The cementing is the oldest thermochemical treatment controlled by the man used to increase the surface hardness of parts in mild steel and soft half. For that one increases the surface content of Carbone (it is necessary however that this steel contains elements such as: Cr, mn, Nor, Mo, B).

It is carried out at a temperature generally between 900 and 930 °C. The duration of treatment depends on the desired depth (from 0,1 to 3 mm). The potential required carbon is commonly of 0.85%. This one is obtained today by Craquage of body fluid directly in the laboratory of treatment. One uses a mixture of Azote and of Méthanol, by cracking methanol will give the CO and the CO₂. CO will bring the carbon incipient . This phase of enrichment is generally followed of a Trempe to oil or polymer and of a returned low temperature. A new process known as of cementing low pressure replaces atmospheric cementing gradually.

Formerly, one practiced the solid cementing. One used for this purpose either of the powders, but the action was unequal and left soft beaches, or grains from 6 to 8 mm of size which offered a better passage to gases and gave better a thermal Conductivité. The cement of Charon was very much used (60 parts of Charcoal and 40 parts of calcium Carbonate)

In addition to one high surface hardness (58 to 63 HRc according to the temperature of the income), cementing brings resistance to the wear and held with the tiredness .

As for the heat treatments of hardening, it is preferable to anticipate the geometrical variations of the parts by leaving an extra thickness of correction.

After cementing, the parts can be soaked, then they pass in a furnace of income at temperatures ranging between 175 and 200  °C.

Accidents of cementing:

1 - Dureté surface unequal - soft Beach after trempe: insufficient carburation, oxidized parts, sulfurous zones ségrégées, parts swines, irregular and insufficient temperature in certain places, portion of cooled pieces too slowly.

2 - Dureté regular but insufficient after trempe: Duration of the too short operation or insufficient temperature, incorrect atmosphere, regeneration or heating before hardening carried out in a furnace decarbonizing or oxidizing, temperature before insufficient hardening, speed of cooling too low.

3 - Ecaillage - Shrinkage cracks - Criques: Noted in the case of a very marked cementing and often too fast generating free Cementite, its point of transformation being different from that of the Pearlite.

4 - Fragility of the cœur: incomplete regeneration in consequence of a too low temperature or of an insufficient processing time.

5 - Déformations: parts badly constant in the furnace, or bad presentation in the bath of hardening or absence of pre-heating.