ESSC & DUPLEX 2019

Austenitic stainless steels have a very good combination of mechanical properties e.g. formability associated with corrosion resistance. Due to the cubic face-centered lattice at room temperature, these steels are not magnetizable and a conventional hardening is not possible. Due to the low hardness, these steels are not optimal for tribological stress and in many cases show low performance. Therefore tribologically loaded components made of these steels, are often treated with a low-temperature carburization for surface hardening. Carbon atoms are embedded on interstitial places and generate an expanded austenitic lattice, also called expanded austenite or S-phase. The corrosion resistance is not affected by this treatment. Some stainless steels show magnetic effects after this heat treatment. The aim of this work is a better understanding and sourcing of these effects. The investigation includes different stainless steels which were treated with a low temperature carburizing process for various times. To evaluate the layer formation, metallographic cross-sections were prepared and examined by means of various etching methods on a light microscope. In addition, hardness profiles and the magnetic properties were measured. To get some more information about the lattice properties the determination of the lattice expansion took place with XRD measurements and also with EBSD. In order to determine the magnetizability, measurements were made with the Fischer Feritscope and also SQUID measurements. The structure of the magnetic layer was determined by MFM measurements and ferrofluid (Fe3O4-Suspension). In order to determine more precisely the possible reasons for the formation of these magnetic effects, further examinations with TEM and SANS are required. There is a relationship between the alloy composition of austenitic stainless steels and the magnetizability after the low-temperature hardening, as can be seen in the classification of the materials in the Schäffler diagram.