Heat treatment processes

Heat Treatment Processes

Annealing

  • Annealing is a heat treatment process that alters the physical and sometimes chemical properties of a material to increase its ductility and reduce its hardness.
  • It involves heating a material to a specific temperature, holding it at that temperature for a certain amount of time, then allowing it to cool slowly.
  • This process helps remove internal stresses, making the material easier to work with and less likely to fracture.
  • Full Annealing is the process where the metal is heated above its critical temperature, held at this temperature until it transforms to Austenite, and then it’s furnace cooled.
  • Process Annealing is used to negate the hardening effects of cold working processes such as rolling, hammering or bending.

Normalising

  • Normalising aims to rectify the irregularities which may have occurred during the manufacturing process.
  • It involves heating the metal to a temperature above its upper critical point, holding it for a short period, then air cooling the metal.
  • The result is a metal with more uniform microstructure and therefore a stronger, more uniform material.

Hardening

  • Hardening involves the transformation of the steel microstructure from austenite to martensite.
  • The process involves heating the metal above the critical temperature, holding it at this temperature, and then quenching it in water or oil.
  • This process increases the hardness and strength of the steel but makes it more brittle.

Tempering

  • Tempering is the process that is used to increase the toughness of iron-based alloys.
  • It involves heating the hardened steel below the lower critical temperature, usually between 150°C and 650°C depending on the required properties, then cooling in air.
  • The process reduces hardness and brittleness but increases the material’s toughness and ductility.

Case Hardening

  • Case Hardening involves changing the surface of a metal while leaving the internal structure largely unchanged.
  • This process is commonly used for steel and produces a hard exterior that resists wear with a tough interior that withstands impact.
  • The common methods for case hardening include carburising, nitriding, and cyaniding. Each of these processes involves adding a specific element to the surface of the metal to increase its hardness.

Understanding these heat treatment processes is vital for manipulating the properties of metals to suit different blacksmithing applications.