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.     

Mehrstufige betriebsähnliche Dehnwechselbeanspruchung warmfester Stähle

Multi-stage service-type strain cycling of heat resistant steels The creep-fatigue behaviour of three heat resistant steels is investigated by service-type three-stage creep-fatigue tests up to 8000 h duration. Creep-fatigue damage is calculated on the basis of the generalized damage accumulation rule. Different cycle counting methods are taken into consideration.     

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.     

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.     

Beschreibung des Kriechverhaltens einiger warmfester stähle

The creep behaviour of important heat resistant steels is examined to establish creep equations. For two well tested materials, equations are proposed, which are valid in the whole range of temperature, stress and time.     

Schichtcharakterisierung nitrocarburierter Stähle

Coating characterization of nitrocarburized steels In this investigation, a systematic characterization of the diffusion coatings was carried out. These coatings, developed by different nitrocarburizing processes, namely salt-bath, gas and plasma nitrocarburizing, were conducted on various steel substrates. The tested substrates were St. 52-3, Ck 45, 42 CrMo 4, 30 CrNiMo 8 and X 20 Cr 13. The thickness of compound layers and their porosity were measured using optical microscopy. The structure of compound layers was characterised using an X-ray diffractometer and their surface roughness by a stylus profilometer. The surface hardness measurements and hardness profiles were carried out according to the Vickers principle.     

Bruchverhalten der Stähle

Fracture Behaviour of Steels Crack formation during production or by monotonic, cyclic, chemical and thermal loading during service. Stable and unstable crack propagation. Clivage, dimple, intercristalline and fatigue fracture. Influence of temperature, loading conditions and microstructure on the transition from tough to brittle fracture behaviour.     

Aktivierte Randaufstickung nichtrostender Stähle

Activated Solution Nitriding of Stainless Steels The solution nitriding of the stainless steels can be optimized by a two stage process. The first stage involves an surface activation and an enrichment of nitrogen in the case due to internal nitriding. After this step at temperatures between 1070 °C and 1150 °C follows the dissolution of the chromium nitrides and a solution nitriding. Investigations of ferritic, martensitic and austenitic steels showed that this technology is superior compared to the one stage technology. The treatment time for an given layer thickness in the high temperature stage is cut in halve. The case concentration of nitrogen can be controlled by a material specific choice of the treatment temperature and the partial pressure of nitrogen. For the investigated steels the desired microstructure of the case could be achieved by partial pressures of nitrogen between 0,35 an 1 bar. The solution nitriding of ferritic-martensitic steels eneables the production of martensitic cases with a hardnesses up to 700 HV 0,3. An austenitic case with higher hardness and stability of the austenit can be produced by enrichment the surface of austenitic and ferritic-austenitic stainless steels with nitrogen.     

Das totaldehnungskontrollierte Wechselverformungsverhalten unlegierter Stähle im normalisierten Zustand bei Raumtemperatur

In total strain-controlled tests without mean strain the cyclic deformation behaviour of unalloyed normalized steels with carbon contents 0,1 ≤ C ≤ 1,05 (wt.-%) is characterized by pronounced softening and slight hardening processes. With increasing carbon content the cyclic deformation curves are shifted to higher stress amplitudes. Cyclic stress strain curves of unalloyed steels determined in tests without mean load are independent of the testing procedure. With increasing carbon content the number of cycles for ε_a,e = ε_a,p (transition point) of strain-controlled SN-curves is shifted to smaller values.     

Abrasiver Verschleiß nitrocarburierter Stähle

Abrasive wear of nitrocarburized steels Diffusion coatings have been used increasingly to improve surface properties of several machine components for tribological applications. In this investigation, the abrasive wear of various diffusion coatings has been studied. These coatings developed by three different nitrocarburizing processes, namely salt-bath, gas and plasma nitrocarburizing, were conducted on five various steel substrates. The substrates were St 52-3, Ck 45, 42 CrMo 4, 30 CrNiMo 8 and X 20 Cr 13. The thickness of the compound layers and their porosity were measured using optical microscopy. The structure of compound layers was characterized using an X-ray diffractometer, and their surface roughness by a stylus profilometer. The surface hardness measurements and the hardness profile were made according to the Vickers principle. The abrasion test was carried out using a pin-on-table machine. The predominant wear mechanisms have been evaluated using scanning electron microscopy. It was found that the employed nitrocarburizing processes have improved the abrasive wear resistance of all tested coating-substrate-combinations. In general, the abrasive wear rate decreases with an increase in the hardness of the compound layer as well as its thickness. The best coating-substrate-combinations to improve abrasion resistance were salt-bath and gas nitrocarburized specimens of the substrate X 20 Cr 13. Plasma nitrocarburized specimens of the substrate St 52-3 and Ck 45 were the worst.     

Mechanisches Verhalten des Schutzschicht-Grundwerkstoff-Verbundes von Gasturbinenschaufeln unter betriebsähnlicher zyklischer Beanspruchung

Mechanical behaviour of the coating-substrate-compound of gas turbine blades under service-type cyclic loading With a special test technique developed for the investigation of the thermo-mechanical loading of materials for gas turbines, aniso-thermal service-type strain cycle tests with different coating-substrate-combinations were carried out. For comparison isothermal standard strain cycle tests with one selected coating-substrate combination were carried out. With this combination also the coating-load was calculated with finite-element-calculation.     

Zähigkeitsanforderungen an Stähle in tieftemperaturbeanspruchten Bauteilen

Toughness Requirements for Steels in Low-Temperature Components In order to exclude the possibility of low-ductility fractures (brittle fractures) in components with safety relevance (e. g. pressurized containments) the materials used have to have an adequate toughness. The toughness requirements for materials are laid down in sets of regulations or in specifications. If the guidelines are compared, however it becomes clear that opinions vary considerably concerning minimum toughness to be guaranted and procedure to be evaluated. In this paper the regulations are discussed.     

Spannungsrißkorrosionsuntersuchungen bei hohen Temperaturen. Verhalten höherlegierter Stähle unter praxisnahen Bedingungen

Stress Corrosion Cracking at Temperature in the range of 180 °C . Tests are described to find out the stress corrosion behaviour of some stainless steels of the austenitic and ferritic-austenitic type in low concentrated aqueous chloride media with temperatures up to 180°C and pressures up to 10 bar. A sensitivity of the austenitic steels could be determined during 6 to 55 hours, the ferritic-austenitic steel X 2 CrNiMoN 22 5 however didn't suffer any SCC during 235 h with the exception of the welded state. In this way – by the use of a pressure vessel – it is possible, to carry out laboratory tests under conditions of practice.     

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.     

Beitrag zum Verfestigungsverhalten der Stähle durch Kaltverformung

Hardening Behaviour of Steels by Cold Working Contrary to common opinion work hardening increases with higher initial hardness (strength) of steel. This is proved by analysing stressstrain curves of tensile tests at overeleastic load carried out with normalized, hardened and tempered steel. Test results taken from literature are supported by own experiments. Practical application of this fact is discussed very shortly.     

Einfluß des Anlassens auf Gefüge und Härte warmfester 9%Cr-Stähle

Influence of tempering on microstructure and hardness of high-temperature 9%Cr-steels The influences of temperature and duration of tempering on hardness and microstructure were investigated at high-temperature martensitic and low-carbon steels with 9% chrome and the further alloying elements molybdenium, vanadium, niobium and partially tungsten. After austenitizing and subsequent air cooling the steels were tempered at temperatures below, at and above Ac_1b for different times and finally a hardness test was performed. Making use of the temperature dependence of the hardness tempering diagrams were constructed and the Hollomon-Jaffe-Parameter on the three steels was determined within its application limits. Micrographs of the structure shows the formation of the carbides and the martensite. At tempering temperatures below Ac_1b a decrease of hardness occurs, above Ac_1b, a hardness rise due to the partial austenitizing was obtained. While hardening below Ac_1b, the tempering quality increases from P 91, NF 616 to E 911.