What is Austenite?

Austenite is a metallic, nonmagnetic solid steel consisting of carbon, iron, nickel and chromium. When steel is heated above 1350 degrees Fahrenheit (732 Celsius), atoms change to form austenite. This solid solution is easily manipulated at extreme temperatures and resists corrosion. These properties make it suitable for manufacturing food-service equipment, architectural applications and medical instruments.

Austenistic stainless steel is one of five classes of metallurgical structures. Austenite stainless steels use chromium and nickel. Sometimes, manganese and nitrogen are added. If the mix is 18 percent chromium and 8 percent nickel, it is called 18-8. An iron, chromium and nickel combination is included in the 300 series. Surgical steel, Type 304 in the series, contains 18 to 10 percent nickel and 18 to 20 percent chromium.

Temperatures above 1350° Fahrenheit (732° Celsius) cause iron to transform into a face-centered cubic (FCC) crystal configuration. When forging this steel, austenite is pliable enough to shape and hammer out imperfections. Annealing is the process of steadily heating the metal and then putting it through a gradual cooling process. Usually, stainless steel is sold annealed, or in its soft condition. Austenistic grades of steel are hardened by cold working as opposed to the heat treatment used for carbon steels.

Cold working is the shaping of metal at a temperature lower than the molten state of that metal. Room temperature is fine for cold working austenite. Cold-work tool steels are used in dies, steel cutting shapes, that form metal at lower temperatures. An air-hardening tool steel is often used to shape molds.

Molybdenum is added to the nickel-chromium mix to help with corrosion resistance to chlorides. Corrosive chlorides include sea water or the de-icing solutions used during snowy and icy weather. Residents in coastal areas and cold climates benefit from these rust resisting components of stainless steels.

Austenite was named after Sir William Chandler Roberts-Austen, an English metallurgist. Roberts-Austen, who died in London in 1902 at age 59, studied impurities in pure metals. His research and procedural improvements were used in a variety of applications and widely affected the industrialized world.

Stainless steels are recyclable, making all types and mixes a natural, environmentally friendly choice. During recycling, the steel is re-melted then formed into new stainless steel. Type 304 austenistic stainless steel is used for today's popular stainless steel kitchen appliances and vent hoods. Austenistic stainless steels have also been used in conventional and nuclear power plants' superheaters and heating components.