The steel is heated to above the austenitizing temperature 30 ~ 50 ℃, heat, bring the organization fully austenitic, and then air-cooled (sometimes accompanied by hair, spray, etc.) to obtain fine flake pearlite or Soxhlet tissue of the heat treatment process, called normalizing.
1 The purpose of normalizing
(1) to adjust the hardness of steel: some bearing anti-tempering performance product requirements, both quenched by 200 ~ 250 ℃ tempering still have a higher hardness after normalizing annealing can be used to get very fine pearlier .
(2) Eliminate the mesh-like lines of carbon and organization: When forging steel stop temperature, the cooling is too slow leaving the analysis of carbide network along the austenite grain carbide; when the temperature is too low final forging steel, grain elongated along the deformation direction is the emergence of the line-like organization. This organization during annealing can not be completely eliminated, thereby reducing the fatigue strength of bearing impact toughness.
(3) Repair of nonconforming product annealing: annealing heat generated coarse pearlite, subject to normalizing, and then a second annealing.
(2) Normalizing process
Normalizing process is to select the heating temperature and the main cooling mode, depending on the purpose of normalizing, normalizing the former fibrous tissue in the form of carbide, and the shape of rings and wall thickness. Normalizing holding time is generally 30 ~ 50min, cooling rate of not less than 50 ℃ / min, to prevent the precipitation of carbide network. For thin-walled parts, spread out cooling or quenching; for thick parts, should be used to spray oil emulsion in cold or cooling, oil cooling generally cool about 300 ℃ to remove the part surface, the surface of the oil to be burned again after release into the cooling oil to the surface until the temperature is not lower than 250 ℃, tempering or normalizing immediately after the first for 400 ~ 450 ℃ tempering the elimination of stress, in order to avoid cracks. Cooling in the general control of emulsion 70 ~ 100 ℃, the use of cooling methods, parts cooled to 550 ~ 650 ℃, remove the air-cooled.