Overburning of forged flanges
Overburning of forged flange refers to that the heating temperature of the blank of forged flange is too high or the residence time in the high-temperature heating zone is too long. Oxygen and other oxidizing gases in the furnace penetrate into the gap between metal grains and oxidize with iron, sulfur, carbon, etc., forming eutectic of fusible oxides, destroying the connection between heavy grains of raw materials of forged flange, and sharply reducing the plasticity of forged flange. For the metal with serious overburning, it will crack with a slight blow when it is removed from the coarse, and a transverse crack will appear at the overburned part when it is drawn out.
There is no strict temperature boundary between overburning and overheating of forged flanges. Overburning is generally judged by the oxidation and melting of grains. For carbon steel, the grain boundary melts during overburning, and fishbone ledeburite appears at the grain boundary due to melting during Overburning of severe oxygen chemical die steel (high speed steel, Cr12 Steel, etc.). Grain boundary melting triangle zone and remelting ball appear when aluminum alloy is over burned. After the forged flange is burned, it is often unable to be saved and has to be scrapped.
Heating crack of forged flange
When heating the billets of large ingots with large cross-section size and forged flanges of high alloy steel and superalloy with poor thermal conductivity, if the heating speed is too fast in the low-temperature stage, the billets of forged flanges will produce great thermal stress due to the large internal and external temperature difference. In addition, at this time, the plasticity of the blank is poor due to low temperature. If the value of thermal stress exceeds the strength limit of the blank, there will be radial heating cracks from the center to the periphery, which will crack the section of the whole forged flange.
