Skip to main content

What is Annealing ?

Annealing:-


Annealing Process :-


Annealing is a heat treatment process by which the properties of steel are enhanced to meet machinability requirements.In this process Hypoeutectoid steels (less than 0.83% carbon) are heated above upper critical temp., soaked and cooled slowly and Hypereutecoid (above 0.83%) are heated above lower critical temp., soaked and allowed to cool slowly.


Annealing Process Steps:




1.Heat material into the asutenite region (i.e. above 1600F) – rule of thumb: hold 

 steel for one hour for each one inch of thickness

2.Slowly furnace cool the steel – DO NOT QUENCH

3.Key slow cooling allows the C to precipitate out so resulting structure is coarse 
pearlite with excess ferrite
4.After annealing steel is quite soft and ductile



The purpose of Annealing is :



1)Reduce hardness and brittleness

2)Alter microstructure for desired mechanical properties

3)Soften steels to improve formability

4)Recrystalize cold worked (strain hardened) steel
5)Remove internal stresses induced by some previous processes such as forming, forging, uneven cooling.

Types of Annealing :-

Full Annealing:-



•Heating 25-50°C above upper critical temp. for steel <0.9% C.



• Heating 50°C above lower critical temp. for higher carbon steel.



• Soaking for sufficient time & controlled slow cooling

Process Annealing:- Also called Sub-Critical annealing 


•Heating at 500-650°C.

• Soaking for sufficient time & controlled slow cooling


Stress Relief Annealing:-


•Heat treat between 550 and 650°C-low carbon steel



•Soaking time – One hour per inch of thickness.



•Cooled down slowly in the furnace or in air. A slow cooling speed is important to avoid 


tensions caused by temperature differences in the material, this is especially important 

when stress relieving larger components


Spherodise Annealing:- This can be done by two methods 

  •  Heating and cooling the material alternatively between temperatures just above and below the lower critical temperature.
  • Steel is heated just below the lower critical temperature about 700 Degree centigrade and the temperature is maintained for about 8 hours and allowed to cool down slowly.

Isothermal Annealing:-
  • Steel is heated above the upper critical temperature
  • Forced cooling is done
  • Cooling is done below the lower critical temperature about 600 to 700 Degree Centigrade

Labels:

Popular posts from this blog

FILLET WELD FRACTURE TEST

FILLET WELD FRACTURE TEST Object :  To break the joint through the weld to permit examination of the fracture surfaces for flaws and to check root penetration and fusion. Method: The specimen is cut to length and a saw cut, normally 2 mm deep, is made along the center of the weld face. The specimen is fractured by bending or hammer blows. Reporting Results: Thickness of parent material.  Throat thickness and leg length.  Location of fracture. Appearance of joint after fracture. Depth of penetration / lack of penetration or fusion.
Read more

TRANSVERSE TENSILE TEST

TRANSVERSE TENSILE TEST Object:   Used to measure the transverse tensile strength under static loading of a butt joint employing butt welds. The reduced section tensile test normally fails in the parent metal and so it is not designed to give the tensile strength of the weld. The radius reduced tensile test is a test of the as deposited diluted weld metal. The all weld tensile test, using a longitudinal section from the weld only, is used to check the as deposited undiluted weld metal. (Usually used by consumable manufacturers.) Method: The test piece is clamped at each end and a load is applied by an hydraulic or screw mechanism. The load is increased until fracture occurs. Reporting Results: Type of specimen (e.g. reduced section).  Whether excess eld metal is removed or not. Tensile strength, in Newtons per mm squared, is calculated from maximum load and original cross sectional area. When excess weld metal is not removed, the cross sectional area shall ...
Read more

ULTRASONIC TEST

ULTRASONIC TEST INTRODUCTION This method is used to test a variety of both metallic & non metallic products such as welds, forgings, castings, sheets, etc. It has an advantage of detecting sub-surface discontinues with accesses to only one side of the specimen. In this method beams of high frequency sound waves are introduced into the material being tested. The sound waves travel through the material with some loss of energy & are reflected back . This is detected & analysed to detect the presence of flaws. This test employs ultrasonic waves. These waves are mechanical waves that consist of oscillations or vibrations. METHOD TRANSMISSION SYSTEM This method employs two Transducers, one for sending & other for receiving the pulses. These may be short or continuous & are transmitted through the material. The result gets displayed on the CRO connected. The settings of the CRO can be adjusted with respect to time & distance. Prior to testing couplant is used to prov...
Read more