Abstract: When 1Cr25Ni20Si2 steel nitriding tank was used as a retort in a gas nitriding furnace, the aging phenomenon would occur with the increase of the nitriding time, resulting in that the nitriding of workpiece could not be carried out. Though many different methods were used to solve the aging problem, they were not effective enough, but it was found that high temperature tempering in the failed nitriding furnace could effectively denitrify and solve the aging problem of retort.

Key words: nitriding retort aging, ammonia decomposition rate, high temperature tempering