When the blank of the forged flange is heated, such as the residual copper oxide chips in the furnace, the oxidized steel is reduced to free copper at high temperature, and the molten steel atoms expand along the austenite grain boundary, weakening the connection between the grains of the forged flange. In addition, when the copper content in the steel of forged flange is high [> 2% (mass fraction)], if heated in an oxidizing atmosphere, a copper rich layer will be formed under the iron oxide scale, which will also cause steel embrittlement of forged flange.
Defects of forged flanges often caused by improper forging process
The defects of forged flanges caused by improper forging process usually include the following types
Cast structure residue of forged flange
The residual structure of forging and casting mainly appears in the forged flange with ingot as blank. The as cast structure of forged flange mainly remains in the difficult deformation area of forgings. Insufficient forging ratio and improper forging method of forged flange are the main reasons for the residual casting structure.
The residual structure of forging and casting will reduce the properties of forged flanges, especially the impact toughness and fatigue properties.
Large grains of forged flanges
The large grains of forged flanges are usually caused by the high initial forging temperature and insufficient deformation, or the high final forging temperature of forged flanges, or the deformation degree falling into the critical deformation zone. The deformation degree of aluminum alloy of forged flange is too large, forming texture; When the deformation temperature of superalloy is too low, the mixed deformation structure of forged flange may also cause coarse grains. The coarse grain size of forged flange will reduce the plasticity and toughness of forgings and significantly reduce the fatigue performance.
