The carburization of forged flange is mainly in the case of oil furnace heating. When the position of forged flange blank is close to the nozzle of oil furnace or in the area where the two nozzles cross inject fuel oil, the oil and air are not mixed well, so the combustion is incomplete. As a result, a reducing carburizing atmosphere is formed on the surface of forged flange blank, resulting in the effect of Carburization on the surface of forged flange. The carburization of forged flange makes the machinability of forged flange deteriorate and it is easy to cut.
Overheating of forged flanges
Overheating of forged flanges refers to the phenomenon of coarse grains caused by excessive heating temperature of metal billets, too long residence time within the specified forging and heat treatment temperature range, or too high temperature rise due to thermal effect.
Widmanstatten structure often appears in carbon steel (hypoeutectoid or hypereutectoid steel) of forged flanges after overheating. After overheating, martensitic steel often appears intragranular texture, and tool and die steel is often characterized by primary carbide angulation to determine the overheating structure. After overheating of titanium alloy, obvious β Widmanstatten structure with flat and straight grain boundary. The fracture of the alloy steel of forged flange after overheating will appear stone fracture or strip fracture. Overheating structure, due to coarse grains, will cause the mechanical properties of forged flanges to decrease, especially the impact toughness.
Generally, after the normal heat treatment (normalizing and quenching) of forged flanges, the structure of overheated structural steel can be improved and the properties can be restored. This overheating of forged flanges is often called unstable overheating; The severe overheating of alloy structural steel can not be completely eliminated after general normalizing (including high-temperature normalizing), annealing or quenching. This overheating is often called stable overheating.
