Black Finish on 430 Stainless Steel

Q. We supply parts to the OEM automotive market and include screws for fastening, some of which are 430 stainless steel. We have been asked to supply the screws with a matte black finish but are concerned about the cost of using a complicated system to plate screws that are inherently anti-corrosive simply to make them black. Do you know of a way to get a black surface finish on the parts that will stand up to the road blast under a car? M.J.

A. You make a very interesting point regarding stainless steel and corrosion. It does seem absurd to spend money to get a black finish on a component that will stand up well in a corrosive environment. The issue here is strictly cosmetic.

That being said, in situations where stainless steel requires a black finish, the method of choice is the hot black oxide process, which requires a hot chemical bath followed by a sealing step. This will give you corrosion protection and an attractive finish. The only problem is that the finish looks pretty and gives you some corrosion protection in an indoor environment, but it is less reliable in an outdoor environment. I do not think the black finish will last long on the underside of an automobile.