Unalloyed case-hardening steel is a hardened steel with a wear-resistant surface and a tough core.
Apart from a low carbon content of no more than 0.2 percent, this case-hardened steel contains no alloy elements. As a result, the material has a relatively high toughness and a low hardness. Unalloyed case-hardened steel is therefore suitable for workpieces that are less heavily stressed. For example, for bolts, bushings and joints.
A specific example: In order to attach the tooth flanks of gears in a wear-resistant manner, the unalloyed case-hardened steel is inserted into an atmosphere containing carbon. At high temperature, the carbon fuses with the edge layer of the material. In the subsequent hardening process, high hardness values are achieved while the core remains soft and tough. This combination of a hard, wear-resistant surface and a tough, comparatively soft core is optimal for heavily stressed toothed parts.