Heat Treatment

• What is heat treatment?


  It is the process of heating and cooling metals to change their characteristics and properties.
• What can different types of heat treatment achieve for metals?


  They can make a metal harder, stronger, or even softer.
• What is a trade-off when improving the hardness of a metal?


  Improving hardness can reduce toughness.
• What is crucial in the heat treatment process besides heating?


  The rate of cooling is equally crucial.
• Where is heat treatment usually carried out?


  In a furnace.
• Can heat treatment be achieved using an oxy-acetylene flame?


  Yes, it can also be achieved using an oxy-acetylene flame.
• What are the three stages of heat treatment?


  • Heating
  • Soaking
  • Cooling
• Why must metal be heated slowly and evenly during the heating stage?


  To avoid cracking.
• What factors influence heating times for metals?


  The type and size of the metal, among other factors.
• What are typical heating temperatures for heat treatment?


  From several hundred degrees to over one thousand degrees Celsius.
• What happens during the soaking stage of heat treatment?


  The metal is held at a certain temperature for a specific period of time.
• If a metal needs to be heated to 900°C, what might be its pre-heating temperature?


  Approximately 300°C.
• How can metals be cooled during the cooling stage?


  By quenching them in water, oil, or other liquids, or through slow and controlled cooling.
• What is furnace cooling commonly used for?


  For slow and controlled cooling of metals.
• What are the four different types of heat treatments?


  • Annealing
  • Normalising
  • Hardening
  • Tempering
• What is the process of annealing?


  It involves heating a metal and holding it at a specific temperature before cooling it slowly.
• How can aluminium be annealed?


  Using a gas flame in a workshop.
• What does annealing do to metals like copper, steel, and brass?


  It softens them to make them more malleable and ductile.
• What is the purpose of normalising steel?


  To refine the internal grain and relieve internal stress.
• What temperature range is used for normalising steel?


  Between $810°C$ and $930°C$.
• How does normalising compare to annealing?


  Normalising is less expensive and produces stronger metal.
• What is the process of hardening?


  It involves heating and quickly cooling metal in oil or water.
• What is the effect of hardening on metal?


  It makes the metal hard but can increase brittleness.
• What is the purpose of tempering?


  To reduce the hardness of metal in order to increase its toughness.
• How is tempering typically carried out?


  By re-heating the steel at lower temperatures and quickly cooling it.
• What should be observed during tempering to achieve a good balance between hardness and toughness?


  Colour changes in the metal.
• How does tempering affect the properties of metal?


  It reduces hardness while increasing toughness.