White metal bearing


I’m new to this forum,

I came across this Oil distribution box the other day. White metal bearing which had gone as hard as cast iron. Took hours to take back to white metal - can anyone shed light on why this would happen?

(Note : photo was after being 90% scraped - you can see the tops of the bearing are still dark…)

Is it dirty oil?

It would be better to see one before it’s scraped. Seawater in oil can cause loss of tin and cause hardness but a photo is more telling.