At what degree will carbon steel pipes decarburize after heat treatment?

When carbon steel is heated to a certain temperature and after a certain period of time, a decarburized layer will appear on the carbon steel. The structural characteristics of the decarburized layer: the carbon in the decarburized layer is oxidized, which reflects in its chemical composition that its carbon content is lower than that of the normal structure; Reflected in the metallographic structure, the amount of cementite (Fe3C) is less than that of normal tissue; reflected in mechanical properties, its strength or hardness is lower than that of normal tissue.
As the heating temperature increases, the depth of the decarburization layer continues to increase. Generally, when the temperature is lower than 1000°C, the oxide scale on the steel surface hinders the diffusion of carbon, and decarburization is slower than oxidation. However, as the temperature increases, on the one hand, the formation rate of oxide scale increases; on the other hand, the diffusion rate of carbon under the oxide scale also accelerates. At this time, the oxide scale loses its protective ability, and decarburization is faster than oxidation after reaching a certain temperature.
The longer the heating time, the more heating times, and the deeper the decarburization layer, but the decarburization layer does not increase in proportion to time. For example, the decarburized layer of high-speed steel reaches a depth of 0.4mm when heated at 1000°C for 0.5h; a depth of 1.0mm after 4h; and a depth of 1.2mm after 12h.