Influence of Inactivation Treatment of Ship's Ballast Water on Corrosion Resistance of Ship Steel Plate

The effect of seawater after ultraviolet inactivation on corrosion of a shipbuilding steel plate was investigated by means of natural corrosion potential experiments and immersion corrosion test. The effects of natural seawater and treated seawater after ultraviolet inactivation on corrosion of the selected steel plate samples were compared with each other. The results showed that there was no obvious change in the chemical composition of treated seawater compared with natural seawater. The corrosion potential slightly increased by 10 mV, whereas the corrosion rate rose significantly by 20%. The experiments verified the naturally formed biofilm in the natural seawater for the inhibition of corrosion on the shipbuilding steel plate. The possible influences of ballast water treatment on biofilm by ultraviolet and electrolysis inactivation under the condition of practical usage were also investigated. And it was found that ballast water treatment methods with no continuous disinfection could protect original tank biofilm structure, reducing the intensity of tank corrosion.     

The role of solution heat treatment on corrosion and mechanical behaviour of Mg–Zn biodegradable alloys

The mechanical properties and bio-corrosion behaviours of T4 solid solution heat-treated Mg–1.5Zn and Mg–9Zn alloys at 340°C under different heat treatment durations were investigated. In vitro corrosion behaviour of the heat-treated alloys immersed in simulated body fluid (SBF) were measured by electrochemical, hydrogen evolution and mass loss tests. Surface examination and analytical studies were carried out using optical and scanning electron microscopy, EDX, and X-ray diffractometry. The results show that the grains size of both the alloys apparently remained unchanged after T4 treatment. T4 treatment at 340°C for 6?h slightly increased the strength and elongation of Mg–1.5Zn alloy while it significantly improved the strength and elongation of the Mg–9Zn alloy because of the presence of residual Mg₅₁Zn₂₀ and Mg₁₂Zn₁₃ secondary phase at the grain boundary. The results of electrochemical tests show that the corrosion rate of both the alloys decrease with increasing treatment temperature. The result also shows corrosion resistance of both the T4 tread alloys much better than that of as-cast samples. The corrosion mechanism exhibited that the occurrence of galvanic and pitting corrosion, which varied with the alloy composition and treatment time.     

The corrosion behaviour of Cr/Co/Mo-alloyed low residual carbon steels in seawater solutions

The general corrosion behaviour of low residual steels alloyed with chromium or cobalt or molybdenum in seawater solutions was studied. The carbon content of low residual steels ranged from 0.1 to 0.4%, chromium content between 1.0 and 4.0%, cobalt content between 1.0 and 3.0%, and molybdenum content between 0.3 and 1.0%. Repeated laboratory tests demonstrated that low levels of chromium reduce the dissolution rate of low residual steels in seawater solutions. The results of this study suggest that cobalt alloying plays a neutral role, whereas molybdenum plays a major role in reducing the corrosion rates, particularly in higher carbon steels.     

Electrodeposition of cobalt–tungsten alloys from alkaline citrate containing bath as alternative for chromium hexavalent replacement

Abstract

Cobalt–tungsten alloys have been considered as potential materials for various applications. This work investigates the wear and corrosion resistance behaviour of cobalt–tungsten–phosphorus alloys electroplated from alkaline citrate containing baths. The wear rates of the cobalt–tungsten alloy electrodeposits were lower than those of the unalloyed cobalt electrodeposits. The wear rate was also lower than those of chromium plated from hexavalent chromium plating bath. It was also demonstrated that the addition of small quantities of phosphorus into Co–W alloys improved the corrosion resistance of the alloy. In fact, the addition of phosphorus further improved the corrosion of the alloy exposed to immersion test in comparison to cobalt–tungsten. The cobalt–tungsten alloys without having any phosphorus component were subjected to further oxidation of tungsten component followed by dissolution in deionised water during the immersion tests.

On a considéré des alliages de cobalt et tungstène comme matériaux potentiels pour diverses applications. Ce travail examine le comportement d’usure et de résistance à la corrosion d’alliages de cobalt, tungstène et phosphore déposés par électrolyse, à partir de bains alcalins contenant du citrate. Les taux d’usures des dépôts de l’alliage de cobalt et tungstène étaient plus faibles que ceux des dépôts non alliés de cobalt. Le taux d’usure était également plus faible que ceux de chrome déposés à partir d’un bain de dépôt électrolytique de chrome hexavalent. On a également démontré que l’addition de petites quantités de phosphore dans les alliages de Co–W améliorait la résistance à la corrosion de l’alliage. En fait, l’addition de phosphore améliorait davantage la corrosion de l’alliage exposé à un essai d’immersion par rapport à l’alliage au cobalt et tungstène. Les alliages de cobalt et tungstène, sans la composante de phosphore, étaient sujets à davantage d’oxydation de la composante de tungstène suivie par la dissolution dans de l’eau déionisée lors des essais d’immersion.     

Metallurgical characterisation of wrinkle bands and their influence on properties of galvanised steel sheet

Abstract

In addition to several well known defects in hot dip galvanised products, there are other defects that, although less frequent, damage the quality of the coated steel sheet. One of these, wrinkle bands, were microstructurally characterised, and their influence on corrosion behaviour of coated sheet was evaluated. Surface characteristics and microstructural features were examined by scanning electron microscopy, microanalysis and glow discharge optical spectroscopy. The results indicated that the major cause of wrinkle bands is related to craters that originated from cold rolling that act as a pool for molten zinc during galvanising. Corrosion resistance was examined via a salt spray test, and the time to red rust formation was up to 72 h shorter on wrinkle bands as compared to other regions.     

Comparative Evaluation of Low Nickel and Nickel Free Lean Duplex Stainless Steels with 316L in a Variety of Corrosive Media

For many applications duplex stainless steels with their superior strength coupled with lower raw material cost have emerged as an attractive alternative to austenitic stainless steels. With emphasis on conservation of scarce resources like nickel and molybdenum there is continuing endeavour to develop essentially molybdenum free lean duplex stainless steels with low nickel content such as 2304 (23Cr–4Ni), 2202 (22Cr–2Ni), 2101 (21Cr–1.5Ni). This paper compares the corrosion behaviour of a low nickel duplex (21Cr–1.5Ni) and a nickel free duplex (21Cr–1.5Cu) with 316L stainless steel in several corrosive media. All the three alloys exhibit similar excellent corrosion resistance under boiling conditions in less aggressive organic acids such as 20 % acetic acid, 25 % lactic acid, 25 % citric acid. However, in stronger organic acids such as 5 % formic acid, 5 % oxalic acid, and mixture of formic and acetic acid, the duplex grades exhibit superior corrosion resistance. This edge over 316L continues on addition of chloride ions in these acids. In boiling 50 % nitric acid solution, the corrosion resistance of these nickel free and low nickel duplex is slightly better than 316L grade. Since 304L grade is generally used in nitric acid plants, tests were also conducted on 304L and these duplex grades were found to be more resistant. Similarly in 50 % phosphoric acid also, the duplex grades exhibit superior corrosion resistance compared to 316L grade. Alloying with nickel and molybdenum is known to give rise to significant improvement in corrosion resistance in this acid. However, even in the absence of these elements, the beneficial effect of higher chromium content is evident. Of all the inorganic acids, sulfuric acid is used in largest volume in the industries. Boiling tests in dilute 1 and 5 % H₂SO₄ indicate that nickel free copper bearing duplex is more resistant than low nickel duplex grade and vastly superior to 316L Thus nickel-free and low-nickel duplex stainless steels offer a very attractive combination of high corrosion resistance coupled with cost effectiveness in a wide variety of corrosive media.     

Combined influence of fluorides and ferric ions on corrosion of titanium and Pd alloyed titanium in 100 g L−1 sulfuric acid solution

Abstract

In hydrometallurgical applications, titanium and its alloys are used as construction material in the most aggressive environments. Under acidic conditions, fluorides are known to be deleterious to titanium, but it is not well known how the presence of small amounts of both fluorides and ferric ions influences the corrosion behaviour of titanium in sulfuric acid solutions. Unalloyed titanium grade 2 (Ti Gr. 2) and palladium alloyed grades, titanium grade 17 (Ti Gr. 17) and titanium grade 7 (Ti Gr. 7), were investigated with electrochemical techniques and immersion tests in 100 g L^?1 sulfuric acid, containing 30 mg L^?1 fluorides and two levels of ferric ions, 0·3 and 3 g L^?1. It was found that the addition of fluorides accelerated the uniform corrosion rate, especially for the unalloyed Ti Gr. 2 in the solution having the lower amount of ferric ions. Palladium alloying was found to have a beneficial effect in reducing the uniform corrosion rate in the presence of small amounts of fluorides.     

Application of superalloys in petrochemical and marine sectors in India

Around the world, oil and gas development activities are increasing due to the growing demands for energy. Increasingly hostile environments involving deep offshore wells, higher pressure and temperature conditions, sour wells etc are encountered during exploration / development. This necessitates use of construction materials with high strength and resistance to corrosion in the severe conditions associated with production/refining. Superalloy grades such as 825, 625 and 718 have been deployed with success to meet these challenges. Technology to produce various millforms / critical components of superalloy grade 718 for aeronautical applications has been established in India. Work has also been carried out in the Country to develop superalloy grades 825 and 625 with no specific reference, however, to petrochemical applications. The high strength nickel-base superalloy grades 686 and 725 have proved to be excellent candidate materials for a variety of marine applications — fasteners, springs etc. The Ni-base superalloy grade C276, exhibiting excellent corrosion resistance to seawater especially under crevice corrosion conditions, is similar to superalloy grade 686. Superalloy grade C276 has been successfully produced in India in different millforms. The paper gives an overview of the development work done in India on superalloy grades 718, 625, 825 and C276 and prospects of using these materials in petrochemical and marine sectors in the country.     

Electrochemical Impedance Spectroscopy and Corrosion Behavior of Co/CeO2 Nanocomposite Coatings in Simulating Body Fluid Solution

A series of Co/CeO₂ (25 nm) nanocomposite coating materials by electrodeposition were successfully prepared containing different cerium oxide composition in the cobalt-plating bath. Stainless steel (304L) was used as support material for nanocomposite coatings. The nano-CeO₂ is uniformly incorporated into cobalt matrix, and the effect on surface morphologies was identified by scanning electron microscopy with energy-dispersive X-ray analysis. Codeposition of nano-CeO₂ particles with cobalt disturbs the regular surface morphology of the cobalt coatings. It should be noted that the as-prepared Co/CeO₂ nanocomposite coatings were found to be much superior in corrosion resistance over those of pure cobalt coatings materials based on a series of electrochemical impedance spectroscopy measurements in simulating body fluid solution. With increase in the nano-CeO₂ particles concentration in the cobalt electrolyte, it is observed that the corrosion resistance of Co/CeO₂ increases. Co/CeO₂ nanocomposite coatings have higher polarization resistance as compared with pure cobalt layers in simulating body fluid solution.     

Corrosion damage in WC–Co cemented carbides: residual strength assessment and 3D FIB-FESEM tomography characterisation

Abstract

The effect of corrosion damage on cemented carbides was investigated. The study included residual strength assessment and detailed fractographic inspection of corroded specimens as well as detailed 3D FIB-FESEM tomography characterisation. Experimental results point out a strong strength decrease associated with localised corrosion damage, i.e. corrosion pits acting as stress raisers, concentrated in the binder phase. These pits exhibit a variable and partial interconnectivity, as a function of depth from the surface, and are the result of heterogeneous dissolution of the metallic phase, specifically at the corrosion front. However, as corrosion advances the ratio between pit depth and thickness of damaged layer decreases. Thus, stress concentration effect ascribed to corrosion pits gets geometrically lessened, damage becomes effectively homogenised and relatively changes in residual strength as exposure time gets longer are found to be less pronounced.     

Iron–manganese: new class of metallic degradable biomaterials prepared by powder metallurgy

Abstract

An Fe–35 wt-%Mn alloy, aimed to be used as a metallic degradable biomaterial for stent applications, was prepared via a powder metallurgy route. The effects of processing conditions on the microstructure, mechanical properties, magnetic susceptibility and corrosion behaviour were investigated and the results were compared to those of the SS316L alloy, a gold standard for stent applications. The Fe35Mn alloy was found to be essentially austenitic with fine MnO particles aligned along the rolling direction. The alloy is ductile with a strength approaching that of wrought SS316L. It exhibits antiferromagnetic behaviour and its magnetic susceptibility is not altered by plastic deformation, providing an excellent MRI compatibility. Its corrosion rate was evaluated in a modified Hank's solution, and found superior to that of pure iron (slow in vivo degradation rate). In conclusion, the mechanical, magnetic and corrosion characteristics of the Fe35Mn alloy are considered suitable for further development of a new class of degradable metallic biomaterials.     

A REVIEW OF PARAMETERS INFLUENCING SOME MECHANICAL PROPERTIES OF TUNGSTEN CARBIDE–COBALT ALLOYS

Abstract

The paper reviews experimental results relating to the influence of composition, structure, and testing conditions on the hardness, compressive strength, and transverse rupture strength of sintered tungsten carbide–cobalt alloys.     

Surface and Coating Analysis of Press‐Hardened Hot‐Dip Galvanized Steel Sheet

The use of continuous galvanized steel sheet as feedstock material for press hardening leads to components of very high strength levels with classical cathodic corrosion protection. The present work provides an insight into this technology with special focus on surface oxidation and intermetallic phase formation during the austenisation process. For that reason hot dipped galvanized 22MnB5 steel sheets, with a blank thickness of 1.5 mm and an average coating weight of 70 g m^?2, were annealed in a temperature range of 400–900°C in steps of 50°C without soaking before quenching in water. Surface and cross‐cuts were analyzed by SEM, EDX, and XRD to illustrate the phase formation and the surface changes during thermal treatment. Corrosion behavior was also studied based on electrochemical investigations and an accelerated, cyclic, automotive corrosion tests called VDA, which is a mixture of salt spray test and alternating climate test. It was found that austenisation of galvanized steel sheet causes a significant change of the coating. The generated coating still offers cathodic protection for the steel substrate and has higher corrosion resistance than standard galvanized steel sheet. Surface oxidation also occurs during the press hardening process leading to a surface covered with successively arranged layers of Al₂O₃ and ZnO, containing also further oxidized alloying elements.     

流动和污染海水诱发并加速铜合金脱成分腐蚀的研究

分析了研究了4种铜合金在舟山、青岛、榆林各海水腐蚀试验站暴露4年以上的腐蚀数据,得到流动海水和污染海水对铜合金脱成分腐蚀的基本规律和机理,双相黄铜及硅青铜对流动海水的腐蚀最为敏感,从前者的脱成分腐蚀机理出发,提出了流动诱发和加速铜合金脱成分腐蚀的新概念。其关键在于,随着原始表现膜的腐蚀消耗,不能形成新的致密的耐冲击的腐蚀产物膜,使合金元素向表在贩扩散过程得不到抑制,从而使双相黄铜的脱成分腐蚀不断被诱发,被加速,其中尤以β相连续的双相铜被加速的趋势最为明显,表面腐蚀产物膜分析表明,这两类铜合 腐蚀产物膜具备致密和耐冲击腐蚀的特征,在污染海水的情况下,由于硫离子等的作用,同时不能形成致密的腐蚀产物膜,同样使双相黄铜的腐蚀被逐年加速,由于这种污染元素的作用在试样露出水面时依然存在,致使潮差暴露也出现类似情况。     

Effect of Zn addition on corrosion resistance of Cu-10Ni alloy in clean and sulphide contaminated seawater

Cu-10Ni alloy has an outstanding resistance to corrosion in seawater due to formation of protective Cu₂O film. However, in presence of S^2? ions, it suffers accelerated corrosion. The present paper investigates the corrosion behaviour of Cu-10Ni, Cu-10Ni-6Zn and Cu-10Ni-12Zn alloys using weight loss, electrochemical impedance spectroscopy and potentiodynamic polarisation technique. The experiments were performed in clean seawater and sulphide contaminated seawater. The Cu-10Ni-6Zn and Cu-10Ni-12Zn alloys were found to exhibit lower corrosion rate than Cu-10Ni alloy in clean and sulphide contaminated seawater. Lower corrosion rate of Zn containing alloys in clean seawater is attributed to the incorporation of Zn²⁺ ions in Cu₂O lattice. Lower corrosion rate of Zn containing alloys sulphide contaminated seawater is attributed to formation of ZnS in the film.     

Corrosion resistance of new copper alloy containing 29Zn, 10Ni and up to 5Mn vis-a-vis Cu-10Ni in sulphide polluted synthetic seawater

Cu-10 Ni alloy suffers from accelerated corrosion in sulphide-polluted seawater. New copper alloys containing 29% Zn, 10Ni and 3 or 5% Mn have been found to be more corrosion resistant than Cu-10Ni alloys in sulphide polluted synthetic seawater. The studies were carried out in synthetic seawater (ASTM D 114–75) and sulphide was added through Na₂S (1 gpl ≈ 41ppm S²⁻). Testing was carried out using cathodic and anodic potentiodynamic polarization methods. Corrosion product film formed on the Cu-29Zn-10Ni-5Mn alloy in sulphide polluted synthetic seawater was characterized using SEM and XRD. The film was found to contain Cu₂O, Cu₂S, NiS and ZnS. Better corrosion resistance of new alloys as compared to that of Cu-10Ni alloy is attributed to formation of ZnS, a bad conductor, in the film and incorporation of Mn³⁺ cations in Cu₂O and Cu₂S lattice.     

AN ELECTRON-MICROSCOPE AND X-RAY INVESTIGATION OF THE MILLING OF TUNGSTEN CARBIDE/COBALT MIXTURES

Abstract

It is well known that some interaction takes place between the two components when mixtures of cobalt and tungsten carbide are milled. To gain a further insight into this phenomenon, the milling process has been studied by means of the electron microscope and by the BET and X-ray methods.

During the milling of cobalt powder the number of stacking faults and the amount of the hexagonal phase both increase. On milling 80:20 tungsten carbide/cobalt mixtures increasing agglomeration of cobalt and fine tungsten carbide particles was found with rise in milling intensity. The larger tungsten carbide particles appeared to have a smooth surface. However, if the cobalt was dissolved in hydrochloric acid, the true surface of the tungsten carbide particles was revealed. This became rougher with increasing milling intensity. From this it can be concluded that, during milling, cobalt settles between the surface irregularities.

The variation in distribution of the cobalt that results from different milling conditions leads to a difference in sintering behaviour. A dilatometric study has been made of this aspect.

The original particle size of the cobalt used for hard-metal mixtures does not affect the properties of the sintered product, if the mixtures are milled very intensively.     

Corrosion resistance of high-strength austenitic chromium–nickel–manganese steel containing nitrogen

The corrosion resistance of high-strength Cr–Ni–Mn austenitic steel containing nitrogen and copper is compared with that of Cr18Ni9 and Cr18Ni10N chromonickel steel by means of the Zive MP2 electrochemical system. The polarization curves and electrochemical characteristics of the alloys are determined in general, pitting, and intercrystallite corrosion by various media: aqueous solutions of NaCl (3%); FeCl₃ 6H₂O (100 g/L); H₂SO₄ (0.5 M); H₂SO₄ (0.5 M) + injected H₂S; and H₂SO₄ (0.5 M) + KSCN (0.01 M). The corrosion rates are calculated. The results indicate that all the steel samples are corrosion-resistant: they exhibit high resistance to intercrystallite corrosion and also to pitting and general corrosion in chloride-bearing media. No pitting corrosion is observed when Cr–Ni–Mn steel of balanced composition containing nitrogen (and especially steel containing both nitrogen and copper) is immersed in sea water, even when the steel’s nickel content is low. This steel outperforms traditional Cr18Ni9 steel in terms of strength and corrosion resistance, even in an acidic medium (0.5 M H₂SO₄).     

DETERMINATION OF STATIC AND FATIGUE COMPRESSIVE STRENGTH OF HARD-METALS

Abstract

Procedures for the assessment of the very high static and fatigue compressive strength of hard-metals are briefly reviewed. A test-piece with enlarged ends has been developed. Using this, stress/strain curves and fatigue–strength data have been obtained on WC–Co hard-metals with various cobalt contents and carbide grain sizes. The results can be rationalized by being plotted against the mean free path in the binder metal.     

Corrosion of Refractory Alloys in Molten Lithium and Lithium Chloride

Abstract

Several refractory materials have been considered over the years as containment material for lithium and lithium halides. Surface modified refractory metals are being extensively investigated for containment of reactive metals, radionuclides and their compounds. An overview of experimental observations and results of liquid lithium corrosion of selected engineering refractory materials are presented. The nature of the degradation and its mechanism has been explained. The influence of temperature, microstructure, stress, impurities and service time on the corrosion behavior for various refractory alloys have been discussed. Selection rules for materials of containment for liquid lithium and lithium compounds have been suggested. Recent experimental observations on the behavior of tantalum and niobium-based refractory metal alloys in a specific molten salt environment comprising LiCl/Li₂O/Li/Li₃N at 725^°C have been included in an effort to select suitable materials for molten salt equipment. It has been observed that oxygen contamination is particularly harmful for the refractory metal alloys where as nitrogen is deleterious to iron-based alloys.