The variations in size that occur during hardening have their origin in the material, the process, and the components. According to our studies the extent to which hardening warpage scatter can be considerably reduced if steel with limited hardenability scattering is used. Our results apply to gas carburization with controlled carbon levels and optimal surface hardening. The case depths ranged from 1 to 1.5mm; the surface hardening varied from 56 to 63 HRC. Notably large variations in size were registered in the case of alloyed case-hardening steels - a material that is often used for large gears in order to ensure a sufficient degree of hardening depth. In the interests of cost-effective production it is, however, desirable that these very same components be manufactured with as small a grinding allowance as possible. In order to solve this problem the engineers at Reese recommend that in such cases steel with a low C-content be used but that in all other cases the normal alloying contents be followed, i.e. the MAAG-steels 10NiCrMo7 for small and 12NiCrMo7 for large or very heavy parts.

The teeth on the tooth tips and on the flanks cool off more rapidly than they do on the dedendum so that in the former case a smaller degree of surface hardness and thus a lesser case depth are attained. More recently an unusual defect has been observed: in cases where relatively large massive components were involved, they splitted apart longitudinal.

Defects in the material together with high internal tensile stress in the core of massive components are thought to be the cause. Core-drillings in the longitudinal axis represent one way of avoiding this problem. In any case one must make sure that the material has been chosen and the production carried out with the utmost care. A prior heating treatment would also serve to increase the core toughness.

Here especially the general rule holds: An early enough consultation between technical designers and hardening engineers can help to minimize costs and avoid faulty estimates.