Beobachtungen über den Einfluß kleiner Zusätze von Cermischmetall auf das Zunderverhalten von Stählen

Observations concerning the influence of small additions of cerium mixed metal on the scaling of steels The addition of appr. 0.1 % cerium mixed metal to steel X 10 CrNi 18 10 has practically no influence on the isothermal oxidation of the steel in air at 800 and 900°C, but improves the adhesion of the scale under temperature cycling conditions. The positive effect of cerium becomes apparent only after extended annealing or after several temperature cycles respectively. In the case of steel 10CrMo9 10 the addition of cerium mixed metal in quantities up to 0.3% has practically no effect. With cerium contents of 0.75%, however, annealing in air at temperatures around 600 °C results in a scale showing excellent adhesion and resisting even quenching in water without spalling. Cerium contents of this level, however, give rise to changes of the mechanical and technological properties of the steel so that their practical use should be out of the question.     

Über den Einfluß der Austenitstabilität von 18/8-Chrom-Nickel-Stählen auf die Verformungseigenschaften und auf das Korrosionsverhalten dieser Stähle

Influence of austenite stability of 18-8 Cr-Ni-steels on the cold working and corrosion properties of these steels The martensite formed during cold working has a negative effect on uniform corrosion only when the specimen is active in the particular medium; if so, corrosion current density increases with the degree of cold working. The martensite generated by cold working reduces on the other hand the susceptibility to intercrystalline corrosion and – in amounts up tn 2% – increases the time to failure in stress corrosion cracking (15 and 45 kp/mm²). The pitting potential is not shifted by the martensite, but pit density increases with the martensite content. In the Kesternich test no negative effect of the martensite is found. It is therefore concluded that reducing the Ni content in 18-8 steels improves workability without having a pronounced deleterions bearing on corrosion behaviour.     

Untersuchungen über den Einfluß einer Voroxidation auf die Aufkohlungen von hitzebeständigen Cr?Ni-Stählen

Investigations into the influence of a preliminary oxydation on the carburization of refractory Cr-Ni-steels The investigation into the carburization behaviour of refractory austenitic steels of the 18 10 and 25 20 CrNi types in atmospheres containing CO₂, CO, H₂ with small contents of water vapour has shown that carburization susceptibility decreases in the order CrNi steel 18 10 - CrNi steel 25 20 (without Mo) - CrNi steel 25 20 (with small Mo addition). Consequently the carburization behaviour depends exclusively on chemical composition and surface condition, not, however, on the structure and grain size. Increasing the Cr and/or Ni contents reduces the extent of carburization and improves the protective effect of pre-oxidation. This effect, however, is not sufficient during long term exposures. Consequently the effect of silicon should be taken into consideration, too.     

Neuentwicklung von Bleilegierungen aufgrund elektrochemischer Untersuchungen über das Korrosionsverhalten in Schwefelsäure

Development of new lead alloys starting from electrochemical investigations into the corrosion behaviour in sulfuric acid The corrosion of lead in sulfuric acid can take place in two different forms, corresponding to the active and passive state respectively of lead, but allowing for any intermediate stage as well. A surface layer is formed on principle, but it has different structure and effect in the two instances and requires a certain minimum duration of corrosion. Corrosion susceptibility can be substantially reduced, in particular by addition of low solubility in lead and which may thus give rise, as precipitates, to cathodic activity. Cu e.g. has a favorable effect which can be further improved by Sn. The same is true with noble metals – in particular Pd – having high hydrogen overtension. Complex alloys as e.g. PbCuPd yield a further increase in corrosion resistance and simultaneously, mechanical strength; an alloy of the type PbCuSnPd is superior to any other lead alloys as to corrosion and creep resistance.     

Untersuchungen über das Korrosionsverhalten von Zirkoniumlegierungen. III. Untersuchungen an Zirkonium-Titan-Legierungen

Investigations into the corrosion behaviour of zirconium alloys III. Investigations on zirconium titanium alloys Investigations on zirconium alloys containing up to 4OO% titanium and, eventually, up to 10% Nb or Mo and small amounts of Fe, Ni and Cr (together 1.5% maximum) have revealed that titanium increases the dissolution power of zirconium for other alloying elements without tending to form two-phase structures. As to corrosion behaviour the better alloys are somewhat superior to other alloys. While titanium impairs the corrosion resistance of pure zirconium with respect to boiling mineral acids (20% HCl, sulphuric or nitric acids) titanium additions up to 10% of improve the corrosion behaviour of ZrNb and ZrMo alloys; alloys of the type Zr10Nb10Ti or Zr10Ti10Ta are comparable, with respect to the corrosion resistance, to pure zirconium. The scaling resistance of zirconium passes through a minimum at a five to ten percent Ti and arrives at its maximum value with 40% Ti. Further improvements may be obtained by addition of 10% Nb.     

Über den Einfluß der Bewitterung auf das Korrosionsverhalten unlegierter und niedriglegierter Stähle

Influence of weathering on the corrosion behaviour of unalloyed and low-alloy steels Accelerated weathering tests with plain carbon steel and low-alloy steels show that the influence of weathering is of considerable importance for the atmospheric corrosion. Attention has to be paid that the steel surfaces are never wet over a longer period of time. The faster the steels will be dry, the better is the long time behaviour of these materials. Frequent short wet periods, followed by dry phases lead to the formation of an increasingly better protective layer. By favorable weathering conditions the influence of the composition of the alloys is comparatively small. Metallographic and electrochemical tests further show that the corrosion protection is not only due to the formation of a compact macroscopic layer. Local passivation effects are significant as well.     

Neuentwicklung von Bleilegierungen aufgrund elektrochemischer Untersuchungen über das Korrosionsverhalten in Schwefelsäure

Development of new lead alloys starting from electrochemical investigations into the corrosion behaviour in sulfuric acid The corrosion of lead in sulfuric acid can take place in two different forms, corresponding to the active and passive state respectively of lead, but allowing for any intermediate stage as well. A surface layer is formed on principle, but it has different structure and effect in the two instances and requires a certain minimum duration of corrosion. Corrosion susceptibility can be substantially reduced, in particular by addition of low solubility in lead and which may thus give rise, as precipitates, to cathodic activity. Cu e.g. has a favorable effect which can be further improved by Sn. The same is true with noble metals — in particular Pd — having high hydrogen overtension. Complex alloys as e.g. PbCuPd yield a further increase in corrosion resistance and, simultaneously, mechanical strength; an alloy of the type PbCuSnPd is superior to any other lead alloy as to corrosion and creep resistance.     

Untersuchungen zum Einfluß von Polyphosphat auf das Korrosionsverhalten von Kupfer in Elektrolytlösungen

Experiments on the effect of polyphosphate on the corrosion behaviour of copper in electrolytic solutions Gravimetric experiments in a circulating equipment were performed on the effect of Graham salt on the corrosion behaviour of copper in electrolytic solutions by means of a high confounded 2^7?4-fractional factorial. The composition of copper samples: 99.7% Cu, 0.002% Bi, 0.005% Sb, 0.01% As, 0.05% Fe, 0.2% Ni, 0.01% Pb, 0.05% Sn, 0.01% S. The aqueous electrolytic solutions contained hydrogencarbonate-, sulphate-, chloride-, nitrate-, manganese-, calcium ions and Graham salt. It appears that Graham salt is unsuitable for the inhibition of copper corrosion. The polyphosphate promotes corrosion. Chloride-, nitrate-, sulphate- und manganese ions also increase corrosion rate whereas it is decreased by hydrogencarbonate ions. Increase of temperature also causes a decrease of corrosion rate. An existing danger of contact corrosion induced by copper cannot be removed by addition of Graham salt if copper and carbon steel, respectively galvanized steel are installed together in equipments of plant water.     

Untersuchungen über das Korrosionsverhalten von Zirkoniumlegierungen II. Verhalten bei Wasserdampfkorrosion

Investigation into the corrosion behaviour of zirconium alloys. 11. Behaviour under steam corrosion conditions An investigation into the corrosion behaviour of about 50 Zr alloys in high pressure high temperature steam (240 atm, 400°C) and hot air (4OO°C) has revealed a clear correlation between the behaviour in the two media. Alloys characterized by lower scaling susceptibility are also less susceptible to corrosion in steam, while, on the other hand, thicker scale layers tend to reduce hydrogen embrittlement. From the alloying additions studied Sn, Fe, Cr and Ni have a clearly favourable influence and W may have a similar effect. Ti has an outspoken negative influence on the behaviour in steam (spalling off of the scale) and Si, too, is deleterious because the SiO₂ being formed is soluble in steam, so that the scale layers retain their penetrability. Mo cannot be recommended either, while Nb is favourable in particular because of its grain refining effect. The favourable effect of Cu additions has been confirmed. Alloys with Fe, Cr and Ni and single types with Mo, Nb and Cu are superior to pure Zr with respect to steam resistance and are in part superior to Zircaloy 2 with respect to their mechanical strength.     

Untersuchungen über den Einfluß des Gefügezustandes auf das Korrosionsverhalten hochlegierter,rost- und säurebeständiger Stähle in reiner sowie in chloridhaltiger Schwefelsäure

Corrosion Properties of High Alloyed Stainless Steels in Pure as well as in Chloride Containing Sulfuric Acid The corrosion behaviour of the high alloyed stainless steels material no. 1.4439 (X3CrNiMoN17135), 1.4539 (X2NiCrMoCu25205), 1.4503(X3NiCrMoCuTi2723) as well as the reference materials AlSI 316 L and alloy 825 was tested in diluted sulfuric acid (5, 10, 20 and 50%) at 50, 100 and 150°C. The test solutions additionally contained impurities as chlorides and cupric ions. On the material side the effect of various microstructures was checked as well: material as received (commercial production), solution annealed under laboratory conditions, cold deformed and for two selected steels electroslag remelted. Corrosion testing methods are: the immersion test will sheet coupons and the measurement of the weightloss; electrochemical testing, i.e. Current potential-and free corrosion potential-time-curves. No pitting corrosion is observed in the presence of chloride ions. In some cases the general corrosion rate is lowered if chloride ions are present. This beneficial effect of chloride ions, however, is observed only at low chloride concentrations (500 ppm). Annealing under laboratory conditions as well as electroslag remelting does not generally improve the corrosion resistance. A negative effect by cold deformation is only observed for standard stainless steel AlSI 316. Cupric ions added to the 20% sulfuric acid solution improve the corrosion resistance of all steels investigated to that extent, that they can be used in practice up to 100°C provided that the concentration of cupric ions in the solution is sufficiently high (2000 ppm). Electrochemical test results indicate that the positive effect of cupric ions is due to the shift of the free corrosion potential into the potential range of stable passivity. Copper alloyed stainless steels show the highest corrosion resistance.     

Untersuchungen über das Korrosionsverhalten von Zirkoniumlegierungen I. Verhalten gegenüber wäßrigen Medien

Investigations into the corrosion behaviour of zirconium alloys I. Behaviour in the presence of aqueous media Extensive corrosion research covering 5O Zr alloys have shown that the good corrosion resistance of pure Zr cannot be improved to any greater extent by alloying. Pur Zr as well as most of its alloys have a high corrosion resistance; even in boiling mineral acids (20% H₂SO₄, HNO₃, and HCl) the corrosion rate is below 0.5 g/m²·d and no attack can be recognized in neutral salt solutions. The metal also resists attack by boiling 2O% KOH. Strong attack, however, it caused bv Fe-III-chloride. The metals do not resist attack by HF, while neutral KF attacks but little, however produces pitting. The effect of alloying additions is due to the structure produces by them: pure grain boundaries or very fine heterogeneous structures show good corrosion resistance. Ti, Hf, Sn and small amounts of Nb have little influence, Mo, W, larger amounts Nb and small pt and Re additions give rise to Local cells, while Fe, Cr and Ni have practically no influence.     

Einfluß von Seigerungen auf das Korrosionsverhalten von austenitischem nichtrostendem Schweißgut

Influence of segregations on the corrosion behaviour of austenitic stainless weld metal Fully austenitic stainless weld metal on solidification acquires a segregation structure. The segregation takes place with the participation of the alloying elements responsible for the corrosion behaviour. Regions of low alloy content are preferentially attacked and microelements form between them and more corrosion resistant regions. The progress of corrosion is enhanced by lamellar segregation structures and is inhibited by cellular structures. The corrosion due to segregations is particularly pronounced when the resistance in one medium is a pronounced function of an alloying element prone to segregation. This is demonstrated on the example of weld metal X 2 CrNiSi 1815 having different Si contents. The effect of the base metal/weld metal macro-element is discussed. Corrosion due to segregation takes place only when the weld metal is subject to attack in the vicinity of its resistance limit.     

Einfluß von Kupfer auf das Korrosionsverhalten verzinkter Rohre in warmen Brauchwässern

Influence of copper on the corrosion behaviour of galvanized tubing in warm water systems Tests carried out with tap water (65°C) containing 0.1 to 0.3 mg/l Cu²⁺ have revealed that copper ions give rise to accelerated corrosion of tube walls. Corrosion takes place in the form of pitting. The intensity and frequency of pits increase as the copper content is increased and the pH value is decreased. Corrosion products formed on the zinc are predominantly a basic zinc carbonate, while copper is found in a coagulated form at the surface or embedded in the surface layer. The copper content of the corrosion products increases as the copper content of the water is increased and may attain up to 12.5%.     

Einfluß einer Eisenaufmischung auf das Korrosionsverhalten von NiCu30 Fe-Stahlplattierungen

The influence of iron pick-up on the corrosion properties of NiCu30Fe/steel clad materials The influence of iron pick-up on the corrosion properties of overlay and butt weldings of NiCu30Fe/steel cald materials was investigated by electrochemical tests in aerated artificial sea water (ASTM Standard D 1141-75) at 25, 50 und 80°C and by exposure to sea water in a sea water test rig on Helgoland. NiCu30Fe plates with defined Fe contents between 0% and 14% were used for comparison. On the Fe being distributed homogeneously, no negative influence of the iron on the pitting resistance was noted in aerated artifical sea water of 25°C up to an Fe content of 10%. The pitting resistance increases with rising temperature (50 and 80°C) and the Fe influence increases slightly. On exposure to sea water on Helgoland, the corrosion in the subtidal zone is mainly caused by marine growth resulting in the formation of shallow pits. In the tidal zone, Fe contents of more than 6.7% cause rust pittings at very low integral corrosion rates (≤0.002 mm/a). With integral Fe contents of between 0.5% and 3% in the final pass, the overlay welds have the same good corrosion resistance properties as commercial NiCu30Fe plate material. The compound butt welds exhibit slight pitting in the weld metal and the heat-affected zone which cannot be conclusively attributed to Fe pick-up but is rather due to the different free corrosion potentials of the NiCu30Mn(Ti) weld metal and the NiCu30Fe cladding material. In the tidal zone which is the preferential application of NiCu30Fe corrosion rates are less than 0.01 mm/a for all specimens welded by different welding methods. Iron contents of up to 8% which can be met by all welding methods when welded in two layers have no negative effect on the corrosion properties.     

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 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.     

Der Einfluß programmierter Schweißtemperaturzyklen auf die Gefügeausbildung und das Korrosionsverhalten von austenitischen korrosionsbeständigen Stählen

Influence of programmed welding temperature cycles on the resulting structure and the corrosion behavior of austenitic steel Studies on corrosion resistant austenitic steels subjected to simulated welding temperature cycles have shown that even after very short annealing times the corrosion resistance is decreased. In the temperature range between 700 and 900 °C carbides are precipitated, while grain growth and twinning are observed at temperatures between 900 and 1100 °C. Above 1280 °C delta-ferrite is formed as early as after 15 sec. Potentiokinetic current density/potential curves have been traced on the basis of tests in 1 N sulfuric acid at room temperature. The passivation current density has turned out to be a suitable corrosion resistance criterion.     

Untersuchungen über das Kleben von Blei

Investigations into adhesive lead joints Lead plate thoroughly prepared for adhesive joining can be connected with other materials with the aid of resin-based adhesives. Picked surface yield higher strengths in the adhesive joint than do surface roughened by mechanical action. Hot-curing epoxy-based adhesive on picked surface yield adhesive strengths superior to the cohesive strength of lead as established in the tensile test. Adhesives requiring high compressive loads for curing, or adhesives based on vinyl resins are not suitable for use with lead. Overlapping joints may neutralize just small fractions of the tensile shearing forces. In such cases lead will become detached from the adhesive layer because of its high degree of deformation. At elevated temperatures, however, the adhesive strength of the adhesive on lead is often superior to the shearing strength of the joint; as a consequence thereof, the lead itself will fail. Adhesive joints with lead can bear temperatures up to 70°C for a long time without any loss of strength. Glass fibre roving embedded in the adhesive layer may increase the tensile strength and yield advantages as far as processing technology is concerned. Lead-coated parts may be deformed even after adhesive joining.     

Einfluss der Schleifbehandlung auf das Korrosionsverhalten von Chrom‐Nickel‐Stählen

The influence of grinding treatment of stainless steels on the corrosion behaviour Mechanical grinding of stainless steels is often used for decoration purposes, for instance in the interior decoration. However, this treatment can cause problems regarding the corrosion resistance. During investigations of the influences of processing parameters of industrial grinding it was shown, that roughness only is not the expected crucial parameter for the corrosion resistance. The variation of different grinding parameters and also the type of abrasives have a substantial influence. Beside the long term tests electrochemical investigation at the ground surfaces are presented. The different corrosion susceptibility of the surfaces could be proven by means of electrochemical noise measurements.     

Einfluß des Elektronenstrahl- und Schutzgasschweißens auf das Korrosionsverhalten von X5 CrNiMo 18 10

The influence of cathode ray and inertgas arc welding on the corrosion behaviour of X 5 CrNiMo 18 10 When subjected to the Strauss test, the specimens welded by these welding processes are found to be not prone to intercrystalline corrosion. With the Huey test, on the other hand, the weld produced by inert-gas arc welding is much more prone to corrosion than the weld produced by cathode ray welding or the base metal. This is probably due to the fact that, because of the high energy density of the cathode ray, a greater homogeneity of the structure is obtained. In particular, the ferrite content, becomes Lower than with arc welding where the heat concentration is lower. In practice, however, ferrite formation is of comparatively little importance. This is because selective corrosion will only occur if the homogeneous austenite of the 18/18 steels is likewise showing marked corrosion, e. g. in certain mixtures of reducing and oxidizing acids (hydrochloric or hydrofluoric-acid with nitric acid).