What does carbon addition of gas radiant tube mean?

Forgings heated by gas radiant tubes often experience carburization on the surface or part of the surface. Sometimes the thickness of the carburized layer of the radiant tube is 1.5-1.6mm, and the carbon content of the carburized layer is about 1% (mass fraction). The carbon content at some points even exceeds 2% (mass fraction), and the ledeburite structure appears. This is mainly due to the fact that when the blank is heated by an oil furnace, when the position of the blank is close to the nozzle of the oil furnace or in the area where the two nozzles cross-spray the fuel, the oil and air are not mixed well, so the combustion is incomplete, resulting in the formation of a reducing carburizing atmosphere on the surface of the blank, thereby producing the effect of surface carburization. Carburization deteriorates the machining performance of the forging and makes it easy to break the knife during cutting.