Normalising aims to give the steel a uniform and fine-grained structure. The process is used to obtain a predictable microstructure and an assurance of the steel’s mechanical properties.

Benefits

After forging, hot rolling or casting a steel’s microstructure is often unhomogeneous consisting of large grains, and unwanted structural components such as bainite and carbides. Such a microstructure has a negative impact on the steel’s mechanical properties as well as on the machinability. Through normalising, the steel can obtain a more fine-grained homogeneous structure with predictable properties and machinability.

Application & materials

Normalisation is mainly used on carbon and low alloyed steels to normalise the structure after forging, hot rolling or casting. The hardness obtained after normalising depends on the steel dimension analysis and the cooling speed used (approximately 100-250 HB).

Process details

During normalising, the material is heated to a temperature approximately equivalent to the hardening temperature (800-920°C). At this temperature new austenitic grains are formed. The austenitic grains are much smaller than the previous ferritic grains. After heating and a short soaking time the components are cooled freely in air (gas). During cooling, new ferritic grains are formed with a further refined grain size. In some cases, both heating and cooling take place under protective gas to avoid oxidation and decarburisation.