Steel materials are categorised according to their alloying elements, their structural components and their mechanical properties. Such a classification of steel materials is helpful in the selection process with respect to functional properties and in the determination of machining conditions.
Classification according to alloy content leads to the following categories:
• unalloyed steels,
• low-alloyed steels (alloy content < 5 %) and
• high-alloyed steels (alloy content > 5 %).
In the case of unalloyed steels, we must further differentiate between those steel materials that are not to be heat-treated (common construction steel) and those that are (grade and special steel).
Besides categorisation according to their alloy content, steels are also classified with a view to their practical uses and applications. We distinguish them as
• case-hardened steels,
• heat-treated steels,
• nitrided steels,
• roller bearing steels,
• tool steels and
• non-rusting, fireproof and high-temperature steels.
In the following, the compositions and structural formation of different steels will be introduced. The machinability of the particular structures in the grinding process is treated in chapter 4.4.