For example, consider the hardening process for steel. Hardening processes generally entail heating steel into the austenite range, followed by rapid cooling and tempering. During hardening, the atmosphere of the workpiece must remain neutral to the carbon content of the material, and the entire part must reach a uniform temperature before cooling. After heating, a soaking stage follows. The soaking time varies, though a general rule of thumb is to soak a workpiece for one hour for every one inch of cross-sectional thickness (but not less than 30 minutes). Tempering is necessary to complete the hardening process and achieve desired properties.

Each variety of steel has its own austenitizing temperature. For example, the austenitizing temperature for stainless steels is generally 1800°F–1850°F, depending on the exact makeup of the steel. Plain carbon steel typically austenitizes in the range of 1500°F–1750°F.

Source: Dan Herring, The Heat Treat Doctor®, Atmosphere Heat Treatment, Volume 1, pages 377–384.