Ermittlung des Zeitstandverhaltens einer austenitischen Schweißverbindung

Evaluation of the Creep Rupture Behaviour of an Austenitic Welded Joint. Part I: Experimental Determination of the Creep Behaviour The creep rupture behaviour of a welded joint of 18% Cr-11% Ni-steel was investigated on specimens of different geometry and size. Differences in the creep rupture behaviour between welded joint specimens and specimens taken from the different zones of the welded joint are discussed. The plasticity-and creep behaviour of the different zones is described by constitutive equations.     

Untersuchung einer mehrlagigen Schweißnaht eines dickwandigen Rohres aus dem austenitischen Stahl X6 CrNiNb 18 10

Analysis of a multi pass weld of a thick walled tube made of austenitic stainless steel X6 CrNiNb 18 10 In this paper, microstructure and residual stresses of a multi pass welding of a thick‐walled tube made of austenitic stainless steel X6 CrNiNb 18 10 (1.4550) are systematically characterized and assessed. Results of microstructural and phase analyses, residual stress and hardness measurements as well as of a tensile test using micro specimen and SEM analyses are presented. Using these data, plastic deformations occurring during the welding process in the vicinity of the weld seam are evaluated. Finally, consequences of an additional heat treatment at 400 °C/24 h are studied.     

Bruchmechanische Untersuchungen an einer Schweißverbindung von 90 mm Dicke aus Almg 4,5 Mn bei Raumtemperatur und bei −196 °C

Toughness Evaluation for a Thick Weld Joint of AlMg 4,5 Mn at ?196 °C To asses the toughness of a 90 mm thick MIG-weld joint of Al Mg 4.5 Mn fracture mechanics and charpy impact material parameters have been determined at 20 °C and ?196 °C. Additional to the mechanical tests extensive metallographic and fractographic tests on specimens of the weld material and base material were done. The results of the fracture mechanics tests and the fracture analysis show, that now brittle fracture will occur at ?196 °C. The further conclusions are, that charpy energy values are no meaningful basis for a toughness evaluation of such an aluminium weld joint. The joint can be used without restrictions at ?196 °C.     

Einfluß der Abkühlgeschwindigkeit auf die δ-Ferrit-Ausscheidung im austenitischen Schweißgut

Influence of the Cooling Rate on the Separation of δ-Ferrite in Austenite Weld Metal There exists a lot of literature concerning the significance of δ-ferrite in welding joints of austenitic stainless steels. An information about the influence of the cooling rate on the primary cristallisation is even more limited. The present results show, that the δ-ferrite-quantity measured at room temperature is hardly influenced by the cooling rate. Furthermore the cooling rate seems to influence the primary cristallisation. The well-known result was verified, that the orientation of the polished section plane yield different δ-ferrite-quantities. Moreover it is shown, that the toughness and therefore the critical crack length increases with decreasing δ-ferrite-quantity.     

Ermittlung bruchmechanischer Kennwerte an austenitischen Werkstoffen nach der Einprobentechnik mittels Gleichstrompotentialsondenverfahren

J-R-Curve Determination on Austenitic Steel Using Single Specimen Technique with DC-Potential-Drop For the evaluation of fracture mechanical properties several methods will be normally used for ductile materials. For the fracture mechanical investigation of very ductile materials there is no standard method achievable at present. Performing continuous measurements of crack length in materials of high ductility appears most difficult. This paper deals with the continuous determination of crack length in two different samples of high ductile austenitic steel by means of DC-potential drop. Due to the indirect way of crack length determination using this method a correction factor depending on deformation has to be introduced. By this it is possible to construct the J-R-curve using single-specimen technique and to evaluate a J₀ value using fractographical methods. Because of rather large displacements arising with fracture mechanical tests of austenitic steels a formula for the correction of the load line displacement is introduced and discussed. The method presented leads to reproducible results which correspond with results obtained using multiple specimen technique.     

Messen des Korrosionspotentials an Schweißverbindungen im Kleinbereich

The small scale measurement of corrosion potential in welded joints . The corrodibility of welded joints is reported on. Potential curves give the possibility to backing the incomplete results in this field and permit a well defined statement concerning the corrosion behaviour. Failures of interpretation due to polarisation are indicated. The pulsating method helps to prevent changes of the concentration by reactions and alteration of the pH-value. This method delivers useful informations and detects the corrosion sensibility of welded joints.     

Ermittlung von Spannungsintensitätsfaktoren aus Isochromaten mittels einer Vielparameter-Vielpunkt-Methode

Determination of Stress Intensity Factors from Isochromatics by means of a Multiparameter-Multipoint-Method A multi-parameter-multiple-point method (VPVP-method) for determination of mode-1 stress intensity factors from isochromatic fringe patterns has been developed and tested in connection with practical examples. In particular the stress field behaviour in compact-tension specimens is thoroughly investigated where variable numbers of series coefficients in the stress field expansion and a variety of data-point combinations featuring remoted and close field influences has been utilized. Cracks approaching free specimen boundaries have been given special attention.     

Wirkung von Oberflächenschutzmaßnahmen auf hochwarmfeste Gasturbinenwerkstoffe. Teil I. Beeinflussung des Zeitstandverhaltens

Influence of coating on the Properties of Heat Resistant Gas Turbine Alloys. Part 1. Creep-rupture Behaviour The influence of coatings and coating thermal cycles on the creep and creep-rupture behaviour of several nickel based gas turbine blade and vane alloys was evaluated. As a result of creep-rupture tests, the scatter bands of the rupture stress and of the stress to reach 0.2% plastic strain show in comparison to the uncoated materials decreased mean values and even more decreased lower bound values. At an austenitic steel for exhaust valves, no influence of coating was observed.     

Messung der Schweißkraft,des Abbrandes und des Kontaktwiderstandes von Kontaktwerkstoffen für die Energietechnik

Measuring of welding force and contact resistance with a testing equipment to classify contact materials for power engineering . Knowledge regarding welding force, erosion and contact resistance is very essential to select and evaluate contact materials which are to be used in electric switchgear. Measuring systems and results which are found in the literature are mostly carried out under test conditions not close enaugh to practice. An automatic test switchgear with which the mentioned technological characteristics can be evaluated is described. Test conditions can be varied in a very wide range so that every condition can be selected suiting the switchgear. Data on welding force, erosion rate and contact resistance of the contact materials like Ag 1000, AgNi 10, AgCdO 12 and AgC3 are given. A statement on the quality of braze between contacts and carrying material can be given.     

Ermittlung des Spannungsintensitätsfaktors KI mit dem spannungsoptischen Verfahren

Determination of Stress Intensity Factor K_I by means of Photoelastic Technique A survey is given of the methods applied for determining stress intensity factor K_I by means of photo-elasticity. In this connection the scope of validity and the accuracy of these methods are discussed.     

Verbesserung des Einzeldraht-Anemometer-Verfahrens zur Ermittlung des Grundgeschwindigkeitsvektors und des Reynoldsschen Spannungstensors

Ohne Zusammenfassung     

Vorhersage der Schwingfestigkeit von Schweißverbindungen auf der Basis des statistischen Größeneinflusses

Prediction of the fatigue strength of welded joints based on the statistical size effect With increasing length of welding seams the fatigue strength decreases. This effect is confirmed in fatigue tests on butt joints and cruciform joints. The influence of the length of the welding seam on the fatigue strength depends on the scatter of the parameters describing the geometry of the welding seam. The theory of the statistical size effect worked well in fitting and predicting the test results. The fatigue strength of welded joints is well predicted, if no other influences like e. g. residual stresses change the fatigue strength. Additionally a method for the calculation of crack propagation is proposed, which takes in account angular and linear misalignement as well as local changes of the geometry of the welding seam.     

Untersuchungen zum Ermüdungs-Rißwachstumsverhalten des austenitischen Stahles X 6CrNi 18 11 (1.4948)

Investigations of the Fatigue Crack Growth Behaviour of the Austenitic Stainless Steel X 6CrNi 18 11 (1.4948) The fatigue crack growth behaviour of the heat resistant austenitic stainless steel X 6CrNi 18 11 (material number 1.4948), which is used as the structural material for the primary and secondary heat transfer systems of the liquid metal fast breeder reactor SNR 300, is described. The parameters under consideration are the temperature in the range from 308 K up to 973 K, the frequency from 0.5 Hz up to 20 Hz, the stress ratio R as well as the heat-to-heat variation. The minimum ligament size criterion as well as the influence of the test technique on crack propagation are discussed. For the various test parameters the constants C and n of the Paris equation are calculated. The test results demonstrate a small influence of the heat-to-heat variation on the crack growth. At low stress ratios and at room temperature the influence of frequency is very small. A strong influence of the stress ratio R on the crack growth rate is observed. For higher R-values and high temperatures a distinct influence of the frequency on the fatigue crack propagation is shown.     

Eine effiziente Methode zur Ermittlung des Schädigungsbereiches bei Wöhleruntersuchungen

An Efficient Method for the Estimation of the “French Damage Area” By a statistically planned and evaluated variant of French's method, the French damage line may be transformed into a quantitatively describable “damage area”. For this purpose a considerable amount of tests has to be applied (app. 400 specimens). A new evaluation of statistically planned investigations of Panagopoulos [23] showed two remarkable results:

• 100% probability of fracture is nearly related to 100% probability of damage
• the arcsin √-transformation is a well fitting model describing the distribution of damage.

A new efficient method for the estimation of the damage area based on this observations was derived and described. The damage area is discussed regarding two level and multi-level tests.     

Deckschichtbildung und Korrosionsverhalten des hochsiliciumlegierten austenitischen Sonderstahls X 2 CrNiSi 18 15 in Salpetersäuren

The Formation of Surface Films and the Corrosion Resistance of the Silicon Containing Austenitic Steel X 2 CrNiSi 18 15 in Nitric Acids The oxide layers consist of two parts: the lower one is mainly Croxide, the upper one is SiO₂. ESCA and AAS measurements were made in order to study the formation of the surface layer on the austenitic steel X2 CrNiSi 18 15 in nitric acids. A film, which is chromium oxide, is formed first. On top of this film a second film consisting of SiO₂ grows. The elements nickel and manganese are not found in the formation of the oxide films. Immediately below the oxide layer the steel is enrichened with chromium and depleted of iron. In order to find the in some cases very small corrosion rates (5 · 10^?5 mm · a^?1) in a reproducible manner, the amounts of iron, chromium and nickel which had been dissolved were measured by means of the AAS method as a function of time. For stationary samples apparent activation energies of 65.2 kJ/Mol (azeotropic nitric acid) and 37.5 kJ/Mol (highly concentrated nitric acid), respectively, were found. These data confirm the assumption that the corrosion rate is determined by reactions at the phase boundaries. No appreciable influence of the flow velocity on the corrosion rate was detected.     

Mikroanalytische Untersuchungen des Ausscheidungsverhaltens in kommerziellen Alitier- und Chromalitierschutzschichten auf Nickelbasislegierungen und austenitischen Stählen

Microanalytical Investigations of the Precipitation Behaviour of Commercial Aluminized and Chromium-Aluminized Coatings on Ni-Base Alloys and Austenitic Steels The precipitation and diffusion behaviour of commercial aluminized and chromiumaluminized coatings on nickel-base alloys and austenitic steels was studied by aid of an electron probe microanalyzer. It is shown, that the protected nickel-base alloys all have a similar layer structure: an external NiAl-layer, which is delimited by an intermediate CrNi-(Mo)-layer to a small Al- containing mixed crystal zone. In the case of aluminized austenitic steels only a very small NiAl-layer can be detected, followed by an extended Al-containing mixed crystal. These layers on Fe-base alloys are predamaged by a perforated zone, due to the Kirkendall-effect. A previous chromium diffusion prevents this effect, but the diffusion behavior was not influenced during an extended heat treatment. The protected nickel-base alloys showed the best durability during long time oxidation tests.     

Ermittlung der Verformungen und Spannungen einer gelochten Gummimembran mit Hilfe von Rasterverfahren

Zusammenfassung Für eine gelochte Gummimembran wird die Verformung mit einem Rasterverfahren in unterschiedlichen Laststufen experimentell ermittelt. Hierzu werden die Koordinaten eines Kreuzrasters auf der Gummioberfl?che mit der digitalen Bildverarbeitung automatisch bestimmt. Aus einem zuvor angepa?ten Stoffgesetz ergeben sich dann die Spannungen und die Schnittkr?fte in Lastrichtung. Durch Vergleich mit den bekannten ?u?eren Lasten wird die Genauigkeit des Verfahrens überprüft.