铸造双相不锈钢点腐蚀行为研究

采用化学浸泡腐蚀试验及微观组织和化学成分分析研究了5种铸造双相不锈钢在6%Fe Cl3溶液中的点腐蚀行为,并与316L奥氏体不锈钢进行了对比。结果表明,铸造双相不锈钢的抗点腐蚀性能均优于316L的,腐蚀速率和点腐蚀深度均小于316L奥氏体不锈钢的;双相不锈钢主要耐点蚀能力合金元素在奥氏体和铁素体相内分布不均匀,铬、钼更多地分配于铁素体相内,而镍、氮则更多地分配于奥氏体相内,铁素体相的耐点蚀指数PRE(Cr%+3.3Mo%+16N%)大于奥氏体相;双相不锈钢的耐点腐蚀性能与化学成分有关,随着PRE的增加,双相不锈钢的耐点腐蚀性能提高,铜元素在铁素体内析出的富铜相导致点蚀优先在铁素体内发生和发展。     

双相不锈钢的显微组织和性能

含有奥氏体和铁素体的双相不锈钢用于化学加工工业和要求高强度和耐蚀性的其他用途,其屈服强度大约比奥氏体不锈钢高1倍,抗点蚀和抗应力腐蚀裂纹的能力优于316型不锈钢。由于成分和双相结构的关系,其制造和使用不同于奥氏体不锈钢。除了铬和钼的含量高以外还含有铁素体、这会促进σ相的形成。双相不锈钢和铁素体不锈钢都容易产生“475℃脆化”,这是奥氏体钢不曾有过的现象。许多不锈钢种都可能形成碳化物和金属间相但不形成σ相。双相不锈钢的等温处理可以产生各种各样的微量成分。大多数退火状态的锻压双相不锈钢,其     

核电主管道不锈钢在高温高压水环境下的疲劳裂纹萌生行为

利用腐蚀疲劳测试系统研究了高温高压水环境下两种压水堆核电站一回路主管道用不锈钢的腐蚀疲劳裂纹萌生行为。结果表明,316LN奥氏体不锈钢的裂纹主要在材料表面的驻留滑移带处萌生,少量裂纹在两簇驻留滑移带交界的亚晶界面处。含有少量铁素体的Z3CN20.09M奥氏体不锈钢的疲劳裂纹依次在试样表面的驻留滑移带处、相界处和点蚀坑处萌生,但主要是在驻留滑移带处。通过研究高温高压水环境下氧化膜的组成和腐蚀疲劳试样横截面的形貌,分析了疲劳裂纹在滑移带处萌生的机理。最后对比分析两种不锈钢裂纹萌生机制的异同,并讨论了铁素体对材料腐蚀疲劳性能的影响。     

新型00Cr23Ni6Mo4Cu3铸造不锈钢的组织及其局部腐蚀行为

采用金相显微镜和ｘ射线衍射仪进行了金相组织观察与分析，并采用快速模拟试验方法研究了新型００Ｃｒ２３Ｎｉ６Ｍｏ４Ｃｕ３铸造不锈钢的局部腐蚀行为。结果表明，该钢经１０５０℃×２ｈ的固溶处理，其组织为铁素体基体上分布有适量的奥氏体。该热处理使组织细化与均匀化。由于铁素体对奥氏体组织有电化学保护作用，因而这种新型双相不锈钢具有优良的耐晶间腐蚀性能和较高的抗点蚀性能，与高合金化的奥氏体Ｃ１５钢相当。     

空气和腐蚀环境下双相不锈钢SAF2507的疲劳性能

对超级双相不锈钢SAF2507分别在空气和3.5%NaCl溶液中进行旋转弯曲疲劳实验,研究两种介质下SAF2507不锈钢的疲劳性能。结果表明:宏观上,双相不锈钢SAF2507在3.5%NaCl腐蚀环境中的疲劳强度较空气中的下降幅度小,为空气下的90%。但微观上,空气中疲劳断口表现为韧性断裂,在铁素体和奥氏体相上呈现大量疲劳辉纹;腐蚀环境下,奥氏体为韧性断裂,而铁素体呈现解理断裂模式。两相上疲劳辉纹的宽度和间距随着晶粒位向及二次裂纹的开裂而不同。在奥氏体-铁素体双相不锈钢的疲劳断口中,不能根据疲劳辉纹的间距进行相的鉴别。     

固溶处理对2205双相不锈钢耐蚀性能的影响

利用箱式电阻炉、金相显微镜、电化学工作站等设备研究固溶处理温度对2205不锈钢在不同介质中显微组织和耐蚀性的影响。结果表明,随着固溶温度升高,奥氏体含量不断减少,铁素体含量不断增多;在p H值不同的溶液中,双相不锈钢的耐蚀性能有一定差异:酸性溶液中,在1 050℃左右进行固溶处理,此时的双相不锈钢奥氏体与铁素体含量比接近1∶1,耐酸性能较好,而在碱性溶液中,1 100℃固溶处理时的腐蚀速度较小,耐蚀性能较好;1 100℃固溶处理的双相不锈钢在含氯离子的环境中虽无明显钝化区,但腐蚀速率较小,具有一定耐点蚀性能。     

含Ti铸造双相不锈钢点蚀行为研究

借助电化学极化曲线以及阻抗法研究了合金元素Ti的加入对铸造双相不锈钢点蚀行为的影响,通过扫描电子显微镜(SEM)、能谱分析(EDS)以及X射线衍射(XRD)研究了铸造双相不锈钢在发生点蚀前后微观形貌、元素分布以及析出相种类的变化并探讨点蚀的萌生机制。结果表明:双相不锈钢中,点蚀主要发生在奥氏体相以及相界处,产生点蚀的原因是奥氏体相中富Cr区的存在以及相界碳化物的析出。在双相不锈钢中加入少量合金元素Ti,可以提高双相不锈钢的耐点蚀能力。     

敏化处理对Z3CN20-09M不锈钢高温水应力腐蚀的影响

为了研究敏化处理对Z3CN20-09M不锈钢高温水应力腐蚀行为的影响,使用敏化处理的Z3CN20-09M不锈钢制成U弯试样,并置于250、290及320℃的高温水中进行应力腐蚀开裂实验,采用扫描电镜观察了高温水实验后试样的氧化膜厚度以及应力腐蚀裂纹的萌生及扩展行为.结果表明:敏化处理增加了氧化膜的厚度,降低了耐蚀能力,使SCC敏感性增大;温度较高时,敏化处理的影响较大;铁素体相容易被侵蚀,大多数点蚀坑产生于铁素体中;SCC裂纹优先在点蚀坑底部和奥氏体/铁素体相界位置处形成;相界面对SCC裂纹的影响取决于SCC裂纹相对于相界面的取向,SCC裂纹扩展方向平行于相界面时裂纹易沿着相界扩展,SCC裂纹扩展垂直于相界面方向时相界面对裂纹扩展起阻碍作用.     

脱硫泵叶轮用新型不锈钢组织与性能研究

研究了固溶状态下新型不锈钢SRTZ1材料显微组织、力学及耐腐蚀性能,试验结果表明:固溶状态下,STRZ1试验钢为典型的由铁素体α和奥氏体γ组成的双相不锈钢材料,具有优异的力学性能。在具备良好的耐点蚀、均匀腐蚀性能的前提下,试验钢的耐冲刷腐蚀及空泡腐蚀性能明显优于对比材料1.4470的。试验钢可代替双相不锈钢材料1.4470作为脱硫泵叶轮用材料,提高叶轮使用寿命。     

拉应力对2205双相不锈钢临界点蚀温度和点蚀行为的影响

采用外加恒电位方法研究拉应力对2205双相不锈钢临界点蚀温度(CPT)的影响,结合动电位极化、恒电位极化及电化学阻抗谱(EIS)等方法分析了不同应力典型温度下的电化学腐蚀特征。结果表明,尽管拉应力降低了2205双相不锈钢的CPT,但在140 MPa应力下即便在85℃时也没有发生点蚀。电化学分析表明,在CPT以下应力降低2205双相不锈钢击破电位(E_b),恒电位极化时试样表面仍处于钝化状态;在CPT以上会发生稳态点蚀。随温度升高,E_b明显降低。140 MPa应力下试样未发生点蚀的原因可能是,试样表面的微裂纹受应力作用,在极化过程中发生裂尖区裂纹扩展和再次钝化,腐蚀特征并不能表征其耐蚀性。     

Pitting corrosion of 2Cr13 stainless steel in deep-sea environment

Pitting corrosion of 2Cr13 stainless steel was investigated by deep-sea exposure test at various depths of 500 m,800 m and 1200 m in the South China Sea for 4 months.With the aid of electrochemical measurements in simulated deep-sea environments and grey relational analysis,the influence of deepsea environments on passive film and the mechanism of pitting corrosion were discussed.The results indicated that with the increase of sea depth,pitting depth of 2Cr13 stainless steel increased,which can be attributed to the change of chemical composition and the degradation of pitting resistance of passive film.Film growth was greatly retarded in the condition of low seawater temperature and low dissolved oxygen content of deep sea,resulting in an unstable and vulnerable film.Pitting depth was most influenced by hydrostatic pressure,which can increase the adsorption and penetration of Cl-ion,and promote the proliferation of point defects in passive film,leading to rapid deconstruction of protective oxides of the film.Pitting sensitivity of 2Cr13 stainless steel increased eventually with the combination of accelerated dissolution and suppressed self-healing of passive film in deep sea.     

Effect of aging on the corrosion resistance of 2101 lean duplex stainless steel

The microstructure and localized corrosion behavior of a 2101 lean duplex stainless steel aged at 700 °C were investigated. The results showed that changes in the microstructure of the duplex stainless steel, due to the formation of precipitates, affected its pitting corrosion resistance. The values of the pitting potential and the critical pitting temperature dropped drastically before aging time up to 30 min. The potentiostatic pitting corrosion measurement indicated more sensitive to the small amount of precipitates compared to the potentiodynamic test. Pitting nucleated mainly in the ferrite phase for the solution-annealed specimen, while the initiation of pitting corrosion for the aged specimen took place at Cr-depletion area around the precipitates, i.e. in the newly formed secondary austenite phase.     

Failure Analysis of AISI 321 Austenitic Stainless Steel Water Piping in a Power Plant

The objective of this work was to analyze a reported pitting damage mechanism in water piping of a power plant. The investigated material was a longitudinal-seam welded pipe which was made of AISI 321 austenitic stainless steel. Pitting occurred on the internal surfaces of the pipe and adjacent to the girth welds. Optical emission spectrometry, metallography, and electrochemical testing were the techniques employed to analyze the failure. The investigation showed that the flowing water contained chloride ions in which AISI 321 austenitic stainless steel is not immune against pitting corrosion. In addition, the polarization data showed the susceptibility of the material to pitting corrosion in the service conditions. Furthermore, the result of double loop electrochemical potentiokinetic reactivation tests showed that the material was sensitized during welding. It was found that the damage was due to pitting corrosion in chloride-containing water. Thus, it was recommended to replace the pipe with material having higher pitting resistance equivalent number to be more resistant against pitting corrosion.     

316L不锈钢表面纳米化后腐蚀性能研究

对表面纳米化和未经表面纳米化处理的316L不锈钢的样品分别进行点蚀实验和应力腐蚀对比实验,在3.5%(质量分数)NaCl水溶液中分别测出它们的极化曲线.结果表明,316L不锈钢表面纳米化后抗点蚀性能下降,抗应力腐蚀性能提高.对应力腐蚀断口的SEM 分析发现,316L不锈钢应力腐蚀断口有明显分区现象,断裂形式为韧性断裂,开裂通道既有穿晶型也有沿晶型.     

Evaluation of Pitting Behavior on Solution Treated Duplex Stainless Steel UNS S31803

The pitting corrosion resistance of duplex stainless steels UNS S31803 annealed at different temperatures ranging from 1050 ℃ to 1200 ℃ for 24 h has been investigated by means of potentiostatic critical pitting temperature(CPT).The microstructural evolution and pit morphologies of the specimens were studied through optical microscopy and scanning electron microscopy.The potentiostatic CPT measurements show that the CPT was elevated with the annealing temperature increased from 1050 ℃ to 1150 ℃ and decreased as the temperature further increased to 1200 ℃.The specimens annealed at 1150 ℃ exhibited the highest CPTand the best pitting corrosion resistance.The pit morphologies show that the pit initiation sites transfer from austenite phase to ferrite phase as the annealing temperature increases.The results were explained by the variation of pitting resistance equivalent number(PREN) of ferrite and austenite phases as the annealing temperature was varied.     

铁氧化菌作用下316L不锈钢点蚀电化学特性的研究

采用电化学测量、交流阻抗技术、扫描电镜观察和能谱分析等实验方法,研究了316L不锈钢在铁氧化菌(IOB)溶液中的腐蚀电化学行为,分析了炼油厂冷却水系统微生物腐蚀的特征及机制,结果表明,在含有IOB溶液中的自腐蚀电位(Ecorr)、点蚀电位(Epit)和极化电阻(Rp)均随浸泡时间的增加呈现出降-升-降的变化趋势;在含有IOB溶液中的腐蚀速率均大于在无菌溶液中;IOB的生长代谢活动及其生物膜的完整性和致密性影响了316L不锈钢表面的腐蚀过程,使不锈钢表面的钝化膜层腐蚀破坏程度增加,加速了316L不锈钢的点蚀.     

Interactions of different types of localized corrosion in surgical implants

Surgical implants often show different types of localized corrosion such as corrosion fatigue cracking, pitting and crevice corrosion on the same part. Interactions of these different corrosion phenomena were investigated. This was done by cyclic loading of electropolished tensile specimens at different constant and changing potentials. Material investigated was a surgical implant steel X2CrNiMo18-15-3 which was immersed in physiological NaCl solution. Pitting and repassivation potentials were determined. Samples with and without artificial cracks as well as masked specimens were tested. Incubation period for first damage, density and size of pits by coulometric and volumetric method were determined. The fracture surfaces were then investigated by SEM. Results show that not in all cases pitting corrosion was the cause for corrosion fatigue cracking. Also pitting is favoured by crack formation. Density of pits increases by a factor of 5 without any change to pitting potential. There are primary pits formed prior to crack initiation and secondary pits formed after crack initiation. At samples without crack there is almost no difference between the optically measured value of total pit volume and the coulometrically determined value. At samples with cracks coulometric volume of pits is much larger than optical one. This proves that there is a significant amount of crevice corrosion in the crack. The corrosion current density in the crack increases by two orders of magnitude when comparing it to electropolished surface of the sample. Results of laboratory experiments are confirmed by failure of a real implant.     

基于点蚀的316L不锈钢在酸性气田环境中的适应性评价

国内外酸性气田的开发使腐蚀环境越来越苛刻,为满足气液混输的工艺要求,发展了耐蚀合金/碳钢的双金属复合管技术。316L不锈钢被广泛用于双金属管的内衬,在含H_2S和CO_2环境中腐蚀速率很低,然而在高含Cl-的溶液中,316L不锈钢容易出现点蚀而诱发集输管线失效,为此,就316L不锈钢在酸性气田集输环境中的点蚀进行评述。讨论了影响316L不锈钢点蚀的材质因素,Mn和Fe的硫化物及Mg、Al、Ca的氧化物等两种夹杂物均能促进钝化膜的溶解而引起点蚀;分析了316L不锈钢点蚀的H_2S、CO_2、温度、Cl-浓度和pH值等环境的适应性条件,发现H_2S环境比CO_2环境更容易发生点蚀,H_2S和CO_2对点蚀发生存在协同机制,温度升高、Cl-浓度增加和酸性介质均会增加316L不锈钢点蚀的敏感性。为进一步优化选材原则,需重点加强环境因素的协同机制、环境适应性的边界条件、点蚀发展的动力学以及新的标准研究。     

Pitting initiation of 316L stainless steel in the media of sulfate-reducing and iron-oxidizing bacteria

Pitting corrosion behavior of stainless steel 316L in the presence of aerobic and anaerobic bacteria isolated from cooling water system in oil refinery was investigated using open circuit potential measurement, electrochemically impedance spectroscopy, scanning electron microscopy examinations, and energy dispersive spectrum analysis. The results show the corrosion potential (E _cor) and polarization resistance (R _p) decrease in the presence of sulfate-reducing bacteria (SRB), iron-oxidizing bacteria (IOB), and a combination of SRB and IOB, in comparison with those observed in the sterile medium for the same exposure time. The presence of SRB demonstrated higher corrosion rates than IOB. The combination of SRB and IOB created the highest corrosion rate. The metabolic activity of bacteria and the integrality and compactness of biofilm influenced the pitting corrosion process, increased the corrosion damage degree of the passive film, and accelerated the pitting corrosion. It is suggested that SRB and IOB in influencing the pitting corrosion of 316L SS is highlighted. The text was submitted by the authors in English.