Process: A heat treatment process in which steel ingots, castings or forging billets are heated to a temperature slightly lower than the solidus line for a long time, and then slowly cooled to eliminate uneven chemical composition.
Objective: To eliminate dendritic segregation and regional segregation during the solidification process of the ingot, and to homogenize the composition and structure.
The heating temperature for diffusion annealing is very high, usually 100 ~ 200 ℃ above Ac3 or Accm. The specific temperature depends on the degree of segregation and the type of steel.
The holding time is generally 10-15 hours. After diffusion annealing, complete annealing and normalizing are required to refine the structure.
It is applied to some high-quality alloy steel and alloy steel castings and ingots with severe segregation.