Kriechermüdungsverhalten warmfester Stähle bei betriebsähnlicher Hochtemperaturdehnwechselbeanspruchung

Creep fatigue behaviour of heat resistant steels under service- type strain cycling at high temperature On three typical heat resistant steels the creep fatigue behaviour is investigated up to about 10 000 h test duration using a service-type strain cycle. In a creep fatigue life analysis the cyclic deformation behaviour and the applicability of the generalized damage accumulation rule are investigated and possibilities of long-term creep fatigue prediction are studied.     

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.     

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.     

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.     

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.     

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.     

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.     

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.     

Einfluß der Zunderung auf das Zeitstandverhalten hitzebeständiger Stähle

Influence of scaling on creep rupture behaviour of heat resistant steel Interrupted and uninterrupted creep-rupture tests and annealing tests on 4 heat resistant steels, performed mainly at 1000 and partly at 1100°C. Determination of the metal loss due to scaling. Validation of an improved method for correcting time dependent strength properties due to metal loss. Determination of further influences.     

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.     

Aussagen der instrumentierten Schwingprüfung zur Dauerfestigkeit unlegierter Stähle

Evidence of the Instrumented Fatigue Test for Fatigue Strength of Structural Steel In the instrumented fatigue test the measurement of the frequency of loading and the power absorption of the resonance endurancetesting machine with electromagnetic energization discovery the rate of damage of the specimen. The energy and the energy gradient per cycle are especially suitable for characterize the fatigue life of the specimen. Rapid methods for evaluation fatigue strength are developed constructive on the results of experiments of fatigue tests in one load stage. The rapid methods are tested with cylindrical specimen (St 52-3) and spot weldings (St 1203). The results of measurement indicate a certain possibility of evaluation fatigue strength.     

Schnellbewertung von Dispersionsgefüge und mechanischen Eigenschaften karbidbildender Stähle

Fast Evaluation of dispersed Microstructure and mechanical Properties of Carbide forming Steels A possibility of a fast evaluation concerning the dispersed microstructure and the properties of C-, Cr- and Mn-alloy steels is presented. The dispersed microstructure was adjusted by precipitation and coarsening from the martensitic initial condition. The quick recording coercive field strength H_C and microstructural parameters obtained from scanning electronmicroscopic investigations were used in the relationship H_C-particle diameter d_p relative to a microstructure fast evaluation. Due to the repeated nucleation the M₃C carbides grow and coarse parallel and in particle generations. Thus always a particle size spectrum is obtained. A fast evaluation of properties is realized by the connection H_C – yield strength R_p0.2 / tensile strength R_m / hardness HV. Since H_C reacts on the size of precipitated particles, and the course H_C – time t / d_p / particle volume (d_p/2)³ encloses two maxima, which both separate the precipitation (A) and coarsening stage (V), at any H_C-value one of the attaching possibilities (A or V) must be excluded. This can be reached by considering the obtained temperature and time limiting values. The magnetic measuring method with the structure-sensitive quantity H_C yields to an assertion relative to the microstructual condition within one minute. The error amounts to ≤0.5%. The application of the H_C-measurement is time- and cost-economic. A special sample preparing is not necessary. The condition of the surface does not enter into the measuring result. The yielded connections H_C – R_p0.2 / R_m / HV can be used like a standard referred to the tested grades of steel.