Failure Investigation of Stainless Steel Adaptor

Adaptors used in check valve inlet pressure sensors were fabricated from austenitic stainless steel. Recently, during pretest operation and during hydrogen pressurization of an engine, a leak was noticed through the adaptor. Subsequent to disassembly, the leak was attributed to a crack in the adaptor. Detailed metallurgical investigations were carried out to understand the cause of cracking. Synergistic effect of chloride ions present in marine environment, the presence of residual stresses and sensitized grains of the material led to intergranular stress corrosion cracking. This article highlights details of investigation.     

Cracking of Aluminum Alloy Rivets Used in Space Application: A Metallurgical Investigation

Adaptors used in check valve inlet pressure sensors were fabricated from austenitic stainless steel. Recently, during pretest operation and during hydrogen pressurization of an engine, a leak was noticed through the adaptor. Subsequent to disassembly, the leak was attributed to a crack in the adaptor. Detailed metallurgical investigations were carried out to understand the cause of cracking. Synergistic effect of chloride ions present in marine environment, the presence of residual stresses and sensitized grains of the material led to intergranular stress corrosion cracking. This article highlights details of investigation.     

Weld decay-resistant austenitic stainless steel by grain boundary engineering

This paper presents an example of grain boundary engineering (GBE) for improving intergranular-corrosion and weld-decay resistance of austenitic stainless steel. Transmission and scanning electron microscope (TEM and SEM) observations demonstrated that coincidence site lattice (CSL) boundaries possess strong resistance to intergranular precipitation and corrosion in weld decay region of a type 304 austenitic stainless steel weldment. A thermomechanical treatment for GBE was tried for improvement of intergranular corrosion resistance of the 304 austenitic stainless steel. The grain boundary character distribution (GBCD) was examined by orientation imaging microscopy (OIM). The sensitivity to intergranular corrosion was reduced by the thermomechanical treatment and indicated a minimum at a small roll-reduction. The frequency of CSL boundaries indicated a maximum at the small roll-reduction. The corrosion rate was much smaller in the thermomechanical-treated specimen than in the base material for long time sensitization. The optimum thermomechanical treatment introduced a high frequency of CSL boundaries and the clear discontinuity of corrosive random boundary network in the material, and resulted in the high intergranular corrosion resistance arresting the propagation of intergranular corrosion from the surface. The optimized 304 stainless steel showed an excellent resistance to weld decay during arc welding.     

反复焊接对超低碳奥氏体不锈钢耐腐蚀性能的影响

通过对反复焊接1～5次的超低碳奥氏体不锈钢的晶间腐蚀试验及应力腐蚀试验，研究了反复焊接对超低碳奥氏体不锈钢的耐腐蚀性能的影响。试验结果显示，在同一部位反复焊接5次后，超低碳奥氏体不锈钢的晶间腐蚀倾向和应力腐蚀敏感性没有发生明显变化，表明超低碳奥氏体不锈钢在选择合适的焊接材料、焊接工艺和焊接方法的前提下，同一部位可反复焊接5次，而其耐腐蚀性能不会受到影响。     

Failure cases related to material issues in wet-process phosphoric acid plant

The present paper describes three failure cases of metallic components handling wet-process phosphoric acid at ambient temperatures in a phosphate fertilizer plant. All the three cases of failure were related not directly to the corrosive environment rather to wrong selection or inferior quality of materials. In the first case, pipeline of stainless steel 316L failed due to inferior quality of material used in the elbow region. The elbow material was not a low carbon grade stainless steel and was also in heavily sensitized condition which led to intergranular corrosion and intergranular cracking. The other two cases were related to failures of pump sleeves made up of cast alloys equivalent to stainless steel 316 and Hastelloy C-276 respectively. SS 316 showed through-wall pitting and cracking while Hastelloy C-276 had undergone extensive corrosion along the interdendritic boundaries. Both the materials contained high carbon content which led to heavy precipitation of carbides (Cr-rich carbides in SS 316 and Mo-rich carbides in C-276) along inter-dendritic boundaries during solidification of the casting reducing their corrosion resistance. Recommendations to avoid such failures are also suggested.     

Grain boundary engineering of titanium-stabilized 321 austenitic stainless steel

Grain boundary engineering (GBE) primarily aims to prevent the initiation and propagation of intergranular degradation along grain boundaries by frequent introduction of coincidence site lattice (CSL) boundaries into the grain boundary networks in materials. It has been reported that GBE is effective to prevent intergranular corrosion due to sensitization in unstabilized 304 and 316 austenitic stainless steels, but the effect of GBE on intergranular corrosion in stabilized austenitic stainless steels has not been clarified. In this study, a twin-induced GBE utilizing optimized thermomechanical processing with small pre-strain and subsequent annealing was applied to introduce very high frequencies of CSL boundaries into a titanium-stabilized 321 austenitic stainless steel. The resulting steel showed much higher resistance to intergranular corrosion after sensitization subsequent to carbon re-dissolution heat treatment during the ferric sulfate–sulfuric acid test than the as-received one. The high CSL frequency resulted in a very low percolation probability of random boundary networks in the over-threshold region and remarkable suppression of intergranular corrosion during GBE.     

304不锈钢晶间腐蚀敏感性的评定

采用共聚焦显微镜测量了经不同敏化处理的304不锈钢晶间腐蚀后的晶间裂纹深度,通过统计晶间裂纹深度值的分布建立了304不锈钢晶间腐蚀敏感性的评价方法。如果晶间裂纹深度值大于0．5μm,则可认为所测试的304不锈钢发生了晶间腐蚀现象。     

硫化氢环境下马氏体不锈钢的开裂原因分析

炼化离心压缩机在服役过程中马氏体不锈钢叶轮表面出现断裂失效现象。通过对叶轮失效件的断口宏观和微观形貌分析、硬度检测,并结合生产服役环境对叶轮裂纹的产生原因进行分析。结果表明:叶轮断口裂纹以沿晶腐蚀为萌生源,扩展后转变为穿晶腐蚀,呈现应力腐蚀特征。断口腐蚀产物分析表明,腐蚀产物中含有硫元素;结合叶轮的服役环境得出叶轮的断裂失效主要原因是硫化物应力腐蚀开裂。     

低铬铁素体不锈钢晶间腐蚀敏感性的测试方法及性能

研究了爆炸复合板复层06Cr13R低铬铁素体不锈钢的晶间腐蚀敏感性测试方法及性能。结果表明：电化学动电位扫描法（双环EPR法）适合用于爆炸复合板复层06Cr13R低铬铁素体不锈钢晶间腐蚀敏感性的检测,其试验结果与草酸电解侵蚀法对应较好;06Cr13R低铬铁素体不锈钢的晶间腐蚀敏感性与铬-镍奥氏体不锈钢不同,其晶间腐蚀敏感性出现在910℃正火处理后,甚至强制吹风急冷条件下也无法避免,而经过800℃退火处理后,其晶间腐蚀敏感性可减轻。     

16Cr奥氏体不锈钢晶间腐蚀的敏感性

为了研究1Cr17Mn6Ni5N奥氏体不锈钢(16Cr奥氏体不锈钢)的晶间腐蚀行为,通过光学显微镜(OM)、X射线衍射仪(XRD)和晶间腐蚀试验研究了其在不同敏化温度和冷却方式下,晶间碳化物的析出和耐晶间腐蚀性能的变化。结果表明:16Cr奥氏体不锈钢在敏化温度区间内加热时,晶界碳化物随加热温度的上升而增加,加热温度为850℃左右时晶界析出碳化物最多,主要为Cr_(23)C_6和Cr_7C_3;在敏化温度区间内相同加热温度时,水冷可显著减少其晶界碳化物的析出;16Cr奥氏体不锈钢对晶间腐蚀不敏感。     

18-8奥氏体不锈钢焊接接头晶间腐蚀的评定及控制

介绍了18-8奥氏体不锈钢焊接件焊接接头抗晶间腐蚀能力的检验和评定方法,对焊接接头晶间腐蚀的原因进行了分析,阐述了在焊接过程中的主要方面实施的有效控制方法,以提高不锈钢焊件抗晶间腐蚀的能力.     

316L-16MnR复合板不锈钢侧晶间腐蚀原因分析

采用GB／T4334．5—2000标准方法对不锈钢-低合金钢复合板进行晶间腐蚀试验,对不锈钢侧产生裂纹的原因进行了分析。结果表明,由于不锈钢板与低合金钢板的结合面上存在着不可抗拒的碳迁移现象,致使不锈钢板侧过渡区内的奥氏体晶界上聚集着大量的网状碳化物,从而造成晶界上的缺陷,使其在经过硫酸．硫酸铜溶液的腐蚀后,进行弯曲时产生了大量的晶间腐蚀裂纹。     

Intergranular stress corrosion cracking of acoustic-filter hooks used in car

Some acoustic-filter hooks used in car fractured in service. The failure mechanism of the hooks is intergranular stress corrosion cracking. The necessary conditions (susceptible composition of the hook materials; presence of chloride in service environment; presence of residual tensile stress and occurrence of sensitization in the fracture region) caused intergranular stress corrosion mechanism. Non-qualified chemical composition of the hooks (much higher carbon content than the specified of AISI 304 stainless steel) is mainly responsible for the failure of the hooks, which is a key inherent factor.     

不锈钢在海水中的腐蚀行为研究进展

简述了国内外不锈钢海水腐蚀的研究进展,介绍了几种合金元素对不锈钢耐腐蚀性能的影响以及不锈钢在海水中发生点蚀、缝隙腐蚀、晶间腐蚀、应力腐蚀等4种主要腐蚀类型的机理,并对不锈钢防护的发展方向进行了展望。     

Marine Atmospheric SCC of Unsensitized Stainless Steel Rock Climbing Protection

A failure investigation into the root cause of fixed austenitic stainless steel climbing anchor hardware in tropical marine climates has been presented. The incident 316L climbing anchor was fixed in a seaside limestone cliff in southern Thailand and underwent transgranular chloride stress corrosion cracking (TGSCC) after 10 years of service. Since stainless steel does not normally undergo stress corrosion cracking (SCC) at ambient temperatures, the conditions known to promote ambient temperature TGSCC of austenitic stainless steel are reviewed. A mechanism that may give rise to TGSCC in limestone climbing anchors in warm marine environments is postulated.     

316L不锈钢表面纳米化后腐蚀性能研究

对表面纳米化和未经表面纳米化处理的316L不锈钢的样品分别进行点蚀实验和应力腐蚀对比实验,在3.5%(质量分数)NaCl水溶液中分别测出它们的极化曲线.结果表明,316L不锈钢表面纳米化后抗点蚀性能下降,抗应力腐蚀性能提高.对应力腐蚀断口的SEM 分析发现,316L不锈钢应力腐蚀断口有明显分区现象,断裂形式为韧性断裂,开裂通道既有穿晶型也有沿晶型.     

新型00Cr23Ni6Mo4Cu3铸造不锈钢的组织及其局部腐蚀行为

采用金相显微镜和ｘ射线衍射仪进行了金相组织观察与分析，并采用快速模拟试验方法研究了新型００Ｃｒ２３Ｎｉ６Ｍｏ４Ｃｕ３铸造不锈钢的局部腐蚀行为。结果表明，该钢经１０５０℃×２ｈ的固溶处理，其组织为铁素体基体上分布有适量的奥氏体。该热处理使组织细化与均匀化。由于铁素体对奥氏体组织有电化学保护作用，因而这种新型双相不锈钢具有优良的耐晶间腐蚀性能和较高的抗点蚀性能，与高合金化的奥氏体Ｃ１５钢相当。     

Stabilisation of ferritic stainless steels with Zr and Ti additions

Abstract

Traditional 11·5 wt-%Cr ferritic stainless steels are single stabilised with Ti or dual stabilised with Ti–Nb additions. A dual-stabilised ferritic stainless steel 409 with Zr–Ti additions was studied, which was selected through thermodynamic and kinetics analysis. The alloy was subjected to thermomechanical processing using both hot and cold rolling and annealing. The intergranular corrosion resistance and microstructure of this alloy was evaluated. Of particular interest was to study the stabilisation behaviour of this alloy under all processing conditions. The results showed that the precipitation of Cr_xC_y was effectively prevented; hence, the alloy used in this investigation had an excellent resistance to intergranular corrosion.     

不锈钢晶间腐蚀弯曲评价方法的影响因素

用嵌含有GTN延性损伤模型的ABAQUS有限元法,模拟研究了不锈钢晶间腐蚀弯曲评价方法中材料力学性能、弯曲角度和压头直径对弯曲试样塑性应变分布、延性损伤和裂纹起裂的影响规律,分析了其对晶间腐蚀弯曲评价结果的影响。结果表明：随着试样弯曲角度的增大和弯曲压头直径的减小,试样拉伸面的塑性应变增加,试样越容易产生弯曲开裂;在晶间腐蚀弯曲评价标准中,当固定弯曲角度和压头直径时,对于塑性、韧性和抗断裂综合力学性能较低的不锈钢材料,在弯曲过程中材料本身会发生开裂;因此,需要考虑材料力学性能对晶间腐蚀弯曲评价结果的影响;对于该研究中的典型的奥氏体不锈钢材料,当其弯曲断裂应变低于0．51左右时,在弯曲过程中材料本身会发生开裂,不宜用弯曲方法来评价其晶间腐蚀敏感性。     

Improvement of Intergranular Stress Corrosion Crack Susceptibility of Austenite Stainless Steel through Grain Boundary Engineering

Intergranular stress corrosion crack susceptibility of austenite stainless steel was evaluated through threepoint bending test conducted in high temperature water. The experimental results showed that the frequent and efficient introduction of low energy coincidence site lattice boundaries through grain boundary engineering resulted in an apparent improvement of the intergranular stress corrosion crack resistance of austenite stainless steel.