Thermal processing of metal alloys
     Heat treatment  (temperature effect)
       •
         annealing   (to get more stable state)
         reduce internal stress, reach softer and ductile structure, …
       •
         hardening   (to get metastable state)
              increases strength, hardness, wear resistance, …
     Thermomechanical treatment 
     (effect of temperature and deformation)
     control of final structure and mechanical properties
     Chemical heat treatment
     (effect of temperature and changes of the chemical composition)
     to get different properties of surface layer as in core of the piece 
     – higher hardness, better wear or corrosion resistance, …
            Heat treatment of steels
               Annealing 
    Lower critical temperature (without transformation)
    •
      Process (recrystallization) annealing
    •
      Stress relief annealing
    •
      Spheroidizing
    Upper critical temperature (partial or whole transformation)
    •
      Normalizing
    •
      Homogenization
     Process (recrystallization) annealing
     550 – 700 °C,  1- 5 hours, cooling in air
     To change the structure and properties of cold worked (strain 
     hardened) steel.
     Recovery and recrystallization processes occur.
     Softening, increase ductility and uniform fine grain structure is 
     achieved.
     Stress relief annealing
     400 – 650 °C, 2 - 10  hours, very slow cooling in furnace
     Reduce internal residual stresses (after machining, heat 
     treatment, …)
     Spheroidizing (soft annealing)
     700 °C, 5 – 25 hours, slow cooling to 600 °C in furnace, then 
     cooling may continue in air.
     Spheroidite structure is developed
       Used to improve machineability and toughness.  
          Normalizing
          50 – 80 °C above upper critical temperature (phase diagram), 
          cooling in air.
          Austenitization of the steel is required and cooling in accordance 
          with CCT diagram to get uniform and fine grain structure.
          Full annealing 
          over A and A with furnace cooling.
                3      1 
          Homogenization
          1100 - 1200 °C (200 °C under solidus!) 
          To reduce structure and chemical composition inhomogeneities 
          after casting.