UNS S32304双相不锈钢等离子弧焊接头的组织及其耐点蚀性能

采用恒电位临界点蚀温度(CPT)法,利用OM,SEM,EDX和恒电位极化技术等研究了等离子弧焊接对双相不锈钢UNSS32304焊接接头微观组织及其耐点蚀性能的影响.结果表明,焊接接头热影响区和熔合区微观组织较母材相比发生了显著变化,两相比例严重失衡,铁素体所占比例均大于70%;两区域微观组织形态发生明显变化.且在铁素体晶粒内及两相相界处析出大量氮化物;焊接接头的耐点蚀性能明显下降,点蚀优先发生在高温热影响区所在的铁素体晶粒内.     

UNS S32750超级双相不锈钢激光焊接头微观组织与耐蚀性能

以UNS S32750超级双相不锈钢为研究对象,采用光学显微镜、扫描电子显微镜、透射电子显微镜、电子探针显微分析仪对激光焊接头微观组织和元素分布进行表征,采用临界点蚀温度测试方法研究激光功率对激光焊接头点蚀行为的影响规律.结果表明,提高激光功率可显著增加焊缝中奥氏体含量,并且在一定程度上抑制Cr₂N析出.此外,激光焊焊缝具有比母材更低的耐点蚀性能.但随着激光功率的增加,焊缝中耐蚀的奥氏体含量增加,同时降低了Cr₂N析出倾向,因此其耐点蚀性能也逐渐增强.与双相钢母材相比,激光焊焊缝中Cr,Ni,Mo等合金元素在铁素体与奥氏体中的分配差异性显著减小,而N原子的分配差异性增加,因此焊缝中铁素体具有比奥氏体更低的耐点蚀指数,进而优先被选择性腐蚀.对于双相钢母材,点蚀主要发生在δ/γ相界和夹杂处,而激光焊焊缝的点蚀主要以铁素体内大量析出的Cr₂N作为点蚀萌生位置,并向弱相铁素体内快速发展.     

双相不锈钢及其焊接接头腐蚀研究进展

双相不锈钢耐点蚀、耐晶间腐蚀和耐氯化物应力腐蚀性能优良,是优良的海洋用金属材料,但其焊接接头常成为薄弱区而发生腐蚀问题.从材料因素综述了双相不锈钢腐蚀研究的进展.首先,总结了合金元素和热处理对双相不锈钢耐腐蚀性能的影响.合金元素分配及其引起的二次相析出及产生的元素贫化区、铁素体/奥氏体相比例的变化决定双相不锈钢的耐腐蚀...     

超级双相不锈钢焊接接头的耐蚀性能

通过SEM和EDS研究了采用不同焊接工艺后超级双相不锈钢UNSS32750焊接接头的两相比例及成分变化,并采用临界点蚀温度和浓硝酸法测试比较了不同焊接工艺接头的耐点蚀和晶间腐蚀性能.结果表明,焊接中较高的热输入、加填焊丝和背面采用氮气保护焊的方法可以稳定焊接接头中的奥氏体相的比例,并且较高的热输入,使得焊接接头冷却速度相对较慢,有助于铬的扩散而消除晶界贫铬现象,减小晶间腐蚀倾向;而与此相反的是较高的热输入,会导致两相中元素分配不均衡使铁素体相优先发生腐蚀,从而恶化材料的整体耐点蚀性能.     

S32750超级双相不锈钢在NaCl溶液中的临界点蚀温度及电化学腐蚀机理

采用电化学测试研究了S32750超级双相不锈钢在3.5%Na Cl溶液中的临界点蚀温度(CPT)及电化学腐蚀机理,结合试样点蚀前后的形貌变化,得出S32750不锈钢的临界点蚀温度为71℃。在低于临界点蚀温度时,不锈钢表面能形成稳定的钝化膜;高于临界点蚀温度时,由于Cl-的活性增加及钝化膜的溶解,不锈钢表面产生点蚀现象,且温度越高,点蚀越剧烈。构建了双相不锈钢S32750临界点蚀温度前后的电化学腐蚀模型。     

显微组织铁素体化对2507双相不锈钢耐点蚀性能的影响

通过JMatPro材料性能模拟软件、扫描电镜、能谱仪和电化学测试等方法研究了显微组织铁素体化对2507双相不锈钢耐点蚀性能的影响机理。结果表明：经1 050～1 250℃保温60 min的固溶处理后,2507双相不锈钢的显微组织发生铁素体化,奥氏体相的吉布斯自由能上升,随固溶温度升高,铁素体相含量增多,铁素体化速率逐渐减小;显微组织铁素体化导致两相中化学元素的含量产生明显变化,即铁素体相中铬、钼含量下降,奥氏体相中镍、氮含量上升;随着耐蚀性较弱的铁素体相含量上升,2507双相不锈钢的钝化膜和蚀孔欧姆压降快速下降,腐蚀电流密度上升,耐点蚀性能快速下降。     

酸洗和固溶处理对不锈钢抗点蚀性能的影响

研究了酸洗和固溶处理对８种不锈钢筋电阻对焊接头抗点蚀能力的影响。研究发现,酸洗和因咱都有效地改善和恢复不锈钢电阻对焊接头的抗点蚀性能。对于普通双相钢,固溶处理比酸洗能更有产地改善接头的抗点蚀性能,并无晶粒粗化。对于奥氏体钢和超纸奥氏体风,固溶处理的效果不及酰洗,且会引起母材晶粒粗化。对含Ｍｏ含Ｎ较高钢种的对焊接头,两者的更佳,尤其是两者综合处理后的接头,其临界点蚀温度ＣＰＴ其至高于对应母材经酸洗以     

固溶处理对2205双相不锈钢在卤水中点蚀的影响

利用电化学方法对不同固溶处理的2205双相不锈钢在卤水中的临界点蚀温度及临界点蚀电位进行了研究,结合显微金相技术研究了固溶处理温度对相含量及耐蚀性能的影响。结果表明：2205双相不锈钢在卤水中的临界点蚀温度介于55～60℃之间,临界点蚀电位随着环境温度的升高而降低;金属碳化物在固溶处理温度750～900℃范围内析出,奥氏体含量急剧减少材料耐蚀性能严重恶化;固溶处理温度1100℃保温1 h的试样耐蚀性能最佳。     

时效处理对2205双相不锈钢耐点蚀性能的影响

通过研究时效热处理对2205双相不锈钢耐点蚀性能的影响,发现590℃和650℃的时效处理降低了材料的耐点蚀性能,并且耐点蚀性能随着时效温度和时效时间的增加而降低;点蚀蚀孔倾向于在铁素体和奥氏体的相界处以及铁素体中的析出相附近形核长大。此外,通过TEM物相分析发现590℃时效析出相有R相,650℃时效析出相有R相和σ相。     

固溶温度对2205双相不锈钢组织和点蚀性能的影响

对2205双相不锈钢热轧板进行了不同温度的固溶处理,采用光学显微镜和扫描电镜分析了不同固溶状态下的组织演变规律,通过FeCl₃溶液浸泡法研究了固溶温度对2205双相不锈钢点蚀性能的影响。结果表明,950 ℃固溶处理后,组织中有s相;经1000~1100 ℃固溶处理后,由奥氏体和铁素体两相组成。随固溶温度升高,铁素体含量逐渐增加,奥氏体晶粒度减小,孔蚀数量、孔蚀平均尺寸和腐蚀速率均呈下降趋势。经1100 ℃×20 min水冷固溶处理后,奥氏体和铁素体含量约各占一半,组织均匀,表现出良好的耐点蚀性能。     

Pitting corrosion behaviour of 2101 duplex stainless steel in chloride solutions

ABSTRACT

The corrosion behaviour of 2101 duplex stainless steel (DSS) in NaCl solution was studied and compared with that of 2205 DSS. The effects of chloride concentration and solution temperature on pitting corrosion behaviour were focused. The relative sensitivity to pitting corrosion of the constituent phases in both 2101 and 2205 DSSs was also explored. Pitting corrosion susceptibility was evaluated by conducting cyclic polarisation curve measurement. The corrosion morphology was examined by a scanning electron microscope equipped with energy dispersive spectrometer. The experimental results showed that the pitting corrosion resistance of 2101 DSS was inferior to that of 2205 DSS by exhibiting a lower threshold chloride concentration and a lower critical pitting temperature. For both 2101 and 2205 DSSs, the ferrite phase was more susceptible than austenite phase to pitting corrosion.

This paper is part of a supplementary issue from the 17th Asia-Pacific Corrosion Control Conference (APCCC-17).     

Corrosion behavior of 2205 stainless steel in simulated flue gas condensate with different chloride concentrations in a waste incineration power plant

The effect of Cl⁻ on the initial corrosion behavior of 2205 duplex stainless steel (2205 DSS) in simulated flue gas condensate from a waste incineration power plant was investigated using Mott–Schottky plot, micro-area electrochemical methods, and microscopic surface morphology observation. The results show that at 150°C, the carrier concentration of the 2205 DSS passive film was maintained at a small value and changed little when the Cl⁻ concentration is less than 25 g/L, indicating that it has good pitting resistance. When the Cl⁻ concentration reaches 30 g/L and above, the carrier concentration of the passive film increases remarkably, and pitting corrosion appears on the 2205 DSS surface. At 180°C, there is no obvious pitting on the surface when the Cl⁻ concentration is not more than 15 g/L. When the Cl⁻ concentration is 20 g/L or above, the carrier concentration of the passive film significantly increases, and pitting corrosion appears on the surface. When the Cl⁻ concentration reaches 30 g/L, the carrier concentration of the passive film increases sharply. The passive film on a 2205 DSS surface is seriously damaged and accompanied by the occurrence of uniform corrosion.     

温度对316L不锈钢耐海水腐蚀性能的影响

运用临界点蚀温度(CPT)、环状阳极极化曲线和电化学阻抗谱等方法研究了不同温度下316L不锈钢的海水腐蚀行为. 结果表明, 晶粒尺寸不同的两种316L不锈钢的CPT基本相同; 随着海水温度升高, 点蚀电位和再钝化电位均呈线性降低, 但是细晶钢的点蚀性能下降更大, 85℃时粗晶钢比细晶钢的点蚀电位约高60 mV. 与粗晶钢相比, 细晶钢在65℃下形成的钝化膜微缺陷更多, 且点蚀诱导时间较短.     

Influence of microstructure on the corrosion resistance of hyperduplex stainless steel

Hyperduplex UNS S32707 is a newly developed austenitic–ferritic stainless steel. The steel contains about 27%Cr, 7%Ni, 4.5%Mo, and 0.4%N, which results in a pitting resistance equivalent factor (PRE) equal to 49. In this study, the pitting corrosion resistance of this new grade of stainless steel was investigated by varying the microstructure using different thermal processes. The critical pitting temperature measurement and cyclic polarization tests confirm the high corrosion resistance of the hyperduplex steel in the solution treated condition. However, deleterious phases form easily during thermal processing and cause a drastic decrease in the corrosion resistance.     

0Cr25Ni7Mo4、316与304不锈钢临界点蚀温度研究

采用外加恒定电位下腐蚀电流-温度扫描方法研究了0Cr25Ni7Mo4、304和316不锈钢在1 mol/L NaCl水溶液中的点蚀行为。利用不锈钢临界点蚀温度评价了材料的耐点蚀性能.测得0Cr25Ni7Mo4和316不锈钢的临界点蚀温度分别为79.5 ℃和15 ℃,304不锈钢在0 ℃以下.对0Cr25Ni7Mo4不锈钢材料优良耐点蚀性能的原因进行了分析讨论.     

Cl离子对 304、316不锈钢临界点蚀温度的影响

采用外加恒定电位下腐蚀电流-温度扫描的方法分别研究了304、316不锈钢在不同浓度NaCl水溶液中的临界点蚀温度.得到了材料临界点蚀温度随Cl-浓度变化的关系曲线.在分析温度与Cl-浓度分别对钝化膜影响的基础上阐述了二者对不锈钢点蚀的综合作用机理.     

氯离子对316L不锈钢临界点蚀温度的影响

在外加恒电位下,通过测腐蚀电流密度-温度曲线的方法研究了Cl~-含量对316L不锈钢临界点蚀温度(CPT)的影响。结果表明:在临界点蚀温度以下,试样表面钝化膜比较稳定,超过该温度后,试样表面开始发生点蚀。Cl~-含量越高,316L不锈钢临界点蚀温度越低,且表面的点蚀坑越多。现场的腐蚀产物分析表明,腐蚀产物表面稀疏,主要元素为O、Fe、C、Cl。现场生产水Cl~-质量浓度高达21.431g/L,对316L不锈钢的腐蚀极其严重。     

pH与温度对2205DSS在盐卤中的孔蚀行为影响研究

利用电化学方法、交流阻抗技术、失重法及金相显微术研究了pH与温度变化对2205DSS在盐卤中耐孔蚀行为的影响.结果表明：随着卤水pH值的增大,2205DSS耐孔蚀性能先略微增强、然后减弱;根据实际制盐工艺条件,卤水的pH值应适当控制在8.7或8.8以内;随温度升高,2205DSS基体抵抗孔蚀能力明显下降;试样在盐卤水介质中的电极反应是不可逆的,其腐蚀反应既受活化极化控制,又受溶液扩散控制.     

FCAW repair welding cycles,HAZ microstructure and corrosion resistance of 2304 duplex stainless steel

Flux-cored arc welding (FCAW) is an automatic welding process widely employed to join duplex stainless steel (DSS) structures in industrial plants because of its high productivity. However, when multiple passes are performed, this process can lead to the formation of non-metallic inclusions originating from the slag in the fusion zone. In this case, the welded joint can be repaired using the same welding process. Some regions next to the heat-affected zone are not removed during the repairing operation. Thus, these regions are subjected to repeated welding cycles and to a high heat input, which can cause microstructural alteration that impairs the corrosion resistance of the welded material. The aim of this work was to study the corrosion resistance of 2304 DSS plates joined using the FCAW process and repaired using the same process. The influence of the repair procedure on the corrosion resistance of the welded joints was evaluated using potentiodynamic polarisation and chronoamperometric curves, which allow the determination of the critical pitting temperature of the samples. The microstructure obtained after each repair cycle was evaluated using optical microscopy and scanning electron microscopy. The results showed that the corrosion resistance was depressed as the number of repair cycles increased.     

Corrosion behaviour of stainless steel exposed to highly concentrated chloride solutions

The characteristics of pitting corrosion of Type 304L stainless steel (SS) exposed to highly concentrated chloride solutions were studied through the evaluation of the corrosion potential, the pitting potential, the structure of the passive layer and the statistics of pitting depth and density. Both as-received and weld metal samples were studied. The weld metal sample was machined from the welding zone of a butt weld of Type 304L SS. The results showed an accelerated anodic dissolution and depressed film resistance at the welding zone, but no dramatic change on pitting corrosion was observed from the statistics of pitting during the test duration up to 720?h. The pitting corrosion resistance was significantly affected by the chloride concentration and slightly affected by the temperature under the investigated conditions.