In addition to hardenability properties, high strength and ductility are also required in tempered steels. In order to achieve a sufficient level of hardness, tempered steels have a relatively high carbon content. Since the depth of hardness is the most important criterion for parts with thick sections, these parts are manufactured from alloyed tempered steels. Part dimensions and strength values are at the forefront in the selection of tempered steels.

Non-alloy tempered steels can only be efficient in small section parts. For parts with thick sections, the homogeneity of the hardness distribution depends on the alloying of the steel. Changes in hardness distribution according to material alloys can be observed with the results of the Jominy test. In simple terms, the Jominy test refers to the hardening values at distances from the cooled end by cooling only one end of a rod-shaped material heated to the hardening temperature. Tempered steels can be hardened by flame and induction, or they can be hardened by flame and induction after they have been reclaimed. In this way, in addition to the chemical composition, the hardness value and hardening depth to be obtained on the surface are taken into consideration in the selection of the material to be heat treated. In unalloyed steels, the depth of hardness can be 3-4 mm, while in alloyed steels this depth reaches 10-12 mm. In addition, it is more appropriate to use high carbon-low manganese Cf grade steels as high manganese will cause cracking during induction hardening. In addition, the reduction of cracking hazard is closely related to the small grain structure of the material.  Tempered steels are categorized in 4 main groups according to their chemical composition.   

Non-alloyed reclamation steels Manganese alloyed reclamation steels Chromium alloyed tempered steels Chromium-molybdenum alloyed tempered steels In non-alloyed steels, the tempered strength increases with the amount of carbon. Up to 16 mm diameter, the lowest yield limit is between 370 N/mm^2 (%C:0.25) and 570 N/mm^2 (%C:0.50). For sizes between 16-40 mm diameter, 50-80 N/mm^2 is lower. Since manganese increases hardenability in manganese alloyed tempered steels, the yield limit of 30Mn4 and 40Mn4 steels shows the properties of C60 steel. In chromium-alloyed tempered steels, the chromium element significantly increases hardenability and has a positive effect on plasticity. For example, in 40Cr4 steel, the minimum yield in the 16-400 mm diameter range is 700 N/mm^2. Molybdenum increases the ability to harden more strongly than chromium.

It also increases temper strength and reduces the possibility of temper brittleness. The tempering process is described as hardening followed by tempering. In the following, hardening and tempering processes for steels are generally described separately.