Although there are thousands of different stainless steel alloys, they can all be divided into three broad categories:
Ferritic stainless steel. The second most common form of stainless steel after austenitic alloys. As the name suggests, ferritic stainless steel is magnetic. These alloys can be hardened by cold work. They are also generally cheaper due to the lower nickel content.
Martensitic stainless steel. The least common class of stainless steel alloys. Their corrosion resistance is usually lower than ferritic or austenitic alloys, but they have a high hardness. Martensitic stainless steel alloys are often ideal for applications that require extremely high strength and impact resistance. When these applications also require corrosion resistance, these alloys can be used with a protective polymer coating.
Austenitic stainless steel. These are the most commonly used types of stainless steel. Austenitic stainless steels typically have a higher chromium content compared to other steel alloys, which gives them greater corrosion resistance. Another common feature of austenitic stainless steel alloys is that they are usually non-magnetic, although after cold treatment they can become magnetic.