hardness increases continuously from the bulk to the worn surface. Maximum values up to 1200 HK 
are measured in the transfer particles. These are typical values for martensitic structures. 
The wear debris was analysed also by transmission electron microscopy (fig. 8). The results confirm 
the findings of optical microscopy: All particles have nanocrystalline structures. Besides, the TEM 
results correspond with the magnetic measurements — for the particles taken from samples which 
show changes of magnetic properties exhibit a-iron in the diffraction pattern as a hint for a 
martensitic structure transformation. 
! 0 pr am 
Fig. 7: Steel 1.4958 Fig. 8: Steel 1.4439. TEM image of debris with 
Cross section through a wear track austenitic and ferritic structure (transformation) 
Conclusions 
As well known [6] nuclei of martensite crystals are formed by stacking faults during deformation. 
Therefore, the transformation behaviour of the alloys is determined by the deformation behaviour. 
The results obtained suggest that the transformation behaviour depends on the intensity of the 
plastic deformation during friction. The metastable alloy 1.4301 exhibit homogenous distribution of 
martensite in the more or less homogenous deformed wear track. In comparison with it the more 
stable alloys 1.4439 and 1.4958 show transformation only at places with severe plastic deformation, 
in the wear debris. Therefore, there is a need to make available materials data of the stability of 
austenitic structure as a prerequisite of reliable function of the machine parts. It must be ensured 
that deformation caused by the stress conditions under service will not be followed by a 
deterioration of the materials because of decreased ductility or changed magnetic behaviour. 
Especially, the use of liquid hydrogen and liquid oxygen requires precautions for the safety during 
the service time. 
References 
[1] Borner, H.; Gradt, T.; Heidrich, M.: Tribologie u. Schmierungstechnik 45(1998)6, 54-57 
[2] Werkstoffkunde Stahl. Berlin: Springer 1985. Bd 2, S.285 
[3] Gavriljuk V.G.; Berns H.: High Nitrogen Steels. Structure, Properties, Manufacture, 
Applications. Springer, Berlin, 1999. 280-281 
[4] Hiibner, W.: Materialwiss. u. Werkstofftechn. (in print) 
[5S] Hiibner, W.: Tribol. Intern. (in preparation) 
[61 Schumann, H.: Kristall u. Technik 10(1975), 401 
The project is supported by the Deutsche Forschungsgemeinschaft (project number Hu 791/1-1) 
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