Verhalten von Stählen unter Hohlladungsbeschuß

Behaviour of Steels under Shaped Charges Bombardement. There is at present not too much known about the behaviour of steel under the very high pressures of some 100 kbars as they will be produced by the hydrodynamic jet force stream of a shaped charge. In a short revue the hithero existing knowledge of the formation of a jet force stream is given as the phenomens in the penetration process of a material. It is recognized by bombardement tests on iron and steels of different compositions and of different heat treatments that there are some changes of the structure near the boundaries of the penetration channels. There is given some information by light- and electronmicroscopical investigations about the occurence during the hydrodynamic penetration process of the jet force stream and about the behaviour of the different structures under local concentrated pressures of shock waves. Microprobe-analyses and scanning electron microscope micrographs supply the understanding.     

Kurzzeitschwingfestigkeit von duktilen Stählen unter mehrachsiger Beanspruchung

Low-Cycle Fatigue of Ductile Steels under Multiaxial Deformations To investigate the fatigue behaviour of cyclically softening and hardening steels under multiaxial elastic-plastic strains, axial strain and shear strain controlled fatigue tests under constant amplitude loading were carried out. S-N curves under axial strain and torsional pure shear as well as under combined axial strain and shear, in and out of phase, were obtained for the cyclically softening tempered steel 30 CrNiMo 8 (similar to AlSI-Type 4340) and the cyclically hardening quenched stainless steel X 10 CrNiTi 189 (AISI-Type 321) in the region of low-cycle fatigue. For both steels, used in the design of vessels, pipings, shafts, etc. the fatigue life to crack initiation is reduced by an out of phase (δ = 90°) shearing of the strained specimens in comparison to the in phase loading. The decrease of fatigue life under out of phase strains is caused by changing direction of principal strains resulting in an interaction of the deformations in all directions of the surface. This interaction is taken into account by a calculation procedure deriving an equivalent strain and predicting the fatigue life under combined strain on the base of S-N curves for unaxial strain.     

Eigenschaften und Verwendungsgebiete von niedriglegierten warmfesten Stählen

Properties and applications of low-alloy steels for elevated temperatures. Demands on steels for elevated temperatures. Tensile and toughness data on Manganese Nickel Molybdenum Vanadium steels with ferritic-bainitic structures in dependence of the chemical composition and the temperature. Influence of pulsating stresses. Examples of application.     

Karbidpartikelbildung und Diffusion in Stählen

Carbide Particle Formation and Diffusion in Steels The adjustment of dispersed microstructures in Cr and Mn alloyed steels by precipitation of carbide particles M₃C was carried out from the martensitic initial condition by annealing in the temperature range T = 500°…700°C about the time t = 1…4290 min. In this connection it was already shown that the nucleation, the particle growth and coarsening run off parallel, where the coarsening is the dominating process. With the increase of the particle volume according to r³ α t (r – particle radius) final particle sizes were obtained asymptotically. The increase of the particle volume in the coarsening stage can be only maintained, if small particles will be dissolved again. This process can be written well with the Ostwald-ripening relationships. Permanent concentration changes at the nucleation sites resp. in the decompositing matrix are necessary. By means of the Ostwald-ripening law the effective chemical diffusion coefficients D_eff of the alloying elements C, Mn, Si Mo and Cr in the α-Fe-matrix could be evaluated. D_eff changes with the decomposition of the matrix by a few orders of magnitude. The diffusibility of the elementes depends on the alloying content in the matrix. C has as expected the greatest mobility, Cr shows the smallest one. The lattice bond seems to be of significance. Moreover the values of activation energy of carbide particle precipitation Q and the frequency factors D₀ in the Arrhenius-relationship were evaluated applied to the steels investigated. With this the necessary diffusion data relative to short till to longtime thermal treatment for the adjustment of heat-treated microstructures are available. The lower and the upper limiting values of the carbide particle size spectra can be taken from the plots referred to the Mn and Cr alloyed steels.     

Festigkeitsverhalten von Schweißverbindungen unter kombinierten phasengleichen und phasenverschobenen mehrachsigen Beanspruchungen

Fatigue Behaviour of Welded Joints under Combined In-and Out-of-Phase Multiaxial Loading Welded crucifix-type specimens from fine grained steel StE 290 and flange-tube as well as tube-tube joints from fine grained steel StE 460 with unmachined and machined welds were investigated under biaxial constant amplitude loading in the range of 10³ to 5 · 10⁶ cycles to crack initiation and break-through, respectively. In order not to interfere with residual stresses they were relieved by a heat treatment. Inphase loading can be treated fairly well using the conventional hypotheses (von Mises or Tresca) on basis of nominal, structural or local strains or stresses. But the influence of out-of-phase loading on fatigue life is severely overestimated if conventional hypotheses are used. However, the introduced hypothesis of the effective equivalent stress leads to fairly well predictions. Herefore, the knowledge of local strains or stresses is necessary. They are determined by boundary-elemente analyses in dependency of weld geometry. This hypothesis considers the influence of out-of-phase loading by taking into account the interaction of local shear stresses acting in different surface planes of the material. Further, size effects resulting from weld geometry and loading mode were included.     

Haftfestigkeit von Metallschichten auf Stählen bei statischer und wechselnder Beanspruchung

Influences of Static and Dynamic Load on the Adhesive Strength of Thermally Sprayed Metal Coatings on Steels It were the aims of this work to produce metal-sprayed specimens and workpieces with high resistance to static and dynamic load, to prove these properties by appropriate measurements and to give advices for practical application. For this purpose, two different substrate materials were metal-coated with five materials by use of three spraying techniques. As a result of the investigations, it can be summarized that specimens, which were shot-peened prior to spray-coating reached the same fatigue limit as only shot-peened specimens, independent on the spraying technique applied.     

Verzug von Stählen infolge Wärmebehandlung

Distortion of Steels Due to Heat Treatment Distortion comprises size and shape distortion. Size distortion is brought about by thermal stresses and structural changes, mainly by hardening and tempering. Thermal stresses cause size-dependant, structural changes size-in dependent distortion. Size-distortion is a system property. Tempering at room temperature over a long period of time influences the size stability. Material anisotropy leads to directional distortion. Shape distortion or warpage originates in residual stresses and differences within the material. Further a nonsymmetrical temperature distribution or geometry of the part have to be considered.     

Vorhersage der Lebensdauer und Dauerfestigkeit von hochfesten,durchhärtenden Stählen

Fatigue Lifetime and Endurance Limit Prediction for High‐Strength Steels Smooth and notched specimens of the bearing steel 100Cr6 (SAE 52100) in a bainitic condition were used to determine the S‐N curves under tensile, torsional and combined in‐ and out‐of‐phase loading. In the area of high‐cycle fatigue, crack initiation was most likely caused by inclusions like Titanium Carbonnitrides or Aluminium Oxides. A micro mechanical model for the crack initiation by inclusions was developed. Another model was developed to describe the influence of these inclusions on the lifetime. A weakest‐link model, using the statistical distribution of inclusions and surface flaws, was used to describe the endurance limit.     

Sprühkompaktieren von Halbzeugen unterschiedlicher Geometrie aus unlegierten und niedriglegierten Stählen

Sprayforming of unalloyed and low alloy steel preforms Sprayforming offers the possibility to produce a variety of preforms in a single step directly from the melt. Numerous processing parameters ensure high flexibility but require detailed knowledge concerning the microstructure of sprayformed material depending on chemical composition and processing parameters. Within the current study fundamental investigations using unalloyed and low alloy steel grades (C15, C105, 100Cr6) for sprayforming of plates and billets have been performed concerning the influence of chromium and carbon content and selected processing parameters. Sprayformed preforms revealed austenite grain sizes up to 500 μm depending on the development of porosity. Different types of porosity have been detected which can be associated with incomplete densification due to high cooling rates, solidification shrinkage and entrapped nitrogen. Atomisation gas pressure and carbon content are parameters of primary importance.     

Die Werkstoffdämpfung von Stählen bei hohen Dehnungsamplituden

Damping of Steels at High Strain Amplitudes The amplitude dependent damping has been investigated in two martensitic chromium steels (X 22 CrMoV 12 1, X 20 Cr 13) and a cold worked austenitic steel (X 12 CrNiWTi 16 13) at room temperature. Due to the magneto-elastic effects, the martensitic steels show a strong amplitude dependent damping. It cound be shown that the damping is reduced remarkably by a reduction of the annealing temperature. The austenitic material shows a very high damping in the cold worked condition. Tempering at relatively low temperatures (above 100 °C) reduces damping to the low values usually expected for austenitic materials. This effect was attributed to the pinning of dislocations during tempering.     

Gezieltes Beizen von Apparaten aus chemisch beständigen Stählen

Controlled Pickling of Apparatus made of Chemical-Resistant Steels Examples of material failure and corrosion trials are used to show that the chemical resistance of austenitic steel depends in many ways on the surface condition. Pickling is the best method for removing layers of oxide in preparation for passivation. Internal tensile stresses which are created near the surface by mechanical working, e.g. by turning, drilling and grinding, can assume higher values than those caused by shaping and welding. As a result stress corrosion cracking often occurs only in the region where the surface has been worked. Because the stresses responsible for this phenomenon rapidly fall off below the surface, it is usually possible to reduce them by pickling to the point at which damage of this kind is prevented. The amount of material which must be removed by pickling is determined by trials and pickling must be controlled accordingly.     

Der Einfluß von Festigkeit und Druckeigenspannungen auf die Wechselfestigkeit von Stählen bei höheren Temperaturen

Influence of Hardness and Comprehensive Residual Stresses on the Fatigue Limit of Steels under Elevated Temperatures The room temperature fatigue behaviour under alternating stresses of bcc steels is characterized by two stationary states existing below two different reversed stress limits: Below the one no crack initiation occurs, below the other no crack propagation can be found even after an unlimited number of stress cycles. The fatigue endurance of unnotched parts is determined by the crack initiation conditions that can be improved by higher hardness of the material. The fatigue strength of notched parts under reversed stresses is decidently determined by the minimum stress required to propagate a crack; this stress can be raised by compressive residual stresses. – At elevated temperatures these two stationary states are not further existent and there are no alternating stress amplitudes that can be endured either without crack initiation or without crack propagation to fracture. Both influencing parameters hardness and compressive residual stresses are dependend on the temperature, this can be explained by Snoek's and by Cottrell's mechanisms and with the temperature depending release of residual stresses corresponding to the temperature sensitive yield point.     

Beitrag zum Einfluß von Druckwasserstoff auf die mechanischen Eigenschaften von Stählen

Contribution to the Influence of Pressurized Hydrogen on the Mechanical Properties of Steels The investigation method of using hollow specimens in tensile tests to examinate steels for hydrogen service is described. Reduction of area after fracture, Z, resulting from these tensile tests with constant strain rates shows not only a significant but also a constant difference between hydrogen and nitrogen when being plotted versus strain rate. Therefore a newly introduced term named “Index of embrittlement” and characterized by the relation of Z with nitrogen and with hydrogen was found to be independent of strain rate. With strain rate ε = 10^?6 s^?1 chosen for a “critical” one because of lacking in a maximum index of embrittlement several European steels for hydrogen service were tested to find out their individual index of embrittlement. Assisted by light optical microscopy it was found that there is a special correlation between microstructure, index of embrittlement and tensile strength of a given steel grade.     

Korrosionsuntersuchungen an drei Stählen und einer Nickellegierung in Mono- und Trichloressigsäure

Investigations Into the Corrosion of Three Steels and one Nickel Alloy in Mono- and Trichloroacetic Acid The corrosion resistance of three steels and one nickel alloy was investigated in aqueous and nonaqueous monochloroacetic acid and in nonaqueous trichloroacetic acid at various temperatures. There is no difference in the corrosion behaviour of the steels whereas the resistance of the nickel alloy is better in all cases by a factor 10. In aqueous monochloroacetic acid the corrosion attack is due to the hydrolytic formation of hydrochloric acid. Nonaqueous monochloroacetic acid behaves more corrosive than nonaqueous trichloroacetic acid.     

Trockener Gleitverschleiß an Ingenieurkeramiken und Stählen durch mineralische Stoffe

Dry Sliding Wear of Engineering Ceramics and Steels in Contact with Minerals Dry and unlubricated sliding wear against flint, corundum and silicon carbide was studied on oxide and non-oxide ceramics by using two different model systems at room temperature.-Wear behaviour of the ceramics was compared with that of steels and hard chromium coating. Type anß size of the abrasive minerals and the load were systematically varied. The results showed that wear resistance of the ceramics can be greater or smaller than that of the steels depending on the experimental conditions. Conclusions may be drawn for applications of modern engineering ceramics.     

Untersuchungen des Gleit- und Furchungsverschleißes an thermochemisch behandelten Stählen

Sliding and sliding abrasion tests of thermochemically treated steels The results of research work during several years are presented summarily. The results were obtained jointly by the Bundesanstalt für Materialprüfung (BAM), Berlin, and Stiftung Institut für Härterei-Technik (IHT), Bremen. The wear tests included hardened, casehardened, nitrided, nitrocarburized, chromized, chromvanadized and vanadized steels and were performed with dry friction in air and in vacuum, and with mixed lubrication. Under these conditions adhesion, abrasion and tribo-oxidation were the main wear mechanisms. The results reveal that the wear evaluation order of the differently heat treated steels depends on the type of wear and the operating wear mechanisms.     

Einfluss der Werkstoffzähigkeit auf das Festigkeitsverhalten unter mehrachsiger Beanspruchung am Beispiel von Schweißverbindungen aus Stahl und Aluminium

Influence of Ductility on the Multiaxial Fatigue Behaviour by the Example of Welded Joints of Steel and Aluminium The multiaxial fatigue behaviour of materials with different ductility under constant and changing principal stress directions is also applicable to welded joints of different materials. For this, welded flange tube connections of the fine grained steel StE 460 and the artificially aged aluminium alloy AlSi1MgMn T6 were investigated under constant amplitude combined bending and torsion. Out‐of‐phase loading, i. e. changing principal stress directions, of the steel joints led to a decrease of fatigue life, which is observed at ductile material states. However, for the aluminium joints out‐of‐phase loading resulted same behaviour as in‐phase loading, which indicates a semi‐ductile material behaviour. The results for the welded steel joints were evaluated on basis of local stresses by the integral hypothesis of the Effective Equivalent Stress EES (WVS). This hypothesis for ductile material states takes into account the life decreasing influence of out‐of‐phase loading by considering the interaction of the shear stresses on different planes. The fatigue behaviour of the aluminium welds is described by the critical plane based combination of shear and normal stresses (KoNoS), which is valid for semi‐ductile material states.     

Auswirkungen der Schädigungsanisotropie auf die Lebensdauer von Stählen bei Zeitstandbeanspruchung

The effect of anisotropic damage on the rupture-time of steel under creep conditions The aim of the investigation is the prediction of the influence of creep history, e. g. pre-damage and pre-loading, on the further creep behaviour after changing the loading direction. The changing of the loading direction has a significant influence on the rupture-time. A model has been developed which describes the dependence of rupture-time from the anisotropic effect of damage.