Refine
Document Type
- Conference Proceeding (4)
- Other Publications (2)
- Article (1)
Has Fulltext
- no (7)
Keywords
Institute
Low temperature carburizing of a series of austenitic stainless with various combinations of chromium and nickel equivalents was performed. The investigation of the response towards low temperature carburized for three stainless steels with various Cr- and Ni-equivalents showed that the carbon uptake depends significantly on the chemical composition of the base material. The higher carbon content in the expanded austenite layer of specimen 6 (1.4565) and specimen 4 (1.4539/AISI 904L) compared to specimen 2 (1.4404/AISI 316L) is assumed to be mainly related to the difference in the specimens’ chromium content. More chromium leads to more lattice expansion. Along with the higher carbon content, higher hardness values and higher compressive residual stresses in the expanded austenite zone are introduced than for low temperature carburized AISI 316L. The residual stresses obtained from X-ray diffraction lattice strain investigation depend strongly on the chosen X-ray elastic constants. Presently, no values are known for carbon (or nitrogen) stabilized expanded austenite. Nevertheless, first principle elastic constants for γ′&minus Fe4C appear to provide realistic residual stress values. Magnetic force microscopy and measurement with an eddy current probe indicate that austenitic stainless steels can become ferromagnetic upon carburizing, similar for low temperature nitriding. The apparent transition from para- to ferromagnetism cannot be attributed entirely to the interstitially dissolved carbon content in the formed expanded austenite layer but appears to depend also on the metallic composition of the alloy, in particular the Ni content.
The evolution of strain induced martensite in austenitic stainless steel AISI 304 was investigated in a rolling contact on a two-discs-tribometer. The effects of surface roughness, slip and normal force as well as the number of load cycles were examined. In comparison to the investigations of martensitic phase transformation during cold rolling, the applied stresses are considerably lower. The formation of strain induced martensite was detected in-situ by means of a FERITSCOPE MP30 and ex-situ by optical microscopy after etching with Kane etchant. Both number of load cycles and magnitude of normal force appeared to be the main influencing factors regarding strain induced martensitic evolution in low stress rolling contacts.
Durch Beanspruchungen bei der Fertigung oder in der Anwendung können metastabile austenitische Stähle eine Phasenumwandlung von ?- Austenit zu ?‘-Martensit durchlaufen. Verbunden damit sind Eigenschaftsänderungen, welche sich signifikant auf das Werkstoffverhalten unter mechanischer, tribologischer oder korrosiver Belastung auswirken können.
Um möglichen negativen Auswirkungen wie ungewollte Magnetisierbarkeit oder Beeinflussung von Fertigungsparameter sowie Korrosionseigenschaften zu unterbinden muss die martensitische Phase zunächst erfasst und quantifiziert werden.
Für diese Aufgabe stehen neben den bekannten und kostenintensiven Verfahren wie EBSD und XRD für die praxisnahe Anwendung das magneto-induktive Messverfahren und verschiedene Ätzmethoden zur Verfügung.
Anhand von Applikationen aus Anwendung, Fertigung und Forschung werden die Wirkweisen, Vorteile und Grenzen verschiedener Ätzverfahren und dem magneto-induktiv messenden FERITSCOPE® MP30 aufgezeigt. Ebenso werden ergänzende Methoden bzw. Techniken zur Validation der Verfahren diskutiert und erläutert.
