Compatibility of EN 19 to EN 24 and EN 8 to EN 24

The shaft is rotating within the gear bore? Without antifirction bearing / bushing ?

If there is a this type of relative movement, friction welding is possible, no material combination will be able to withstand it.

Put some bearing inside and ensure proper lubrication.

Another way (not preferable) is creating a hydro bearing by putting some hole through the shaft and radial holes at the bearing area the oil film will act to lubricate and create the journal (It is not preferable due to the notch effects created)

It is not the compatibility problem, as I understand (if I did) it is a basic design problem.

"earlier we were using En8 material for gear."

Did you have cold welding as well with former material?

What is the pressure between gear and shaft uniform or variable along contact length?

Which dimensions the contact zone has (d x l) ?

How is the "bearing" lubricated?

Did you for economy reasons eliminate a bronze or plastic bushing?

Since the gear turns faster than shaft from tribological point of view it is as a stationary shaft with a turning gear. The contact area will thus be on the shaft a lot smaller than on internal gear surface. It is a principle in wear that the smaller surface should be weaker than the bigger since if not it works as a "cutting tool". In your data the hardness is the opposite.

The loading cycle is only 4.5"/60"= 7.5% which gives the feeling that you work with very high pressures since a cold welding occurs only if local temperature is high enough. It seems that the generation is so intensive that the heat cannot be diffused in the contact parts. It is also to analyse how generated heat due to friction is eliminated from shaft and from gear. The question is how fast do you notice cold welding?

Do you notice cold welding on all area or only on one region of the contact? Where?

Provide if possible a picture from gear bore and shaft. Indicate which forces act on gear and dimensions of gear and if helical or not.

I'm thinking a lubrication issue, i have a mental picture of a camshaft lobe and valve lifter metal to metal.