Keywords: annealing, annealingprocess, diffusionannealing, homogenizingannealing, completeannealing, spheroidizingannealing, recrystallizingannealing, stressreliefannealing, grainrefinementannealing, malleableannealing, high-temperatureannealing, incompleteannealing, low-temperatureannealing, isothermalannealing, heattreating, deformation, cracking, pearlitic,

I. Definition of annealing:

    The metal material is heated to a certain temperature (temperature according to different annealing methods), hold a certain time, and then slowly cooled (with the furnace cooling), in order to obtain close to the equilibrium state organization of a heat treatment process.

Second, the classification of annealing process:

　　Types of annealing, the name is very much, the same kind of annealing from different perspectives can be called different names.

(A) “authentic” annealing:  

    For steel, the more “authentic” annealing process should be (to obtain close to the equilibrium transformation of the organization - pearlite):

    A heat treatment process that results in flaky spherical P-transformation products in a steel part.

    Depending on the composition of the steel, the “authentic” annealing process is divided into:

　　Complete annealing: Heating to the austenite phase region 20-30°C above the Ac3 temperature. Mainly used for sub-eutectic steels.

  　Incomplete annealing: heating to the Ac1 temperature above 20 ~ 30 ℃, mainly used for over-eutectic steel.

 　 Spheroidizing annealing: A special case of incomplete annealing with a slightly different process. Used for over-eutectic steels to obtain a spherical pearlitic organization.

  　The difference between these types of annealing is shown in the table below:

       Sub-eutectoid steels Hypereutectoid steels

 Complete annealing Complete recrystallization (structural changes) of defective structures (Weissian, coarse grains, banding) to obtain an F + P organization.  

    Not suitable for complete annealing

Incomplete annealing Does not change the form and distribution of ferrite in the original organization, but only adjusts the spacing of pearlite flakes. (Saves energy and time compared to complete annealing) (Spheroidal annealing)

  (Spheroidal annealing) Spheroidal pearlite organization is obtained.

　　The heating temperature ranges for these types of annealing are shown in the figure below:

Annealing heating temperature range

(B) several other processes called “annealing”:

　　We have already studied several other less “authentic” annealing processes:

　　Diffusion annealing (homogenizing annealing): Elimination of dendritic segregation in castings and ingots (forging billets).

                        (regional resolution)

 　 Recrystallization annealing (intermediate annealing): elimination of work-hardening and complete restoration of plasticity in cold-deformed metals.

 　 Stress relief annealing (reply annealing, low-temperature annealing): due to deformation processing as well as casting, welding caused by residual internal stresses, eliminate internal stresses, reduce hardness, stabilize the size and prevent deformation and cracking of the workpiece.

　　The heating temperature range of these three annealing processes is shown in the figure below:

Fire process heating temperature range

(C) the comprehensive classification of annealing process

　　 Let us take a comprehensive look at the types of annealing process, annealing process can be categorized from the following different perspectives:

1. According to the different purposes of annealing

       Homogenizing annealing (diffusion annealing) - casting annealing

       Complete annealing

       Spheroidal annealing - annealing to improve cutting performance

       Intermediate annealing (recrystallization annealing): annealing to eliminate work hardening

--Annealing of forgings

       Low-temperature annealing (stress relief annealing): to remove internal stress -- casting, forging, welding parts

　　2. According to the organization of the annealing transformation characteristics:

           Refined grain annealing

           Spheroidization annealing

           Recrystallization annealing

           Malleable annealing

　　3. According to the annealing process method classification:

           High temperature annealing (diffusion annealing, homogenization annealing)

           Complete annealing

           Isothermal quenching

           Incomplete annealing

           Low temperature annealing

4. Categorized by process:

　　 Pre (heat treatment) annealing - intermediate (heat treatment) annealing - final (heat treatment) annealing

Annealing related furnace: hooded vacuum bright annealing furnace, aluminum alloy cable annealing furnace, horizontal vacuum bright annealing furnace, well vacuum bright annealing furnace, cart furnace, box furnace and so on.

More Definition of annealing and classification of annealing: en.chengchi.net/view-254.html