5.
Diffusion annealing
Diffusion annealing, also known as homogenization annealing, is mainly used for alloy steel ingot or castings, which always produce dendrite segregation of alloying elements during the solidification process after pouring, that is, chemical composition non-uniformity. Diffusion annealing is to eliminate or weaken dendrite segregation by heating austenitizing at high temperature for a long time, so that the uneven distribution of elements through diffusion.
The commonly used diffusion annealing temperature is 1100℃-1200℃, and the holding time is 10-15 hours. The higher the alloying element content in the steel pipe, the higher the heating temperature used. After a long time of high temperature heating diffusion annealing, austenite grains have been overgrown, such as no more hot processing, must be a complete annealing or normalizing to refine the grains.
6.
Low temperature annealing
Low temperature annealing is to heat steel to a temperature lower than Ac1 annealing, also known as stress relief annealing, mainly used to eliminate castings, forgings, welding parts, cold stamping parts and machining parts in the residual stress, improve stability, to prevent hardening deformation cracking. It includes softening annealing and recrystallization annealing.
The commonly used softening annealing temperature is 650-720℃, and it is air-cooled after heat preservation. After softening and annealing the ingot, the internal stress is eliminated, the ingot cracking is avoided, and the hardness is reduced to facilitate the surface cleaning of the ingot. After softening and annealing, the internal stress and hardness of forged rolled alloy structural steel can be eliminated, and the hardness reduction effect is more significant for the alloy steel with high stability of supercooled austenite. Recrystallization annealing is the process by which cold-work hardened steel is heated to a temperature between T and -Ac1, usually 650-700 ° C. The purpose is to restore the deformed grains to equiaxed grains by recrystallization, thus eliminating work hardening.
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