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Stainless steel is a widely popular metal used in various applications such as Fasteners. Both commercial and residential projects hold up better with stainless steel fasteners behind the scenes. There are certain alloys used to make up stainless steel that provide the levels of corrosion resistance you can count on. Some of the stainless steel fasteners available are Nuts And Bolts, Hex Bolts and Hex Head Cap Screws.

As a simple definition, stainless steel is any ferrous alloy containing at least 12 percent chromium. It always has iron content and often contains carbon and other alloys, but chromium is the essential element that offers a rust free, stainless finish.

Characteristics of Chromium

Chromium does not corrode. So the more chromium that is in any type of stainless steel (and there are hundreds of different types), the more resistant to corrosion that mixture is. Adding other alloys will increase or decrease the level of resistance, but the mixtures can be balanced to create a strong metal that can handle extreme temperatures, pressures and levels of moisture.

Adding carbon for example, decreases the corrosion resistance and more chromium is needed to bring it back to the expected levels. When nickel is thrown in the mix the stainless steel becomes stronger and highly stable in both very low temperatures and extremely hot conditions.

Why Don’t Stainless Steel Fasteners Rust?

Stainless steel forms a super thin layer of invisible oxide immediately. This spontaneous film is on the exposed surface of the fastener and acts as protection against oxidization, making it impervious to rust even in very moist conditions like marine applications.

When stainless steel fasteners are machined tiny pieces of other metals can attach to the surface, causing imperfections and eventually staining and corrosion. To protect the fasteners and provide the bright finish that is a trademark of stainless steel, these fasteners need to go through passivation before being shipped out to the consumer.

Explaining the Passivation Process

Passivation is the process of immersing stainless steel into a bath of nitric acid and water. This immersion will remove all of the other metals that have been caught on the surface, effectively washing the steel and bringing it back to the original condition. Once the metal is taken out of the liquid, it will again form the protective layer of oxide and reach the full level of corrosion resistance once more.

Various Stainless Steel Groups

Stainless steel is catalogued by three major groups and one hybrid including:

  • Ferritic stainless steel – this group makes up around 5 percent of the stainless steel fasteners on the market. It is magnetic and has the least amount of corrosion resistance.
  • Martensitic stainless steel – around 10 percent of stainless steel fasteners are made from this type which is very strong and also magnetic.
  • Austenitic stainless steel – the most common type that makes up about 80 percent of the stainless steel fastener products, this group is highly corrosion resistant and non-magnetic.
  • Precipitation Hardening stainless steel – gaining in popularity, this hybrid group creates a balance between the rust protection of austenitic and the strength of the others.

These groups all have benefits and drawbacks and each will suit different applications. All stainless steel fasteners have a high level of corrosion resistance thanks to the chromium content. They will continue to dominate the commercial and residential construction markets due to the level of reliability and strength they offer in a wide variety of circumstances.

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