• Annealing is a thermal process used to bring a metal closer to its equilibrium state. In this soft state, the uniform microstructure will allow for excellent ductility and workability. In order to perform a full anneal in ferrous metals, the material must be heated above its upper critical temperature long enough to fully transform the microstructure to austenite. The metal must then be slow-cooled, usually by allowing it to cool in the furnace, to allow maximum ferrite and pearlite phase transformation. Other metals such as brass, silver and copper may be fully annealed by the same process, but may be quickly cooled, even water quenched, to finish the cycle.


  • Normalizing is a type of annealing process used to relieve stress in hardenable steels after cold work and to improve ductility and toughness properties. The steel is heated slightly above its upper critical temperature and held for sufficient time to allow new, smaller grains to form and high energy grain shapes to coalesce, also known as grain refinement.
    Normalizing can also eliminate denritic segregation that may remain from the casting process. The steel is air cooled from the normalization temperature, yielding a microstructure that lends the desired toughness and ductility properties with a nominal tensile strength.
  • Method : heat to normalizing temperature and maintain


  • Quenching is an accelerated method of bringing a metal back to room temperature, preventing the lower temperatures through which the material is cooled from having a chance to cause significant alterations in the microstructure through diffusion. Quenching can be performed with forced air convection, oil, fresh water, salt water and special purpose polymers.
    The slower the quench rate, the longer thermodynamic forces have a chance to alter the microstructure, which is in some cases desirable, hence the use of different media. When quenching in a liquid medium, it is important to stir the liquid around the piece to clear away steam from the surface; steam pockets locally defeat the quench by air cooling until they are cleared away.


  • Tempering is a heat treatment process that improves the ductility and toughness of metals. In steel, martensite phase is formed when excess carbon is trapped in the austenitic lath and quickly cooled (usually by water quenching). This untempered martensite must be heated below the lower critical temperature of the steel to allow the carbon to diffuse out of the body-centered tetragonal structure, creating a more ductile and stable body-centered structure.

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