Effect of molybdenum on SCC of 17-4PH stainless steel under different aging conditions in chloride solutions

Type 17-4 PH martensitic precipitation-hardenable stainless steel, having a combination of high mechanical properties and good corrosion resistance is widely used in aerospace, chemical, and petrochemical and food industries This alloy has a high resistance to stress corrosion cracking but age hardening treatment, increases its sensitivity to stress corrosion cracking. There are several works investigating the influence of different aging treatments on the microstructure, mechanical properties and corrosion resistance of 17-4 PH steels, however there are little works studying the simultaneous effects of aging treatments and molybdenum content on corrosion properties of these steels. In this research, the effect of molybdenum on stress corrosion cracking resistance of 17-4 PH alloy using U-bend samples in chloride solutions, as well as its effect on passivity, has been investigated. Quantometer, Scanning Electron Microscope(SEM) and potentiostat were used to determine the chemical composition, microstructure and anodic polarization behavior of the alloys. It is found that molybdenum has a useful effect on stress corrosion cracking resistance under the peak aged conditions, and this is because of development of delta-ferrite phase by increasing the molybdenum content and subsequently decreasing the strength of the alloy.     

Failure analysis of a slot-welded impeller of recycle hydrogen centrifugal compressor

A recently failed slot-welded impeller of recycle hydrogen centrifugal compressor has been investigated by material tests, theoretical calculation and numerical simulation, which focus on the environmental susceptibility of material, the corrosivity of environment and the characteristic components of the stress state. It is found that the matrix of FV520B precipitated hardening stainless steel used in the failed impeller did not match the optimal combination of strength, toughness and corrosion resistance, and large volumes of δ ferrite with banded appearance further increased the environmental susceptibility of material; the electrochemical corrosion environment came into being due to the presence of hydrogen sulfide and condensed water vapor in the recycle medium; the high hoop stress in the failed impeller was mainly caused by the shrink fit during manufacturing and the centrifugal force during operation. Based on these results, the failure of this slot-welded impeller can be mainly attributed to sulfide stress cracking (SSC), and hydrogen induced cracking (HIC) is found to accelerate SSC by breaking the continuity of material and hence increasing local stress. Additionally, the prevention and mitigation measures against failure have been discussed, which can provide some insight into improving the reliability of centrifugal compressor impeller.     

Cracking due to Cu and Ni segregation in a 17-4 PH stainless steel piston rod

The 17-4 PH stainless steel is employed to produce piston rods in industry due to the high strength and toughness, good workability and nice corrosion resistance. In the present failure analysis, obvious long cracks were observed along the longitudinal direction on the surface of the commercial 17-4 PH stainless steel piston rod after heat treatment. The cracks were carefully looked into by observing the crack tip and characterizing the microstructure along the cracks. The results showed that the cracks were mostly initiated from the surface of the rod and propagated along the phase boundary between martensite and δ ferrite. The EDXA showed that the segregation of Cu and Ni should be responsible for the cracking after heat treatment. In order to define when the crack was coming into being, oxidation film along the crack was considered as a clue. The scrutiny of the oxidation film on the crack edge illustrated that the crack should be formed right in the heat treatment of aging.     

高Cl~-环境对M152和17-4PH高强钢应力腐蚀开裂行为的影响

利用中性盐雾实验、慢应变速率拉伸实验研究M152和17-4PH高强钢在高Cl~-环境中的应力腐蚀行为和机理。结果表明:M152和17-4PH钢在高Cl~-环境中均有一定的应力腐蚀开裂(SCC)敏感性,且随着前期中性盐雾时间的延长,其伸长率逐渐降低,SCC敏感性逐渐升高;通过扫描电子显微镜对试样的断口和侧边裂纹进行观察比较发现,中性盐雾时间的延长会使M152和17-4PH高强钢的断裂机制由韧性断裂向脆性断裂转变。分析得出M152和17-4PH钢在高Cl~-环境中发生SCC是阳极溶解(AD)和氢脆(HE)的协同作用,Cl~-会加速AD过程。经过不同时间中性盐雾后17-4PH钢的SCC敏感性均比M152钢要高,HE作用也越明显。高Cl~-环境中,17-4PH高强钢相对M152钢更易发生SCC。     

Stress-corrosion-cracking behavior of heat-treated Al−Zn−Mg−Cu alloy with temperature

Stress corrosion cracking is a typical fracture process for metals and alloys. Among aluminum alloys, the Al−Zn−Mg−Cu group is characterized by high performance as far as its mechanical properties are concerned. However, it is susceptible to stress corrosion cracking. Within this large group, the AA-7075-type alloy is most extensively used in manufacturing light structural components, mainly in the aircraft industry. We study the characteristics of the AA-7075 alloy in a 3.5% NaCl aqueous solution at 20 and 80°C. Stress corrosion cracking was observed for all analyzed AA-7075 temper conditions in different tested environments. It was very rapid at 80°C, especially for the T6-aging condition. In all studied cases, the maximum and minimum susceptibility to stress corrosion cracking were exhibited by the AA-7075-T6 temper and T73 temper, respectively. As compared to AA-7075-T6, the AA-7075-RRA temper has better resistance to stress corrosion cracking but its mechanical properties are lower. E.T.S.I. Industriales, Universidad Politécnica de Madrid, Spain. Published in Fizyko-Khimichna Mekhanika Materialiv. Vol. 35, No. 4, pp. 59–62, July–August, 1999.     

Characterization of 17-4 PH stainless steel foam for biomedical applications in simulated body fluid and artificial saliva environments

Highly porous 17-4 PH stainless steel foam for biomedical applications was produced by space holder technique. Metal release and weight loss from 17–4 PH stainless steel foams was investigated in simulated body fluid and artificial saliva environments by static immersion tests. Inductively coupled plasma-mass spectrometer was employed to measure the concentrations of various metal ions released from the 17-4 PH stainless steel foams into simulated body fluids and artificial saliva. Effect of immersion time and pH value on metal release and weight loss in simulated body fluid and artificial saliva were determined. Pore morphology, pore size and mechanical properties of the 17-4 PH stainless steel foams were close to human cancellous bone.     

Failure of a 17-4 PH stainless steel sailboat propeller shaft

In this study, a 17-4 PH precipitation hardening stainless steel propeller shaft failed in use when installed in a sailboat working in a marine environment. Failure analysis was conducted on the propeller shaft. Results indicate that the failure was caused by the fracture of the propeller shaft by torsional fatigue and stress corrosion cracking (SCC). SCC progressed transgranulary in the martensitic matrix.     

Stress corrosion cracking—A new approach to testing methods

So far, the primary objectives of the investigation of stress corrosion cracking have been to understand the basic mechanisms and also to find suitable testing methods for screening materials according to their degree of susceptibility, with an aim to avoid failures caused by stress corrosion cracking in various applications and environments. Because of the complexity of interplay among various mechanical, metallurgical, and environmental factors, considerable ambiguity and debates still exist about the basic mechanisms. As a consequence, several different mechanisms were proposed to explain failures related to the interaction of metals with environments. The development of standard and practical testing methods is another area of studies on stress corrosion cracking. Although there exist some standard testing methods capable of the quantitative assessment of susceptibility to cracking, most of these methods require long durations of tests and are characterized by significant variability in their results. We discuss a new method, which has gained importance in the last few years. The applicability of this method as a standard testing procedure is checked and explained on the basis of the results obtained in testing an aluminum alloy in a chloride solution. Corrosion Department, Institute für Werkstofforschung GKSS-Forschungszentrum Geesthacht GmbH, Germany. Material Science Division Bhabha Atomic Research Centre, India. Published in Fizyko-Khimichna Mekhanika Materialiv Vol. 33, No. 4, pp. 107–114, July–August 1997.     

Comparisons of 30Cr2Ni4MoV rotor steel with different treatments on corrosion resistance in high temperature water

Three different treatments, including the heat treatment, deep cryogenic treatment and laser surface melting, were carried out on the 30Cr2Ni4MoV rotor steel. Electrochemical polarization curve and stress corrosion test at the high temperature autoclave were employed to evaluate the corrosion resistance of treated specimens in high temperature water. Results indicate that the conventional heat treatment will increase the value of K_IH for specimens with the lower yield strength, and hence reduce the susceptivity of stress corrosion cracking. However, for the deep cryogenic treated specimen, no apparent improvement was observed on the hardness and corrosion resistance due to the limited carbon precipitate and austenite transformation. In comparison, the best corrosion resistance of laser treated specimens was gained among the three-method-treated specimens according to results of the electrochemical polarization tests at temperature of 90 °C. Nevertheless, some micro-cracks produced on the tensioned surface during the fabrication of self-loaded U-bend specimen due to the large deformation, and thus lead to a decreased stress corrosion cracking resistance in the environment of high temperature water.     

Improve stress corrosion cracking resistance and mechanical properties of Al‐Zn‐Mg‐Cu‐Zr alloy with heterogeneous lamellae structure produced by high pressure torsion

High pressure torsion experiment followed with heat treatment were carried out on as‐cast Al‐Zn‐Mg‐Cu‐Zr alloy at 400 °C under the pressure of 1 GPa. The microstructure, mechanical property and stress corrosion resistance properties for the as‐cast and high pressure torsion processed samples were studied. The results show that high pressure torsion processing can improve the mechanical property by the refinement of grains and grain boundary precipitates, as well as the homogeneous distribution of fine matrix precipitates. On the other side, the grain refinement, broken of coarse grain boundary precipitates and narrowed precipitates free zone caused by the high pressure torsion result in the improvement of stress corrosion cracking resistance. And due to the influence of heterogeneous lamellae structure, the sample after 0.5 high pressure torsion turn shows preferable mechanical property and stress corrosion cracking resistance than the sample after 2 high pressure torsion turns.     

Zerstörung von Hubschrauberturbinen durch Einsatz eines Stahles in korrosionsanfälligem Zustand bei gleichzeitig nicht werkstoffgerechter Konstruktion

Failure of Helicopter Turbines Caused by Use of Steel in Corrodible Condition Aggravated by Incorrect Construction. Impeller compressors of steel X 15 Cr 13 were not drawn up as usual to 725 °C but only to 540 °C after hardening, in order to maintain high strength. By this treatment the steel becomes especially sensitive to corrosion, because a network of Chromium carbide is precipitated on the former austenit grain boundaries. Nevertheless the impellers reached the stipulated lifetime, since the corrosive agent — the condensed moisture of the air — is eliminated by centrifugal force. After an apparently insignificant variation of construction, the water was retained in a rim and the impellers were destructed due to stress corrosion and corrosion fatigue.     

Environmental fatigue crack propagation in medium strength titanium sheet alloys

Results are reported for an investigation of environmental fatigue crack propagation resistance in four commercial titanium alloys of medium strength. The materials were IMI 130 (commercially pure titanium with low oxygen content), Ti-70 (commercially pure titanium with high oxygen content), IMI 230 (Ti-2.5 Cu) and Ti-5Al-2.5Sn. The environments were dry argon, normal air, distilled water and 3.5% aqueous NaCl. The conclusions were (1) the ranking of the materials in terms of conventional mechanical properties does not permit a ranking in terms of crack propagation resistance, (2) the material with the highest elastic moduli, Ti-5Al-2.5Sn, also had the best crack propagation resistance in the absence of stress corrosion, (3) there is a correspondence between the degree of isotropy of the static yield strength and the orientation dependence of crack propagation resistance, (4) for all the materials there was a trend of higher crack growth rates at similar ΔK values in the order; dry argon, air, distilled water, 3.5% aqueous NaCl, (5) in the aqueous environments only Ti-5Al-2.5Sn gave evidence of stress corrosion cracking.     

压气机过盈配合的弹塑性有摩擦接触的研究

增压器压气机叶轮、轴套和轴采用过盈配合技术联成一体,这是三维多体弹塑性有摩擦接触问题,是两种非线性相互耦合的边值待定问题。采用有限元参数二次规划法,并结合多重子结构技术,充分利用两种方法各自的长处分析求解柴油机涡轮增压器叶轮与轴套、轴套与轴的三维弹塑性有摩擦接触问题,针对不同的过盈量、摩擦因数、转速和轴套壁厚进行了大量计算,获得了叶轮、轴套与轴之间接触应力的相应分布规律。轴套与轴的装配过盈量是影响轮轴接触应力的重要因素。在选择叶轮、轴套和轴三者装配尺寸时,尤其采用压力组装法时应严格控制轴套与轴的过盈量。研究结果表明,此方法对压气机弹塑性接触特性是有效的,能够反映接触区域的接触法向应力、变形以及摩擦力的大小和分布情况。     

镍基高温合金690的研究现状

690合金是一种面心立方结构的镍基高温合金,具有优异的高温力学性能和耐腐蚀性能,被广泛应用于核电、石油化工和航空航天等领域.文中对690合金的微观组织演化、热成形特性、高温失塑裂纹和耐应力腐蚀性能等方面的研究现状进行了总结分析.目前,部分合金元素对690合金组织性能的影响较为复杂,成形工艺参数对690合金高温变形行为和...     

DH63-32型离心空压机检修总结

介绍豫光金铅制氧厂DH63-32型离心空压机检修前存在的排气量减少、级间冷却器阻力增大和轴振动值偏高等问题及原因,阐述空压机存在的机械故障及其处理措施,最后总结了空压机检修经验。     

Sulphide stress cracking of 17-4 PH for applications in oilfield components

The precipitation-hardening stainless steel 17-4 PH is widely used for oilfield components (tubing hangers and valve stems) due to its favourable combination of high strength and corrosion resistance. In oil and gas production systems containing hydrogen sulphide (H₂S), however, this material is highly susceptible to sulphide stress cracking (SSC). Numerous investigations conducted in the past decades outlined its corrosion performance and confirmed its cracking propensity. These studies indicated failures by SSC at low stress levels and highlighted the effects of the main environmental variables: partial pressure of H₂S, environment pH, temperature and chloride content. This review describes a series of surface modification techniques, particularly the low-temperature plasma nitriding, which can potentially be used to prevent SSC.

This review was submitted as part of the 2017 Materials Literature Review Prize of the Institute of Materials, Minerals and Mining run by the Editorial Board of MST. Sponsorship of the prize by TWI Ltd is gratefully acknowledged     

Failure of backstay rod connectors on a luxury yacht

A backstay rod connector on a luxury yacht fractured while the vessel was docked. The fracture of this connector caused the backstay assembly to fall to the deck. A second connector contained a large crack. Both connectors were made from 17-4 PH stainless steel. One half of the fractured connector was recovered. The fracture initiated by pitting and crevice corrosion and was followed by stress-corrosion cracking (SCC) that ultimately led to the fracture. The second connector most probably cracked in the same way. Adverse conditions inherent to service use of the connectors could have facilitated the stress-corrosion process. Nevertheless, use of a stress-corrosion-susceptible material is unacceptable, and any connectors made from 17-4 PH steel aged below 866 K (1100°F) should be replaced. Candidate replacement materials are stainless steels type 316, Nitronic 50, a duplex steel such as SAF 2205, and 17-4 PH in the H1100 and H1150 conditions.     

Fatigue life assessment of centrifugal compressor impeller based on FEA

Fatigue life assessment of centrifugal compressor impellers has been a critical issue in industrial practice and application. In this paper, both centrifugal load and aerodynamic load have been considered in the analysis of the impeller life using finite element analysis (FEA). The analysis showed the regions of stress concentration and the mean stress of the finite element at the maximum stress point. The S–N curve of the impeller is therefore fitted by a computational model. The model is proved to be reliable by comparing the computed results with the experimental data. Thereby the failure mechanism of the impeller can be expressed analytically and its reliability can be assessed online.     

0Cr17Ni4Cu4Nb钢锻件延迟断裂失效分析

通过化学分析、力学性能检测、表面残余应力检测、金相检验和断口分析的方法,分析了0Cr17Ni4Cu4Nb钢锻件开裂的原因,结果显示,该锻件的开裂是由于回火不足引起的应力腐蚀开裂。     

S135钻杆断裂原因分析

通过化学成分分析、力学性能测试、显微组织分析等手段对某断裂失效的S135钻杆进行了材质理化检验;采用SEM和EDS分别对断口形貌及表面腐蚀产物成分进行了分析。结果表明：该钻杆的材料性能符合APISpecSD规范要求,钻杆断裂的主要原因是硫化氢应力腐蚀开裂,并伴有一定程度的二氧化碳腐蚀。