What are the Four Main Categories of Stainless Steel?
There are many different alloys of stainless steel running into the thousands of different variables. According to the World Steel Association, there are over 3,500 different grades of steel, encompassing unique physical, chemical, and environmental properties, however, they can all be divided into four main categories, Austenitic Stainless Steels, Ferritic Stainless Steels, Martensitic Stainless Steels, and Duplex.
Austenitic Stainless Steels are the steels most often used in day-to-day products and these steels tend to be non-magnetic, although after cold working they may become magnetic. Austenitic stainless steels usually have a higher chromium content when compared to other steel alloys which gives them a higher corrosion resistance.
Ferritic stainless steels are the second most commonly used forms of stainless steel and, as the name suggests, ferritic stainless steel is magnetic. These alloys can be toughened through cold working and because they have a lower nickel content, they are often cheaper.
Martensitic stainless steel is the least common category of stainless steel alloys, and they are also the least resistant to corrosion out of al the four main stainless steel categories, but this is compensated by being the hardest out of the main categories. Martensitic stainless steel alloys are ideal for applications needing very high tensile strength and impact resistance. These steels are sometimes used with a protective polymer coating to add extra corrosion resistance when a hardened steel is required, combined with higher levels of corrosion protection.
Duplex stainless steels are basically combinations of ferritic and austenitic stainless steels. Stronger than both ferritic and austenitic stainless steels, they have a lower nickel content than austenitic steels and therefore, they are also less expensive than austenitic steels.
Duplex stainless steel is used a great deal in the underwater oil industry mainly due to its corrosion resistance capabilities, which enables it to withstand the corrosive properties of sea water over long periods of time. Duplex stainless steels are fairly malleable and can be more easily shaped to create a variety of different components. Two of the more common types of duplex stainless steel include S31803 and S32205 stainless steel.