In the past, lead was used to improve the metallic running properties. deva.metal® materials were and still are partly produced with the addition of lead powder. New alloys are now being produced without lead. Lead is considered harmful to health. Furthermore, it causes a grain change in deva.metal®. Read here.
The friction or the coefficient of friction μ depends on the normal force. In polar friction pairings, the adhesive portion of the coefficient of friction is very high due to the attraction of the friction surface at low normal force.