Crevice Corrosion of Several Supper Stainless Steels in the Simulated LT-MED Environment

Susceptibility and morphological characteristics of crevice corrosion for SS316, SS904 L, SS254 sMo and SS2507 in the simulated low-temperature multi-effect distillation environment were investigated by cyclic polarization test, scanning electron microscope and laser microscope. The results show that the crevice corrosion resistance of four kinds of stainless steel is ranked as SS254 sMo ≈ SS2507SS316 SS904 L. There are ‘‘cover' structures over the edge of active crevice corrosion regions of SS904 L, SS254 sMo and SS2507, but SS316 is an exception. Galvanic corrosion characteristics appeared in the crevice of duplex supper stainless steel SS2507.     

人工模拟体液中pH值对离子注N人体医用合金腐蚀行为的影响

采用电化学测试技术研究了在人工模拟体液中pH值变化对离子注N人体用SUS316L不锈钢,Co-Cr合金,工业纯Ti和Ti-6Al-4V合金腐蚀行为的影响。结果表明,随着pH值的降低,试样的腐蚀电位负移,SUS316L不锈钢和Co-Cr合金的点蚀电位与缝隙腐蚀电位降低,使材料发生局部腐蚀的敏感性提高,工业纯Ti和Ti-6Al-4V合金的腐蚀电流密度增大,提高离子释放速度,加大对人体的潜在生理危害。     

Application of the multichannel electrode method to monitoring of corrosion of steel in an artificial crevice

Crevice corrosion of iron was evaluated using the multichannel electrode method in which 10 individual working electrodes (WEs) of pure iron were embedded in resin, placed in an artificial crevice in the range from 0.5 mm to 2.0 mm, and immersed in 0.51 mol dm⁻³ NaCl solution. The WEs were connected to an electronic circuit which allowed galvanic coupling between them and measurement of their individual coupling current or open circuit potential. Time-transient of the spatial distribution of coupling current and open circuit potential showed sequential transition of the coupling current on WEs at the middle position of the crevice from cathode to anode. The WE near the opening of the crevice initially showed a large anodic current, then a decreasing the anodic current corresponding to the current transition of other WEs, and finally a large cathodic current coupled with the other anodic WEs in the crevice. The transition of coupling current was explained by the change in pH and concentration of dissolved oxygen in the crevice. Thickness of the gap of the artificial crevice affected the transition behavior of coupling current distribution. For example, slower current transition with smaller coupling current was found in the case of a narrower gap. Such properties were related to the introduction and consumption of dissolved oxygen in the crevice solution and the circulation of gap solution from/to the outside of the crevice.     

An experimental study of crevice corrosion behaviour of 316L stainless steel in artificial seawater

The effects of applied torque on corrosion behaviour of 316L stainless steel with crevices were investigated using the cyclic potentiodynamic polarization method. Three kinds of crevices (316L-to-polytetrafluoroethylene, 316L-to-fluoroelastomeric and 316L-to-316L) were tested in artificial seawater at 50 °C. Corroded surface morphology was also investigated using scanning electron microscopy. Results indicate similar trends in crevice corrosion susceptibility with increasing applied torque. Among the three crevices, the 316L stainless steel specimen, coupled to the 316L stainless steel crevice former, is the most susceptible to crevice corrosion.     

Susceptibility of 316L stainless steel to crevice corrosion in submersible solenoid valve

The susceptibility of 316L stainless steel to crevice corrosion was investigated by using immersion test and electrochemical test. Three kinds of crevices including 316L‐to‐polytetrafluoroethylene (PTFE) crevice, 316L‐to‐fluoroelastomeric (FKM) crevice and 316L‐to‐316L crevice were tested in artificial seawater at 50°C. The results indicate that 316L stainless steel specimen is the most susceptible to crevice corrosion when it is coupled to 316L stainless steel crevice former, while it is the least susceptible when it is coupled to FKM crevice former. It suggests that during submersible solenoid valve design, the crevice of metal‐to‐metal should be moderately large so that crevice corrosion can not initiate and propagate, and FKM O‐ring rather than PTFE O‐ring should be selected as obturating ring. The corroded surface morphology was investigated using scanning electron microscopy (SEM) and atomic force microscopy (AFM). Three regions including passive region, active region and variable region can be observed on crevice corrosion sites.     

Electrochemical behavior of SUS316L stainless steelafter surface modification

1　INTRODUCTIONAsametallicimplantdevice ,coronarystentsneedgoodmechanicalperformance ,wonderfulanti corrosionbehavioraswellasbloodcompatiblecapabil ityforinvivoenvironments.Nowadaysthestentsaremadebyausteniticstainlesssteel,cobalt basedalloy ,titaniumanditsalloy[1] .Amongthesematerials ,SUS316Lstainlesssteelisthemostcommonusedonebecauseofitscheapcost ,goodmechanicalbehaviorandlowcorrosionrate .Itdoeshowever ,frequentlycorrodeinthebody ,andreleasesomenoxiousionssuchasCr,Ni,Moions .Theio…     

Numerical simulations study of the localized corrosion resistance of AISI 316L stainless steel and pure titanium in a simulated body fluid environment

The resistance of both AISI 316L stainless steel (AISI 316L SS) and commercially pure titanium (cpTi) to localized corrosion in a simulated body fluid solution was investigated using numerical simulations. The resulting model, based on transport equations in dilute solutions, is designed to predict the susceptibility of these two biomaterials to crevice corrosion initiation. The results show that cpTi and AISI 316L SS alloy are very resistant to the initiation of crevice corrosion in 0.9% NaCl solution and AISI 316L SS alloy is more susceptible to corrosion initiation over the long term than cpTi.     

316L奥氏体不锈钢的腐蚀行为

综述了316L奥氏体不锈钢应用过程中的腐蚀行为,包括晶间腐蚀、应力腐蚀开裂、缝隙腐蚀、环烷酸腐蚀、大气腐蚀和海水腐蚀。同时介绍了合金元素Mo、N和Al,以及电解质类型、温度、浓度等因素对其腐蚀行为的影响。最后讨论了应用中存在的问题,并对未来的发展做了一些展望。     

316L不锈钢法兰腐蚀失效分析与对策

对316L不锈钢法兰在苯甲酸环境中因腐蚀失效进行了分析，发现不锈钢因焊接导致的晶间腐蚀是不锈钢法兰腐蚀失效的主要原因，此外，焊接材料与基体材料的不同以及使用了导电的垫片石墨会引起电偶腐蚀，不锈钢法兰之间存在缝隙会引发缝隙腐蚀，提出了解决措施．     

Amorphous carbon coated stainless separator for PEFCs

An SUS316L stainless steel separator was coated with amorphous carbon by using an electron cyclotron resonance (ECR) plasma sputtering technique, and used in a polymer electrolyte fuel cell (PEFC). Characteristics of this carbon film were investigated with Raman spectroscopy and XPS. Quantitative depth profiles and chemical depth profiles of the deposited carbon layer were measured with GD-OES and XPS, respectively. The contact resistivity between a carbon paper and the carbon coated SUS316L steel was also measured. The performance of PEFC single cells assembled with carbon coated SUS316L separators, uncoated SUS316L separators, and conventional carbon separators were compared. The results revealed that an assembled PEFC having carbon coated SUS316L separators provided better performance than one having uncoated SUS316L, and the PEFC showed comparable performance to one having conventional carbon separators.     

Corrosion behaviour of HVOF sprayed SUS316L stainless steel in seawater

SUS316L stainless steel was coated onto the SUS316L plate by the high velocity oxy-fuel (HVOF) spray technique. Its corrosion behaviour in seawater was investigated by the electrochemical method and the microscopy. The coating had corrosion resistance inferior to the bulk plate. The corrosion of the HVOF sprayed SUS316L coating was related to both its porosity and its oxygen content. Depending on them, the corrosion took place at the small pore and the boundary between the spray particles on the surface.     

海洋大气环境下TC4钛合金与316L不锈钢铆接件腐蚀行为研究

研究了TC4-316L异种金属铆接件在模拟海洋大气环境条件下的腐蚀行为。利用失重法、X射线光电子能谱分析(XPS)、扫描电子显微镜(SEM)、激光共聚焦显微镜等方法分析了试样的腐蚀动力学、锈层成分、腐蚀形貌。结果表明,TC4-316L铆接件在周期浸润实验1200 h后,316L不锈钢发生了腐蚀,而TC4钛合金并没有明显的腐蚀现象;316L不锈钢腐蚀产物包含FeOOH,Fe3O4和Fe2O3,而TC4钛合金表面主要为TiO2和Ti2O3等钛的氧化物组成的氧化膜。与单件316L不锈钢相比,由于电偶腐蚀与缝隙腐蚀的共同作用,TC4-316L铆接件中的316L不锈钢腐蚀加速。     

Evaluation of weld metal hot cracking susceptibility in superaustenitic stainless steel

Solidification cracking susceptibilities of two types of superaustenitic stainless steel, 254SMO and SR50A, were evaluated by transverse Varestraint tests. The susceptibilities were compared with those of conventional austenitic stainless steel 316L, and factors influencing the difference of susceptibility were discussed. The comparison showed that 254SMO and SR50A are more sensitive to solidification cracking than 316L. In the transverse Varestraint tests, both total and maximum crack lengths are longer in the superaustenitic stainless steel. Because of the longer maximum crack length, the superaustenitic stainless steel also has a wider brittleness temperature range of cracking than 316L: about 178 °C for the superaustenitic stainless steel and 43 °C for 316L. It is believed that straight subgrain boundaries owing to the cellular dendritic solidification and segregations of sulfur and phosphorus in the subgrain boundaries of superaustenitic stainless steel make it more sensitive to solidification cracking. In addition to the solidification cracking, reheat cracking is also observed within the previous weld bead in the superaustenitic stainless steel because of fully austenitic solidification with significant segregations. This suggests that caution should be given to the occurrence of reheat cracking when superaustenitic stainless steel is multi pass welded.     

Effect of the Crevice Former on the Corrosion Behavior of 316L Stainless Steel in Chloride-Containing Synthetic Tap Water

To restrain the failure of the plate heat exchanger (PHE) in customer boiler working fluid, the effect of crevice former type on the corrosion behavior of the 316L stainless steel plate was investigated using electrochemical methods and surface analyses in chloride-containing synthetic tap water (60 °C). The localized corrosion under metal–metal crevice condition was initiated more easily than that under the metal-gasket crevice condition due to the restricted mass transport at the gasket crevice mouth. However, the anodic current under the metal–metal crevice condition was lower than that under metal-gasket crevice condition at a higher anodic potential, indicating that that the metal dissolution under EPDM crevice would be higher than that under metal crevice under the accelerated corrosion condition. Because narrow crevice gap that was formed under gasket accelerated the anodic dissolution at the crevice mouth, the perforation tendency under metal-gasket crevice condition is much higher than that under metal–metal crevice condition. As a result, the crevice geometry, especially the crevice gap, mainly affected the corrosion behavior of PHE material.     

Fatigue strength of 316L-type stainless steel in simulated body fluids

The fatigue strength of commercial SUS316L stainless steel was studied in PBS(−) (phosphate buffer solution) with different dissolved oxygen contents and CPBS (a 0.9 mass% NaCl-containing citric phosphate buffer solution) with different pH levels, i.e., 5.0, 6.0, and 7.5. The results obtained are as follows. (1) The fatigue behaviour in PBS(−) was hardly affected by the dissolved oxygen content. (2) The fatigue strength in a high-cycle region was much lower in CPBS of pH 7.5 than in PBS(−) of pH 7.5. (3) The fatigue strength in CPBS decreased with decreasing pH from 7.5 to 5.0.     

Enhancing the localised corrosion resistance of 316L stainless steel via FBR-CVD chromising treatment

The resistance of stainless steels to localised corrosion can be adversely affected by environmental and metallurgical heterogeneities existed in complex industrial infrastructures such as seawater desalination plants exposed to aggressive evnironments. It is therefore critical to enhance the localised corrosion resistance and understand the corrosion behaviour of stainless steels in complex and aggressive industrial environmental conditions. In this work, the localised corrosion resistance of chromised stainless steel 316L (SS316L) in simulated seawater desalination systems has been investigated by electrochemical and surface analytical techniques. It has been found that chromising processes have improved the localised corrosion resistance of SS316L by reducing its susceptibility to pitting, crevice, and welding zone corrosion in simulated seawater desalination environments. This increased corrosion resistance has been explained by electrochemical polarisation studies and surface analysis showing that the chromising treatment at 1050°C resulted in a continuous and stable chromium-enriched layer on the SS316L surface.     

A comparison of hydrogen embrittlement susceptibility of two austenitic stainless steel welds

Slow displacement rate tensile tests were carried out to assess the effect of hydrogen embrittlement on notched tensile strength (NTS) and fracture characteristics of AISI 316L and 254 SMO stainless steel (SS) plates and welds. 254 SMO generally exhibited a better resistance to hydrogen embrittlement than 316L. The strain-induced transformation of austenite to martensite in the 316L SS was responsible for the high hydrogen embrittlement susceptibility of the alloy and weld. Sensitized 254 SMO (i.e., heat-treated at 1000 °C/40 min) base plate and weld comprised of dense precipitates along grain boundaries. Interfacial separation along solidified boundaries was observed with the tensile fracture of 254 SMO weld, especially the sensitized one. Dense grain boundary precipitates not only reduced the ductility but also raised the susceptibility to sulfide stress corrosion cracking of the sensitized 254 SMO plate and weld.     

Role of nitrogen on the corrosion behavior of austenitic stainless steels

The role of nitrogen in the mechanisms of localized corrosion resistance and repassivation were electrochemically investigated using a nitrogen-bearing austenitic stainless (SUS316L) steel in 0.1 and 0.5 M Na₂SO₄ solutions and a 3.5% NaCl solution. Almost 100% of the nitrogen compounds dissolved into the bulk solution after crevice corrosion were transformed into NH₃. That is, the mole amount of ammonia in the solution was approximately equivalent to the mole amount of nitrogen dissolved in the steel. This suggests that NH₄⁺ consuming H⁺ in the pit controlled the local decrease of pH and promoted the repassivation. NO₃-N and NO₂-N were not detected by chemical analyses in the high potential and thermodynamically stable zone as NO₃⁻ in the potential-pH diagram. The repassivation in nitrogen-bearing SUS316L steel in a 0.1 M Na₂SO₄ solution was studied using the scratching electrode technique, which measured the partially destroyed passivation films on the steel. This technique showed that nitrogen dissolved in the steel has a strong repassivation capacity.     

Influence of ultrasound on pitting corrosion and crevice corrosion of SUS304 stainless steel in chloride sodium aqueous solution

The change of polarization curves and surface morphologies of SUS304 stainless steel was investigated in 3.5 mass% NaCl solution with or without the application of ultrasound (US). As the result, both the pitting corrosion and the crevice corrosion were largely suppressed by the application of US. The reason is attributed to the decrease in the concentration of hydrogen and chloride ions in pits or in the crevice by removing the corrosion product and stirring the liquid there.     

不锈钢气相管焊接热影响区应力腐蚀开裂研究

针对一起SUS304L不锈钢化工气相管焊接热影响区(HAZ)应力腐蚀开裂(SCC)的失效综合分析，发现该不锈钢SCC为穿晶应力腐蚀开裂而不是常见的不锈钢HAZ的晶间应力腐蚀，认为SUS304L不锈钢在此服役环境中对SCC无法免疫。根据材料发生SCC失效微观特征与使用环境的关系，给出了选材和焊接加工的建议。