Der Einfluß eines Magnetfeldes auf Korrosionsprozesse

Magnetic field effect on corrosion processes The corrosion products of low carbon steel at static conditions were studied by means of Mössbauer spectroscopy. The corrosion media are sea water and model solution in the presence or absence of an external magnetic field. The magnetic field acts on the dispersity of the appearing phases and increases the paramagnetic components in the rust. The corrosion media and the orientation of the coupons have been of importance for the corrosion processes.     

Einfluß sulfatreduzierender Bakterien auf den kathodischen Korrosionsschutz

Influence of sulfate-reducing bacteria on cathodic protection Sulfate-reducing bacteria (SRB) are frequently encountered at coating defects of cathodically protected pipes buried in soil. In laboratory experiments the corrosion behaviour of steel St 37 was studied at potentials in the range of ?0.5 V > U_Cu/CuSo4 > ?1.27 V and at the open circuit potential in the presence of a mixed culture containing SRB. For simulation of real conditions the experiments were performed on steel samples in sand columns through which a glucose-containing mineral salts solution was continuously pumped. On the basis of the corrosion rates determined an immediate corrosion risk was not evident for a homogeneous mixed electrode even at the open circuit potential. There was only an increase in protective current demand compared to sterile conditions. Hydrogen permeation through the low-alloy steel was slightly higher in the presence of SRB-containing mixed cultures than under sterile and H₂S-free conditions. The observed permeation current densities indicated that at potentials of U_Cu/CuSo4 < ?0.85 V hydrogen-induced corrosion damage was not to be expected under sulfate-reducing conditions.     

Einfluß der Luftfeuchtigkeit auf den Gleitverschleiß metallischer Werkstoffe

Influence of atmospheric moisture on gliding wear of metallic materials A study on gliding wear has been undertaken using a Siebel-Kehl machine and – without lubrication – iron and steels (couples of identical materials), brass (Ms 58) and cast bronze (G Sn Bz 10), coupled with steel C 45, in air of different humidities and water vapour concentrations, and under vacuum. With these conditions, tribochemical reactions and the metal oxide layers formed thereby in the gliding surface, as well as their adhesion, play a vital part. In the range of severe wear the wear-preventing oxide formation is enhanced by dry air, while it does not come to bear generally in moist air, although there may be a transition to an oxidic mechanism even there. Experiments made in water vapour atmosphere and under vacuum have confirmed this fact. The effect of the formation of oxide and protective layers is considerable in the case of the ferrous metals, in particular soft iron, quite in contrast to the conditions prevailing with bronze and brass. The influence of the humidity of the act in the mild wear range is inverse to that in the severe wear range. The action of water vapour on the boundary faces is greatly exeeded by the influence of the tribochemical reactions, at least with the ferrous materials.     

Der Einfluß der Metallstruktur auf das Passivierungsverhalten von Nickel

The Influence of Metal Structure on the Passivation Behaviour of Nickel The results of potentiostatic anodic polarisation of deformed and undeformed nickel single crystals in 0.5 m NiSO₄ Ph 3.5 are described. With rising plastic deformation the passivation potentials become more negative and the current densities required for passivation are growing. The beginning of the transpassivation region shifts in cathodic direction also. Recrystallisation of the more deformed specimens effects a partial return of the passivation potential in to the noble direction but the beginning of transpassivation continues in falling off. The shape of the i.e. curves is discussed in connection with the changes in metal structure.     

Der Einfluß von Zusatzelementen auf die Zunderfestigkeit von Heizleiterlegierungen

Influence of elemental additions on the scaling resistance of electrical heater alloys The influence of trace elements on the useful life of heater alloys is discussed; this influence had first been recognized by W. Hessenbruch almost 40 years ago and had been systematically studied. It is known from Hessenbruch's work, that in particular cerium and calcium increase the scaling resistance of heater alloys. A short discussion is devoted to metallurgical problems in connection with the addition of these highly reactive elements. Although it is generally known that alloy additions increase the useful life of the alloys and although this effect is largely utilized on an industrial level, a definitive clarification of the mechanism of action of these improving elements is still lacking. Opinions diverge already with respect to the question for the form — metallic or oxidic — in which these elements enter into action. The opinions maintained with respect to this phenomenon are discussed. A new experimental technique has enabled to give an answer in terms of an action of elements dissolved in their metallic state.     

Der Einfluß des Gefügezustandes auf die Oxydationseigenschaften von Zirkonium-Vanadium-Legierungen

Influence of structure on the oxidation behaviour of zirconium vanadium alloys The oxidation of the alloys ZrV 1 and Zr V 3 has been studied on a comparative basis to zirconium after various mechanical and thermal pretreatements; the aggressive medium was steam of 300°C.It has been shown that recrystallizing annealing after cold deformation has but little influence on the oxidation resistance; a considerable diminution of the oxidation susceptibility has been achieved, however, by grain refining after a cold deformation or annealing of the martensitic structure. This type of treatment has a positive effect in particular on the structure of the protective layer. In view of the fact that the oxidation susceptibility increases with the concentration of the alloying element it may be suggested that the intermetallic compound ZrV₂ has a negative effect. Consequently, the oxidation resistance is improved by quenching from high temperatures which prevents the formation of segregations.     

Der Einfluß unterschiedlicher Nitratgehalte auf das Korrosionsverhalten von verzinkten Stahlrohren

The influence of different nitrate contents of drinking water on the corrosion behaviour of galvanized steel pipes At the water works Biblis and Alsbach of Südhessische Gas und Wasser AG, Darmstadt, field tests were performed over a period of 2 1/2 years to describe the influence of different nitrate contents in drinking water and the corrosion behaviour of different qualities of galvanized steel pipes. The results obtained showed, that weight loss and corrosion rate measurements give no information on this subject. Optical inspection and flushing tests could prove, that selective corrosion occurred in the water with higher nitrate content. Galvannealed pipes showed local corrosion attack after a certain exposition time in water with higher nitrate content, depending on flow velocity. Air blown galvanized pipes and galvannealed pipes in water with higher nitrate content additionally produce „Zinkgeriesel”︁ during flushing. The selective corrosion attack also takes place to a very small extent in galvanized steel pipes, where quality is in accordance to the German Standard DIN 2444.     

Der Einfluß von Bakterien auf die Eisenkorrosion in Brack- und Meerwasser

Influences of bacteria on iron corrosion in brackish and sea waters The corrosion of steel in seawaters is subject to seasonal variations; the corrosion maxma being in spring and autumn. The variations are not attribuable to changes in water temperature, salt concentration or oxygen content but are due to the co-action of biotic and abiotic factors, the former givin rise to temperature dependent variations of corrosion. The activity of bacteria becomes bovious only at temperatures above 10 °C; at these temperatures metablolism is activated and the products of matabolism may attack iron (or bac-     

Über den Einfluß einer schwingenden Beanspruchung auf den Ablauf der interkristallinen Spannungsrißkorrosion

The influence of dynamic stresses on the progress of intercrystalline stress corrosion cracking Tests with steels sensitive and nonsensitive to stress corrosion cracking permit a seperation of the influences of static and dynamic stresses, respectively. The lightly alloyed steel resistant to stress corrosion does not lose its resistance even under dynamic stresses whilst the other steel, susceptible to stress without showing any recognisable correlation with the frequency. In the case of welded specimens, the service life is significantly reduced (mainly due to the overheating during welding). However, the resistance to dynamic stresses can be considerably by annealing at 800°C.     

Der Einfluß von Kriechverformung auf die Ausbildung der Oxidschicht auf der Hochtemperaturlegierung Ni20Cr

Influence of creep deformation on the formation of the oxide layer on the high temperature alloy Ni20Cr The formation of the Cr₂O₃-layer on Ni20Cr has been investigated at 850°C in H₂/H₂O (p(O₂) = 10^?19 bar) under simultaneous creep deformation with flat samples. The damage of the protecting oxide layer by cracks has been observed in dependence on deformation rate and strain. For additional information about the influence of the plastic deformation of the oxide layer and the healing of the cracks, preoxidized samples have been deformed in pure Ar-atmosphere. At strain rates below 10^?9s^?1 cracks cannot be observed. When strain rates < about 3 × 10^?8s^?1 are applied, cracks occur only above grain boundaries of the alloy, at higher strain rates they also lie in regions above the grains of the alloy. For > about 3 × 10^?8s^?1 the crack density depends no more on but only on strain . The different damages of the oxide layers in the two atmospheres allow the conclusion, that at from 10^?9s^?1 to 10^?7s^?1 beside the plasticity of the oxide layer in particular the crack healing influences the sum of the crack openings measurably. With increasing strain rates the contribution of plasticity can be neglected.     

Der Einfluß von Martensit auf das Korrosionsverhalten von 18 Cr-10 Ni-Stahl

The effect of martensite on the corrosion properties of 18 Cr-10 Ni steel The corrosion properties of the martensitic phases formed in an austenitic matrix by (i) cooling to low temperature (-196 and ?269°C resp. ?320 and ?452°F) and (ii) cold working at room temperature was investigated for two chromium-nickel stainless steels of the 18 Cr10 Ni type. Austenite and martensite have the same chemical composition but different lattice structures. In sulfuric acid, both martensitic phases formed at low temperature and by cold working arc preferentially attacked in the active range of corrosion. The effect of potential on the corrosion attack was elucidated by potentiostatically controlled experiments with subsequent light-optical and SEM-investigation of the specimens. Selective corrosion attack of the martensitic phase was found down to a potential being 0.8 V more negative than the cathodic limiting potential of the active corrosion range of a fully austenitic steel, irrespective of the way of the martensite transformation. The preferential attack of martensite may be explained by the supposition that the deposition of cathodically protecting layers possibly consisting of nickel is rendered more difficult at the martensitic surface areas. In sulfuric acid, no differences in the corrosion properties between austenite and martensite were found in the passive and transpassive range. In chloride containing aqueous solutions, the resistance to pitting is not effected by martensite formed at low temperature. From this it is concluded that also martensite formed by cold working does not effect the pitting resistance.     

Einfluß des Metallsubgefüges auf den anodischen Auflösungsmechanismus von Eisen

Influence of the metal substructure on the anodic dissolution mecanism of iron The electrochemical behaviour of iron shows a pronounced dependence on the metal substructure. The surfaces formed at the rupture of the specimens are dissolved according to a non-catalytic mecanism while a heat treatment of these rupture surfaces produces a change in the mechanism so that the dissolution occurs according to a catalytic mechanism. The two mechanisms are characterized by a rather different dissolution potentials; these differences can be attributed to the state of deformation of the crystal latice.     

Der Einfluß von CO2 auf die Korrosionskinetik von Zink in Modellwässern

Influence of CO₂ on the corrosion kinetics of zinc in water Mechanism and kinetics of Zn and Zn/Fe corrosion in water containing various contents of CO₂ is studied by impedance spectra completed by gravimetric corrosion measurements. Electrode impedance is clearly found to be a function of P, the diffusion parameter is of essential importance. A_d as a function of P yields the same curves as the rest potential dependence on CO₂ and moreover the gravimetrically measured corrosion velocity rises linearly with CO₂. –Determination of corrosion velocity according to STERN-GEARY cannot be realized in the systems under investigation. –Experimental results lead to the conclusion that the main corrosion reaction takes place at the metal/layer-phase. The corrosion mechanism is discussed.     

Über den Einfluß des Sauerstoffes auf die Korrosion in Dosenkonserven aus Weißblech

Influence of oxygen on the corrosion in tinplate cans The research was made with stell plate (thinnest plate, 0,07% C, from rimmed prematerial) and purest tin in a cell according to the galvanic element. Corresponding storages were made in unlaquered and laquered cans. Citrate buffer, pH 2.4, was used as electrolyte. Oxygen effects pitting corrosion on the steel surface. The corrosion activating effect connected with this pitting even then remins when oxygen is spent after some time of storage of cans. But the steel surface is protected simultanously by tin ions soluted from the tin surface, because these ions get adsorbed particularly on the endangered regions of the steel surface and inhibit the pitting corrosion. But this protection only happens in media where the steel plate is electropositive to tin. The question of the suitability of can filling free of oxygen therefore can not be answered in general, but has to be anwered individually taking into account the relations described.     

Untersuchungen über den Einfluß des Zinks auf das Korrosionsverhalten von Spannstählen

Investigations on the influence of zinc on the corrosion behavior of high strength steels Corrosion and fracture behavior of hot dip galvanized high strength steels with and without damaging zinc layer was studied in deionized water, in tap water, and in saturated calcium hydroxide solution through which nitrogen, air, and carbon dioxide were bubbled separately. Hydrogen permeation measurements have been carried out for steel specimens which were cathodically polarized by means of the zinc layer. It has been observed that the hydrogen activity reached to a maximum of 1-2 in neutral solutions and 4-10 in saturated calcium hydroxide solution or in dilute acid solutions containing carbon dioxide, before decreasing to low values. The decrease of hydrogen activity is due to the formation of surface layers. Constant load tests by application of a load amounting to 100-110% yield strength caused no hydrogen induced brittle fracture within 300-400 h neither with nor without damaging zinc layer. At a constant strain rate of 5· 10^?7/s only 8 mm cold drawn steel wires were found to be almost unsusceptible to hydrogen that was absorbed during the test. Under notched conditions, all the steels investigated showed macroscopic brittle fracture.     

Einfluß des entstehenden Rostes auf den Verlauf der atmosphärischen Korrosion von Stahl

Influence of incipient rust on the pattern of the atmospheric corrosion of steel The corrosion pattern with continuous rust formation has been compared with the results obtained and accumulated at certain intervals during the same time from analogous specimens. It was found, firstly, that there is a critical value of SO₂ concentration and, secondly, that the existing rust is capable of keeping certain quantities of SO₂ away from the surface. The latter effect explains the flattening-out of the corrosion rate to constant values, as well as the fact that, in pure atmosphere, the stationary conditions are reached later than in an industrial atmosphere.     

Der Einfluß des Molybdängehaltes auf die Korrosion austenitischer Cr-Ni-Stähle im Aktivzustand

The influence of the molybdenum content on the corrosion rate of austenitic Cr-Ni steels in the active condition The corrosion rate of steels X 5 CrNi 189, X 5 CrNoMo 18 10, X 5 CrNiMo 18 12 and X 5 CrNiMo 17 13 has been investigated under potentiostatic conditions in the active zone in 2 n H₂SO₄ flushed with nitrogen and sulphur dioxide. The active rest potential of the steels is in the vicinity of the active-passive transition, and the corrosion rate increase at cathodic polarisation. With increasing Mo content, the corrosion rate is reduced in the active condition, but the passivation potential and the corrosion rate in the passive condition are not influenced. In the acid flushed with SO₂, the corrosion rate is increased in the active range, and the latter is extended in the direction of the electronegative potentials. With these steels, even a pre-activation of the specimens has an influence on the test results. In the active-passive transition zone, the steels in the test solution containing SO₂ are partially passive and subject to local corrosion attacks.     

Der Einfluß von pH-Wert und Sauerstoffgehalt von Pufferlösungen auf das Korrosionsverhalten metallischer Werkstoffe

Influence of pH and oxygen content of buffer solutions on the corrosion behaviour of metallic materials The application of solutions to the decontamination of materials in nuclear installations is based on the condition that their corrosion behaviour is clearly understood. Since electrochemical corrosion is due to cathodic and anodic partial reactions which are influenced in different ways by the pH of hte solution and the oxygen content it is suggested that the results of electrochemical experiments with buffer solutions be used as a model for predicting the corrosion behaviour of materials in other solutions. In the tests described here potentiocinetic current-potential-curves have been traced and galvanic corrosion tests have been made. The results obtained in ascorbic acid, postassium hydrogen phthalate, ammonium citrate and acetate, sodium and potassium tartrate, ammonium hydrogen phosphate, sodium carbonate, hexamethylene tetramin, ethylene diamine enable – on the basis of summarized current-potential-curves – the metals studied to be classified in four groups characterized by clear differences concerning the influence of pH on the corrosino behaviour.     

Über den Einfluß einer schwingenden Beanspruchung auf den Ablauf der interkristallinen Spannungsrißkorrosion schwach legierter Stähle

The influence of fluctuating stresses on the progress of intercrystalline stress corrosion cracking of slightly alloyed steels Because of the extensive testing programme required, the results of the investigations here reported should be regarded as provisional and should preferably be supplemented by further verifications. Even so, the following conclusions can be drawn: – A slightly alloyed steel resistant to intercrystalline stress corrosion cracking under static stresses will not lose its resistance to CaNO₃ solution even when subjected to fluctuating stresses ranging from 0.7 to 0.9 σ_B. In the case of the steel prone to stress corrosion cracking, the service life was likewise not affected by a stress fluctuating around a mean value. Nor was it possible to observe any correlation with frequency. The cracking was found to originate at the smallest cross-section and, in the conical part, also at points where the stresses were up to 3–4 kp/mm² lower. Notched and welded specimens of the resistant steel were found to have a long service life under static stress. In contrast, welded specimens subjected to fluctuating stresses failed comparatively early. Cracking occurred in the proximity of the weld and is likely to be due not so much to internal stresses but to the changes in the grain structure caused by the welding heat. Heat treatment within the range of 600 to 700° C was found to result in slight improvements only. It was only through annealing at high temperature (800° C) that it became possible to regenerate the welded specimens.     

Einfluß der Wärmebehandlung auf den Verlauf der Stromdichte-Potential-Kurven bei einem 13%igen Chromstahlguß

Influence of the heat treatment on the trend of the current density/potential curves with a 13 per cent. chromium steel casting With decreasing chilling rate after hardening, there is an increase in the segregation of Cr carbides along the delta ferrite where the Cr content is reduced. The degree of this reduction is reflected in the current density/potential curves where, with decreasing chilling rate, a gradually more pronounced second current density maximum is encountered which disappears, gradually if the specimens are tempered at a temperature ranging from 550 to 600° C. A further proof for the reduction in the Cr content is obtained from an electron-microscopic observation: it is not the carbides themselves but a small seam in the delta ferrite immediately adjacent to the carbides which is particularly corrosionprone. In practice, it follows that heat treatment conditions with a maximum of current density at about + 100 mV_H are less capable of passivation and therefore less reliable in application.