Heat treatments Flashcards

1
Q

What are some uses of heat treatments?

A
  • increase strength, hardness & wear resistance
  • increase ductility and softness
  • increase toughness
  • obtain fine grain size
  • to remove internal stresses induced by differential deformation e.g. high temps
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2
Q

What is annealing?

A

A heat treatment process in which material is taken to an elevated temp, kept there for some time and then left to cool, usually in an off furnace.

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3
Q

What are the purposes of annealing?

A
  • relieves internal or residual stresses
  • increase softness, ductility, toughness and machinability
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4
Q

What are the stages of annealing?

A
  1. material is heated to required temp
  2. soak the treated material at the required temp by leaving it soaking for half-hour for every 25mm thickness
  3. material is placed inside at an off furnace to cool at around 50-100 degrees per hour
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5
Q

What is normalising?

A

A material is taken to an elevated temp, kept there for some time and then left to cool AT A FASTER RATE than annealing by placing it in the air to cool

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6
Q

What are the purposes of normalising?

A
  • controls much more precisely a defined grain size to produce finer mixtures and phases
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7
Q

What are the stages of normalising?

A
  1. material is heated to required temp
  2. it is then soaked for 10-20 mins for every 10mm of thickness
  3. the treatment is then completely cooled by cooling in air
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8
Q

What are the stages of hardening and tempering?

A
  1. a steel is heated to required temp and held there
  2. the steel is then quenched in water or oil
  3. this is followed by tempering (a soak at a lower temperature) which develops the final mechanical properties and relieves stresses.
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9
Q

What are the purposes of hardening and tempering?

A
  • inducing high hardness and wear resistance
  • it is done to all heavy- duty carbon steel machine parts
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10
Q

What is case hardening?

A

A process used with mild steel to give it a hardened skin.

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11
Q

What are the stages of case hardening?

A
  1. the metal is heated to the required temp until it is a cherry red colour
  2. it is then dipped in carbon powder
  3. this is repeated 2-3 more times before quenching the metal in water to harden the skin
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12
Q

What are the purposes of case hardening?

A
  • hardens the surface
  • improves resistance to surface indentation, fatigue and wear
  • can be used to make the gear teeth, cams, bearings etc
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