13 - Enhancement of materials - Metal enhancement Flashcards

1
Q

What are the 5 types of metal enhancement?

A

~Work hardening

~Annealing

~Case hardening

~Hardening

~Tempering

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2
Q

Work hardening

A

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

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3
Q

Annealing

A

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

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4
Q

Case hardening

A

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

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5
Q

Hardening

A

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

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6
Q

Tempering

A

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

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