Forged flanges forged from steel with white spots are prone to crack and sometimes fall into pieces during heat treatment (quenching) of forged flanges. The white spot of forged flange reduces the plasticity of steel and the strength of parts. It is the stress concentration point. Like a sharp knife, it is easy to become fatigue crack and cause fatigue failure under the action of alternating load. Therefore, white spots are absolutely not allowed in the forging raw materials of forged flanges.
Coarse grained ring of forged flange
The coarse-grained ring of forged flange is often the defect of aluminum alloy or magnesium alloy extruded bar.
Extruded bars of aluminum and magnesium alloys supplied after heat treatment of forged flanges often have coarse-grained rings on the outer layer of the circular section of the forged flange. The thickness of coarse-grained ring of forged flange increases gradually from the beginning to the end during extrusion. If the lubrication condition during extrusion is good, the coarse-grained ring can be reduced or avoided after heat treatment. On the contrary, the thickness of the ring will increase.
There are many factors that cause the coarse crystal ring of forged flange. But the main factor is the friction between the metal and the extrusion cylinder during the extrusion process. This friction results in the crushing degree of the outer surface grain of the bar cross section of the extruded forged flange is much greater than that of the grain at the center of the bar. However, due to the influence of the cylinder wall, the temperature in this area is low, and it cannot be completely recrystallized during extrusion. During quenching and heating, the non recrystallized grains recrystallize and grow up to swallow the recrystallized grains, so a coarse-grained ring is formed on the surface of the forged flange.
