How to dehydrogen annealing forgings

Post-forging heat treatment of large forgings after forging forming, immediately after the heat treatment is called post-forging heat treatment. The purpose of post-forging heat treatment of large forgings is mainly to de-stress, recrystallize grain refining and dehydrogenation at the same time.
1. Recrystallization treatment After several recrystallization treatment of large forgings, grain refinement, microstructure improvement, performance improvement.
2. Dehydrogen annealing will reduce the hydrogen in the forgings to the limit hydrogen content below, and make its distribution uniform, in order to avoid the danger of white spots, hydrogen embrittlement.

The solubility and diffusion coefficient of hydrogen in phase 7 and phase A are different, especially the low solubility and large diffusion coefficient of hydrogen in phase A, which makes hydrogen continuously diffuse outward during the annealing process. Dehydrogenation annealing is often combined with recrystallization. The temperature of dehydrogen annealing is usually 650℃. After annealing, it should be cooled as slowly as possible to prevent new internal stress. General cooling is divided into two stages: above 400℃, due to the good plasticity of steel, internal stress is not easy to form, so the cooling can be faster; Below 400℃, the cooling rate will slow down. For forgings with more alloy elements and higher performance requirements, one or even multiple recrystallization heat treatment is required after forging, in order to improve the structure and performance of forgings.