Verschleißverhalten ledeburitischer Chromstähle mit Niob und Titan

Wear Behavior of Ledeburitic Cr-Steels with Niobium and Titanium By addition of niobium, titanium, titanium and carbon to a steel with 2% C and 12% Cr alloys with MC-Carbide content of 1; 2,5 or 5 vol.% were produced. The wear behavior of these alloys was investigated in comparison to common ledeburitic Cr-steels by means of a slow turn-test and the pin-on-disc method. The influence of carbides (amount, hardness and distribution) is described as well as a change in the matrix, caused by varying austenitizing and tempering temperature, Except for the alloys with 2,5 and 5 vol.% TiC and an alloy with 2,5 vol.% NbC at high matrix hardness, which show increased wear as compared to the ledeburitic Cr-steels, the wear rate is lowered by addition of MC-carbides. In the pin-on -disc test the wear rate is more significantly lowered by increasing the content of ratained austenite than by carbides.     

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.     

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.     

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.     

Theoretisch-numerische Untersuchungen zu Experimenten mit Kriechrißwachstum

Theoretical-Numerical Investigations of Experiments with Creep Crack Growth Numerical results are presented to calculate the C* -integral that is path independent only in the long-time range. The crack tip modelling – elastic or elastic-plastic – is of minor influence on C* – whereas values of C* depend strongly on the material constants describing the creep law. The agreement between numerically and experimentally determined C* data is rather satisfactory in the secondary creep regime. A line integral R* is proposed that is path independent in the whole time domain.     

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.     

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.     

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.     

Entwicklung und Verschleißverhalten von Si3N4-Schneidkeramik

Development and wear behaviour of silicon nitride ceramic Cutting tools based on silicon nitride ceramic have been employed successfully in industrial ranges of application especially in cutting of grey cast iron. Nevertheless their availability is still limited due to various reasons, depending on the specific material properties. In order to improve the wear behaviour and the reliability of these tools a new silicon nitride ceramic matrix, bonded with grains of carbides, was developed. The paper presents results obtained during investigations on material specific wear mechanisms in face milling and turning. The responsible wear mechanism in turning are the high tool temperatures. They leads to a softening of the grain boundary phase so that the Si₃N₄-grains can be removed by the chip flow. The wear in milling is due to the high mechanical load accompanied with the frequency in period of cutting     

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.     

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.     

Untersuchungen Zur Festigkeit labormäßig hergestellter Silicium-Mangan-legierter Sinterstähle

Investigations on Mechanical Properties of Si? Mn-sintered steels Produced under Laboratory Conditions The influence of graphite additions on microstructure and behaviour under static and cyclic loading is studied for a newly developed sintered steel. For an optimum carbon content fatigue tests are carried out on notched and unnotched specimens. The results of these constant amplitude axial loading experiments are promising and show some advantages compared with the results of commercial sintered steels.     

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.