HDR双相不锈钢海水管路的腐蚀与预防

利用电化学方法,研究了HDR双相不锈钢在人工海水中的腐蚀特性。结果表明,HDR双相不锈钢的自腐蚀电位、点蚀电位较正,具有良好的耐腐蚀特性;与常用材料组成电偶对时,因HDR钢与碳钢、铸铁、黄铜等材料电位相差较大,会发生严重的电偶腐蚀。解决HDR不锈钢海水管路系统的腐蚀,关键是将HDR双相不锈钢与其它金属件之间进行有效的、完全的电绝缘隔离,才能防止电偶腐蚀。     

非金属夹杂物对439M铁素体不锈钢耐点蚀性能的影响

研究了非金属夹杂物对Ti单稳定化及Ti、Nb双稳定化的439M铁素体不锈钢耐点蚀性的影响。通过金相显微镜、扫描电镜及能谱分析得到Ti单稳定化的钢中的非金属夹杂物。除了Ti的碳氮化物外还含有较多的氧化物及复合型夹杂物。而Ti、Nb双稳定化的钢中主要为Ti和Nb的碳氮化物,而且多为复合型包裹生长。Ti和Nb稳定化元素的加入,起到了固定钢中间隙元素C、N的作用,Ti、Nb的复合添加能改善钢中夹杂物的质量。通过电化学测试系统对钢的耐点蚀性能的研究表明,Ti、Nb双稳定化的不锈钢的耐点蚀性能比Ti单稳定化的不锈钢好,Nb的加入能提高不锈钢的点蚀电位。结合扫描电镜及能谱分析可知,点蚀易于在富含Ca的复合型夹杂物与基体之间的界面处发生,由此可见,富含Ca夹杂物的点蚀诱发敏感性最强。     

深冷处理后回火温度对15Cr超级马氏体不锈钢组织及耐点蚀性能的影响

利用场发射扫描电镜、透射电镜以及电化学综合测试系统对15Cr超级马氏体不锈钢(SMSS)经不同热处理工艺处理后的显微组织变化和第二相碳化物及其对该钢腐蚀行为的影响进行了研究。结果表明,试验钢经不同热处理工艺处理后组织均由板条马氏体、奥氏体以及M₂₃C₆型碳化物颗粒组成,随着回火温度的增加,试验钢中逆变奥氏体含量增加,且在650 ℃回火时达到体积分数最大值41.41%。当回火温度高于600 ℃时第二相碳化物开始析出,且650 ℃回火后碳化物数量及尺寸较600 ℃增多。点蚀电位随着回火温度的增加而降低,第二相碳化物的析出降低了试验钢的点蚀电位,促进了亚稳点蚀位置的形成,从而降低了试验钢的耐腐蚀性能。     

含铜马氏体抗菌不锈钢的研究

在马氏体不锈钢中添加适量铜,经过固溶和时效处理,在不锈钢中弥散析出ε-Cu相,可赋予不锈钢优良的抗菌性能.用透射电镜观察了析出相的形貌分布,还用电子能谱分析了析出相的组成.抗菌检测结果表明,含铜马氏体不锈钢对大肠杆菌和金黄色葡萄球菌具有高效杀灭作用,而仅经过固溶处理的不锈钢则没有杀菌作用.耐蚀性测试结果表明,含铜不锈钢的耐点蚀性能下降,其原因在于钝化膜与ε-Cu相之间存在腐蚀电位而发生电偶腐蚀.     

高温高Cl-含量环境中H2S/CO2分压对超级双相不锈钢UNS S32750点蚀行为的影响

在高温、高Cl~-含量及不同H_2S/CO_2分压条件下对超级双相钢UNS S32750进行了腐蚀浸泡试验,并采用失重法、激光共聚焦显微镜、X-射线光电子能谱(XPS)分析了超级双相不锈钢UNS S32750的均匀腐蚀速率、点蚀形貌和表面钝化膜组成。结果表明:在试验条件下当H_2S/CO_2分压不大于30kPa/150kPa时,超级双相不锈钢UNS S32750具有良好的耐均匀腐蚀和点蚀性能;但当H_2S/CO_2分压为100kPa/500kPa时,H_2S造成了钝化膜的局部破坏,引发阳极性溶解,使超级双相不锈钢UNS S32750发生点蚀;钝化膜主要由FeS_2、NiO、NiS、Cr_2O_3及Fe(OH)_2组成。     

热处理工艺对2205双相不锈钢耐蚀性能的影响

对2205双相不锈钢采用不同温度进行热处理,然后用光学显微镜和电子扫描电镜观察其在0.33mol/L FeCl3+0.05 mol/L HCl溶液中腐蚀后的形貌;测试其显微硬度的变化、在沸腾的65%的硝酸溶液中浸蚀24 h的腐蚀速率和在25℃的3.5%NaCl溶液中的点蚀电位。研究表明:2205双相不锈钢在750~900℃保温4h有σ相析出,材料的显微硬度增大。同时随着热处理温度的升高,2205双相不锈钢的点蚀电位降低,腐蚀速率增大。     

含Ti铸造双相不锈钢组织与耐腐蚀性能研究

运用电化学实验测试含Ti铸造双相不锈钢的耐腐蚀性能,并与不含Ti铸造双相不锈钢进行对比;为了探究Ti的作用,对含Ti铸造双相不锈钢进行金相组织观察以及碳化物定量定性分析,并利用布氏硬度计测定硬度;采用扫描电镜(SEM)和能谱分析(EDS)对含Ti铸造双相不锈钢未腐蚀和腐蚀试样表面形貌观察。试验结果表明,含Ti铸造双相不锈钢中碳化物类型主要是Cr_(23)C_6和(Ti,Nb)C,Ti能减少铸造双相不锈钢中Cr_(23)C_6以及富Cr区形成,提高其耐腐蚀性能;含Ti铸造双相不锈钢中奥氏体为弱相,奥氏体中富Cr区附近以及铁素体和奥氏体相界处是含Ti铸造双相不锈钢腐蚀发生的主要区域。     

加氢装置脱H_2S汽提塔塔顶系统的腐蚀评价及选材

模拟脱H2S汽提塔塔顶系统现场工况,采用浸泡腐蚀挂片、恒电位阳极极化法、U型弯曲应力腐蚀等方法对20号钢、304L、321、316L及2205不锈钢在湿硫化氢环境中的均匀腐蚀、点蚀和应力腐蚀开裂敏感性进行了研究,并利用体视显微镜和SEM对金属试样的微观腐蚀形貌进行了观察。结果表明:20号钢耐蚀性较差,易在低温下发生氢鼓泡,奥氏体不锈钢304L、321、316L及双相不锈钢2205的腐蚀速率较小,耐蚀性好,其中304L和321不锈钢耐点蚀性能稍差,表面出现了轻微点蚀造成的蜂窝状的局部腐蚀;H2S的存在明显提高了奥氏体不锈钢在Cl-环境中的点蚀敏感性;304L、321及316L不锈钢焊接试样均具有较好的耐应力腐蚀开裂性能。     

00Ni18Co12Mo5Ti钢在酸性介质中的腐蚀行为

运用化学浸泡法和塔菲尔(Tafel)极化曲线外推法研究了00Ni18Co12Mo5Ti马氏体时效钢经硝酸和氢硫酸两种不同钝化处理后在Cl-介质中的腐蚀行为,对比分析了00Ni18Co12Mo5Ti钢与不锈钢和低合金钢在FeCl_3溶液中的腐蚀速率,并观察了腐蚀后的表面形貌。结果表明:00Ni18Co12Mo5Ti钢在两种不同钝化处理后的腐蚀速率稳定,硝酸钝化后其腐蚀速率是不锈钢的9倍,是低合金钢的40%;氢硫酸浸泡后其腐蚀速度稍低于不锈钢,是低合金钢的20%。扫描电镜结果显示,00Ni18Co12Mo5Ti钢的腐蚀类型为微观点蚀。     

2507双相不锈钢在含硫酸盐还原菌冷却水中的腐蚀

采用电化学测试、失重法、扫描电镜及能谱分析等方法研究了2507双相不锈钢在含体积比为0.5%、1%、2%硫酸盐还原菌(SRB)冷却水模拟溶液中浸泡30d后的腐蚀行为。结果表明:当浓度低于1%SRB时,钢表面生长缓慢,对于钢腐蚀影响相比于未添加SRB的基本没变化。而浓度达到2%SRB时,钢表面生长活动明显旺盛,对于钢的腐蚀倾向性显著增加,相比于不添加SRB的钢腐蚀速率增长了4倍多,钢表面多处生成斑状黑褐色腐蚀产物FeS。但2507双相不锈钢在含SRB冷却水中腐蚀程度均属于轻度腐蚀,且点蚀电位高达约1.2 V。     

Evaluation of the Fracture Toughness of a SMSS Subjected to Common Heat Treatment Cycles in an Aggressive Environment

Supermartensitic stainless steels (SMSS) are an alternative to corrosion-prone carbon steels and expensive duplex stainless steels in offshore tubing applications for the oil and gas industry. Due to their differentiated alloying, SMSS exhibit superior toughness, corrosion resistance, and weldability properties when compared with another viable option, conventional martensitic stainless steels. However, when cathodically protected in a seawater environment they can be susceptible to embrittlement due to hydrogen charging. In the present study, SMSS samples were removed from deep water pipelines and their fracture toughness in the as-received condition and with different heat treatments was evaluated. Tests were carried out in air and in harsh environmental and loading conditions, which were ensured by subjecting specimens to cathodic overprotection, simulating effects seen in structures with complex geometries, and to incremental step loads in a synthetic seawater environment, thus favoring hydrogen diffusion to the precrack tip. The fracture surfaces of the specimens were analyzed in order to identify hydrogen-induced embrittlement and fracture toughness values of specimens tested in air were compared to values obtained in environment-assisted experiments. The influence of microstructure was evaluated by control of the retained austenite and δ-ferrite contents of the specimens. The results show a significant drop in the fracture toughness of steel in the studied environment, with a fracture mode which is clearly more brittle and dependent on microstructural characteristics of the samples.     

超级马氏体不锈钢的等离子渗氮和氮碳共渗

超级马氏体不锈钢(SMSSs)是典型的新一代13%Cr马氏体钢,含碳量较低,并含镍和钼,故具有更好的可焊性和低温韧性。研究表明,不锈钢低温等离子渗氮或氮碳共渗可形成硬的表层从而提高耐磨性。本文对SMSS试样分别在400℃、450℃和500℃进行了等离子渗氮和氮碳共渗,并对处理后的SMSS试样分别采用光学显微镜、显微硬度、XRD和干磨损试验进行了表征。X射线衍射分析证明,氮化铬含量随着渗氮和氮碳共渗温度的升高而增加,也显示出铁和铬的碳化物含量随着处理温度的升高而增加。不同温度下处理后的试样均随着处理温度的升高,磨损体积减小、耐磨性提高。对经等离子处理和未处理的试样所观察到的主要磨损机制都是凿削磨损。     

Effect of nitrogen on microstructure and corrosion resistance of Cr15 super martensitic stainless steel

ABSTRACT

To investigate the influence of nitrogen on structure and corrosion resistance of Cr15 super martensitic stainless steels (SMSS), two types (N-free and N-0.12%) of specimens were quenched at 1050°C and tempered at different temperatures, and then, optical microscope, transmission electron microscopy, X-ray diffraction, potentiodynamic polarisation, immersion experiments and Kelvin Probe Force Microscope were used to characterize its microstructures and corrosion properties. The experimental results show that the microstructure in the N-free Cr15 super martensitic stainless steel is a biphasic tissue with alternating martensite and austenite distribution while quenched at 1050°C and tempered between 600 and 700°C. The nitrogen addition increases the content of austenite, and changes the austenite morphology significantly into the coarse block and strip distribution. What’s more, micro-galvanic corrosion is formed between austenite and martensite, which deteriorates the corrosion resistance of the SMSS.     

Development of delta ferrite on the weld and HAZ produced by pulsed plasma arc welding on a supermartensitic stainless steel

Delta ferrite is considered an undesirable phase in the microstructure of martensitic stainless steels, given its power to influence the performance of fatigue strength, toughness and corrosion under stress. This study aimed to investigate the effect of pulsed plasma welding on the distribution and amount of delta ferrite on a supermartensitic stainless steel (SMSS). Weld beads were obtained by surface melting on a sample of SMSS alloy using conventional and pulsed current. Then, the microstructural characterization was performed, in particular of the delta ferrite via metallographic analyses by optical and scanning electron microscopy. The experiments showed that for the same heat input, the pulse current promoted the formation of delta ferrite in the form of bands along the weld bead and a significant reduction of this phase in the heat-affected zone compared to conventional welding.     

Plasma nitriding and nitrocarburising of a supermartensitic stainless steel

Abstract

Supermartensitic stainless steels (SMSSs) are a new generation of the classic 13%Cr martensitic steels, lower in carbon and with additional alloying of nickel and molybdenum offering better weldabilty and low temperature toughness. Several works have shown that plasma nitriding and nitrocarburising of stainless steels at low temperatures produces a hard surface layer which results in increased wear resistance. In this work, SMSS samples were plasma nitrided and nitrocarburised at 400, 450 and 500°C. The plasma treated SMSS samples were characterised by means of optical microscopy, microhardness, X-ray diffraction and dry wear tests. The thickness of the layers produced increases as temperature is raised, for both plasma nitriding and nitrocarburising. X-ray diffraction demonstrates that the chromium nitride content grows with temperature for nitriding and nitrocarburising, which also showed increasing content of iron and chromium carbides with temperature. After plasma treating, it was found that the wear volume decreases for all temperatures and the wear resistance increased as the treatment temperature was raised. The main wear mechanism observed for both treated and untreated samples was grooving abrasion.     

Chloride-induced stress corrosion cracking of Duplex stainless steels. Models,test methods and experience

Stress corrosion cracking (SCC) induced by chlorides frequently causes problems in applications where standard austenitic stainless steels are being used. Often this problem can be solved by the use of duplex stainless steels. In this report the mechanisms for SCC have been surveyed, and the cause for the high SCC resistance of duplex stainless steels has been discussed and evaluation of test methods for SCC and how duplex stainless steels respond to them, as well as practical experience of duplex stainless steels. The study shows that no single mechanism can be attributed to the good resistance to SCC of duplex stainless steels. Probably a synergistic effect of electrochemical and/or mechanical effects is responsible for the good performance. Test methods for SCC often give relatively good correspondence with real applications, but ranking is often doubtful, and comparisons of different material types should be made with caution. Numerous cases with SCC on standard austenitic stainless steels have been solved by the use of duplex stainless steels.     

Influence of tempering treatment on microstructure and pitting corrosion resistance of a new super ferritic–martensitic–austenitic stainless steels with 17%Cr

Supermartensitic stainless steels (SMSSs) allow high mechanical strength with better corrosion resistance and toughness than conventional martensitic stainless steels. The SMSS steels with 12–13%Cr have been studied and applied in the oil and gas offshore production. The increase of Cr content, and the addition of Mo and W is now being investigated to increase mechanical and pitting corrosion resistance. In this work, a new 17%Cr steel, with Mo and W additions was studied. Depending on the final tempering treatment, the steel has a complex microstructure of austenite, ferrite, martensite and precipitates. The pitting corrosion resistance also depends on the microstructure produced by tempering. It was found that the pitting potential slightly decreases with the increase of tempering temperature and is further decreased by the double-tempering treatment. The pits initiate and grow preferentially in the martensite or tempered martensite islands, due to the lower Cr, Mo and W contents of these areas.     

热处理对超级马氏体不锈钢腐蚀性能的影响

对两种(含W、Cu,不含W、Cu)超级马氏体不锈钢(SMSS)进行1050℃保温0.5 h后淬火及不同温度(550℃、650℃、750℃)保温2 h的回火处理,在饱和CO2浓度下,Cl-浓度为2.12%的NaCl溶液中采用电化学方法研究其耐蚀性能。循环极化曲线分析结果证实,回火温度对耐腐蚀性能有重要影响,并且550℃时耐腐蚀性能最好;含W、Cu的SMSS具有较高的点蚀电位。交流阻抗分析表明,回火温度为550℃的样品具有最高的阻抗值,形成的钝化膜最稳定。     

Corrosion behavior of shape memory stainless steel in acid media

The corrosion behavior of three Fe-Mn-Si-Cr-Ni-(Co) shape memory stainless steels (SMSS) in 0.5 M H₂SO₄ solution was studied through electrochemical and immersion tests. The test results were compared with that of a type 304 (SS 304) austenitic stainless steel. The three SMSSs exhibited a passive behavior in 0.5 M H₂SO₄ solution; however, their anodic behavior in the active dissolution region was markedly different. The passive current densities of the SMSSs were similar to that of SS 304, although the critical anodic current required for passivation was higher. The corrosion rate of the SMSSs was much higher than that of SS 304. It was observed that the amount of Cr and Mn plays an important role in the corrosion behavior of SMSSs. The best corrosion behavior in acid media was shown by the SMSS that contained the highest amount of Cr and the lowest amount of Mn.     

节镍型双相不锈钢的研究进展

高氮低镍双相不锈钢具有较高的强度和优良的耐局部腐蚀性能。同时,以低成本的锰、氮代替昂贵的镍可以大大降低生产成本。分析了锰、氮代镍的一些冶金学问题,并对目前国内外节镍型双相不锈钢的研究进展作了大致的介绍。