低合金船体钢点蚀敏感性的研究

通过极化试验比较了4种含有不同合金元素的低合金钢的点蚀诱发敏感性，并用电子探针对钢中的主要夹杂物及点蚀诱发后的腐蚀形态作了鉴定。结果表明：镍—铬系钢比锰系钢具有更好的耐点蚀性能；点蚀总是从夹杂物与周围钢基体毗邻的界面处开始诱发；含有硫化物的复相夹杂对点蚀的敏感性更强。     

稀土处理对Mn-V-Ti钢点蚀性能影响的研究

实验室冶炼了5炉稀土处理及未处理的锰系低合金船体钢,并收集了一种工业生产的同种钢。通过冶金分析、极化试验、闭塞电池试验及挂片试验,研究了夹杂物变性对钢材点蚀诱发及扩展的影响;结果表明:钢中夹杂物是点蚀的诱发源,硫化物夹杂物的数量对钢材的点蚀性能有显著影响。稀土硫化物夹杂数量少,体积小,能显著降低钢的点蚀诱发敏感性,降低钢的蚀坑扩展速度,提高钢的耐蚀性。     

碳钢中夹杂物诱发点蚀的规律和特性研究

选用5种低碳钢，通过浸泡试验、显微腐蚀试验和极化试验，考察了碳钢在3％NaCl(质量分数，下同)溶液中夹杂物诱发点蚀的规律和特点．结果表明：样品刚浸入溶液时其最初电位高于点蚀电位，钢中一些夹杂物活化，先诱发点蚀；局部活化使钢样的电位迅速下降，当降至点蚀电位之下，未发生点蚀或未充分诱发点蚀的夹杂物受到保护，不再活化；在阳极极化试验中，当钢样的电位极化到点蚀电位或点蚀电位以上，钢中的夹杂物几乎都会活化而诱发点蚀．     

Si含量对Fe-Si合金耐海水腐蚀性能的影响

为了研究Si对低合金钢耐海水腐蚀性能的影响,采用真空电弧炉冶炼了不同Si含量的低合金钢,通过电化学试验及挂片试验研究了钢在海水中的均匀腐蚀特性,通过闭塞电池试验研究了钢在海水中的耐点蚀能力,并对腐蚀形貌及夹杂物进行了扫描电镜观察及能谱分析。结果表明:当Si含量小于0.9%时,其在海水中的均匀腐蚀速度随Si含量的增加而增加;当Si含量大于0.9%时,其在海水中的均匀腐蚀速度随Si含量的增加而减小;随Si含量增加,点蚀扩展速度减小,合金的耐点蚀能力增加;合金中的夹杂物对点蚀诱发有促进作用。     

脱氧对碳钢耐点蚀性能的影响

选择四种不同脱氧程度的碳钢,在pH=10的3%(质量分数)NaCl溶液中进行极化试验,比较钢的点蚀诱发敏感性;在人造海水中进行模拟闭塞腐蚀电池试验和室内挂片试验,评价钢的点蚀扩展速度.结果表明:沸腾钢A,B钢中的主要夹杂物为橄榄状硫化物和土豆状氧化锰夹杂,镇静钢C,D钢的主要夹杂物为条片状硫化物夹杂和硅酸盐夹杂.在相同条件下,沸腾钢比镇静钢表现出更弱的点蚀诱发敏感性和更小的点蚀扩展速度.同是镇静钢,过低的磷含量可显著促进蚀孔的扩展.     

一种低磁钢耐海水腐蚀性能的研究

45Mn17Al3低磁钢质优价廉,但在海水中使用腐蚀严重.通过对45Mn17Al3奥氏体低磁钢试样进行室内腐蚀挂片试验、电化学性能测试、显微腐蚀试验及冶金因素分析,初步探讨了该型钢在海水介质中发生腐蚀的微观机制.室内腐蚀挂片试验和电化学性能测试结果表明,低磁钢的耐蚀性比3C钢要差;显微腐蚀试验结果证明,钢中的夹杂会诱发点蚀;冶金因素分析结果显示,钢中存在大量的AlN夹杂物,而且其微观组织比3C钢的粗大.45Mn17Al3中高的Al含量和大量的AlN夹杂的存在对该型钢耐海水腐蚀性能有重要的影响.     

Ni-Cu-P钢耐点蚀性能的机理研究

选择Ni-Cu-P钢和碳钢各两种,在pH=10的3%(质量分数)NaCl溶液中进行极化实验,比较钢的点蚀诱发敏感性;在3%海盐水中进行间浸挂片实验,评价钢的点蚀扩展速率;利用扫描电镜(SEM)、电子探针(EPMA)、X射线衍射(XRD)分析钢中夹杂物、腐蚀形貌和锈层的特征。结果表明:Ni-Cu-P钢比碳钢表现出更弱的点蚀诱发敏感性和更小的点蚀扩展速率。较弱的脱氧可降低碳钢的耐点蚀性能,但对Ni-Cu-P钢不产生明显影响。锈层分析结果发现,Ni-Cu-P钢和碳钢内锈层的主要成分接近,但Ni-Cu-P钢的内锈层明显比碳钢致密。Ni-Cu-P钢中Ni和P能有效降低酸化蚀坑内钢基体的腐蚀速率;Cu则有助于致密锈层的形成。     

Cu对低合金钢耐海水腐蚀的影响

为研究Cu对低合金钢耐海水腐蚀性能的影响,选择含Cu低合金钢和碳钢各两种进行对比实验.利用室内间浸挂片、实海潮差区挂片和模拟闭塞腐蚀电池实验比较钢的耐全面腐蚀和点蚀能力;利用扫描电镜(SEM)、能谱分析(EDAX)、电子探针(EPMA)和X射线衍射(XRD)分析钢中夹杂物和锈层的特征.结果表明:Cu的添加不仅可提高钢的...     

X80管线钢在阴极极化条件下的点腐蚀行为

目前对于阴极极化条件下管线钢发生点蚀的特征和机理研究不多。采用光学显微镜、扫描电子显微镜(SEM)和阴极极化技术,研究了X80钢在3.5%Na Cl溶液中不同阴极极化电位下点腐蚀起始与特征。结果表明:阴极极化条件下,点腐蚀易在非金属夹杂物边缘处萌生并沿基体扩展。当阴极极化电位为-850 m V(vs CSE,下同)和-900 m V时,基体和夹杂物周围均发现有点蚀出现;-1 000 m V时,点蚀仅出现在非金属夹杂物周围;当极化电位提升到-1 200 m V时,试样表面未发现明显腐蚀。     

溶解氧对碳锰钢点蚀电位测定的影响

选择常用的碳素船体钢和锰系船体钢各一种,在除氧及不除氧的3%NaC l溶液中进行了极化试验,测定了钢的点蚀电位,并利用电子探针分析了腐蚀形貌。结果表明,钢样在除氧溶液中的阳极极化是典型的钝化-点蚀过程;在相同的电位区间,钢样在不除氧的溶液中的表观极化行为与前者截然不同,但是钢样自身的极化过程仍是钝化-点蚀过程,点蚀仍是由钢中的夹杂物诱发,所测点蚀电位值比溶液除氧条件下的结果更正;在有溶解氧条件下测得的点蚀电位同样可以比较不同钢之间的点蚀诱发敏感性,其结果更方便、准确。     

S2O2-3对DP980高强钢在NaCl水溶液中的点蚀行为的影响

钢是一种冷轧双相高强度结构钢,成本低且具备良好的强度和塑性,在海工领域有巨大的潜在应用价值,但其在苛刻海水环境下的耐腐蚀性能,尤其是耐点蚀等局部腐蚀的能力有待深入研究.本文采用动电位极化法对DP980高强钢在含S₂O₃^2-离子的NaCl水溶液中的点蚀行为进行了研究,结果发现：在纯硫代硫酸钠水溶液中,DP980高强钢不发生点蚀;在不同质量分数的NaCl水溶液中,DP980高强钢发生点蚀,且随着Cl^-离子浓度的增大,DP980高强钢试样的耐点蚀性能下降明显;向NaCl溶液中加入浓度为0.001、0.01、0.1、1 mol/L的Na₂S₂O₃时,DP980高强钢试样的点蚀敏感性降低,点蚀受到明显抑制;随着Na₂S₂O₃浓度的升高,DP980高强钢的腐蚀主要以均匀腐蚀的形式发生;当试样浸泡在不同质量分数(0.1%、1%、10%)NaCl的1 mol/L Na₂S₂O₃溶液后,对试样表面腐蚀产物及腐蚀形貌进行扫描电镜观察及能谱分析,显示试样均发生均匀腐蚀,腐蚀产物为铁的硫化物,且未发现明显的点蚀.     

含Ce2O3氧化物对改善双相不锈钢亚稳态点蚀的机理研究

利用扫描电镜、原子力显微镜、恒电位脉冲等研究了2205双相不锈钢在中性含Cl-环境下氧化物引起点蚀萌生的机理。实验发现MgO-Al_2O_3系夹杂物中MgO偏聚处以及MgO-Al_2O_3-CaO系夹杂物中CaO富集处会引起夹杂物处基体同周围基体接触电势差增加。此外,CaO富集处易使夹杂物表面出现显微缝隙并使基体裸露,产生亚稳态蚀坑。经Ce处理后发现夹杂物成分变为含Ce_2O_3·11Al_2O_3或Ce_2O_3·Al_2O_3为主的复合夹杂,夹杂物与基体接触电势差减小并且在含Ce_2O_3复合夹杂物处未发现点蚀萌生现象,最后阐述了非金属氧化物引起点蚀的机理以及Ce与氧化物反应的机制。     

Effects of phosphate on the chloride-induced corrosion behavior of reinforcing steel in mortars

The influence of phosphate as a corrosion inhibitor on the corrosion behavior of as-received and pre-rusted reinforcing steels in mortar specimens was investigated after 360 days exposure in 3.5% NaCl solution. This involved the use of electrochemical techniques for studying the steel surface reactions and microscopic observations of the steel–mortar interface. The electrochemical methods, including electrochemical impedance spectroscopy (EIS) and measurements of corrosion potential (E_corr) and linear polarization resistance (LPR), were employed to evaluate the corrosion tendency and general corrosion rate of steel. In addition, the pitting corrosion resistance of steel was also determined by cyclic polarization (CP) measurements. The results indicate that different from nitrite, which is generally accepted as an anodic inhibitor, phosphate may be a cathodic inhibitor according to its reduced corrosion rate and more negative E_corr at the same dosage as nitrite in mortar specimens. The study also reveals that the inhibiting efficiency of phosphate against general corrosion of both as-received and pre-rusted specimens is lower than 10%, which is inferior to nitrite in some respects. However, as indicated by cyclic polarization measurements, the presence of phosphate provides slightly higher pitting corrosion resistance in comparison to nitrite. Furthermore, it suggests that the corrosion inhibition mechanism of phosphate in mortars mainly depends on a dual effect occurring at the steel–mortar interface. Furthermore, it is confirmed that phosphate has little effect on the long-term mechanical properties of mortars.     

Potentiodynamic Polarization Behavior and Pitting Corrosion Analysis of 2101 Duplex and 301 Austenitic Stainless Steel in Sulfuric Acid Concentrations

The corrosion behavior of 2101 duplex and 301 austenitic stainless steel in the presence of sulfate (SO₄ ^2?) anion concentrations was investigated through polarization techniques, weight loss and optical microscopy analysis. The corrosion rates of the steels were comparable after 3M H₂SO₄. Results confirm that the duplex steel displayed a higher resistance to pitting corrosion than the austenitic steel. Experimental observation shows that its pitting potential depends on the concentration of the SO₄ ^2? ions in the acid solution due to adsorption of anions at the metal-film interface. The duplex steel underwent stable pitting at relatively higher potentials and significantly higher corrosion current than the austenitic steel. The duplex steel exhibited lower corrosion potential values thus less likely to polarize in the acid solution. Solution concentration had a limited influence on the polarization behavior of the austenitic steel and hence its reaction to SO₄ ^2? ion penetration from analysis of the pitting potentials and observation of its narrower polarization scans compared to the duplex steel which showed wide scatter over the potential domain with changes in concentration.     

Corrosion behavior of plasma sprayed ceramic and metallic coatings on carbon steel in simulated seawater

Al₂O₃, ZrO₂ and Ni60 coatings were produced on carbon steels by plasma spray. Ni60 was used as the bond coat in all the cases. The microstructure of these coatings was analyzed by scanning electron microscopy (SEM). The corrosion behavior of the plasma spray coated samples as well as uncoated samples was evaluated by open circuit potential (OCP) measurements, potentiodynamic polarization tests, and electrochemical impedance spectroscopy (EIS) in simulated seawater. The results showed that Ni60 coating protected carbon steels against the corrosion and plasma spraying ceramic powders on metallic coating improved the corrosion resistance of the coatings further. The corrosion resistance of the Al₂O₃ coating was superior to that of the ZrO₂ coating due to the relatively few defects in Al₂O₃ coating.     

Effect of mechanical milling on the corrosion behavior of Al–Zn/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> composite in NaCl solution

Ceramic particle reinforced aluminum metal matrix composites (MMCs) have resulted in potential use in aerospace and automobile industries. The composites have been processed by mechanical milling followed by traditional powder metallurgy route. The Al crystallite size is reduced to 27 nm after 60 h of milling. Results of the corrosion tests, evaluated using the potentiodynamic method in the NaCl solution, indicate that corrosion of the investigated composite materials depends on the weight fraction of the reinforcing particles. It has been found out, based on the determined anode polarization curves, that the investigated materials are susceptible to pitting corrosion. Moreover, experimental results suggest that the milled composite material Al–Zn/Al₂O_3p has higher corrosion resistance in the selected environment compared to unmilled composite Al–Zn/Al₂O_3p. Polarization curves show that the milling procedure improves the composite corrosion resistance in passive conditions. This is illustrated by the corrosion potential, which becomes nobler with milling.     

Effect of treating atmosphere in plasma post-oxidation of nitrocarburized AISI 5115 steel

In this study quenched and tempered AISI 5115 steel was plasma-nitrided and nitrocarburized at 550 °C for 5 h in atmospheres of 80% N₂ balanced with various amounts of CO₂ and H₂ gases. The amount of CO₂ varied from 0 to 10 vol%. The highest amount of ε phases was formed in the compound layer after treating in atmosphere containing 7 vol% CO₂. Optimized compound layer was post-oxidized for 1 h at 450 °C under O₂/H₂ volume ratios of 1/1 and 3/1 as well as 100% oxygen. The treated samples were characterized using metallographic techniques, XRD, SEM, roughness measurement and potentiodynamic methods. The results showed that the growth rate of the oxide layer increased with increasing O₂ in the oxidizing gas mixture. X-ray diffraction analysis of oxidized layers confirmed the formation of highest amount of magnetite at post-oxidation in an atmosphere with the O₂/H₂ volume ratio of 1/1. Electrochemical polarization tests proved the enhancement of corrosion resistance by plasma post-oxidation and the highest corrosion resistance obtained after oxidizing under an O₂/H₂ volume ratio of 1/1.     

Effect of carburization on electrochemical corrosion behaviours of TiAl alloy

Electrochemical corrosion behaviours of the untreated and the carburized of Ti-46.5Al (mol %) alloy were investigated. X-ray diffractometry (XRD) and scanning electron microscopy (SEM) were applied to characterize the carburized layer. Potentiodynamic polarization curve, electrochemical impedance spectroscopy (EIS) and SEM morphology of the corroded surface were used to evaluate corrosion resistance of both carburized and untreated TiAl alloy in 1 mol/L HCl. The outer layer of the carburized TiAl alloy is a continuous Ti₂AlC scale. Polarization curve and electrochemical impedance spectroscopy (EIS) of the carburized TiAl alloy present a nobler corrosion potential, a more positive pitting potential and a higher polarization resistance, respectively, compared with the untreated sample. After anodic corrosion or immersion corrosion, a deposited layer can be observed on the surface of the carburized titanium aluminide alloy. By contrast, pitting and crevasse corrosion occur on the surface of the untreated TiAl alloy after anodic corrosion and some corrosion products and slight corrosion appear on the surface of the untreated TiAl alloy after immersion corrosion.     

Laser surface hardening of AISI 420 stainless steel treated by pulsed Nd:YAG laser

The AISI 420 martensitic stainless steel was surface-hardened by a pulsed Nd:YAG laser. The influences of process parameters (laser pulse energy, duration time and travel speed) on the depth and hardness of laser treated area and its corrosion behavior were Investigated. In the optimum process parameters, maximum hardness (490 VHN) in the laser surface treated area was achieved. The pitting corrosion behavior was studied by potentiodynamic polarization technique in 3.5% NaCl solution at 25 °C. Metallographical and electrochemical corrosion studies illustrated beneficial effects of laser surface hardening by refining the microstructure and enhancing the pitting corrosion resistance of the martensitic stainless steel. The pitting corrosion resistance of laser surface treated samples in 3.5% NaCl solution depends on the overlap ratio clearly. The pitting potential (E_pp) decreased significantly by increasing the ratio of pulse overlapping.