yes. sometimes they will even rust if you put clear coat on them. thats what sucks about raw steel
They rust with clear coat because the steel is usually handled by dirty, sweaty, oily hands right before the clear coat is applied.
If you really want to get a "rust" free clear coat you'll have to handle the bars with lab like procedures.
*Get some cotton gloves so you don't transfer the oil from your hands.
(even clean hands have natural body oil on them)
*Wipe down the bars with some Acetone
* Clear coat
really isn't worth it though- the bars get so banged up