1, your powder metallurgy blank is soaked in oil, of course it won't rust.

2. There is water in the cooling liquid of gear hobbing, which has penetrated into powder metallurgy.

If the process produced by other factories is the same as yours, it is estimated that the formula of powder metallurgy is somewhat different. It may be better to add some copper powder and cobalt powder and reduce the content of iron powder (for reference only).