Most of large gear casting manufacturers use cast steel to produce girth gear. The gears need to be annealed, normalized, and tempered before the milling of the teeth to improve the hardness and strength of the gears. The gears also need to be heat treated. The preliminary heat treatment of the cast steel gear is generally an annealing or normalizing process, and according to actual situation, different preliminary heat treatment methods are required.

1. Low carbon steel can generally be treated by normalizing to obtain relatively uniform iron elements and fine-grained pearlite structure;

2. As for medium carbon steel and alloy steel, we use complete annealing or isothermal annealing to obtain ferrite and flaky pearlite structure;

Both of the above preheat treatment methods can deal with defects and stresses such as crystals, ferrite and Weiss body structure which occur in casting, which can effectively improve the cutting performance, and can also refine the structure, prepare the structure for the final heat treatment, and reduce deformation cracking. 

3. The low temperature annealing process can be used to eliminate the stress of casting;

4. For large steel castings, dendrite segregation occurs, and a uniform fire is required for annealing. If the uniform annealing temperature is high, the structure at the back becomes abnormally coarse. After the uniform annealing, a complete annealing or normalizing is required, so that the grains can be refined, the mechanical properties can be improved, and the processability can be improved, to prepare the organization for the final heat treatment.

The large girth gear produced by CHAENG uses a unique heat treatment technique in the casting process, which optimizes the gear structure, improves the hardness, and greatly improves the wear resistance and impact resistance.