HASTELLOY® Alloy C-22 –ein neuer und vielseitig anwendbarer Werkstoff für die chemische Industrie

HASTELLOY® alloy C-22–a new and versatile material for the chemical process industries HASTELLOY® alloy C-22 is designed based on a critical balance of chromium, molybdenum, and tungsten contents. Such a balance provides unique corrosion resistance in the Ni-Cr-Mo system to oxidizing acids, localized corrosion, and non-oxidizing acids. Alloy C-22 also possesses thermal stability equivalent to HASTELLOY alloy C-4 in high heat input welding procedures. Applications of HASTELLOY alloy C-22 demonstrate its ability to solve difficult plant corrosion problems in services where other high performance alloys have failed.     

Performance of Corrosion-Resistant Alloys in Concentrated Acids

Nickel alloys containing optimum amounts of chromium(Cr),molybdenum(Mo) and tungsten(W) are widely used in the chemical processing industries due to their tolerance to both oxidizing and reducing conditions.Unlike stainless steel(SS),Ni-Cr-Mo(W) alloys exhibit remarkably high uniform corrosion resistance in major concentrated acids,like hydrochloric acid(HCl) and sulfuric acid(H_2SO_4).A higher uniform corrosion resistance of Ni-Cr-Mo(W) alloys,compared to other alloys,in concentrated acids can be attributed to the formation of protective oxide film of Mo and W in reducing acids,and Cr oxide film in oxidizing solutions.The localized corrosion resistance of Ni-Cr-Mo(W) alloys,containing high amount Cr as well as Mo(or Mo + W),is also significantly higher than that of other commercially available alloys.The present study investigates the role of alloying elements,in nickel alloys,to uniform corrosion resistance in concentrated acids(HCl,HCl + oxidizing impurities and H2SO4) and localized corrosion performance in chloride-rich environments using ASTM G-48 test methodology.The corrosion tests were conducted on various alloys,and the results were analyzed using weight loss technique and electrochemical techniques,in conjunction with surface characterization tools.     

Influence of nickel additions on the corrosion behaviour of low nitrogen 22% Cr series duplex stainless steels

Four 22% Cr duplex stainless steel alloys containing varying nickel contents of approximately 5%, 7%, 9% and 13% were melted in a vacuum induction furnace, hot rolled, solution annealed and water quenched. Their corrosion behaviour was investigated in sulphuric acid and sodium chloride solutions using potentiodynamic polarization and chronoamperometric techniques. Increasing nickel contents have an appreciable influence on the observed corrosion behaviour. Polarization curves show similarities in the uniform corrosion behaviour of the alloys in the various solutions, but significant differences in their pitting resistance in chloride environments. Alloy 2209 (22% Cr - 9% Ni) generally exhibited the highest resistance to uniform corrosion, while alloy 2213 (22% Cr - 13% Ni) displayed the best pitting corrosion resistance. X-ray diffraction analysis of the surfaces of the alloys after corrosion in the different media revealed different corrosion products. Scanning electron micrographs revealed that the alloys were differently attacked by chloride ions, with different pit depths and morphologies. The corrosion behaviour exhibited by the alloys was attributed to the influence of nickel on phase modification, microstructural refinement, and the types of films formed in different environments. Uniform corrosion behaviour of the alloys was concluded to be predominantly controlled by phase composition and ratio, while pitting resistance was chiefly controlled by an alloy’s nickel contents.     

Corrosion resistance of nickel-chromium dental casting alloys

The corrosion resistance of twelve NiCr dental casting alloys has been assessed by registrating their potentiodynamic polarization curves, polarization resistance curves, and potential-time curves, in a de-aerated and aerated artificial saliva. It has been found that not only the presence of chromium is needed to reduce the electrochemical activity of such alloys, but also that of molybdenum and manganese. The tendency to passivation is enhanced by these two elements, along with the resistance to pitting in a chloride-containing electrolyte. Alloys with low Cr content and without Mo did always corrode in the tested conditions.     

An XPS study of anodic behavior of amorphous nickel-phosphorus alloys containing chromium,molybdenum or tungsten in 1 m CHl

The surfaces of amorphous Ni-18P, Ni-IOCr-20P, Ni-9Mo-19P and Ni-5W-18P alloys immersed or anodically polarized in 1 M HCl solution were analyzed in connection with their corrosion and anodic behavior. All alloys were more corrosion-resistant than crystalline nickel metal because of formation of phosphate-containing surface films on the Ni-18P, Ni-9Mo-19P and Ni-5W-18P alloys and because of spontaneous passivation due to formation of passive hydrated chromium oxyhydroxide film on the Ni-10Cr-20P alloy. The latter alloy was stable up to the transpassive region of chromium although intrusion of phosphate in the film was responsible for the higher passive current density in comparison to the amorphous Fe-Cr-13P-7C alloy of the same chromium content. The formation of thick porous phosphate films containing nickel, and molybdenum or tungsten by anodic polarization was not effective in passivating the Ni-18P, Ni-9Mo-19P and Ni-5W-18P alloys, and they suffered pitting corrosion by anodic polarization.     

Fe-Cr-Mo系铁素体不锈钢在氯化物介质中的实验电位-pH图研究

通过测定合金在含 1N Cl~-的不同 pH 值的水溶液中的阳极极化曲线,绘制了三个系列的12种铁素体不锈钢(17Cr-xMo,25Cr-xMo,30Cr-xMo,其中 x=0、2、4、6)的实验电位-pH 图。合金中的 Cr 含量对点蚀起始过程影响极为显著;Mo 含量对点蚀击穿电位的影响则与合金中 Cr 含量有密切关系。添加少量的 Mo 可使低电位、低 pH 值条件下的活化腐蚀区大大缩小,因而对局部腐蚀的发展过程起重要的阻滞作用;Cr 也有类似的影响,但远不及 Mo 的影响那么明显和意义重大。适量的 Cr 和 Mo 的综合作用可使合金具有抵抗局部腐蚀发生及发展的优良性能。     

Electrochemical behavior of Co-Cr and Ni-Cr dental cast alloys

The cast structures influencing the electrochemical corrosion behavior of Co-Cr and Ni-Cr dental alloys were studied using potentiodynamic polarization and AC impedance in 0.9% (mass fraction) NaCl solution at (37±1) °C. The phase and microstructure of the alloys that were fabricated using two different casting methods viz. centrifugal casting and high frequency induction casting, were examined using X-ray diffraction analysis, scanning electron microscopy and energy dispersive spectroscopy. The roles of alloying elements and the passive film homogeneity on the corrosion resistance of Co-Cr-Mo and Ni-Cr-Mo dental cast alloys were reviewed. The results of electrochemical study show that the dependence of corrosion resistance on the microstructure associated with the casting methods is marginal. The Co-Cr alloy exhibits more desirable corrosion resistance properties than the Ni-Cr alloy. There is severe preferential dissolution of Ni-rich, Cr and Mo depleted zones in the Ni-Cr alloy.     

On Limit of Molybdenum Content of Pitting-Corrosion-Resistant Austenitic Steels

The role of molybdenum in the pitting resistance of iron–chromium–nickel–molybdenum experimental alloys and their welds is investigated. The accelerated tests are performed in a 5% solution of FeCl₃. It is shown that alloying with molybdenum enhances the pitting resistance of an alloy only until of molybdenum the solubility limit of molybdenum in the matrix is reached; the limit in turn grows with the Ni content. Thus, to enhance the pitting resistance of an alloy corrosion, one should hold a balanced proportion between the contents of Mo and Ni in the alloy.     

掺杂镍对镁合金表面冷喷涂锌基涂层性能的影响

目的研究镍添加对冷喷涂锌基涂层耐蚀性的影响,为镁合金提供有效的防护涂层。方法采用低压冷喷涂技术在镁合金基体表面分别制备锌基和锌/镍基复合涂层,通过微观观察、摩擦磨损实验、电化学极化法和电化学阻抗谱测试及全浸泡腐蚀试验,研究镁合金表面冷喷涂涂层的结构、摩擦磨损行为和耐蚀性。结果镁合金表面冷喷涂锌基涂层后,其硬度和耐磨性得到显著提高,掺镍后的锌/镍基涂层具有更高的硬度和耐磨性。锌基和锌/镍基涂层均能为镁合金提供腐蚀防护,锌/镍基涂层比锌基涂层具有更好的耐蚀性。相对镁合金来说,锌基涂层和锌/镍基涂层的自腐蚀电位分别正移了260 mV和560 mV;长期腐蚀后锌/镍基涂层形成了更致密的腐蚀产物膜,腐蚀电阻显著高于锌基涂层。结论冷喷涂锌基和锌/镍复合涂层均能对镁合金提供防护作用,掺杂镍后的锌/镍基复合涂层具有更高的硬度、耐磨性和耐蚀性。     

Influence of the molybdenum content of high-alloy stainless steels and of the precipitation of intermetallic phases on pitting resistance in chloride-containing media

The influence of molybdenum on the resistance of stainless steels and nickel alloys (NiCrMoFe) to pitting corrosion is determined by means of electrochemical measurements (0.5 M NaCl/N2, 0…90°C) in both homogeneous and heterogeneous materials. As far as homogeneous materials are concerned, this influence is due to the inhibiting effect of molybdate formed at the interface passive layer/electrolyte and to a change in structure of the passive layer. The molybdate becomes effective as inhibitor of pitting corrosion only after the transpassive dissolution potential of molybdenum has been exceeded. Due to the precipitation of intermetallic phases, the pitting potential is shifted in cathodic direction. From a certain amount of precipitated intermetallic phases onward, the pitting potential remains constant. Consequently, the pitting potential is not dependent on the concentration of the alloying elements in the depleted matrix. Pitting corrosion preferably occurs at the phase boundaries intermetallic phase/depleted matrix and is due to lattice irregularities. Pit nucleation is observed at potentials at which the molybdate required for the inhibition of pitting corrosion has not yet been formed. Additions of molybdate to the electrolyte inhibit nucleation at the phase boundaries. Molybdenum segregates heavily in the weld microstructure of the afore-mentioned materials when compared with chromium. Pitting corrosion occurs at the dendrites that are poorer in molybdenum. A comparison of solution-annealed materials with different molybdenum contents shows that the molybdenum concentration of the dendrites imparts the same pitting resistance as is observed with solution-annealed materials with the same constant molybdenum content, respectively.     

Die Lochkorrosionsbegrenzung bei hochlegierten Sonderedelstählen und NiCrMo‐Legierungen in Chloridlösung – Einflußfaktoren und Ausmaß

Limit of pitting corrosion at high‐alloyed special steels and NiCrMo alloys in chloride solution The phenomenon of the limit of pitting corrosion in direction to positive potentials is studied by potentiokinetic polarization after a jump in the transpassive range and by potentiostatic tests at technical wrought materials and at model alloys of the systems NiCrMo and NiMo in CaCl₂ solution in the concentration range 1 to 9 mol/l chloride at pH‐values of 1 to 9 at temperatures of 30 to 110°C. Surface‐analytical investigations gives in connection with knowledges from anodic polarization studies directions to the mechanism of the limit of pitting corrosion. Ranges of the limit of pitting corrosion are obtained at materials with a Mo content above 6.5% and contents of chloride of the media above 2 mol/l chloride. Increasing temperatures, increasing contents of chloride and sulfate shift the potential of the limit of pitting corrosion being always above 0.2 V (SCE) at potentiostatic determination to noble direction. There are indications that the mechanisms of limit of pitting corrosion is resulting from an inactivation of pitting nuclei by the formation of hardly soluble molybdenum chlorides in the potential range of limit of pitting corrosion.     

The open-circuit ennoblement of alloy C-22 and other Ni-Cr-Mo alloys

The open-circuit corrosion and anodic oxidation behavior of the C-series of Ni-Cr-Mo alloys (C-4, C-276, C-2000, and C-22) and alloy 625 have been studied at 25°C and 75°C in 1.0 mol·L⁻¹ NaCl+1.0 mol·L⁻¹ H₂SO₄. A combination of open-circuit potential, potentiostatic polarization, and electrochemical impedance spectroscopy were employed in the study. The composition of the films formed was determined by x-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectrometry. Passive oxide film resistances increase and defect oxide film concentrations decrease as films thicken and chromium and molybdenum segregate to the alloy/oxide and oxide/solution interfaces, respectively. The high-chromium alloys exhibit higher film resistances and lower film defect concentrations consistent with the more positive potentials observed on these alloys. The results show that the observed ennoblement in corrosion potentials with time is coupled to the Cr/Mo segregation process and the suppression of defect injection at the alloy/oxide interface. By all measures, C-22 exhibited the best passive properties. For more information, contact D.W. Shoesmith, University of Western Ontario, Department of Chemistry, London, Canada, N6A 5B7; (519) 661-2111, ext. 86366; fax (519) 661-3022; e-mail dwshoesm@uwo.ca.     

Localised corrosion behaviour of alloys 33 and 24 in simulated flue gas desulphurisation environment

Abstract

Potentiodynamic anodic polarisation measurements have been carried out on type 316L stainless steel (as a reference material) and on alloys 33 and 24 in a simulated flue gas desulphurisation environment in order to assess the localised corrosion resistance. The results showed that the pitting corrosion resistance was higher in the case of alloys 33 and 24 than in the reference material owing to the higher contents of nitrogen, chromium, and molybdenum. An accelerated leaching study conducted on the alloys 33 and 24 showed only minor tendencies for the leaching of metal ions at various impressed potentials. Observations by SEM confirmed the lower tendency towards pitting of the alloys 33 and 24.     

Corrosion characteristics of the wrought Ni‐Cr‐Mo alloys

This paper concerns the wrought, nickel‐chromium‐molybdenum (Ni‐Cr‐Mo) alloys, a family of materials with a long history of use in the chemical process industries. Their attributes include resistance to the halogen acids and resistance to pitting, crevice attack, and stress corrosion cracking in hot, halide salt solutions. The purpose of this paper is to characterize the performance of the Ni‐Cr‐Mo alloys in several key chemicals, using iso‐corrosion diagrams. These indicate the expected corrosion rates over wide ranges of concentration and temperature. Furthermore, the differences between individual Ni‐Cr‐Mo alloys, and their behavior relative to the stainless steels are defined. The data indicate benefits of both a high chromium content and a copper addition, as used in Hastelloy® C‐2000® alloy.     

Hydrogen effects on the passive film formation and pitting susceptibility of nitrogen containing type 316L stainless steels

The effects of hydrogen on the passivity and pitting susceptibility of type 316L stainless steels have been investigated with alloys containing different nitrogen contents (0.015, 0.198 and 0.556 wt.% N). The study revealed that electrochemically pre-charged hydrogen significantly reduced the pitting resistance of alloys conatining 0.015 and 0.198 wt.% nitrogen contents. In alloy with highest nitrogen content (0.556 wt.% N), an increase in the passive film current density with hydrogen was observed without affecting breakdown potential. Auger electron spectroscopy (AES) analysis of the passive film indicated the presence of nitrogen in the passive film. On other hand, for hydrogen charged samples, nitrogen was found to be significantly less in the passive film. In Electrochemical impedance spectroscopy (EIS) measurement, the decrease in semi-circle radius of Nyquist plot, and the polarization resistance, R_P associated with the resistance of the passive film was observed with hydrogen, indicating that hydrogen decreased the stability of the passive film. The present investigation indicated that precharged hydrogen deteriorated the passive film stability and pitting corrosion resistance in these alloys, and the increase in nitrogen content of the alloy offsets the deleterious effect of precharged hydrogen.     

镍基合金电加热管腐蚀与防护

通过草酸浸蚀试验、动电位扫描测试、自腐蚀电位测试、电偶腐蚀试验和扫描电镜(SEM)观察,研究镍基合金Incoloy800、Incoloy840以及用它们制成的加热管在试验条件下的腐蚀情况;分析加工工艺对两种镍基合金腐蚀性能的影响;比较两种镍基合金加热管抗腐蚀性能的差异。结果表明,加工工艺显著降低了Incoloy840镍基合金的点蚀电位,对Incoloy800镍基合金的点蚀电位影响较小;对两种镍基合金晶间腐蚀敏感性几乎都没有影响;In-coloy800加热管试样晶间腐蚀敏感性小于Incoloy840加热管;Incoloy800加热管点蚀电位高于Incoloy840加热管;自腐蚀电位高低顺序为:Incoloy800加热管,Incoloy840加热管,Mg;Incoloy800加热管/镁电偶对电偶电流密度大于Incoloy840加热管/镁电偶对,Incoloy800加速电偶阳极镁腐蚀的作用更大。     

Einfluß von Chrom,Molybdän und Stickstoff auf die Korrosionsbeständigkeit des Ni-freien,austenitischen Edelstahles Macrofer 2515MoN (W.-Nr.: 1.4653)

Influence of chromium, molybdenum and nitrogen on the corrosion resistance of the Ni-free, austenitic stainless steel Macrofer 2515MoN (German Alloy No. 1.4653) Nitrogen alloyed, Ni-free, austenitic stainless steels comprising of more than 1 wt.-% nitrogen are a new group of alloys with promising properties. They show a very interesting combination of high strength and toughness with a high corrosion resistance. This combination of properties make the alloys not only suitable for fasteners but also for parts for medical and dental applications. This work shows the influence of chromium, molybdenum and nitrogen on the corrosion resistance of Fe25Mn-alloys in media typical for the above mentioned applications. According to these results Fe25Mn-alloys with appr. 20 wt.-% chromium, about 3 wt.-% molybdenum and appr. 1,3 wt.-% nitrogen have an excellent corrosion resistance in Ringer solution, artificial saliva and artificial sweat. The critical pitting temperature (CPT) as well as the critical crevice temperature (CCT) with 61°C respectively 37°C tested according ASTM G 48A provided significantly higher temperatures when compared to the commercially well established Ni-austenite X6CrNiMoTi17-12-2 (German Alloy No. 1.4571).     

非晶合金Zr55Al10Cu30Ni5在3.5%NaCl溶液中的电化学行为

利用电化学极化曲线方法和电化学阻抗（EIS）技术研究了非晶合金Zr55Al10Cu30Ni5在3.5%NaCl溶液中的电化学行为。极化曲线测试结果表明，非晶合金Zr55Al10Cu30Ni5在3.5%NaCl溶液中具有很好的耐蚀性能，阳极过程表现出钝化特征，当极化电位很高时，非晶合金出现了点腐蚀。电化学交流阻抗测试表明，在阴极极化，开路电位和钝化电位下，非晶合金的Nyquist图由单容抗构成，具有很高的电荷转移电阻，表现出优良的耐蚀性，在点蚀电位附近和点蚀电位区EIS分别有两个时间常数和三个时间常数，非晶合金在3.5%NaCl溶液中浸泡12h后，耐蚀性能有所下降。     

Effects of copper addition on the formation of inclusions and the resistance to pitting corrosion of high performance duplex stainless steels

To elucidate the effects of copper addition on the formation of inclusions and the resistance to pitting corrosion of alloys, potentiodynamic and potentiostatic polarization tests, a SEM-EDS analysis of inclusions, and thermodynamic calculations of the formation of inclusions were conducted. The addition of copper to the base alloy increased the number and area of numerous (Mn, Cr, (Al), (Fe)) oxides and oxy-sulfides due to an increase in the activity of chromium and resulted in decreased pitting resistance. The thermodynamic prediction of the formation of inclusions was in good agreement with the experimental results.     

Laser alloying of aluminium alloys with chromium

The microstructure and corrosion resistance of laser-alloyed aluminium and ANSI 7175 aluminium alloy with chromium were investigated. Surface layers alloyed with chromium contain relatively large amounts of intermetallic compounds dispersed in a matrix of -Al. The intermetallic compound particles present needle-like morphologies, organized in a dense network or distributed radially. Al₇Cr, Al₁₁Cr₂ and -Al phases have been identified by X-ray diffraction. The alloyed layers may contain cracks, pores, inclusions and undissolved chromium particles, depending on the chromium concentration and the particle size. However, homogeneous layers were produced by a two-step process, consisting of laser alloying followed by remelting. The second treatment eliminates porosity and refines the structure. The hardness attains a Vickers hardness of 155 HV in chromium-alloyed aluminium and exceeds 300 HV in chromium-alloyed 7175. The corrosion behaviour of the above alloys was assessed using anodic polarization techniques. Laser alloying of aluminium and 7175 with chromium improves the pitting corrosion resistance of the alloys. The effect depends on the chromium content of the alloyed layers and is more significant in 7175 alloy.