核电站不锈钢覆面焊接接头的点蚀行为及设计改进

采用电化学方法研究了Cl~-含量、温度、介质pH、SO_4~(2-)含量、含氧量对S30403、S32101和S32205不锈钢焊接接头在硼酸溶液中点蚀行为的影响。结果表明:S32205焊接接头对温度的影响更为敏感,对Cl~-和SO_4~(2-)不敏感,且存在临界温度区T_(b0)60℃、40℃T_(r0)60℃,在区间内点蚀电位E_b和再钝化电位E_r分别急剧降低;S32101和S30403焊接接头的E_b和E_r基本接近,对Cl~-更为敏感,对温度和SO_4~(2-)不敏感。介质中溶解氧浓度对S32205焊接接头的E_b和E_r的影响较大,但对S32101和S30403焊接接头的影响不明显;焊接接头的点蚀电位随温度变化的规律与基材的基本相同。     

核电厂水池覆面钢板在硼酸溶液中的腐蚀行为

采用晶间腐蚀试验,电化学试验及应力腐蚀试验等研究了核电厂水池覆面钢板S32205、S32101和S30403在硼酸溶液中的腐蚀行为。结果表明:三种材料在给定试验条件下的晶间腐蚀倾向很小;S32205不锈钢的缝隙腐蚀发生电位和保护电位最高,分别为0.64V和0.1V;S32101和S30403不锈钢的缝隙腐蚀发生电位基本接近,约为0.25V,S30403不锈钢的保护电位(0V)略高于S32101不锈钢(-0.1V)的;三种材料的耐缝隙腐蚀和应力腐蚀性能均为S32205不锈钢S32101不锈钢S30403不锈钢;三种材料经恒载荷应力腐蚀试验后均未发生断裂。     

含氯环境下温度对2205双相不锈钢点蚀行为的影响

采用化学浸泡实验研究了6%FeCl_3+1%HCl混合溶液中温度与浸泡时间对2205双相不锈钢点蚀行为的影响,并分析2205双相不锈钢在含Cl~-环境下点蚀机理。通过高分辨相机与激光共聚焦显微镜及X射线光电子能谱(XPS)观察并分析样品表面形貌及钝化膜成分,采用电化学手段及原子力显微镜分析模拟海水溶液中温度对2205不锈钢耐腐蚀性能的影响。结果表明:2205双相不锈钢的临界点蚀温度(CPT)在45℃左右,当温度低于45℃时,延长浸泡时间样品表面未出现明显点蚀;温度高于45℃时,随浸泡时间延长点蚀在样品表面随机萌生并长大扩展,55℃时点蚀坑尺寸达到500μm。随着温度的升高,样品钝化区间缩短,点蚀电位显著降低,由30℃时的0.74 V降低到60℃时的0.27 V。XPS结果显示,随温度增加,样品钝化膜稳定性增加,表现为金属稳定氧化物及氢氧化物的含量增加。样品阻抗值的大小随温度的升高不断减小,在30℃时样品阻抗值为5.066×10~5Ω·cm~2,温度升高到60℃阻抗值减小到1.814×10~5Ω·cm~2。随着温度的逐渐升高,2205不锈钢腐蚀速率增大,电化学阻抗值减小,钝化膜的保护能力下降,耐点蚀性能变差。     

环境因素对1.4539超级奥氏体不锈钢点蚀行为的影响

采用浸泡腐蚀试验和电化学试验研究了温度、载荷和Cl~-含量对1.4539不锈钢耐点蚀性能的影响。结果表明:介质温度低于50℃时,1.4539不锈钢具有良好的耐点蚀性能,介质温度超过50℃后,随着温度的升高,点蚀电位迅速降低;当载荷产生的拉应力高于0.54σ_s时,材料的钝化区消失,阳极曲线转变为活性溶解,且随着拉应力的增大,阳极电流密度迅速增大;在受Cl~-含量和拉伸载荷耦合作用的电化学体系中,当NaCl质量分数不超过5%,拉伸载荷可明显提高1.4539不锈钢的Cl~-腐蚀敏感性,NaCl质量分数不低于7%时,拉伸载荷对1.4539不锈钢的Cl~-腐蚀敏感性影响降低。     

H_2S/CO_2环境下两种镍基合金的腐蚀行为

应用电化学极化法和溶液浸泡法对两种耐蚀合金(G3和Incoloy 825)在50℃氯化铁溶液中的点蚀敏感性进行了研究;采用高温高压釜研究了在含H2S/CO2气体介质中材料的高温腐蚀性能以及试验温度的影响。利用能谱分析仪(EDS)、扫描电镜(SEM)等分析了腐蚀后试样表面的微观形貌及组成。结果表明,Incoloy 825合金极化曲线中阳极曲线部分很平缓,无钝化区出现,极化度较低,G3阳极区有钝化区,点蚀电位相对较高;G3耐点蚀性能优于Incoloy825,其点蚀临界温度高于50℃;随着温度升高,两种材料的腐蚀程度加剧,其中Incoloy 825在高温下出现点蚀现象。     

海水温度和浓缩度对316L不锈钢点蚀性能的影响

运用循环阳极极化曲线研究了不同温度和浓缩度的海水介质中316L不锈钢的点蚀行为.结果表明,在1~3倍浓缩度范围内,316L不锈钢的点蚀电位和再钝化电位均随着温度的升高而线性降低,但当浓缩度高于2倍、温度大于85℃时,点蚀电位变化较小;在25~95℃温度范围内,点蚀电位和再钝化电位与海水浓缩度的对数呈线性关系.浓缩度对316L不锈钢点蚀性能的影响比温度更小,并根据点缺陷理论分析了二者对点蚀的作用机制.     

乏燃料池用S32101/ER2209双相不锈钢焊接板的点蚀行为

采用化学浸泡试验和电化学试验,在三氯化铁和3.5%NaCl溶液、以及模拟乏燃料池的硼酸水溶液中,研究了核电站乏燃料池覆面用S32101/ER2209双相不锈钢焊接板的点蚀行为。结果表明:在各种测试环境中,焊接板不同区域耐点蚀性能的顺序为焊缝区母材区热影响区,焊缝金属的耐点蚀性能最优主要是由于其Cr、Mo、Ni含量较高,而热影响区的耐点蚀性能最差是因为显微组织不良;在30,40,60℃纯硼酸溶液的电化学试验中,即使在高电位下也未观测到焊接件有明显点蚀发生,名义点蚀电位高达1 000mV(SCE)以上,而添加200mg/L Cl~-后,点蚀倾向显著增加,且温度升高导致点蚀敏感性升高。符合技术规范的纯硼酸溶液是足够好的服役环境,但加入侵蚀性Cl~-后,焊接件的点蚀抗力大幅降低,因此乏燃料池在服役期间,应严格监控水质及控制水温以避免点蚀。     

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.     

微量Cl~-和温度对7150-T76铝合金电化学腐蚀性能的影响

利用开路电位、循环极化法和腐蚀形貌表征研究了微量Cl~-与温度对7150-T76超高强度铝合金电化学腐蚀性能的影响。结果表明:低温低Cl~-浓度的溶液中,铝合金主要发生点蚀;温度升高、Cl~-浓度增大,晶间腐蚀的倾向逐渐变大。微量Cl~-(20 mmol/L)致使开路电位(OCP)显著负移;温度升高OCP逐渐降低,且在60~70℃温度范围内发生突变,表明腐蚀机理发生变化。还分析了循环极化曲线的各个电位和电流密度参数随Cl~-浓度和温度的变化。点蚀转换电位Eptp的出现表明被侵蚀后的铝合金表面的钝化是分步进行的,Eptp随Cl~-浓度的增大逐渐负移。自腐蚀电流密度随温度的升高先增大再减小,而自腐蚀电位逐渐负移,均可归因于高温溶液中溶解氧减少的缘故。此外,也论证了自腐蚀电位和再钝化电位的差值ΔE3(Ecorr-Erep)作为评价局部腐蚀发展程度标准的局限性。     

试验条件对动电位极化曲线测量不锈钢点蚀电位的影响

基于国内外常用不锈钢点蚀电位的测试标准,采用动电位极化曲线测量法,研究了最终打磨后的停留时间、电位扫描速率和溶液预除氧时间等测试条件对304L奥氏体不锈钢和S32101双相不锈钢在3.5%NaCl溶液中自腐蚀电位(E_(corr))和点蚀电位的影响。结果表明:最终打磨后停留时间由0 h延长至24 h,两种钢的E_(corr)显著提高,点蚀电位也有所升高;电位扫描速率由10 mV/min提升至20 mV/min后,两种钢的点蚀电位变化不明显;溶液预除氧时间由0.5 h提升至1 h时,两种钢的E_(corr)降低、点蚀电位升高。     

Localized corrosion of (lean) duplex stainless steels in immersion units of urban wastewater treatment plants

With lower alloying cost and higher mechanical properties, lean duplex stainless steels can be an alternative to the more commonly used austenitic stainless steels. However, these alloys are still not the preferred choice, probably due to a lack of field experience. A study was thus initiated in view of defining the limits of use of selected (lean) duplexes for urban wastewater treatment units. The present paper shows the localized corrosion performance of selected lean duplexes in chloride contaminated solutions. The results are compared with austenitic S30403 and S31603 and with the more standard duplexes S82441 and S32205. The effect of welding was also investigated. Exposures in field municipal wastewater plants were conducted for 1 year in low and high chloride content units. The results show that lean duplexes S32101 and S32202 can be used as alternatives to S30403 and S31603 in low chloride electrolytes. At 500 ppm of chloride content, duplex stainless steel S32304 showed better corrosion resistance than S30403 and S31603. For higher chloride contents (1000 ppm and above) the standard duplexes S82441 and S32205 shall be preferred.     

Localized corrosion of lean duplex stainless steels in H2S-containing wet atmosphere from urban wastewater treatment units

With lower alloying costs and higher mechanical properties, lean duplex stainless steels can be a good alternative to the more commonly used austenitic stainless steels. A study was initiated to define the limits of the use of lean duplex stainless steels for urban wastewater treatment (WWT) units. This paper gives and discusses the corrosion results in an aerated wet atmosphere containing H₂S at different levels. Exposures were performed both at laboratory scale and in the field WWT plant for 1 year. A specific probe was also designed to study the corrosion process below water condensate film contaminated with H₂S. Under such conditions, the properties of stainless steel were strongly modified with an enhanced risk of localized corrosion. The results obtained on lean duplex materials (UNS S32101, S32202, and S32304) are compared with austenitic UNS S30403 and UNS S31603 and with the more standard duplexes UNS S82441 and UNS S32205. The results show that lean duplexes can be used in aerated wet atmospheres in case of moderate contamination of H₂S (<10 ppm) and chloride (<200 ppm). For higher contaminations (e.g., H₂S around 100 ppm/chloride around 1000 ppm) the duplex S32205 should be preferred.     

321不锈钢在淡化海水中的耐腐蚀性能

采用电化学测试和慢应变速率拉伸(SSRT)方法,结合扫描电镜(SEM)评价321不锈钢在淡化海水中的耐蚀性.循环伏安实验表明,随着温度的升高,点蚀击破电位负移,耐点蚀性能下降;321不锈钢在淡化海水中的临界点蚀温度(CPT)为30.5℃.SSRT实验结果表明,321不锈钢在淡化海水中具有一定的应力腐蚀开裂(SCC)敏感性,随着温度的升高,应力腐蚀敏感性增大.在35℃和50℃,321不锈钢在淡化海水中的断裂为韧性断裂;而在70℃,断口微观形貌呈现韧窝+少量准解理形貌,SCC敏感性增强.     

940X新型不锈钢的耐蚀性能

通过盐雾试验和点腐蚀电位测试,对比了新型940X不锈钢和9Cr18不锈钢的耐蚀性能.结果表明,在NaCl溶液中940X不锈钢的耐全面腐蚀和耐点腐蚀的性能比9Cr18的高.并结合化学成分及金相能谱分析了940X不锈钢的耐蚀机理.     

Lateral and radial corrosion propagation behavior of 9–21% Cr and 18% Cr + 2.8% Mo stainless steel reinforcing materials in simulated concrete environments

The life of a concrete structure exposed to deicing compounds or seawater is often been limited by chloride induced corrosion of the steel reinforcement. A complete assessment of the potential benefits afforded by new candidate rebar alloys must address both the lateral and radial corrosion propagation behavior in comparison to conventional steel as well as other factors that might affect the risk of corrosion‐induced concrete cracking. The radial (depth) and lateral (length) corrosion propagation behavior of 18% Cr + 2.8% Mo (S31653) stainless steel, 21% Cr (S32101) duplex stainless steel, and 9% Cr steel compared to plain ASTM A615 carbon steel were characterized in saturated Ca(OH)₂ solution. Radial pit growth was found to be Ohmically controlled for all materials but repassivation occurred more readily at high applied potentials for 18% Cr + 2.8% Mo and 21% Cr stainless steels. Conversely, pit growth on plain steel propagated at all applied anodic potentials and did not repassivate until deactivation by cathodic polarization. Stainless steel also showed the highest resistance to lateral corrosion propagation from an active site during microelectrode array testing. 21% Cr duplex stainless and 9% Cr steel showed similar radial propagation behavior and corrosion morphology, which was intermediate to that of plain steel and S31653 stainless steel. Based on an existing concrete cracking model, it is expected that 9–21% Cr and 18% Cr + 2.8% Mo corrosion resistant rebar materials would require a greater depth of corrosion attack than carbon steel before damaging concrete via corrosion product formation.     

含Cl^-溶液中SO4^2-对316不锈钢临界点蚀温度的影响

采用外加恒电位下腐蚀电流-温度扫描方法研究了在0．5％Cl^-溶液中，SO4^2-浓度对316不锈钢点腐蚀行为的影响．结果表明，随着SO4^2-浓度的增加，钝化电流增加，开路电位降低．当SO4^2-浓度低于0．42％时，316不锈钢的临界点蚀温度比不存在SO4^2-时的临界点蚀温度低；当SO4^2-浓度大于0．42％时，临界点蚀温度比不存在SO4^2-时的临界点蚀温度高．从离子竞争吸附的角度进行分析，对SO4^2-加速与抑制点蚀两种作用规律的形成原因进行了解释．     

Pitting transients analysis of stainless steels at the open circuit potential

Metastable pitting of stainless steels in chloride containing oxidising electrolytes is investigated at rest potential using a new experimental technique allowing to record simultaneously the potential and corrosion current variations. Different industrial surface conditions (BA and 2B) are tested for both ferritic (FeCr type) and austenitic (FeCrNi type) stainless steels. It was shown that the number of pitting events decreases with the exposure time and that BA condition provides better resistance to pitting than 2B. As far as pitting mechanisms are concerned, the potential recovery after pitting does not reflect the pit repassivation but rather refers to the discharge of the surface capacity. Analysing the pitting transients provides quantitative information on the cathodic reaction through the passive film (transfer resistance and surface capacitance). Differences in pitting transient shapes are discussed as well.     

Depassivation-repassivation behavior of type-312L stainless steel in NaCl solution investigated by the micro-indentation

Repassivation behavior of type-312L stainless steel containing 6% of molybdenum was examined in NaCl solution using in situ micro-indentation technique, together with type-304 and 316L stainless steels. High stability of the passive film formed on the type-312L stainless steel was also examined by depth profiling analysis of passive films using glow discharge optical emission spectroscopy (GDOES). In 0.9 mol dm⁻³ NaCl solution at 296 K the type-304 and 316L stainless steels are passive only up to 0.3 V (SHE), above which pitting corrosion occurs. In contrast, no pitting corrosion occurs on type-312L stainless steel. Despite the significant difference of the pitting corrosion resistance, the repassivation kinetics of the three stainless steels, examined by micro-indentation at 0.3 V (SHE), is similar. The presence of molybdenum in the stainless steel does not influence the repassivation kinetics. The charge required to repassivate the ruptured type-312L stainless steel surface increases approximately linearly with the potential, even though the passivity-maintaining current increased markedly at potentials close to the transpassive region. Repassivation occurs without accompanying significant dissolution of steel, regardless of the stability of passive state. Depth profiling analyses of the passive films on the type-312L stainless steels formed at several potentials revealed that molybdenum species enrich in the outer layer of the passive film, below which chromium-enriched layer is present. The permeation of chloride ions may be impeded by the outer layer containing molybdate, enhancing the resistance against the localized corrosion of the type-312L stainless steel.     

温度对904L不锈钢耐点蚀性能的影响

采用FeCl3溶液浸泡试验、动电位极化、电化学阻抗谱及体式显微镜研究了904L超级奥氏体不锈钢在不同温度下的点蚀行为。结果表明:溶液温度为25℃时,904L不锈钢具有优异的耐点蚀性能,随着溶液温度的升高,其耐点蚀性能下降,在65℃FeCl3溶液中基体表面产生严重的点蚀坑。在不同温度模拟海水溶液中的电化学测试结果同样表明:随着试验温度的提高,自腐蚀电流密度增大,点蚀电位下降,点蚀敏感性提高;EIS均为单一的容抗弧,温度升高,容抗弧半径减小,材料腐蚀速率增大,耐蚀性降低。