What Are the Different Grades of Stainless Steel?
Posted by Eric Goldman on
Stainless steel is a metal alloy that is extremely strong, versatile, and durable, with applications ranging from kitchen equipment to construction materials. However, not all stainless steel is the same. There are numerous variations, or grades, each ideally suited to certain uses.
This grading system was originated by the AISI (American Iron and Steel Institute), but is now regulated by SAE International (formerly the Society of Automotive Engineers). This system classifies stainless steel by its crystalline structure and properties. There are five basic families of stainless steel (formerly six), and dozens of individually numbered grades within those families.
The most common grade is SAE 304, an austenitic stainless steel containing chromium and nickel. It is reasonably corrosion resistant, easily shaped, and less thermally and electrically conductive than carbon steel. It has a high shine and is used for everything from cookware to screws.
When more corrosion resistance is needed, marine grade SAE 316 is a good choice. In addition to chromium and nickel, it also contains molybdenum, a hard and corrosion resistant metal. SAE 316 is also much less reactive at very high temperatures. It is used in applications that require frequent contact with salt or saltwater, as well as chemical processing and the manufacturing of medical equipment.
SAE 420 is used for basic kitchen cutlery. It is a good mid range stainless steel with reasonable corrosion resistance, strength, and hardness. It can also be polished to a high shine. However, better kitchen knives are made of SAE 440, which is one of the hardest, strongest, and most corrosion resistant types due to its high carbon content.
The 500 series consists of heat resistant chromium alloys. These stainless steel types are used in a variety of specialty industrial applications. The 100 and 200 series are of lower quality and not frequently used today.
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