Untersuchung von ferromagnetischen Effekten an austenitischen rostfreien Stählen nach einer Niedertemperatur-Karburierung

Schuler, Philipp Steffen; Krupp, Ulrich (Thesis advisor); Gümpel, Paul (Thesis advisor)

Aachen : RWTH Aachen University (2022, 2023)
Dissertation / PhD Thesis

Dissertation, Rheinisch-Westfälische Technische Hochschule Aachen, 2022

Abstract

The present work deals with different austenitic stainless steels on which ferromagnetic effects were partially detected after low-temperature carburizing. Due to the very good corrosion resistance of austenitic steels, they are used in a wide range of applications, from the chemical industry to the watchmaking industry. Because of the face-centered cubic lattice, these steels are very sensitive to wear under tribological stress. Since conventional hardening is not possible, due to the lack of ferrite-austenite transformation, the only option here is surface hardening by means of low-temperature carburizing, for example. The hardened surface layer, produced in this process, consists of an expanded austenitic lattice. The expansion being caused by the interstitially embedded carbon.In this work, nine different austenitic stainless alloys were subjected to low-temperature carburization and subsequently investigated. The focus was placed on the investigations concerning ferromagnetism. No magnetizability was observed in the low alloy austenitic steels after treatment, while the higher alloyed steels exhibited very significant magnetizability. Grain orientation-dependent magnetic domain structures were detected in the ferromagnetic layer regions. It was further demonstrated that only purely part of the formed layer exhibited ferromagnetic properties and that these were caused by critical lattice expansion. The lattice parameter range in which ferromagnetic properties predominate in the layer, could be detected by different methods. By a supplementary evaluation of the results by means of the alloy-dependent stacking fault energy, a differentiated result evaluation could be carried out. Furthermore, a minimum stacking fault energy could be determined for the alloys investigated, above which the alloys form ferromagnetism in the layer. Also a different expression of lattice defects could be recognized, depending on the alloy as well as the grain orientation.From the results it is clear that the alloy composition is decisive for the formation of ferromagnetism in the layer. The occurring ferromagnetism is explained by the lattice expansion, whereby the alloy-dependent plastic deformation behavior, which can be described by the stacking fault energy, also plays a superimposed role.

Institutions

• Division of Materials Science and Engineering [520000]
• Chair of Materials Engineering of Metals and Department of Ferrous Metallurgy [522110]