Annealing process and it's importance

1. Heat Treatment
Heat Treatment (H. T.):
A combination of heating & cooling operations, timed and applied to material
or alloy in the solid state in a way that will produce a desired properties.
All basic (H. T.) of steel involves the transformation or decomposition of ( g ).
H. T. of steel 1st stage ( heat above A3)
2nd stage ( cool at different cooling rates )
Types of (H. T.) of steel:
a - Annealing Process.
b - Hardening by Continuous cooling.
c - Isothermal treatment.
1 - Softening. 2 - Improvement machinability. 3 - Stress relief.
4 - Grain refinement. 5 - Homogenizing.
The purpose of Annealing Process:

2. Steps of Annealing Process
Types of Annealing Process:
1 - Heating above A3. 2 - Hold at a temperature for a definite time.
3 - Cooling to the Room Temperature ( R. T. ) at slow rate.
1 - Full Annealing. 2 - Homogenizing. 3 - Normalizing.
4 - Stress relief anneal. 5 - Process Anneal ( Recrystallization – Anneal).
6 - Spherodizing.
Full Annealing:
 Heating the Steel to the proper temp. and then cooling slowly ( typical
cooling rate 1 oC / min) through the transformation range ( in furnace ).
 The purpose of annealing ( a ) - refine the grain. ( b ) - softness.
( c ) - improve electrical & magnetic properties. ( d ) - improve machinability.
 Refinement of the grain size of hypoeutectiode steel will occur about 50 of
above the lower critical temp. line ( A3,1 ). See fig. 2.

3. Spherodizing
Stress relief
Fig. (2) The Change in microstructure
during annealing of:
( a ) - 0.2% C.
( b ) – 1.0% C.

4. b - improve machinability.
c - modify & refine cast dendritic structure.
d - refine the grain & homogenize the structure.
 less proeutectoid ( a ) in normalized hypoeutectiode steel & less
proeutectoid Cementite ( Fe3C ) in hypereutectoid steel as compared with
annealed one because of there is less time for the formation of proeutectoid
constituent.
 The faster the cooling rate, the lower the temp. of ( g ) transformation and
the finer the Pearlite ( see fig. 3 ).
Normalizing:
Homogenizing Treatment:
 It is carried out by heating to ( 100 of ) above
( A3 ) or ( Acem ) followed by cooling in still air
(cooling rate 5-10 oC) to Room Temp. ( RT ) to :
a - produce harder & stronger steel than
annealing.
 A heat treatment of an alloy intended to make it uniform in composition by
eliminating Coring & Concentration gradient.
 It is achieved by heating to a temp. ( 1100 – 1200 oC ) for ( 10 – 20 hour )
followed by slow cooling in air or furnace.
 Sometimes needed to refine the coarse grains.
Fig. (3) The difference in P structure
due to annealing & Normalizing

5. Stress relief annealing
• Internal stress distortion and warpage
• Heat treatment that is used to eliminate internal or residual stresses
in metallic components
Source of internal stress:
- (1) plastic deformation processes such as machining and grinding
(2) Non uniform cooling of a piece that was processed or fabricated
at an elevated temperature, such as a weld or a casting
(3) a phase transformation that is induced upon cooling wherein
parent and product phases have different densities
• General process: heating to there commended temperature,
held there long enough to attain a uniform temperature, and finally
cooled to room temperature in air

6. Annealing temperature relati'e low, up to 378%
effects of cold working and other heat treatments are not
affected
Stress relief annealing(cont.)
It is useful in removing residual stresses due to
Cold Work ( C. W. ) process.
 It is carried out at a Temp. below ( A1 ) ( 1000 –
1200 of ).

7. Process Annealing (Recrystallization – Anneal):

 It is used in the sheet & wire industries after ( C. W. ) see ( fig. 4 ).
 It is carried out by heating the steel to a Temp. below ( A1 ) ( 1000 – 1250 of ).
Fig. (4) The cold – work cycle & Recrystallization diagram

8. Heat treatment that is used to negate the effects of cold
work -that is, to soften and increase the ductility of a
previously strain hardened metal.
It is commonly utilized during fabrication procedures that
require extensive plastic deformation, to allow a
continuation of deformation without fracture or excessive
energy consumption
Recovery and recrystallization processes are allowed to
occur fine grained microstructure heat
treatment stop before grain growth
Process annealing (cont.)

9. Process annealing (cont.)
• Surface oxidation or scaling may be prevented or minimized by
annealing at a relatively low temperature (but above the
recrystallization temperature) or in a nonoxidizing atmosphere
• Some people call it recrystallization annealing
• Yield strength and tensile strength drasticallyr educed
• Commonly used in the production of steel wires,nails, etc

10. Spherodizing:
 This process will produce a Spheroidal or Globular form of carbide in ( a )
matrix ( as shown in fig. 5 ) to improve machinability.
 One of the following methods may be used for Spherodizing:
1 - prolonged holding at a Temp. just below ( A1 ).
2 - Heating & cooling alternatively between a Temp. that just above and
just below ( A1 ).
3 - Heating to a Temp. above ( A1 ) and then either cooling very slowly in
furnace or holding at a Temp. just below ( A1 ).
Fig. ( 5 ): Stages of Spheroidized Annealing.