Improvement of pitting corrosion resistance of stainless steel by electric current pulse

ABSTRACT

The electric current pulse (ECP) was applied on the liquidus of 304 stainless steel during solidification and the pitting corrosion of the water-quenched specimens was explored in the present work. The results revealed that the utilisation of ECP can inhibit manganese sulphide from segregating around oxide inclusions during solidification and consequently, the pitting corrosion resistance of ECPed steel was significantly improved. Hence, the application of ECP during solidification might be an efficient way to improve the pitting corrosion resistance of the 304 stainless steel.

This paper is part of a themed issue on Materials in External Fields.     

The abrasive corrosion behavior of plasma-nitrided alloy steels in chloride environments

Both corrosion and abrasive corrosion behavior of plama-nitrided type 304 and 410 stainless steels and 4140 low alloy steel were investigated in 3% NaCl solution (pH = 6.8) by electrochemical corrosion measurements. Surface morphology and alloying elements after corrosion and abrasion corrosion tests were examined by scanning electron microscopy and energy dispersive analysis of X-rays. The results indicated that the plasma-nitrided SAE 4140 steel containing -(Fe,Cr)_{2 – 3}N and -(Fe,Cr)₄N surface nitrides which produce a thick and dense protective layer exhibited a significant decrease of corrosion currents by inhibition of the anodic dissolution of iron, whereas the plasma-nitrided type 304 and 410 stainless steels containing the segregation of chromium nitride CrN exhibited a extensive pitting corrosion by acceleration of the anodic dissolution of iron. It is concluded that the susceptibility to pitting is consistent with the degree of chromium segregation, and decreases as follows: 304 stainless steel > 410 stainless steel > 4140 steel. Also, the results of abrasive corrosion testing for the plasma-nitrided alloys are strongly related to the subtleties of the nitrided microstructures resulting in a pitting and spalling type of abrasive corrosion of type 304 and 410 stainless steels, and excellent abrasive corrosion resistance for SAE 4140 steel.     

304L(D)双牌号不锈钢的点腐蚀行为研究

304L(D)双牌号不锈钢产品的制造不可避免焊接过程,焊接接头也是最容易出现失效的位置,而现今304L(D)双牌号不锈钢的性能及使用在国内外均没有系统的研究及相应的标准。采用失重法结合腐蚀SEM形貌观察及蚀坑内部元素EDS谱,从腐蚀速率与化学成分方面分析了304L(D)双牌号不锈钢母材及焊缝的耐点腐蚀性能。结果显示:焊缝处耐点蚀性能最优而母材最次。所得腐蚀数据可以作为今后制定304L(D)双牌号不锈钢使用条件的参考。     

Effect of Temperature on Pitting Corrosion Resistance of 316 Stainless Steel Coated by Cerium Oxide Film in 3.5% NaCl Solution

One of the main problems of stainless steel is its poor pitting corrosion resistance in the aggressive environment containing Cl-, such as seawater. In this paper we investigated the corrosion behavior of the 316 stainless steel coated by cerium oxide nanocoating prepared by sol-gel process. Potentiodynamic polarization and electrochemical impedance spectroscopy （EIS） were used to study the corrosion behavior of cerium oxide nanocoatings in 3.5% NaCl solution. The microstructure of the cerium oxide was examined by scanning electron microscopy （SEM） and the formed phases was identified by X-ray diffraction （XRD）. The pitting corrosion resistance of the cerium oxide nanocoating was found to be improved after heat treatment of the cerium oxide nanocoating at 300℃ for 30 min.     

Corrosion failures of AISI type 304 stainless steel in a fertiliser plant

A urea plant, operating on ammonia and carbon dioxide (CO₂) gases, had to be shutdown due to corrosion in the intercooler and aftercooler of its CO₂ gas cleaning circuit. Extensive general corrosion of AISI type 304 stainless steel parts, such as sealing strips, fins, demisters and the shell, of these two components which were in contact with the duplex stainless steel tubes, caused the shutdown of the fertiliser plant within 6 months. Investigations of the corrosion products by X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) techniques showed the presence of carbon and ammonia based compounds, thus suggesting the role of ammonia and CO₂ gases, or the product of their reactions, in the corrosion of type 304 stainless steel. Electrochemical polarisation studies showed that duplex stainless steel possessed a more positive open circuit potential and a nobler critical pitting potential than type 304 stainless steel thus confirming that the corrosion of type 304 stainless steel was caused by the galvanic action with the duplex stainless steel heat transfer tubes. Hence, it was recommended that (i) the same material (type 304 stainless steel) be used for all parts of the intercooler and aftercooler to avoid galvanic corrosion, (ii) condense water carried over by CO₂ gas by cooling it to low temperatures immediately after it comes out from the scrubber, (iii) slight modification of the process to add up to 0.8% oxygen in the CO₂ gas before entry into the intercooler, which will help in retaining/formation of an effective passive film on type 304 stainless steel.     

模拟2倍浓缩海水中聚环氧琥珀酸和Na2MoO4对304不锈钢的缓蚀作用

为开发适用于循环冷却海水／不锈钢体系的绿色缓蚀剂,采用电化学阻抗谱、极化曲线及表面腐蚀形貌分析,研究了聚环氧琥珀酸（PESA）、Na2MoO4在模拟2倍浓缩海水中对304不锈钢的缓蚀作用。结果表明：在模拟2倍浓缩海水中,PESA与Na2MoO4均能在304不锈钢表面形成保护膜,产生缓蚀作用;PESA为阳极吸附型缓蚀剂,...     

模拟冷却水中304不锈钢的耐蚀性影响因素研究

用电化学方法研究了Cl^-、S^2-、NO3^-、温度以及某电厂水质稳定剂对304不锈钢耐蚀性的影响。极化曲线表明：在[Cl-]／[SO4^2-]约为0．56时，点蚀电位开始下降，并随着Cl-浓度的增大逐渐降低；S2-的加入使钝化电流显著增大；NO3-浓度增加使点蚀电位逐渐升高；溶液温度的提高使点蚀电位降低，钝化电流也有所增大，钝化膜的耐蚀性降低;实验表明采用的某厂水质稳定剂可引起304不锈钢点蚀电位的下降。Mott-Schottky图显示S2-浓度的增加使体现p-型半导体(氧化铬)性质的直线段发生较大变化，说明硫离子影响了铬氧化物的性质。     

No corrosion of 304 stainless steel implant after 40 years of service

When exposed to 0.9% NaCl type 304 stainless steel undergoes severe pitting corrosion within a matter of days. However, a Sherman plate fabricated from type 304 stainless steel remained inside a patient's arm for almost 40 years without any visible indications of corrosion. Given the previous understanding of the pathological environments this was considered quite remarkable. It is proposed that the low dissolved oxygen levels found in human-body fluids makes the long-term in vivo environment much more benign than would be anticipated from in vitro experiments. Furthermore, it is proposed that previous cases of localized pitting corrosion on stainless steel implants most likely arose due to the development of short-term aggressive conditions due to pathological changes in the surrounding tissue as a result of the trauma of the implant procedure. In the present case the Sherman plate was sufficiently small that the surrounding tissue was not aggravated sufficiently to lead to the development of such an environment aggressive. The conclusion that surgical implants are at most risk during the first few weeks of service implies that short-term corrosion protection methods, such as coatings, may be more effective than previously thought.     

304不锈钢在盐湖卤水中的腐蚀行为

用腐蚀挂片试验方法研究了304不锈钢在盐湖卤水中暴露2a的腐蚀行为,井运用室内电化学试验方法研究了其电化学行为。结果表明：盐湖卤水浸泡2a后,304不锈钢腐蚀速率为0．0003mm／a,主要表现为点蚀,试样侧面加工缺陷处存在较深的点蚀坑;在卤水中浸泡768h后,304不锈钢表面钝化膜局部被破坏,出现点蚀孔。     

Improved corrosion resistance and biofilm inhibition ability of copper-bearing 304 stainless steel against oral microaerobic Streptococcus mutans

304 stainless steel(SS) used as orthodontic wire during orthodontics faces the risk of microbiologically influenced corrosion(MIC) due to diverse flora environment. Hereinto, Streptococcus mutans(S. mutans)is the most important cariogenic bacteria. In this work, MIC behavior of a new 304-Cu SS in presence of S. mutans was studied by the observations using scanning electron microscopy(SEM) and confocal laser scanning microscopy(CLSM) including live/dead staining, extracellular polymeric substance(EPS)staining and pitting corrosion, electrochemical test, and X-ray photoelectron spectroscopy(XPS). Above results showed that 304-Cu SS possessed excellent biofilm inhibition ability and presented lower corrosion current density(icorr), larger polarization resistance(Rp) and charge transfer resistance(Rct) in the presence of S. mutans, indicating that 304-Cu SS had a better MIC resistance against S. mutans. It was further affirmed by XPS results that the presence of Cu-oxide in passive film of 304-Cu SS inhibited the formation of biofilm.     

Cl~-和H_2S对不锈钢电化学行为的协同影响

目前,对Cl~-和H_2S共存条件下不锈钢的腐蚀尤其是点蚀行为鲜有研究。采用动电位扫描和交流阻抗测试研究了304,316L和2205 3种不锈钢在含有不同浓度Cl~-和H_2S的溶液中的电化学行为。结果表明:在含有1 200 mg/L Cl~-的溶液中,随H_2S浓度增大,304和316L的点蚀敏感性均增大,但此条件下的H_2S浓度并未对2205双相不锈钢产生影响。当Cl~-浓度增大到1 500 mg/L时,2205产生了点蚀现象,说明虽然H_2S促进了不锈钢点蚀的发生,但Cl~-是诱导不锈钢产生点蚀的关键因素。     

Soft microelectrode linear array for scanning electrochemical microscopy

A linear array of eight individual addressable microelectrodes has been developed in order to perform high-throughput scanning electrochemical microscopy (SECM) imaging of large sample areas in contact regime. Similar to previous reports, the soft microelectrode array was fabricated by ablating microchannels on a polyethylene terephthalate (PET) film and filling them with carbon ink. Improvements have been achieved by using a 5 μm thick Parylene coating that allows for smaller working distances, as the probe was mounted with the Parylene coating facing the sample surface. Additionally, the application of a SECM holder allows scanning in contact regime with a tilted probe, reducing the topographic effects and assuring the probe bending direction. The main advantage of the soft microelectrode array is the considerable decrease in the experimental time needed for imaging large sample areas. Additionally, soft microelectrode arrays are very stable and can be used several times, since the electrode surface can be regenerated by blade cutting. Cyclic voltammograms and approach curves were recorded in order to assess the electrochemical properties of the device. An SECM image of a gold on glass chip was obtained with high resolution and sensitivity, proving the feasibility of soft microelectrode arrays to detect localized surface activity. Finite element method (FEM) simulations were performed in order to establish the effect of diffusion layer overlapping between neighboring electrodes on the respective approach curves.     

Pitting corrosion and stress-corrosion cracking of buffer tanks in a brewery

The paper presents results of the expertise performed to identify the causes of corrosion of water container for storage of hot water, which is used to production of beer in the brewery. The container was affected by corrosion within a very short time of exploitation, which has led it to deep perforation. During the exploitation of the container significant damages caused by the pitting corrosion and stress-corrosion cracking were detected. It was determined that corrosion processes of the water container were strictly connected with a very high concentration of chloride ions present in a hot water and the presence of static mechanical stresses. Additional impact was also involved with the application of inadequate type of steel for this usage. AISI 304 stainless steel is not resistant to pitting corrosion under investigated conditions.     

SO42-浓度对304不锈钢在NaCl溶液中点蚀行为影响的研究

利用动电位极化、电化学阻抗谱(EIS)和激光电子散斑干涉(ESPI)研究了3.5%NaCl溶液中,SO24-浓度对304不锈钢点蚀行为的影响。使用0.3V(vs SCE)极化条件下的计时电流法结合ESPI确定了点蚀诱导时间。结果表明:当SO24-浓度为0.5%时,不锈钢的耐蚀性最差;当SO24-浓度低于1%时,不锈钢的耐蚀性较不存在SO24-时的耐蚀性差;当SO24-浓度高于1%时,不锈钢的耐蚀性较不存在SO24-时的耐蚀性好。在3.5%NaCl+0.5%Na2SO4溶液中,点蚀诱导时间是4s,在3.5%NaCl溶液中和3.5%NaCl+4%Na2SO4溶液中点蚀诱导时间分别是9s和94s。     

不锈钢在烟气脱硫系统中的腐蚀行为

火电厂烟气脱硫系统的设备腐蚀问题比较严重,选材较为关键.为此,选用304不锈钢和2205双相不锈钢,考察了其在烟气脱硫模拟介质(死亡绿液)中不同温度和不同浸泡时间的腐蚀行为.结果表明:304不锈钢在死亡绿液中随温度变化腐蚀性很敏感,易发生点蚀,不宜用作烟气脱硫装置及其零部件;2205双相不锈钢在烟气脱硫模拟介质中不同温度和时间范围内都有良好的耐蚀性,可用作烟气脱硫装置及其零部件的材料.     

A discussion on evaluation criteria for crevice corrosion of various stainless steels

In this study,crevice corrosion performances of a newly developed LDSS 2002 and three commercial stainless steels(AISI 304,AISI 316L and DSS 2205)were investigated and discussed.Crevice repassivation potential(ER,CREV),which was measured by the potentiodynamic-galvanostatic-potentiodynamic(PDGS-PD)test,was applicable to crevice corrosion evaluation of 304 and 316 L stainless steels.However,much lower(ER,CREV values were obtained for DSS 2205 and LDSS 2002.These abnormal(ER,CREV values for duplex stainless steels may be related to the selective attack of the less corrosion-resistant phase,the lower corrosion potential in the crevice-like solution,and more crevice corrosion sites in the PD-GS-PD test.A critical chloride concentration of crevice corrosion(CCCCREV)measurement was introduced for crevice corrosion evaluation of various stainless steels.The derived CCCCREVwas proved to be a valid criterion for crevice corrosion evaluation of both the austenitic and duplex stainless steels.An order of crevice corrosion resistance of AISI 304≈LDSS 2002相似文献   

Effects of electropulsing on inclusion size and corrosion-resistance of 304 stainless steel

Electropulsing has been imposed on molten AISI 304 stainless steel and its effects on the inclusion size and corrosion properties have been investigated. The average size of inclusions in electropulsing-treated samples was finer than that in untreated ones. A theoretical analysis shows that the mobility of solute atoms increases with electropulsing treatment. This promotes the nucleation of inclusions. Owing to a smaller inclusion size, the electrochemical experiments reveal that the pitting corrosion resistance of the electropulsing-treated stainless steel is significantly improved. The beneficial effects of electropulsing on the refinement of inclusions and the resistance to pitting corrosion increase with an increase in current density. Electropulsing treatment, therefore, provides a promising means to improve pitting corrosion resistance.     

热网换热站不锈钢换热板点蚀的临界条件

热网二级换热站一般采用板式换热器,在其使役过程中不锈钢换热板一旦出现腐蚀穿孔,不但影响一次水水质,而且干扰换热器稳定运行,甚至影响居民供热,因此阐明换热板发生点蚀的临界条件对于科学设定水质控制标准和防止点蚀发生具有重要意义。为此,通过材料化学分析、XRD、SEM及电化学测试等方法对这一问题进行研究。结果表明:在65℃条件下,304不锈钢点蚀的临界Cl;浓度为125 mg/L,316L不锈钢点蚀的临界Cl;浓度为230 mg/L;不锈钢表面一旦形成垢层,表面会发生局部酸化,此时不锈钢更容易发生点蚀;运行过程中为了防止不锈钢换热板点蚀,不仅要严格控制循环水中Cl;浓度,还应防止换热板表面结垢或附着腐蚀产物。     

Boiler Stack Economizer Tube Failure

A metallurgical evaluation was performed to investigate the failure of a type 304 stainless steel tube from a boiler stack economizer. The tube had three distinct degradation mechanisms: pitting corrosion, chloride stress corrosion cracking, and fatigue fracture. The primary failure mechanism for the tube was fatigue fracture, but the other mechanisms may have eventually caused a tube failure in the absence of fatigue. This paper details the visual, SEM/EDS, and metallographic examinations used to determine that these failure mechanisms were each present in the same tube.     

A review—Pitting corrosion initiation investigated by TEM

Passive metals have superior resistance to general corrosion but are susceptible to pitting attack in certain aggressive media, leading to material failure with pronounced adverse economic and safety consequences. Over the past decades, the mechanism of pitting corrosion has attracted corrosion community striving to study. However, the mechanism at the pitting initiation stage is still controversy, due to the difficulty encountered in obtaining precise experimental information with enough spatial resolution. Tracking the accurate sites where initial dissolution occurs as well as the propagation of the dissolution by means of multi-scale characterization is key to deciphering the link between microstructure and corrosion at the atomic scale and clarifying the pitting initiation mechanism. Here, we review our recent progresses in this issue by summarizing the results in three representative materials of 316F, and Super 304H stainless steel as well as 2024-Al alloy, using in situ ex-environmental TEM technique.