Working with a metal when its cold e.g. bending, rolling, hammering distorts the crystal structure and causes them to be harder in that area increasing tensile strength of the metal
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annealing
heat the metal until the crystal start to grow and its cooled slowly to reduce internal stresses making it softer and more ductile
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hardening
heat the metal to a glowing point and then quench it (put it in a liquid to cool it rapidly) this adjusts the carbon position and changes the carbon structure
it is quenched so the carbon doesnt return to its original structure
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tempering
common follow up of hardening
heat the metal to a suitable temperature and allow it to cool naturally reducing internal stresses, increases toughness, decreases hardness
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normalising
used to chnage crystal structure so they become uniform in size
increases touhgness and ductility
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case hardening and nitriding
Case hardening: 'baking' the metal with a carbon heavy compound to make the outside harder used for gears and steering components
Nitriding: siimilar to case hardening but uses nitrogen instead for the function of making the metal corrosion resistant
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