Rust on metal stamping parts

Q. Sir/Mam, Good afternoon.

I have a problem; same as one of the posts I read in finishing.com. We are supplier/manufacturer of metal stamping parts. We have Finished Good parts; after 1 month stock in warehouse, rust developed causing problems and also claims from our customer. Material used: SECC (non painted product)



What are the possible causes of rust and how to prevent this. Hope you can you help me solve this problem.

Thank you very much.