How Do Stainless Steel Fasteners Gain Anti-Corrosive Properties?

Nowadays, stainless steel fasteners are more widely used than any other materials and for all the good reasons. Their popularity in various industrial applications stems from their high durability, prolonged lifespan and impeccable appearance. In addition, manufacturers can incorporate a pre-determined amount of other metals to provide stainless steel screws, nuts and bolts with enhanced anti-corrosion properties.


It’s all about what goes in the mix...
Stainless steel is essentially an alloy integrating a large percentage of iron, carbon, chromium and other metals – in lower quantities. While the resilience of the alloy is guaranteed by iron, the 12% chromium present in the alloy is what grants it proofing against rust as well as the flawless appearance. Take note that because chromium itself does not corrode, the higher the percentage of chromium, the longer the metal will survive rust.
It is necessary to mention that the other metals incorporated in the stainless steel mixture can increase or decrease the alloy’s resistance to corrosion. For instance, if carbon is found in the mix, it means the alloy’s corrosion resistance is diminished. In order to compensate and maintain some anti-corrosive properties, manufacturers will have to add more chromium and bring the resistances back to the expected levels. On the other hand, utilizing nickel – a metal known for its anti-rusting properties – will only make the stainless steel stronger and capable of able to perform well under severe cold and extreme heat conditions.

.. and the mix itself
In addition to the rust resistance metals that are incorporated in it, stainless steel gains additional anti-corrosive properties thanks to the thin layer of invisible oxide that forms immediately after the alloy cools down. The super slim coating is typically formed on the exposed surface and acts like a barrier against oxidation. Because the protective sheet prevents rust from getting in even under extreme moisture conditions, stainless steel can be safely employed in marine applications.
The only situation when you could experience rust-related issues with stainless steel fasteners is when they are inserted via commercial power tools. To be more precise, when the screws or bolts are machined in, there is a chance the protective film scratches from the small pieces of the other metals. However, the cases when your stainless steel fasteners will present imperfection that can lead to staining and corrosion are rare. To prevent potential issues resulting from damage to the surface, manufacturers apply an addition bright finish, which is also the trademark of the alloy.
Quality stainless steel fasteners undergo passivation
Before shipping them out for the actual applications, manufacturers will make sure the stainless steel fasteners undergo a passivation process. The process implies immersing the fasteners in a mix of nitric acid and water; this has the role of removing any trace of other metals that may have been caught on the surface of the stainless steel. With all impurities eliminated, the steel is effectively ‘washed’ and it will regain its original properties. Once the alloy is taken out of the liquid, the small protective film of oxide will develop on the surface, thus ensuring the full level of corrosion resistance of the stainless steel.