There are four main types of stainless steel, with materials classified by structure and composition. The most common variety is austenitic; 65 percent of the stainless steel produced falls in this category. Austenitic steels can be found in products ranging from cutlery and cookware to automotive trim and industrial applications. The material contains at least 16 percent chromium, no more than 0.15 percent carbon and usually includes nickel or manganese for added durability [sources: American Welding Society, Styria].
Ferritic stainless steels usually contain up to 27 percent chromium, as well as aluminum or titanium but have little or no nickel. That means that while these materials are highly resistant to corrosion, they are less durable than their austenitic cousins. Ferritic steels are more affordable than austenitic varieties and are commonly used in mufflers, exhaust systems, kitchen counters and sinks [sources: American Welding Society, Styria].
Martensitic stainless steels are less corrosion resistant than austenitic and ferritic varieties, but are noted for their extreme strength and durability. The material contains 12 to 14 percent chromium, along with small amounts of molybdenum (0.2 to 1 percent) and carbon (0.1 to 1 percent). These steels also contain little or no nickel (less than 2 percent). Martensitic stainless steels are magnetic and are often used in products where this feature is useful, like a kitchen backsplash to which a spice rack or other metal object can be attached without using fasteners [sources: American Welding Society, Styria].
Finally, duplex stainless steels combine the benefits of austenite and ferrite to provide enhanced decay resistance and beefed up strength and durability. Metallurgists typically look to create a mix that's half austenitic and half ferritic. The result is a material that features more chromium and less nickel than is found in pure austenitic steels (about 22 to 25 percent chromium and 5 percent nickel, as well as a high level of molybdenum. These steels are primarily used in chemical plants and piping applications [sources: American Welding Society, Styria].
You may have noticed our use of the term "resistant" when referring to these stainless steels' capacity for avoiding blemishes. So is the material just stain-resistant or completely stain-proof?