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).     

Electrochemical study of AISI 304 stainless steel during the exposure at the disinfectant solutions with fungal suspensions

The effect of fungal suspensions on the disinfectant solution (Actisept with sodium dichloroisocyanurate as active substance, which releases 140 ppm active chlorine) and the corrosion behavior of type AISI 304 stainless steel (SS) were evaluated through linear polarization. The work presents a study of biocide Actisept solution as reference solution and the mixed solutions: reference biocide Actisept solution with three fungal suspensions (10 vol%), Aspergillus niger, Candida mycoderma, and Saccharomyces cerevisiae. The fungal suspension has an important influence on the synergistic effect of the SS corrosion in the following order: Saccharomyces cerevisiae > Candida mycoderma > Aspergillus niger. The E_corr values from the mixed solutions decreased with immersion time of the samples. In the case of Aspergillus niger, the corrosion rate was lower than that of any other type of fungal suspension tested, because the arrangement in solutions, the size and composition of Aspergillus niger spores were more favorable to protect the spores of the chemical and the electrical stressing. The results showed that there is a synergistic effect between the active substances from the disinfectant, fungal suspensions and applied potential, thus this effect can be taken into consideration for the hygienic and safety food industry.     

Advances in the research of nitrogen containing stainless steels

The current status of nitrogen containing stainless steels at home and aboard has been introduced. The function and existing forms of nitrogen in the stainless steels, influence of nitrogen on mechanical properties and anti-corrosion properties as well as the application of nitrogen containing cast stainless steels were discussed in this paper. It is clear that nitrogen will be a potential and important alloying element in stainless steels. And Argon Oxygen Decarbonization (AOD) refining can provide an advanced manufacture process for nitrogen containing stainless steels with ultra-low- carbon and high cleanliness.     

固溶处理对含Gd不锈钢第二相与硬度的影响

研究了不同固溶处理温度对含Gd不锈钢第二相与硬度的影响。结果表明,含Gd不锈钢在1000～1150℃固溶处理30 min后,沿晶界析出的连续第二相只发生部分熔断,大量第二相弥散分布于基体中,由“灰色”相包裹着“亮白色”相,“灰色”相元素组成及含量相对稳定。在1000～1070℃保温30 min固溶处理后,“亮白色”相的Ni几乎完全溶解,Gd浓缩富集,尺寸缩小,“灰色”相长大缓慢,部分“灰色”相形貌变为短棒状。固溶温度升高至1150℃,“亮白色”相中Ni溶解的同时Gd发生扩散及微量溶解,大部分“亮白色”相消失,“灰色”相发生粗化、球化。固溶处理后合金硬度均低于固溶处理前,随着固溶温度的升高,合金硬度呈上升趋势。     

The chloride stress-corrosion cracking behavior of stainless steels under different test methods

Chloride-induced stress-corrosion cracking (SCC) is one of the failure modes of stainless steels. Highly alloyed austenitic stainless steels S32654, S31254, and N08028, and duplex grades S32750 and S31803 possess much improved resistance to SCC compared with S30400 and S31600 steels. With the development of a database, SSData, experimental data collected from calcium chloride tests, autoclave tests, and drop evaporation tests were evaluated. Stress-corrosion cracking data generated by autoclave tests agreed well with the practical service conditions and can be used to discriminate alloys for SCC resistance in sodium chloride solution. Drop evaporation test data can be used in situations where evaporation may occur and cyclic loading may be involved. The SCC resistance of alloys under each method increased with increasing molybdenum equivalent Mo + 0.25Cr + 0.1Ni. For a given alloy, the testing result depends on the stress state and environment; different test methods can give different ranking orders concerning SCC resistance. The performance of duplex stainless steels in a chloride-containing environment at higher temperatures was not as good as expected when dynamic loading was involved.     

Electrochemical corrosion behavior of 300M ultra high strength steel in chloride containing environment

The electrochemical corrosion behavior of 300M ultra high strength steel in chloride containing environment was investigated by potentiodynamic polarization technique, electrochemical impedance spectroscopy (EIS) and scanning electron microscopy (SEM). The results show that uniform corrosion occurs on 300M steel during the electrochemical measurements because no anodic passivation phenomenon is observed on polarization curves within the measurement range. The tests also show that 300M steel is highly susceptible to chloride containing solution, which is characterized by corrosion current density increasing with the addition of chlorides, and corrosion potential shifting towards positive direction and corrosion resistance decreasing, positively suggesting that chloride ions speed up the corrosion rate of 300M steel. Meanwhile corrosion products on the 300M steel surface formed during the salt spray test are too loose and porous to effectively slow down the corrosion rate. Additionally, a schematic structure of uniform corrosion mechanism can explain that 300M steel has better property of stress corrosion cracking (SCC) resistance than stainless steels.     

Electrochemical study of stainless steels used in an oil company by electrochemical impedance

Localized corrosion is a serious problem for stainless steel exposed in a chloride solution. In this context, the present work concerns the study of electrochemical behavior of 316 (A and B) and 430 (C and D) stainless steels, where A and C are laboratory steels, while steels B and D were taken from heat exchangers tubes (after 10 years of operation). This study has addressed three different aqueous environments: (1) monoethanolamine (MEA) 15%, (2) natural seawater (NSW), and (3) NaCl 3%, using the technique of potentiodynamic polarization curve complemented by electrochemical impedance spectroscopy (EIS). The obtained experimental electrochemical parameters (E_corr, J_corr, E_r, C_d, R_tc, and constant phase element) were used to compare the corrosion resistance of the tested steels. As a result, the nobility of these steels in NaCl 3% and in MEA 15% solutions is established in the following order: 316 (A) > 316 (B) > 430 (C) > 430 (D), where E_r moves increasingly toward the positive direction, indicating a good protection against corrosion. In addition, the results show that the effect of the electrolyte (aggression) is characterized by increased corrosion potential and a decrease in the passivity domain for all samples. The hierarchy of the nobility of steels A and C in these electrolytes can be determined as follows: MEA 15% > NSW > NaCl 3%.     

不锈钢中铁素体腐蚀方法对比分析

铁素体作为奥氏体、马氏体和双相不锈钢的一种相组织,其含量直接影响不锈钢的焊接性、耐蚀性、力学性能和加工性,在其测定时往往由于腐蚀问题导致结果误差偏大。从检测标准出发,通过列举国内外目前针对铁素体含量及分布状态的表征方法,采用化学和电解两类方法进行铁素体腐蚀,从溶液配比、腐蚀温度、腐蚀时间、溶液可重复使用性和腐蚀效果等方面进行对比分析。结果表明：采用氢氧化钠水溶液电解铁素体整体效果较好,呈现红褐色,同时可以通过其在该溶液电解腐蚀显现的特征颜色进行该相的识别。     

奥氏体不锈钢焊缝金属的电化学腐蚀性能

采用PASTAT30型恒电位仪测试了SUS 316奥氏体不锈钢钨极氩弧焊TIG,熔化极氩弧焊MIG和钨极氩弧焊加填丝TIG M焊缝金属的电化学腐蚀性能.结果表明,在质量分数9.8%H2SO4溶液中,母材及焊缝的抗电化学腐蚀能力由大到小的顺序为母材＞TIG M焊缝＞MIG焊缝＞TIG焊缝,在质量分数5.0%HCl溶液中为母材＞MIG焊缝＞TIG M焊缝＞TIG焊缝,由此可知TIG焊缝金属的抗腐蚀能力最弱.由Tafel曲线可知,SUS316奥氏体不锈钢在H2SO4溶液中的钝化区间较长,在HCl溶液中的钝化区间很短暂,所以不锈钢在盐酸溶液比硫酸溶液中抗腐蚀性能差.晶间腐蚀试验结果与9.8%H2SO4溶液中电化学腐蚀试验结果相同.     

双相不锈钢中α-相组织的两种显示方法探讨

采用GB/T 13305—2008《不锈钢中α-相面积含量金相测定》中的两种组织显示方法揭示出双相不锈钢的显微组织,并通过能谱分析对两种方法显示出的铁素体相和奥氏体相的化学成分进行了分析研究。结果表明,用NaOH或KOH水溶液电解侵蚀显示出的铁素体相和奥氏体相的显微组织是正确的,而用氯化铁盐酸乙醇水溶液所揭示出来的铁素体相和奥氏体相的显微组织是错误的,试验条件尚需进一步推敲。     

不锈钢表面含Cu功能梯度复合改性层的制备及抗菌性能

为提高奥氏体不锈钢(ASS)的耐磨性及赋予其抗菌性能,应用改进的活性屏离子渗氮(ASPN)技术,将纯铜冲孔板置于不锈钢冲孔板上面作为活性屏的顶盖,对316奥氏体不锈钢在低温下(430℃)进行表面渗氮处理,在其表面形成由含Cu抗菌沉积层和S相(氮在奥氏体中的过饱和固溶体γ_N)硬质支撑层组成的功能梯度复合改性层。用扫描电镜(SEM)及其所附能谱仪(EDS)、X射线衍射仪(XRD)表征复合改性层的组织形貌、成分及相结构。用显微硬度计和往复摩擦磨损试验机测试了基体和复合改性层的显微硬度和摩擦磨损性能,用金黄色葡萄球菌进行体外抗菌试验评价复合改性层的抗菌性能。结果表明,在偏压达到250 V后,形成了连续分布的硬质S相扩散层和含Cu沉积层组成的复合改性层。改性层表面最高硬度可达928 HV0.05,与Si₃N₄小球对磨时比磨损率较基体降低约57.76%,显著提高了不锈钢的耐磨性。抗菌试验表明,复合改性层与金黄色葡萄球菌接触24 h后,对金黄色葡萄球菌抗菌率提高到98.5%。改进的活性屏离子渗氮技术制备的功能梯度复合改性层可以有效提高...     

不锈钢薄板激光搭接焊残余应力测量方法对比研究

为了研究不锈钢车体非熔透激光搭接焊中的残余应力,采用2 mm+2 mm厚SUS 301L不锈钢板冷轧板进行了CO_2激光搭接焊试验,选择压痕应变法、全释放应变法和X射线衍射法测量接头中的残余应力。结果表明,压痕应变法测量的纵向峰值应力为237 MPa,横向为124 MPa,测量结果为1 mm2区域近表面的平均残余应力;全释放应变法测量得到的纵向、横向应力峰值分别为155 MPa和55 MPa,测量结果为5 mm×5 mm整个解剖试样的平均残余应力;X射线衍射法测量的纵向、横向应力峰值分别为344 MPa和163 MPa,测量结果为1~2 mm区域表层中的平均残余应力,且误差范围较大。     

退火对含钒铁素体不锈钢碳氮化物形成规律的影响

采用TEM及XRD技术对新型含钒铁素体不锈钢冷轧退火态下的碳氮化物进行了研究。结果显示,退火态下主要存在三类析出相：一类是z-phase相（包括不规则板状和短杆状）,含有分布不均匀的V,是CrVN的复杂氮化物,另一类是颗粒状的M23C6,第三类是细小的MX。随着退火温度的升高,析出相逐渐发生回溶,其平均尺寸减小,Z-phase相中的V含量由边缘向中心呈递减趋势,相应地使抗拉强度提高,塑性下降。     

不同侵蚀方法在双相不锈钢显微组织显示中的应用

采用草酸溶液电解、氢氧化钾溶液电解、热的碱性铁氰化钾溶液和王水侵蚀方法,研究了四种侵蚀方法对双相不锈钢SAF2906显微组织的侵蚀效果。结果表明,采用草酸溶液电解的方法可以显示双相不锈钢显微组织,但在光学显微镜下铁素体和奥氏体两相组织区分不明显;热的碱性铁氰化钾溶液或者氢氧化钾溶液电解两种侵蚀方法可以很好地区分铁素体和奥氏体两相组织和辨别诸如σ相等有害相的存在,利用金相图像软件可以进行两相比例的测定;王水侵蚀的方法具有同时显示奥氏体和铁素体两相晶界的侵蚀效果。     

An investigation on the effect of bleaching environment on pitting corrosion and transpassive dissolution of 316 stainless steel

Pitting corrosion and transpassive dissolution of 316 stainless steel in a solution containing five percent of commercial bleaching liquid was investigated by employing potentiodynamic polarization method and recording corrosion potential during immersion. Today commercial bleaching liquids are widely used as a cleaner additive. Therefore those house appliances made from stainless steels are in contact with aqueous solution containing bleaching liquid. This may cause severe localized corrosion and transpassive dissolution. In order to investigate the possibility of tranpassive dissolution of stainless steel by bleaching liquid, potentiodynamic polarization and recording the variation of corrosion potential of specimens were carried out in 0.2 M Na₂SO₄ solution containing 5%wt. commercial bleaching liquid. A 500 mV drop in transpassive potential and also instantaneously ennobled corrosion potential revealed the possibility of transpassive dissolution due to the oxidizing effect of the species such as free chlorine and its derivatives in bleaching liquid. Evaluation of the occurrence of localized corrosion at the presence of Cl^? and bleaching liquid was investigated by similar electrochemical experiments in 0.2 M Na₂SO₄ + 0.4 M NaCl containing 5%wt. bleaching solution. Initiation of stable pitting at potentials lower than the transpassive potential as well as a sharp increase of the corrosion potential in this environment demonstrates the possibility of pitting corrosion.     

Electrochemical characteristics of stainless steel using impressed current cathodic protection in seawater

Stainless steels such as STS 304, 316 and 630 are frequently used as shaft materials in small fiber reinforced polymer (FRP) fishing boats. If the shaft material is exposed to a severely corrosive environment such as seawater, it should be protected using appropriate methods. The impressed current cathodic protection was used to inhibit corrosion in shaft materials. In anodic polarization, passivity was remarkably more evident in STS 316 stainless steel than in STS 304 and STS 630. The pitting potentials of STS 304, 316, and 630 stainless steels were 0.30, 0.323, and 0.260 V, respectively. The concentration polarization due to oxygen reduction and activation polarization due to hydrogen generation were evident in the cathodic polarization trends of all three stainless steeds. STS 316 had the lowest current densities in all potential ranges, and STS 630 had the highest. Tafel analysis showed that STS 316 was the most noble in the three. In addition, the corrosion current density was the lowest for STS 316.     

铁路货车车体用TCS铁素体不锈钢焊接方法分析

TCS铁素体不锈钢采用奥氏体型焊材,实芯焊丝、药芯焊丝和电焊条方法,焊接接头力学性能可以满足使用要求.相比之下,实芯焊丝焊缝的夹杂物含量低,韧性较高,更适合TCS铁素体不锈钢的焊接.药芯焊丝和电焊条的焊接工艺性能稍好,但焊缝的韧性较低.