Aluminum alloy oxide film of forged flange
The aluminum alloy oxide film of forged flange is usually located on the web of forged flange and near the parting surface. There are fine cracks on the macrostructure and vortex on the macrostructure. The characteristics on the fracture can be divided into two categories: first, it is flat and flaky, and its color ranges from silver gray and light yellow to brown and dark brown; Second, they are small, dense and shiny dots.
The aluminum alloy oxide film of forged flange is formed when the exposed melt level interacts with water vapor or other metal oxides in the atmosphere during the casting process. The oxide film is rolled into the liquid metal during the casting process of forged flange.
The oxide film in forged flanges and die forgings has no obvious influence on the longitudinal mechanical properties, but has a great influence on the mechanical properties in the height direction. It reduces the strength properties in the height direction of forged flanges, especially the elongation, impact toughness and corrosion resistance in the height direction.
White spot of forged flange
The main characteristics of the white spots of forged flanges are round or oval silver white spots on the longitudinal fracture of the billet and small cracks on the transverse fracture. The size of white dots varies, and the length is 1 ~ 20mm or longer. White spots of forged flanges are common in alloy steels such as nickel chromium steel and nickel chromium molybdenum steel, and also found in ordinary carbon steel, which are hidden defects. White spots are produced under the joint action of hydrogen, structural stress during phase transformation and thermal stress. It is easier to produce when the steel of forged flange contains more hydrogen and the cooling (or post forging heat treatment) after thermal pressure processing is too fast.
