welded 2024-T4 aluminum alloy was investigated by slow strain rate tensile test. Microstructure and microhardness of the welded joint were studied. The results showed that the size of second phase particles increased with increasing travel speed, and the distribution of second phase particles was much more homogeneous at lower travel speed. The minimum microhardness was located at the boundary of nugget zone and thermomechanically affected zone. In addition, the SCC susceptibility of the friction stir welded joint increased with the increase of travel speed, owing to the size and distribution of second phase particles in the welds. The anodic applied potentials of ?700, ?650, ?600 mV, and cathodic applied potential of ?1200 mV facilitated SCC while the cathodic applied potential of ?1000 mV improved the SCC resistance. The SCC behavior was mainly controlled by the metal anodic dissolution at the open circuit potential, and hydrogen accelerated metal embrittlement.     

Hydrogen effects during IGSCC of pure Al-5Mg alloy in NaCl media

The conditions to propagate an intergranular stress corrosion crack in pure, precipitate-free, Al-5Mg alloy in 30 g/l NaCl have been determined. SCC tests are performed on specimens with a thin notch which favours single cracking and solution confinement. Slow strain rate tests in a simulated confined medium without oxygen are used to simulate the natural confinement. They show that the main cathodic reaction during SCC is the reduction of hydrogen. Reversible grain boundary embrittlement is obtained by localised hydrogen pre-charging. The role of hydrogen during intergranular stress corrosion cracking is therefore established, in close relation with localised dissolution.     

Effects of testing variables on stress corrosion cracking susceptibility of Al 2024-T351

In the present study, the effects of testing variables on stress corrosion cracking (SCC) susceptibility of Al 2024-T351 in 3.5% NaCl solution were examined using slow strain rate test (SSRT) method with controlled applied potentials and a constant load test (CLT) method. The SSRTs were conducted at various strain rates and applied potential, while the CLTs were performed with different exposure time, with different grain directions of ST (short-transverse) and L (longitudinal) to understand how the testing parameters affected on the SCC susceptibility of Al 2024-T351. The percent reductions in tensile elongation in an SCC-causing environment over those in air tended to express the SCC susceptibility of Al 2024-T351 most properly for both SSRT and CLT. The present fractographic examination suggested that both anodic dissolution and hydrogen embrittlement played a role in the SCC process of Al 2024-T351 in 3.5% NaCl solution at both anodic and cathodic applied potentials, and the contribution of each mechanism could vary with different testing variables. It was also found that the SCC susceptibility of Al 2024-T351 obtained from the CLT result could provide the similar SCC evaluation result obtained by SSRT with a proper selection of testing variables. The metallurgical aspect of SCC behaviour of Al 2024-T351 was also discussed based on the microstructural and fractographic examinations.     

Mechanisms of stress corrosion cracking for iron base alloys in hot Ca(NO3 )2 solution

Abstract

The stress corrosion cracking (SCC) susceptibilities of a series of iron base alloys were evaluated in a 2M Ca(NO₃ )₂ solution at a temperature of 90°C. The inclusion distributions in each material were established using quantitative metallography and energy dispersive X-ray analysis (EDX). Electrochemical and microcorrosion measurements were also performed. Cracks were predominantly associated with pits that initiated at ruptures in the oxide film at potentials more anodic than -25 mV or by dissolution at sulphur containing inclusions at potentials more cathodic than -25 mV. Reducing the inclusion content and/or the activity of the inclusions in iron base alloys moves the minimum potential for cracking to more anodic potentials but does not eliminate SCC. The addition of sulphate to the test solution increased the susceptibilities of the alloys.     

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.     

34CrNi3Mo钢在NaOH水溶液中应力腐蚀开裂机理的研究

本文应用恒电位下应力腐蚀开裂(SCC)的断裂力学试验方法、氢渗透、声发射和电子金相技术,研究了34CrNi3Mo钢在30％NaOH水溶液中SCC机理:在开路电应下,只有当温度>50℃时方可出现SCC;在80℃时,当给定电位E于-1150mV(SCE)时,为活性通道溶解(APC)型SCC,而当给定电位负于-1150mV(SCE)时,州为氢脆(HE)型SCC。由此可见,即使是同—钢—环境体系,SCC的机理也是可变的,因此,想把SCC机理归纳成一个统一的模型是不妥当的。     

Anodische Spannungsrißkorrosion eines Stahls in flüssigem Ammoniak

Anodic stress corrosion cracking of steel in liquid ammonia Steel rods W.No. 1.8907 were tested for stress corrosion cracking in liquid ammonia at about 20 °C under controlled electrochemical conditions at constant rate of elongation. Stress corrosion cracking was not observed in pure ammonia at the free corrosion potential of the steel corroding in the active state, but only upon polarization to the passive state. The susceptibility to stress corrosion cracking grew with the temperature and was negligible at temperatures below about 10°C. In presence of oxygen at pressures exceeding about 0.1 bar, stress corrosion cracking occurred at the free corrosion potential in the passive range at more negative electrode potentials than in absence of oxygen. Additions increasing the specific conductivity of ammonia and 0.15% water inhibited stress corrosion cracking. The small danger of hydrogen embrittlement was enhanced by cathodic polarization and by addition of acids.     

Kinetics and mechanism of crack growth during stress corrosion cracking of zirconium alloys

Using the electroresistivity method the influence was investigated of the anodic and cathodic polarization on the crack growth rate during stress corrosion cracking (SCC) of Zr alloys in aqueous and nonaqueous electrolytes. The ambiguous effect of the cathodic polarization on CGR was observed. The role of local dissolution and hydrogen embrittlement by SCC of Zr alloys has been discussed in terms of the previously developed method of identification of the SCC mechanism.     

带镀层GC-4超高强度钢的腐蚀断裂

应用慢拉伸及断裂力学方法研齐了带镀层的GC-4钢(40CrMnSiMoVA)在3.5％NaCl中的应力腐蚀特性,并与裸钢作了对比。结合扫描电镜及宏观断口分析,探讨了失效机理。研究表明,阴、阳极镀层均使钢的KIscc降低,da/dt(Ⅱ)显著增加,其影响依无氰Cd、Cd-Ti、Cr的次序增加。慢拉伸试验结果说明,阴、阳极极化均使GC-4裸钢延性降低。根据BL-WOL试样裂纹扩展在表面处较内部为快以及阴、阳极镀层、平面应变状态对断口形貌的影响,可以认为带镀层与不带镀层GC-4钢的腐蚀断裂机理为裂尖阳极溶解与氢脆共同作用,并且裂尖溶解将直接参与导致裂纹扩展.从而对高强度钢腐蚀断裂的纯氢脆机理作出修正。