Steel is heated to the austenitizing temperature above 30 ~ 50 ℃, insulation, so that the organization fully austenitic, and then air-cooled (sometimes supplemented by the hair, spray, etc.), fine lamellar pearlite or Soxhlettissue heat treatment process, called normalizing.
(1) the purpose of normalizing
(1) to adjust the hardness of steel: Some bearings require the tempering resistance, both after quenching, 200 ~ 250 ℃ tempering still has high hardness can be normalizing, annealing, very fine pearlite .
(2) eliminate the carbide network, and lines like organization: When the steel stop forging temperature, and cooling slowly leaving the carbides along austenite grain parse out the carbide network; when the steel final forging temperature is too low, the grain be elongated along the deformation direction and striation organization. This organization in the annealing process can not be completely eliminated, thereby reducing the impact toughness of the fatigue strength of bearing.
(3) repair the nonconforming product anneal: annealing overheating coarse pearlite, subject to the normalizing, and then a second annealing.
(2) normalizing process
Normalizing process to select the heating temperature and cooling, depending on the purpose of normalizing, normalizing the former Carbide Morphology of fibrous tissue, as well as the shape and thickness of the ferrule. Normalizing the holding time is generally 30 ~ 50 min, the cooling rate of not less than 50 ℃ / min, and prevent the precipitation of the carbide network. Spread for thin-walled parts, cooling or quenching; should be used for thicker parts, spray, oil or cold emulsion cooling, oil cooling generally cold to the part surface to remove about 300 ℃, until the surface oil is burning once again put into the cooling oil to the surface temperature of not lower than 250 ℃ up, should be tempered immediately after normalizing the first to eliminate the stress of 400 ~ 450 ℃ tempering in order to avoid cracks. Cooling emulsion is generally controlled at 70 ~ 100 ° C by circulating cooling method, the workpiece cooled to remove the air-cooled 550 ~ 650 ℃. 撤消修改


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