Black Oxide is a popular finish on our black bolts, nuts and washers at Monster Bolts for good reason.
Black Oxide is an exterior finish commonly used on fasteners that has a basic protection from corrosion and abrasion resistance. Mostly found on steel fasteners but you will often find stainless steel fasteners offered with a black oxide option. Black oxide does not alter the dimensions of the fastener like galvanized coatings do, so it is ideal for close-tolerant machined parts. Generally black oxide adds less than 10 millionth of an inch (0.00001″) to the part applied to…, a human hair for example is about 1 thousandth of an inch (0.001″).
Black Oxide is typically used in combination with oil or wax to further protect against rusting and to improve the appearance.
Will Black Oxide Bolts Rust
Yes. Black Oxide adds a basic protection from corrosion and abrasion to fasteners. Like any material, black oxide treated steel fasteners can rust in the right environments. This obviously is not the case for Black oxide coated stainless steel, as stainless still retains its normal corrosion protection.
Why add black oxide to stainless steel
Black oxide is most commonly added to stainless steel nuts and bolts for aesthetic reasons, meaning a customer wants the benefits of stainless steel fasteners for their corrosion resistance, but desires a black product.
What is Black Oxide
Black oxide is a conversion coating process between the oxidizing salts used and the material. The end result is an incredibly thin layer of magnetite added to the ferrous material (metal). The chemicals used include Sodium Hydroxide (lye) and Sodium Nitrate (Chile Saltpeter). Three tanks are used and parts are move into a hot bath (between 194 to 286°F) containing an alkaline detergent (lye), then water, and lastly a bath of sodium nitrate. Oil is applied while the parts are still hot which acts to seal the finish. This process is generally referred to Hot or Mild Temperature bath depending on the temperature used.
What is Thermal Black Oxide
Thermal black oxide is a coating process finish that is formed during the heat treatment process where parts are quenched and tempered for strength.
What metals can be used with black oxide
- Steel and Alloy Steel
- Stainless Steel
- Copper (often called Ebonol C)
- Zinc (often called Ebonol Z)