Nickel-Molybdän-Sinterstähle für hochbeanspruchte Teile

Nickel-Molybdenum Sintered Steels for High Duty Parts . Fe-Ni-Mo steels without additions and with 0,45% P resp. 0,5% C added were sintered at 1150°C resp. 1250°C for 1 h in H₂. 2% Ni and 1,5% Mo resp. 4% Ni and 3% Mo were added as alloying elements. The strength of the sintered Fe-Ni-Mo alloys without additional elements did not exceed remarkably that of the sintered steels used up to now. Fe-Ni-Mo steels with 4% Ni and 3% Mo sintered at 1250°C with an addition of 0,45% P resp. 0,5% C have a tensile strength of 740 N/mm² resp; 830 N/mm². However the impact toughness of the alloy with P is remarkably higher than that of the alloy with C. The C-content determines mainly the strength properties of the alloys with C and influences the diffusion of the Mo too. The influence of the Ni and Mo on the properties of the alloys with P is more obvious. Alloys with 4% Ni and 3% Mo containing 0,45% P have good static and dynamic strength and therefore are capable for high duty parts.     

Langzeitverhalten einiger warmfester Stähle unter betriebsähnlicher Kriechermüdungsbeanspruchung

Long–term behaviour of some heat resistant steels under service–type creep–fatigue loading The long-term creep-fatigue behaviour of four heat resistant steels is investigated by service-type strain cycling with test durations up to 30 000 h. The creep-fatigue life is analysed on the basis of the generalized damage accumulation rule. The influences of prior service-type strain cycling on the basic creep and fatigue properties are taken into account.     

Flächenpressung unter Schrauben aus austenitischen Chrom-Nickel-Stählen

Allowable limits for loads under heads of fasteners out of stainless austenitic chromium nickel steels. Safety and load carrying capacity of fastened joints are determined through the strength of the fasteners, the pressure under the head and nuts which can be endured without plastic deformations and the variation of the actual preload. The strength of screws of stainless steels are known with its variations since long time. The allowable pressure under the head and nut of fasteners for the various austenitic chromium steels in the solution annealed and cold formed condition are not known so far. The result of such investigations for the important austenitic chromium steels are published herewith. The now known loadability limits must be recognized. After loading above these limits a recreational effect was observed for which interpretations and explanations still have to be found.     

Vorbeanspruchungsabhängige Schadensakkumulation bei der Kriechermüdung warmfester Stähle

Influenced prior loading on the creep fatigue damage accumulation of heat resistant steels On two heat resistant power plant steels the influence of prior strain cycling on the creep rupture behaviour and the influence of prior creep loading on the strain cycling behaviour is investigated. These influences concern the number of cycles to failure and the rupture time being the reference values of the generalized damage accumulation rule and they are used for a creep fatigue analysis of the results of long term service-type strain cycling tests.     

Zeitstandverhalten warmfester Stähle bei zyklischer und bei intermittierender Beanspruchung

Creep and Creep Rupture Behaviour of Heat Resistant Steels under Cyclic and Intermittent Loading Conditions On typical heat resistant steels creep and creep rupture tests under rectangular cyclical conditions of tension stress or/and temperature were continued. Comparable creep and creep rupture tests with tension and compression phases and with intermittent loading conditions were started. Besides this single-stage loading conditions, double-stage loading conditions were investigated. The test results are analysed with the modified life fraction rule. Concepts of relative life are improved and partly new established.     

Multiaxial fatigue behaviour of Sintered Steels under combined in and out of phase bending and torsion

This paper discusses the fatigue behaviour of sintered steels under multiaxial loading. These steels are the Fe-1.5% Cu and the Fe-2.0% Cu-2.5% Ni, sintered at low and high temperatures, in the densities 7.1 and 7.4 g/cm³, which are used in the production of several ready to assemble automotive parts. Fully reversed or pulsating combined loading with constant frequency and amplitudes acting in and out of phase, was applied to round notched specimens (K_tb = 1.49, K_tt = 1.24) in the finite fatigue life region (10⁴ ≤ N_f ≤ 2 · 10⁶). The mechanics of crack initiation and propagation as well as rupture were studied using fractography and microfractography. These analyses led to a mechanical model based on local normal stresses for the fatigue life evaluation. The fatigue life evaluation on the base of the local bending stress obtained under uniaxial loading describes the test results for in phase combined bending and torsion satisfactorily. But the increase of fatigue strength and life by out of phase loading is overestimated in the case of fully reversed loading. However for design purposes the out of phase loading can be neglected because of its beneficial effect in increasing fatigue life for this type of material. If the dependence of the different stress concentrations under combined in and out of phase loading on the supportable local bending stress obtained under uniaxial loadings is considered, then the calculation procedure covers all test results.     

Rißfortschritt in ultrafesten Stählen und deren Schweißverbindungen bei dynamischer Beanspruchung

Crack propagation in ultra-high-strength steels and their welded joints under dynamic loading . Reported are results of investigation into the propagation of cracks in the base metal and weld metal of an ultra-high-strength steel. The material used in the investigations was a Ni? Co? Mo? alloy maraging steel with a yield point of 170 kp/mm². The steel was arc welded and TIG welded. The joints exhibited a drop of static strength in the range of 5 to 8 percent related to the base metal. Under zero-to-tension stress cycles the fatigue strength corresponded that of other high-strength steels, under tension-compression stress cycles the steel exhibited a higher fatigue strength. It was possible to show striations with the aid of scanning microscopy. Comparing the track propagation calculated in the microscopic range with the results obtained from the crack growth curves produced approximate agreement.     

Rost‐ und säurebeständige Stähle unter Komplexbeanspruchung

Rust and acid resistant steels under complex loading With corrosion fatigue investigations under different loadings (R = 0,27, ‐1 and 10) and with inner pressure tests a duplex steel (1.4462) and a super austenitic steel (1.3974) are compared. The investigations were carried out in 10 % HNO₃, artificial seawater according to DIN 50905 and in two very important liquids for application (artificial seawater according to DIN 50905 with H₂S aerated and water with chloride, fluoride, bromide, iodide). For comparison the same tests under only mechanical loads were done in acid free oil. The results show that the super austenitic steel has an significantly higher resistance against corrosion fatigue as the duplex steel under one‐ and three dimensional loads up to 10⁷ cycles. The proportion between the results in the corrosive liquids and the oil can be described by a factor. In artificial seawater factors between 0,67 and 0,92 and in 10 % HNO₃ between 0,67 and 0,83 were determined depending from the loading for the duplex steel. With the super austenitic steel factors between 0,86 and 1 in artificial seawater and between 0,7 and 1,0 in 10 % HNO₃ were received.     

Einfluss der Schweißparameter auf das Ermüdungsverhalten hochfester Baustähle

High strength low alloy steels are used in many different engineering areas. A commonly used joining technique for those steels is fusion welding. Generally, these components have to withstand fatigue due to dynamic loading. Using thermal joining techniques affect the mechanical properties of the steel. This study focuses on the influence of the heat input on the microstructure of high strength low alloy steels (S690). Furthermore, the fatigue behaviour with special regard to crack initiation and crack propagation is characterized.     

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.     

Beständigkeit verschiedener Stähle und Nickelbasiswerkstoffe unter dem Einfluß aufnitrierend wirkender Gase in der Ammoniak-Synthese

Resistance of Various Steel Types and Nickel-Base Alloys Under the Influence of Nitriding Gases in Ammonia Syntheses Plants The paper describes test results obtained during 5 years of practical trials with heat-resisting steels, steels for hydrogen service, austenitic steels and nickel-base alloys under the nitriding operation conditions found in an ammonia plant at temperatures of more than about 400°C. During the test, nitriding rates and depths at high temperatures and under stresses were established, as well as changes in the mechanical properties as a result of nitriding. Based on the test results and the knowledge of the subject matter, recommendations and service condition limits for material selection are given. The superior behaviour of austenitic materials, especially with increasing nickel contents, could be confirmed. An attempt is made to find an explanation for the reduced resistance to hydrogen attack under the influence of nitridation.     

Charakterisierung des Ermüdungsverhaltens hochbeanspruchter Eisenbahnvollräder für den Hochgeschwindigkeitspersonenverkehr bei betriebsrelevanten Temperaturen

Fatigue assessment of highly loaded railway monobloc‐wheels for application in high‐speed passenger‐traffic trains under thermal service conditions Railway wheel steels rank among the most loaded components of railway vehicles. Whereas increasing driving speeds increase in particular the cyclic mechanical loading, increasing acceleration and braking torques lead to enormous thermal loads. Hence, a detailed knowledge about the microstructure‐related characterisation of the fatigue behaviour of railway wheel steels under thermal service conditions is the fundamental precondition for a save and economic operation of railway systems. Current investigations concentrate on the fatigue behaviour of actual UIC‐conform high‐speed passenger‐traffic railway wheel steels, which were provided in industrial relevant heat treatment conditions. Microstructural gradients are a consequence of the industrial heat treatment and the size of the component. Specimens were machined from defined depth positions of the wheel rim from original monobloc wheels. Plastic strain amplitude, change in temperature and change in electrical resistance measurement techniques were used to characterise the fatigue behaviour in detail. The specimen position and therefore the local microstructure influence the fatigue behaviour in a characteristic manner.     

Kriech- und Bruchverhalten warmfester Stähle in kennzeichnenden Fällen veränderlicher Zeitstandbeanspruchung

Creep and Creep Rupture Behaviour of Heat Resistant Steels under Variable Loading Conditions The creep and creep rupture behaviour under rectangular cyclical conditions was measured on 8 typical heat resistant steels up to 35 000 h test duration. The results are described by the modified life fraction rule. The main dependencies of the characteristic of that rule, the relative life, are investigated. Concepts for the evaluation of the relative life are presented in regard to design and supervision of components.     

国产低屈服点钢材循环加载试验研究

为研究不同荷载作用下国产低屈服点钢的材料力学行为,对LY100、LY160及LY225钢材共46个试件进行了单调拉伸试验及12种不同加载制度的循环加载试验。对国产低屈服点钢的单调性能、滞回性能、破坏形式、延性特征等进行了分析,并与其他结构钢材的力学性能进行了对比。结果表明,低屈服点钢在循环荷载作用下有明显循环强化现象,塑性变形能力强,且与普通钢材相比延性及耗能能力突出。该试验结果为后续研究低屈服点钢本构模型提供基础。     

Zur Zähigkeit von Vergütungsstählen

On Toughness of Quenched and Tempered Steels Toughness as consumed fracture energy is dependent on fracture mechanism. Grain size and loading conditions influence the transition from ductile dimple fracture to brittle cleavage fracture. In quenched and tempered steels packet size and particle distribution are of importance as well as brittle intergranular fracture modes by grain boundary segregation of impurities in ferrite (temper embrittlement) or precipitates in austenite. Anisotropy of toughness arises from banded structures.     

Entwicklung mit Hilfe des Warmpreßverfahrens hergestellter Sinterstähle mit optimaler Warmstreckgrenze,Dauerfestigkeit und Kerbschlagzähigkeit – Teil 1

Development of Hot-Forged Sintered Steels with Optimum Yield Point at Higher Temperature, Fatigue and Impact Strength . The material characteristic values of hot-forged sintered steels are reported. Besides the usual properties, (ultimate tensile strength, yield strength and elongation at room temperature). The behaviour of materials at higher temperature is of great importance. Further, fatigue strength and impact strength must be considered. The influence of heat treatment on these properties were investigated and brought to a correlation with the formation of microstructures. The hot forging P/M preform requires a special attention on alloying elements and alloying techniques. Optimum properties results when using completely alloyed powders or mixed powders by employing special master alloys. This and further problems involving alloying techniques and particularly the behaviour of carbon as an alloying element is reported in details. The correlation between mechanical properties and fracture behaviour is discussed.     

Entwicklung mit Hilfe des Warmpreßverfahrens hergestellter Sinterstähle mit optimaler Warmstreckgrenze,Dauerfestigkeit und Kerbschlagzähigkeit – Teil 2

Development of Hot-Forged Sintered Steels with Optimum Yield Point at Higher Temperature, Fatigue and Impact Strength . The material characteristic values of hot-forged sintered steels are reported. Besides the usual properties, (ultimate tensile strength, yield strength and elongation at room temperature). The behaviour of materials at higher temperature is of great importance. Further, fatigue strength and impact strength must be considered. The influence of heat treatment on these properties were investigated and brought to a correlation with the formation of microstructures. The hot forging P/M preform requires a special attention on alloying elements and alloying techniques. Optimum properties results when using completely alloyed powders or mixed powders by employing special master alloys. This and further problems involving alloying techniques and particularly the behaviour of carbon as an alloying element is reported in details. The correlation between mechanical properties and fracture behaviour is discussed.     

Werkstoffverhalten und Mikrostrukturentwicklung hochfester Mn‐Al‐Si‐Leichtbaustähle unter Zugbelastung

Material behaviour and microstructure evolution of high‐strength Mn‐Al‐Si‐light‐weight steels under tensile loading Because of their extraordinary combination of high strength and superior ductility high‐strength high Mn‐steels with reduced density and additions of aluminium and silicon are interesting candidates for structural applications. The initial microstructure consisting of stable austenite or austenite and ε‐ and α'‐martensite was achieved by alloying. During plastic deformation intense strain induced martensitic transformation and / or mechanical twinning was observed. These deformation mechanisms are used to extend the limited forming capability and contribute to a high energy absorption (in impact tests) up to very high strain rates. Tensile tests reveal that the properties are maintained up to strain rates of about 1000 1/s. The flow stress behaviour is strongly influenced by the initial microstructure and their evolution during deformation processes is determined by the rates of martensite and twin formation, respectively.     

Versuchs- und Rechendaten zur Dauerschwingfestigkeit von metallischen Werkstoffen unter mehrachsiger Beanspruchung

Experimental Data and Calculated Results about the Fatigue Endurance Limit of Metals under Multiaxial Alternating Load An extensive catalogue of present available experimental data about the fatigue endurance limit of metallic materials under multiaxial loading conditions and thereupon determined deviation ratios between experimental results (long life fatigue tests) and calculated values by five newer computation methods is demonstrated (a further showed statistical analysis of these devations indicates, that in relation to the other failure criterions the ?Quadratische Versagenshypothese”? QVH is preferably recommended for a reliable application). The tabulated data-catalogue totally includes 530 referenced loading cases (limited to various biaxial states of combined normal and torsional alternating stress with sinusoidal synchronous or out-of-phase amplitudes and superimposed mean stresses) with experimental results (probability of survival of P_S = 50%) on metallic materials (unalloyed and alloy steels, non-ferrous metals and wrought aluminium alloys, cast irons and sintered metals).