Stainless steel does not easily corrode, rust or stain with water as ordinary steel does. The origins of stainless steel date back to the early 1900’s, when scientists noticed that chromium had a greater attraction to oxygen than iron did, so they added the element to steel. Studies prove that when at least 10% chromium was added, the chrome united with oxygen to form a very tight transparent layer over the steel surface that prevents rusting. This transparent layer is self-healing when damaged by scratches, wear or denting.
Stainless steels are materials of enduring strength and beauty. They possess toughness at both extremes of the temperature scale, yet can be fabricated into intricate shapes for many uses. The selection of a particular grade of stainless steel composition will depend on what requirements a particular application poses. The “grades” of stainless steel refer to its quality, durability and temperature resistance. Environment, expected part life and extent of acceptable corrosion all help determine which grade of stainless steel to use. Stainless steels are commonly divided into four groups, depending on the specific amounts of alloying elements, which control the microstructure of the alloy. Below we look at the four different stainless steel compositions offered, and the benefits of each unique composition.
300 Series Austenitic – Typical Grade: 304
Austenitic stainless steels are the most specified grades produced because of their excellent formability and corrosion resistance. All 300 series steels contain chromium and nickel for enhanced surface quality, formability and increased corrosion and wear resistance. Austenitic is the most popular stainless steel group and is used for numerous industrial and consumer applications, such as cookware, processing equipment, and power plants. The austenitic grades are not magnetic.
400 Series Ferritic – Typical Grade: 430
Ferritic stainless steel consists of iron-chromium alloys, they are magnetic and have a low carbon content. Many users of ferritic grades see cost savings because of the lower chromium and nickel content. It also produces less tool and machine wear. Ferritic stainless are found in automotive applications, kitchens and industrial equipment.
400 Series Martensitic – Typical Grade: 410
These steels of the 400 series usually contain a minimum of 11.5% and up to 18% chromium, and have higher levels of carbon than ferritics. They are capable of being heat treated to a wide range of useful hardness and strength levels. Martensitic steels are used in gas turbines, sports knives and multipurpose tools.
Precipitation Hardening – Typical Grade: 17-4
Precipitation hardening stainless steels are chromium-nickel stainless, which contain alloying additions such as aluminum, copper or titanium that allow them to be hardened by a solution and aging heat treatment. It has excellent mechanical properties and a high strength level may be obtained by using the hardening treatment. Scaling and distortion is minimized. They are used in aerospace, chemical and food processing applications.
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