What Makes Stainless Steel Stainless?
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An enemy of corrosion and useful in a vast variety of applications, stainless steel is a powerhouse metal used for both commercial and residential fasteners. There are a few essential ingredients in stainless steel that contribute to this material's ability to resist corrosion.
By definition, stainless steel is a ferrous alloy that contains chromium at a minimum rate of 12 percent. It also contains iron and carbon, along with other alloy elements, but the chromium base is what creates that stainless effect.
Why Chromium?
Chromium is non-corrodable. That mean the more chromium contained in a grade of stainless steel, the better corrosion resistance that material has. When you add in other alloy elements, the resistance will either deepen or weaken and the mixture can be tweaked to create a fine balance between strength, resistance to temperature changes and the ability to fight off corrosion.
When carbon is added to a stainless steel alloy, the corrosion resistance of the chromium is tampered with and additional chromium needs to be included to offset it. On the other hand, when nickel is added the corrosion resistance is strengthened and the material has more stability, especially in extremely low temperatures and in very high heat.
How Does Stainless Steel Resist Rust?
Stainless steel has a unique ability to spontaneously form a very thin layer of oxide on the surface of the metal. This exposed film is invisible, but it protects the material underneath from further oxidization. This layer acts as a rust-free coating, so to speak.
Often during machining stainless steel fasteners can pick up impurities or wind up with tiny bits of other metals adhered to its surface. These bits are not protected by the oxidized film and so a small amount of corrosion and staining will occur. As a result, the passivation process is commonly done before shipping out the stainless steel fasteners.
What Is Passivation?
During the passivation process the stainless steel product is effectively cleaned up, removing all of the possible surface debris that formed during the manufacturing process. It is done to provide the optimal levels of corrosion resistance and bright appearance that stainless steel is known for.
The product is dipped in a liquid solution containing water and nitric acid. After soaking, the stainless steel emerges clean and forms the thin film of oxide again.
Groups of Stainless Steel
There are three main groups that stainless steel is catalogued into: austenitic stainless steel; ferritic stainless steel; and martensitic stainless steel. Also, a hybrid group called precipitation hardening can be found on the market.
Manufacturers will tell you that each group has its advantages and disadvantages, depending on the application. While austenitic stainless steel is very common in the commercial market, ferritic varieties offer a magnetic option and martensitic are known for their strength. Precipitation hardening stainless steel products are seen more commonly now offering a nice balance between each of the other group's strengths.
Austenitic stainless steel offers the highest resistance to corrosion and makes up about 80 percent of all the stainless steel products on the market. The ferritic group contributes around 5 percent, while martensitic makes up 10 percent and precipitation hardening captures about 5 percent so far.
Stainless steel fasteners will continue to be popular for both residential and commercial applications due to their unique properties and dependable performance. |
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Author Resource:-
AJ Best writes about alternative energy sources and other eco-friendly issues. She writes for Melfast commercial fasteners, nuts and bolts, and plastic fasteners http://www.melfast.com
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By :
Anne Dickens
Submitted
2011-01-29 19:42:44 |
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