Einfluß von Kaltverformungen bis 10% auf das Kurzzeitschwingfestigkeitsverhalten des austenitischen Stahles X 10 CrNiTi 18 9 (1.4541)

Influence of Prestrains up to 10% on the Low-Cycle-Fatigue Behaviour of the Austenitic Steel X 10 CrNiTi 18 9 (AISI 321) For an optimum design of locally elastic-plastic strained components in the low-cycle fatigue range the influence of prestrains due to manufacturing or an overloading has to be considered. Fatigue tests in strain-control with unnotched specimens from the cyclic hardening steel X 10 CrNiTi 18 9 show no significant influence of th prestrain. But in the load-controlled testing mode with notched specimens the improvement of fatigue-life is due to the decrease of local notch strain with increased prestrain. Hence an evaluation of the results on the basis of notch strains obtained in load-control shows that all fatigue data can be presented, like the strain-controlled tests, by the S-N-curve of the not prestrained material state investigated.     

Einfluß von Schweißen und Kaltumformung auf das Kurzzeitschwingfestigkeitsverhalten von austenitischem Stahl

Influence of Welding and Cold Forming on the Low-Cycle-Fatigue Behaviour of Austenitic Steel The low-cycle-fatigue behaviour of the austenitic steel X 10 CrNiTi 189, as received and welded, was investigated after cold forming up to 10 per cent by strain controlled tests. The fatigue life to crack initiation of the unwelded material is 10 times higher than the fatigue life of the butt-welded and unfinished material. The grinding of the butt-welds however leads to an increase of the fatigue life by a factor of 4 in comparison to the unfinished state. In comparison to these results obtained under 1 Hz the reduction of the frequency to 0.1 Hz causes a significant cyclic hardening and decrease of the fatigue life. The cold forming remains in all cases without influence. This hardening is a result of the diffusionless transformation of the austenitic microstructure into ferromagnetic α′-martensite under the lower frequency. The increase of the hardness caused also by the cold forming makes the stainless material more sensitive to corrosion.     

Einfluß der Laminatkomponenten von CFK-Werkstoffen auf das statische und das dynamische Verhalten

Influence of Different Laminate Components on the Static and Dynamic Properties of CERP The static and the dynamic properties of a conventional and a modified, toughened matrix system reinforced with two high strength carbon fibres of a different strain to failure was investigated. Three different laminates were chosen, an unidirectional laminate [0₈], a cross ply laminate [0₂, 90₂, 0₂, 90₂]_s, and a nearly quasi-isotropic laminate [0₂, ±45, 90 ]_s. It is shown, that the damage development under static as well as dynamic loading is delayed when using a toughened matrix system. This delay in damage development results in improved mechanical properties. However, when using a toughened matrix system together with fibres of a high strain to failure, the improvement of the static properties does not lead in the same extent to an improvement of the dynamic properties.     

Einfluß des Richtens auf das mechanische Verhalten von Federlegierungen

Influence of Levelling Processes on the Mechanical Behaviour of Spring Alloys Levelling processes – that means straightening of wire or level rolling of strip – have an impairing effect on the R_p0,2 and R_p0,1 proof strength of cold worked spring alloys and on the hysteresis behaviour of flat springs respectively. SEM and TEM investigations indicate that recovery is initiated by levelling processes and is intensified by a subsequent age hardening treatment. This may lead to a modification of age hardening behaviour and effectivity for those alloys which show different age hardening mechanisms in the cold worked and recovered state respectively. The detrimental influence of level rolling on the hysteresis behaviour is found to be due to an increased subgrain size after age hardening treatment. The results show that improvement of geometry by levelling processes is only possible at the cost of decreased spring properties.     

Einfluß der Gefügeparameter auf das Korrosionsverhalten von Eisenbasis-Legierungen

Structural Parameters on the Corrosion Behavior of Iron Alloys Composition and refinement of the microstructure of carbonaceous iron alloy can be changed by rapid quenching. This process may improve the corrosion resistance.     

Einfluß der Trennverfahren auf das Ermüdungsverhalten von Stahlblechen

Influence of Cutting Method on the Fatigue Behaviour of Steel Sheets The present paper gives the fatigue behaviour of test specimens which have been obtained by laser cutting, plasma cutting or punching from steel sheets. The paper demonstrates the different damage to the surface introduced by the three techniques. For thin sheets (1.5 mm) laser cut specimens show advantages, for thicker sheets (6 mm) plasma cut sheets exhibit better fatigue properties.     

Einfluß der Temperatur und der Umgebungsbedingungen auf das Ermüdungsverhalten metallischer Werkstoffe

Influence of Temperature and Environmental Conditions on Fatigue Behaviour of Metallic Materials The corrosion fatigue behaviour of metallic materials is influenced by environmental conditions. With increasing temperature a similar diminishing of fatigue strength can be observed as in the usual tensile properties. Air and water vapour decrease the number of cycles to fracture because they accelerate the crack propagation by adsorptive and reactive processes at the crack tip. By the effect of pure hydrogen or hydrogen sulfide and mixtures from both appears a marked increasing of crack propagation rate in fracture-mechanical test pieces alternating loaded at low frequency (1 Hz). Corrosive mediums influence also the formation of cracks. A mechanical electrochemical failure mechanism leads to a total loss of fatigue strength. Depending on performance of materials in an aggressive solution active or passive corrosion fatigue occurs. With regard to the form of appearance the two kinds differ in characteristic manner.     

Einfluß des Reinheitsgrades,der Kaltverformung und des Schweißens auf das Zeitstandverhalten von X20 CrMoV 12 1-Rohrstahl bei 550 °C

Influence of purity, cold work and welding on creep rupture behaviour of X20 CrMoV 12 1 tubes at 550 °C In the water steam circuit of the German Thorium High Temperature Reactor (THTR 300) a high tempered martensitic X20 CrMoV 12 1 steel with low P and S contents and improved impact toughness was used at the first time for live steam and reheater pipes. There were similar and dissimilar weldings (with austenitic steel alloy 800). Small pipes were cold bended. Therefore ABB started a material testing programm supported by BMFT. Creep rupture tests at 550 °C til 60 000 h led to following results:

• Creep rupture strength and 1 % creep strain limit of the tougher grade lie in the lower half of the commercial steel scatterband.
• Under service creep loadings tertiary creep begins after a life-time of about 60% resp. a plastic elongation of about 1 %.
• The creep damage can be described by microstructural classes.
• Only for small stress ranges there are nearly constant creep stress exponents which are independent from the melts.
• Low loading speeds reduce static elastic moduls.
• Cold work reduces creep rupture strength and deformation.
• Under stress transverse to welding joints the design according to creep rupture strength of the base material must include a reduction factor. The fine grained part of the HAZ is the weakest area.

With the results of long-time examinations the design of future HTR-plants, fossil-fired power stations, and chemical plants may furtherly be optimized.     

Zum Einfluß von Si und P auf das Verzinkungsverhalten Von Baustählen

The influence of Si and P contents in steels on the galvanizing behavior The galvanizing behavior of 40 structural steels in current use was investigated in relation to the complex influence of the Si/P content under conditions that are usual in the hot dip galvanizing industry (440/450/460 °C,5/10/15 min immersion time). The effect of P on the increase of coating thickness on steels with 0,01 to 0,40 % Si begins to be perceptible at > 0,020 % P. The influence of P increases with decreasing Si content of the steels and decreasing temperature of the melt. In steels with ≤ 0,12 % Si, an increased P content causes a shift of the thickness maxima in the temperature range from 440 to 450 °C, such as is otherwise typical of steels of 0,12 % to 0,28 % Si with < 0,020 % P. Zinc coatings on steels with the critical P/Si content (0 to 0,20 % Si/> 0,020 % P) as a rule are more unstable. With increased immersion time at the temperature stated above, floating away of the ξ phase into the zinc melt may occur. This could also be observed with Sandelin steels in the most critical Si range (0,07 to 0,10 %) with < 0,020 % P, with an immersion time of 15 min. It is possible to reduce the thickness of zinc coatings by adding small amounts of Al to the zinc melt (< 0,03 %). This effect of Al at a concentration that is below what is required for the known inhibitory action by the formation of an thin Fe₂Al₅-or Al-containing δ₁ film on the steel surface is attributed to the instability of the ξ phase, a proportion of which floats away into the zinc melt.     

Einfluß positiver und negativer Mittelspannungen auf das zyklische Spannungs-Dehnungsverhalten von normalisiertem Ck 45

Influence of Positive and Negative Mean Stresses on the Cyclic Stress-Strain Behaviour of Normalized Steel SAE 1045 In technical parts cyclic loads are often superimposed by static load components. In such cases, mean stresses influence the cyclic deformation behaviour and produce cyclic creep effects. Single step push-pull fatigue tests were carried out with normalized specimens of the steel SAE 1045. Using cyclic deformation curves and cyclic creep curves, the influence of different mean stresses will be discussed.     

Einfluß einer Mitteldehnung auf das Ermüdungsverhalten der Aluminiumlegierung AlMg5Mn

The effect of a superimposed mean strain on the fatigue behavior of the aluminum alloy AlMg5Mn The cyclic stress-strain response of the aluminum alloy AlMg5Mn in three different strength conditions is studied with emphasis on the influence of a superimposed mean strain and mean stress, respectively. The cyclic deformation behavior is characterized by a pronounced cyclic saturation independent of the prior heat treatment. Decreasing strength of the material is connected with a increasing extent of mean stress relaxation and cyclic creep, respectively. However, these transient effects are mainly restricted to the initial stage of cyclic life. In order to validate the lifetime data observed, a comparison with data from the literature is performed. For this purpose, it is necessary to apply a damage parameter which takes the damaging effect of a mean stress into account, since the cyclic lifetime values reported have mostly been obtained in tests without mean stress or mean strain. It is found that the damage parameter PSWT after Smith, Watson and Topper is suitable for the two conditions with higher strength. In the case of the soft condition, the damage caused by plastic mean strain is underestimated. As a consequence the cyclic lifes observed lie at the lower boundary of the scatter band of the literature data.     

Zum Einfluß wechselnder Temperaturen auf das Zeitstandverhalten von Nickellegierungen

On the Effect of Alternating Temperatures on the Creep Strength of Nickel Alloys. The design of parts for duty under creep stresses, such as turbine blades, had conventionally been rested on the assumption of linearly accumulating damage in the presence of alternating temperatures. Experimental work on nickel alloys has now shown that the damage will not generally accumulate linearly. Temperature alternations, when superimposed upon creep stresses, will cause multiplicative damage by impairing the creep strength and on occasion substantially promoting creep.     

Der Einfluß von Niob auf die Zeitstandfestigkeit von Schleudergußlegierungen mit 25% Chrom und 20% Nickel

The Influence of Niobium on the Creep Rupture Strength of Centrifugally Cast Alloys Containing 25% Chromium and 20% Nickel . The material most frequently used in chemical furnace construction is G-X 40 CrNiSi 25 20 steel. Because of the change to larger units and the increase in operating pressure and temperature it is often no longer possible to obtain sufficiently long on-stream times with this alloy. The development consequently turned to new alloy variants which held out promise of an improved creep rupture strength, with undiminished resistance to corrosion. By adding niobium to alloys containing 25% chromium and 20% nickel it is possible to improve the thermal stability of centrifugal castings. The creep rupture strength data of two niobium-containing melts of this type of steel were determined experimentally. The creep rupture strength characteristics of the CrNi-containing centrifugally cast alloys with and without niobium was compared by platting the scatter jointly on one chart.     

Spannungsfaktoren eines Risses in der Umgebung eines Kreisloches und ihr Einfluß auf das Bruchverhalten

Stress Intensity Factors in the Neighbourhood of a Circular Hole and their Influence on Crack Behavior . A photoelastic method was developed to determine the stress intensity factors K_I and K_II for cracks subjected to mixed-mode loading. The constants in the near field expansion about the crack tip were computed using a non-linear optimization program to give a best fit to the observed isochromatics. Copying the latter onto an equal density film increased their sharpness and, thus, the accuracy of the determination. The method was applied to cracks lying perpendicular to the external stress near a circular hole in a plate under uniaxial tension and the results used to describe the paths of cracks in the neighbourhood of a hole.     

Einfluß von Luftfeuchte und Werkstoffgefüge auf das tribologische Verhalten von Siliciumcarbid‐Keramik unter einsinniger Gleitbeanspruchung

Influence of humidity and microstructure on the tribological behaviour of silicon carbide ceramic in unidirectional sliding contact Tribological tests were carried out on self‐mated SiC in a laboratory tribometer (system: flattened ball‐on‐disc) to characterize the behaviour of silicon carbide ceramic under unidirectional sliding at relative humidities between 5% and 80%. Furthermore the influence of distilled water in the contact zone was investigated on friction and wear. The microstructures of the SiC ceramics variied concerning size and shape of the crystallites, pores and graphite particles. The results show that the friction coefficient increased with increasing relative humidity while the amount of linear wear tended to decrease simultaneously. The smallest friction coefficient and also a relatively small amount of linear wear were measured at the presence of distilled water compared to sliding contact in humid air. Tribological mechanisms could be explained based on studies of the worn surfaces by scanning electron microscopy and atomic force microscopy as well as considering the experimental data recorded during and after the tests.     

Einfluß des Sauerstoffes auf die Entladung bei der Spektralanalyse von Metallen in Edelgasen

Influence of Oxygen on the Discharge during Spectral Analysis of Metals in Inert Gases . This article features new considerations and tests for explaining the various types of discharge as well as the influence of oxygen. It describes a phenomenon hitherto not described in this context, i. e. the elimination of the oxygen effect by gettering. Some practical hints should particularly help checking the influence of oxygen.     

Einfluß des ZrO2-Zusatzes auf mechanische Eigenschaften und den ungeschmierten Gleitverschleiß von TiB2-ZrO2-Mischkeramiken

Effect of ZrO₂ addition on mechanical and tribological properties of TiB₂-ZrO₂-composites TiB₂-ZrO₂-composites were produced by hot-pressing in argon. The mechanical and tribological properties of the composites were investigated in relation to the amount and the type of the ZrO₂ added. Addition of ZrO₂ reduced the sintering temperature of the TiB₂-ZrO₂-composites and led to growth inhibition of the TiB₂ phase. ZrO₂ also increased the bending strength and fracture toughness of the composites. Tribological tests were carried out using laboratory tribometers under unlubricated oscillating sliding contact against Al₂O₃-, Si₃N₄- and SiC-counterbodies. Abrasive wear of the ceramics against 80 mesh SiC grits was studied by using an abrasive wheel test. During sliding contact the composites showed high wear resistance but caused extensive wear of the counterbodies and high friction coefficients compaired to self-mated monolithic Al₂O₃- and ZrO₂-ceramics. Volumetric wear loss of the TiB₂-ZrO₂-composites due to abasive SiC grits was by a factor up to 30 lower than that of a commercial monolithic Al₂O₃. Wear resistance of the composites increased with decreasing amount of ZrO₂ and was higher for the composites with addition of partially stabilized tetragonal ZrO₂ than for those with addition of monoclinic ZrO₂.     

Einfluß von Verfahrensparametern beim Fließpressen auf das Ermüdungsverhalten

Effect of Process Parameters in Extrusion on Fatigue Behaviour Fatigue test specimens were produced by forward extrusion and subsequent heading from conventional steels, P/M steels and AlMg4.5Mn. The strain, die-opening angle, temperature and in some cases the lubricant were varied. For purpose of comparation in some cases also specimens were prepared by machining. S/N curves or cyclic deformation curves were determined mainly by stress-controlled tests. For all materials the time strength was increased by cold forming whereby the effect of strain was stronger than that of the die-opening angle. The time strength of steel is less increased by warm (semihot) forming than by cold forming. The fatigue strength, however, is not necessarily increased by cold or warm forming. After cold forming the P/M steels contrary to conventional steels revealed mainly quasielastic deformation until fracture. After warm forming, however, P/M steels, due to the decrease of porosity, behaved almost like conventional steels. For AlMg4.5Mn specimens prepared by forming – probably due to worse surface quality – revealed a lower fatigue strength than those prepared by machining. Here also a feasible effect of the choice of the lubricant was stated.