Stability of low-temperature-gaseous-carburization layer in AISI316L stainless steel at high temperature

In this paper, the stability of low-temperature-gaseous-carburization (LTGC) layer in AISI316L stainless steel was investigated by exposing at temperature between 100 ℃ to 400 ℃ from 150 h to 3000 h in air. Test results show that, after carburization, a carburized layer with high carbon content, hardness and huge compressive residual stress form on the surface of 316L. The carburized layer is phase stable at the temperature not exceeding 400 ℃ that there are no undesired Cr carbides (such as M₂₃C₆) precipitate after heat exposure for 3000 h. The carburized layer thickness and hardness is basically stable at the temperature not exceeding 300 ℃. While for the stability of beneficial huge surface compressive residual stress, the highest service temperature should not exceed 200 ℃. Test results also showed that thickness reduction of carburized layer due to oxidation is also an important factor that affecting the stability of carburized layer. Because of high carbon atmosphere in the carburizing progress, a soot layer also forms on the surface of carburized layer and carbon atoms in the soot layer will diffuse in the carburized layer in the early stage of heat exposure progress.