Molybdenum and steel bimetallic (galvanic) corrosion potential

[DanT]

We have a hardened 8620 steel sleeve with a steel shaft keyed inside it, so there can be sliding motion but no relative rotation. The sleeve is relieved in the middle so there is no contact there. ONe end of the sleeve is sprayed with nearly pure Molybdenum on the ID and ground for a sliding fit. The other end of the steel sleeve is fitted for a similar minimal slidng clearance. After a few hours of operation there are some deeply etched rusted areas on the steel shaft. The Initial semi-confirmed report is that the etching occurred in the area where there is steel/steel contact. I found pure moly in some Galvanic series charts as being below most steels.

 

[Goahead]

Hi,
As a solid lubricant, Molybdenum Disulfide will not cause rusting. But do you run steel on steel dry (without oil
lubrication)? If yes there is no surprise with rusting.
Best regards,

http://www.welding-advisers.com/

 

[DanT]

This is the nearly pure metal molybdenum, not moly disulfide. We are introducing well filtered machine oil via an air-oil system down at one end of the bar, where the steel bar is in a steel bore. It is reported that the bar was damp with oil at the other end, where the steel bar is in the pure moly bore.