Steel surfaces were covered with (i) Ag and Cu or (ii) Ag, Cu and graphene nanomaterials-contg. polystyrene layer and subjected to microbial. tests (no. of S. aureus bacteria after the incubation time 0-24 h at 35 degrees C) as well as to tribological tests (stem/shield type tribotester, rotational speed 1.67 s(-1), pressure 0.5 MPa). The steel with the (ii) layer showed the highest antibacterial action and good tribol. properties. It was used as a knife material in a homogenizer for food prodn.