13 - Enhancement of materials - Metal enhancement Flashcards
What are the 5 types of metal enhancement?
~Work hardening
~Annealing
~Case hardening
~Hardening
~Tempering
Work hardening
When the metal is ‘cold worked’ such as through bending, rolling or hammering
-Crystals within the matal are distorted and changed, improves the tensile strength and hardness of the worked area
-Crystals cannot move freely within the metal structure, so could also lead to less ductility, or even cracking in the worked area
Annealing removes the effects of work hardening
Annealing
Used to make the work-hardened metal easier to work. Makes it less brittle and more ductile
-Metal is heated and then cooled very slowly, allows the crystals to move into place again
Case hardening
Used for hardening the surface of steels with less than 0.4% carbon content (low-carbon steel)
-Produces an outer casing with improved hardness, wear resistance. Inner core remains soft
Step 1)
Carburising:
-Changes the chemical composition of the surface so that it can absorb more carbon.
Step 2)
Quenching:
Hot metal is quenched in water to cool it quickly and seal the hard surface case while not affectinb the properties of the inner core
Hardening
Medium and high carbon steel are heated to alter their crystalline structure, holding them at this temperature and then quenching them in water or oil
Increases hardness, but also brittleness
Tempering
Heat treatment, reduces the excess hardness and brittleness. Increases toughness and ductility
Metal is heated to below the critical point for a given time and then air cooled. The temperature determines the amount of hardness removed.
Tempring colour on the metal: indicates the temperature at which brittleness is removed