Heat-
      Heat treatment is a method used to alter 
    Treatment
      the physical, and sometimes chemical 
      properties of a material. The most common 
      application is metallurgical
      It involves the use of heating or chilling, 
      normally to extreme temperatures, to 
      achieve a desired result such as hardening 
      or  softening of a material
     It applies only to processes where the 
      heating and cooling are done for the specific 
      purpose of altering properties intentionally
     Generally,  heat  treatment  uses  phase 
      transformation  during  heating  and  cooling 
      to change a microstructure in a solid state. 
          Types of Heat-Treatment (Steel)
      Annealing
      Tempering, and Quenching
      Precipitation hardening
      Case hardening
   Annealin
   gA heat treatment process in which a metal is exposed to an 
    elevated temperature for an extended time period and 
    then slowly cooled.
    Purpose:
    •Relieve stresses of cold working
    •Increase softness, ductility and toughness
    •Produce specific microstructure
   Annealin
   gThree Stages of Annealing
     1.    Heating to a desired temperature
     2.    Holding or soaking at that temperature
     3.    Cooling usually to room temperature
     Note: Time in above procedures is important
     - During heating and cooling temp gradients exit b/w inside and 
     outside portions of part. If rate of temp change is tool high, 
     temp gradients will induce internal stress in part and hence 
     cracking
     2                                     
        1                3
    T
                                 T       α+Fe3C
           α+Fe3C
             Time
                                         Time