13 - Enhancement of materials - Metal enhancement

Question 1

What are the 5 types of metal enhancement?

Answer 1

~Work hardening

~Annealing

~Case hardening

~Hardening

~Tempering

Question 2

Work hardening

Answer 2

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

Question 3

Annealing

Answer 3

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

Question 4

Case hardening

Answer 4

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

Question 5

Hardening

Answer 5

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

Question 6

Tempering

Answer 6

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