What is Stainless Steel?
Stainless steel is the name given to iron alloys containing at least 12% Cr. Stainless steel, which forms a thin protective layer of chromium oxide when chromium interacts with oxygen, is preferred for its excellent resistance to corrosion. The main alloying elements in stainless steels are chromium, nickel, molybdenum and manganese in order of importance.
History of Stainless Steel
Stainless steel was invented in 1913 by the British materials scientist Harry Brearly. During his research into different steels for weapons, Brearly noticed that steels containing 13% Cr resisted corrosion for months.
Types of Stainless Steel
- Austenitic [Fe-Cr-Ni-(Mo)
They form the most important part of corrosion resistant steels. It is the most common type of stainless steel. They are non-magnetizable. They have high shaping and welding capabilities. They are suitable for use at very low and very high temperatures. They contain between 16 – 25% chromium and 0.02 – 0.08% carbon.
- Ferritic [Fe-Cr-(Mo)]
They contain up to 30% chromium and less than 0.12% carbon. They cannot be hardened by heat treatment. They are preferred because of their resistance to stress corrosion cracking. Their forming and welding capabilities are lower than austenitic stainless steels. They are magnetic and cheaper.
- Duplex [Fe-Cr-Ni-(Mo)-N]
Their microstructure is 50% austenitic and 50% ferritic. In this way, their strength is also at a higher level. They show resistance to stress corrosion cracking. They have high weldability; however, attention should be paid to the electrode and heat level. They are moderately formable. Due to their 50% austenitic phase, they are magnetic, although not as magnetic as ferritic, martensitic and PH types.
- Martensitic [Fe-Cr-C-(Ni-Mo)]
These steels are similar to ferritic steels with chromium and lower carbon content (maximum 1%). This makes them suitable for hardening and temper hardening as with carbon and low alloy steels. They are suitable for use in high strength and moderately corrosive environments. They are common in flat shapes such as plate and sheet. They are magnetic.
- Precipitation Hardened [Fe-Cr-Ni-(Mo-Al-Cu-Nb)-N]
They can have very high strength by adding copper, niobium and aluminum to their structure. They have high strength and corrosion resistance. They are used in aviation and some industries requiring advanced technology.
