Defects caused by improper heating of forged flanges can be divided into:
(1) The defects of forged flange caused by the change of histochemical state of the outer layer of billet due to the influence of medium, such as oxidation, decarburization, carburization, sulfurization, copper infiltration, etc;
(2) Defects of forged flanges caused by abnormal changes in internal organization structure, such as overheating, overburning and lack of heat penetration;
(3) Due to the uneven distribution of temperature in the blank of forged flange, the blank of forged flange cracks due to excessive internal stress (such as temperature stress and structural stress).
Here are some common defects of forged flanges.
Decarburization of forged flanges
Decarburization of forged flange refers to the phenomenon that the carbon in the surface layer of metal is oxidized at high temperature, which makes the carbon content in the surface layer significantly lower than that in the interior.
The depth of decarburization layer of forged flange is related to the composition of steel, the composition of furnace gas, temperature and the holding time at this temperature. Decarburization is easy to occur when heated in an oxidizing atmosphere, high carbon steel is easy to decarburize, and steel with high silicon content is also easy to decarburize.
Decarburization of forged flanges reduces the strength and fatigue performance of forged flange parts, and weakens the wear resistance.
Carburization of forged flanges
The carburization of forged flange often occurs on the surface or part of the surface of forgings heated by oil furnace. Sometimes the thickness of carburized layer of forged flange is 1.5 ~ 1.6mm, the carbon content of carburized layer is about 1% (mass fraction), and the carbon content of local points is even more than 2% (mass fraction), resulting in ledeburite structure.
