Influencing the Functional Properties of Stainless Steels by Different Surface Treatments

Parts from stainless steels owe their chemical resistance to the functional properties of their surfaces. They are responsible for the corrosion resistance and also for other properties like adhesion of substrates or ease to clean. The passive layer forms the phase boundary between metal and environment. It is formed either spontaneously during the fabrication or can be produced in an accelerated way by specific chemical treatments. The quality of the passive film is dependant of the alloying content of the metal, but also largely influenced by other factors like fabrication processes, surface topography and type of mechanical and chemical surface treatment. The passive layer is also a kind of living system whose properties and stability is largely influenced by the environment where it is used in.

Mechanical and chemical treatments like grinding, passivation in nitric acid or pickling in a mixture of hydrofluoric and nitric acid were used to prepare the surface of the specimens. With a combination of electrochemical techniques and measurements of the surface energy and roughness, the functional properties were determined. With these results a passivation index based on the contribution of the individual parameters was calculated. In addition, cleaning experiments were performed to investigate the correlation between the surface treatment and the cleanability of the specimens.