3.1 a Heat Treatments

Question 1

Name the 4 heat treatments

Answer 1

Normalising
Case hardening
Annealing
Hardening and tempering

Question 2

explain the process of case hardening

Answer 2

heated to red heat at 900c

removed from heat and placed into a cooling compound which is high in carbon

heated again to a red colour and quenched in cold water

it now has a hard surface but soft inner core

Question 3

What metals is case hardening used for

Answer 3

mild steel and medium carbon steel

Question 4

explain the process of annealing aluminium

Answer 4

soap is applied

heated till soap goes black

heat removed

cool running water applied

Question 5

what is annealing used for

Answer 5

the relieve the internal stresses of non-ferrous metals like aluminium and copper

Question 6

explain the process of annealing copper

Answer 6

heated till dull red

heat removed

can be quenched or air cooled

placed in acid bath to remove oxides

remove acid under cool running water

Question 7

what is the process of removing copper oxides called

Answer 7

pickling

if not removed, it can be damaged

Question 8

what is normalising

Answer 8

used on ferrous metals that have become hardened, in order to return to original, unhardened state.

Question 9

explain the process of normalising

Answer 9

steel is heated until red hot at 900c

heat removed and air cooled

Question 10

explain the hardening process

Answer 10

the metal is gradually heated till red hot

removed from heat and quenched

cools rapidly, becomes hard yet brittle

Question 11

what metal is hardening and tempering used on

Answer 11

high carbon steel only

Question 12

explain the process of tempering

Answer 12

cleaned using emery cloth till shiny

reheated slowly and carefully till a thin line of oxide appears

this line will change colour depending on temperature. different colours represent different uses

its then quenched again, and iron carbide content is frozen at that particular level