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Elementary facts about stainless steel

08 June 2015
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Stainless steel is a term used for a group of materials resistant to corrosion, acids, and some are also high-temperature resistant (refractory steels). Regarding chemical composition, stainless steels is alloy of iron and a minimum of 10.5% chromium.

Why is 10.5% of chromium so important?

It is the minimum necessary share of chromium in iron alloy, to start a chemical reaction of chromium and oxygen, whose product is very thin protective oxide layer that covers the entire exposed surface. Thickness of this layer is about 2-3 nanometers, just enough to prevent further oxidation reactions, such as corrosion. If the protective layer is scratched or accidentally damaged, it gets renewed immediately thanks to oxygen and humidity of air.

Resistance of stainless steel increases with a higher share of chromium, which is sometimes more than 30%, and adding 8 % of nickel.

In the region of former Yugoslavia, stainless steel is also known as “inox” (from the French inoxydable) or “rostfrei” (from the German), where both terms mean stainless. Some use the term “nirosta” - which is the brand name of company from Krefeld, Germany - ThysseKrupp Nirosta, which was bought by Finnish group Outokumpu in December 2012, and the company is now called "Outokumpu Nirosta". Brand name “prokrom” is also used for stainless steel.

Stainless steels are divided into:
 - Ferritic stainless steels
 - Austenitic stainless steels
 - Austenitic-ferritic (duplex) stainless steels
 - Martensitic stainless steels

Where are stainless steels used?

Products made of stainless steel are those that we mostly use every day in a household (spoons, forks, knives, pots ...), in medicine (scalpels, scissors, pliers ...), building fences and larmiers, various office supplies, food industry, etc. Stainless steel is very worthy material. Nice looking, easy to maintain and sterilize, available and of affordable price.

The main characteristics of stainless steel:
- resistant to corrosion and acids
- poor conductivity of electricity and heat
- in some forms non-magnetic
- certain kinds resistant to high temperatures and fire

 
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