MARTENSITIC METALS M006
These metals become strong and hard as a result of heat treatment. They have low corrosion resistance so their use is restricted in the mechanical seal business where corrosion resistance is a necessity.
High temperature metal bellows seals are often manufactured from AM350, a heat treatable stainless steel that becomes martensitic at the heat treatment temperature and therefore is limited to non or very low corrosive applications such as petroleum oil.
Ball bearings are made from martensitic steel so they can carry the high radial and axial loads that are required in a centrifugal pump application.
That is the reason ball bearings rust so easily. Stainless steel bearings would not rust, but they do not have the load carrying capability we need in centrifugal pump applications.