Heat treatments of metal

Question 1

What is work hardening?

Answer 1

• When a metal is cold worked
• The metal is: Hit with a hammer, rolled, drawn or bent to cause the crystal structure to become stressed
• This can cause the metal to become hard or it can also it could cause the metal to crack

Question 2

What is annealing?

Answer 2

• Annealing is the process of returning a metal back to its soft ductile state by heating it for a period of time
• This allows the crystals to change shape and grow
• The metal must be allowed to cool very slowly

Question 3

What is hardening?

Answer 3

• Hardening is a process by which the carbon content in the material can be changed to harden the material
• For example: If medium carbon steel is heated to a specific temperature, the carbon moves within the structure pf the metal
• The metal is quenched to cool it very quickly and make the carbon stay in its new state
• This then hardens and strengthens the metal

Question 4

What is tempering?

Answer 4

-When the material has been hardened it can be brittle, to avoid the cracking of the metal it can be tempered to make it slightly less brittle
-The metal must be heated to a specific temperature depending on the application of it:
300 degrees = Hard (Springs and spanners)
240 degrees = Less tough (Drills)
230 degrees = Harder (Lathe tools)

Question 5

What is quenching?

Answer 5

-During the hardening process, the metal is quenched
-This is the rapid cooling of the metal after heating
-Depending on the way the material is quenched, the metal will cool at different speeds:
Brine = Fast cooling
Water
Oil
Air = Slowest cooling