Erfahrungen mit Warmwasserbereitern aus nichtrostenden Stählen

Experience with Water Heaters of Stainless Steel . Different stainless steels and their importance in the construction of domestic water heaters. Types of corrosion and their importance in water heating practice. Important aspects for manufacture. Experience gained with stainless steel water heaters.     

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.     

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.     

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.     

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.     

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.     

Ausmauerungen in chemisch beanspruchten Behältern und Apparaten

Brick-lining of Vessels and Process Units for Chemical Service. Bricklinings are used as an internal protection in chemically attacked vessels and process units. They generally consist of an impermeable membrane and the masonry itself. Materials of the single parts of the lining are described and guidelines for chosing materials and designing the lining are given. After some details of installing the lining typical examples of bricklined vessels and process units are given.     

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.     

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.     

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.     

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.     

Kaltgewalztes Flachzeug aus unlegierten weichen Stählen — Nach DIN 1623 Blatt 1

Cold-Rolled Flat Products of Plain Carbon Mild Steel According to DIN 1623 Sheet 1 . Cold-rolled flat products of plain carbon mild steel and among the most important finished products made by iron and steel works and rolling mills as well as being among the most important semi-products for industrial manufacture. Metallurgical and rolling developments during the course of the last twenty years have resulted in considerable improvements in the main cold forming properties of sheet and strip. The chief demand made of manufacturers of cold-rolled flat products is for sheet and strip which has been fully annealed and rerolled for good cold formability. Because of the various stresses on materials in the different forming processes, it is difficult to make a reliable prediction from test results about the behaviour of the material during actual forming operations. The new edition of sheet 1 of DIN 1623 prescribes the conventional test methods and their results as regards ensuring cold formability. The Standard does not include the additional means of using numerical values for vertical anisotropy r, work hardening exponent n and the maximum drawing ratio (ßo)_max.     

Simulation der Wärmebehandlung von Stählen am Institut für Werkstoffkunde I

Simulation of the heat treatment of steels at the Institut für Werkstoffkunde I The simulation of manufacturing processes is an important tool in simultaneous engineering. The aim is to cut the time necessary for development and to optimize processes by simulation of the complete manufacturing chain. The field of heat treatment offers a large variety of applications for the use of simulation tools. The geometry of the part, the composition of the material, the heat treatment process as well as the initial state of the parts interact with each other in complex ways and have an influence on the distortion of the part. The calculation of the microstructure and of the hardness distribution helps to determine suitable charging and quenching conditions as well as plant engineering. Calculated residual stresses and distortions can be taken into account in the development and construction of new parts. The Institut für Werkstoffkunde I of the Universität Karlsruhe (TH) is engaged in research programms in this field dealing with numerical as well as experimental problems for almost 30 years.     

Modellierung der Stängelkristallitbildung beim Hartlöten von Kohlenstoffstählen mit Kupfer

Simulation of columnar crystallite formation in brazed seams of copper‐brazed carbon steels When brazing steels of different carbon content with copper filler metal, columnar crystallites form on the carbon‐rich iron surface if the width of the brazing gap is smaller than 100 μm. Braze seams with such microstructures were described as early as the 1950ies and it was found out, that the strength of such a joint is significant enhanced, if this crystallites penetrate the entire seam. Extensive experimental investigations in recent years confirm, that the final average length of the crystallite increases superproportionally with decreasing brazing gap width and is almost inversely proportional to the difference in carbon content of the joined steels. Although many attempts to explain this phenomenon are known from literature, the mechanism of columnar structure formation has not been clarified properly until now. The aim of the present work was to develop an appropriate physical model, that describes the growth of crystallites as a function of carbon content in the base materials, the initial brazing gap width and the applied process parameters (temperature, time). The model is an appropriate tool for a general choice and development of filler metal‐base material combinations forming columnar crystallites in the braze seam.     

Untersuchungen zur Schwingungsrißkorrosion von unlegierten Stählen in wäßrigen Medien

Although a lot of work is done up to now in investigating corrosion fatigue many questions about the corrosion fatigue process of steel are still open. This applies for instance to the quantitative proportion at the complete damaging process which the corrosion strain component will assume and it applies moreover to special details of the crack initiation stage. The damaging process of corrosion fatigue of steel in the active state is generally supposed to proceed in the following three stages: “formation of pits”, “crack initiation” and “crack propagation”. The objective of the present study was at first to get by statistical means a quantitative assumption about the influence of the corrosive medium and secondly to get information about the contribution of pitting to the crack initiation process. Tension-compression experiments were conducted with specimen from steels Ck 15 and Ck 35 in the normalized state both without a corrosive influence (inert spindle oil) and with corrosive influence (desalted water, 3% NaCl-solution). It was found that the damaging process in its principal course is not affected by the kind of the corrosive medium but is hardly influenced by the extent of the load-amplitude at a given load-frequency.     

Aktivierungsenergie der wiederholten Karbidausscheidung in Stählen

Activation energy of repeated carbide precipitation processes in steels Dispersion microstructures in steels can be formed from the martensitic condition by repeated precipitation and coarsening of M₃C (or M₆C) particles. The precipitation stage comprehends the nucleation and the growth of one particle generation according to r ∝ t^1/2 (r – particle radius, t – time), and already after some minutes it turns into the dominating coarsening according to r ∝ t^1/3 (OSTWALD-ripening). The coarsening of the first precipitated particle generation is superposed with the following precipitation of further generations. They can be proved by the coercive field strength, the yield strength, microstructural mean values from scanning electron micrographs and by hardness tests. The occurring maxima of precipitation allow the evaluation of the activation energy for the effective volume diffusion in the α – Fe phase. By including the electronegativity (after L. Pauling ) the covalent bond in the M₃C phase is considered. With that is possible to attach the estimated activation energy to the main alloying (and diffusing) element and also to the total composition of the steel.     

Ergebnisse von Zeitstandversuchen mit glatten und gekerbten Proben aus den Stählen 20 CrMoV 13 5 und X20CrMoWV 121

Results of Creep Tests With Smooth and Notched Specimens of the Steels 20 CrMoV 13 5 and X20 CrMoWV 121 Two hydrogen resistant steels, viz. 20 CrMoV 13 5 W.-Nr. 1.7779) and X20 CrMoWV 12 1 (W.-Nr. 1.4935) used for bolts and nuts as well as for pressurized components were tested with respect to their creep resistance. Using smooth and notched specimens creep data for 450°C 500°C and 550°C were established. Steel 20CrMoV 13 5 was investigated in two quenched and tempered states (225…250 HB, 285…310 HB. The tempering treatments of X20 CrMoWV 12 1 (W.-Nr. 1.4935) lead to hardness levels of 215…226 HB resp. 275… 310 HB. Creep tests at 450°C and 500°C resp. at 500°C and 550°C were undertaken with smooth and notched specimens of 20 CrMoV 13 5-resp. X20 CrMoWV 12 1 -steels. At each temperature two resp. three different hardness levels were investigated which were produced by changing the quenching and tempering procedure. The results prove the X20 CrMoWV 12 1-steel to show high ductility in all three Q + T conditions even after long creep tests. This holds true for the 20 CrMoV 13 5-steel in the soft condition and at a test temperature of 450°C only. The creep strength of both steels is about proportional to the ultimate strength of both steels is about proportional to the ultimate strength at room temperature. With regard to the allowable stresses it could be shown that in each case the creep strength for 100.000 hours divided by a safety factor of 1.5 is smaller than the 1% creep limit for the same time.     

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.