Tempering vs. Annealing: What’s the Difference?

The heat treatment of metal is a process that involves the heating or chilling of metal. This process is often conducted at extreme temperatures. The purpose of this process is to achieve a certain result, which is to alter the chemical composition of the metal without changing its shape. This includes the hardening or softening of the metal. 

There are various types of heat treatment which include tempering, annealing, cases hardening, normalizing, and quenching. The common objectives of these processes include:

  • Increase ductility
  • Increase strength
  • Improve machining
  • Improve toughness
  • Increase in hardness
  • Improve formability
  • Improve elasticity

As previously mentioned, there are various types of metal heat treatment. However, the two most crucial heat treatment methods are tempering and annealing. 


Metal tempering is done by specialized companies, such as a metal tempering company. 

Iron alloy metals such as steel are used in a variety of applications. The problem is that while the metal is particularly hard, it is too brittle for many applications. Thus, the steel needs to be tempered. This process usually occurs after hardening to minimize excess hardness.

Tempering is used for a variety of purposes, including:

  • Structural stability
  • Ductility
  • Hardness
  • Strength
  • Toughness

Metal is heated to just below the critical point in the air, vacuum, or inert atmosphere. The temperature is adjusted based on how much harness needs to be removed from the metal. Lower temperatures are used to reduce brittleness and maintain hardness. Higher temperatures are used to reduce hardness. Higher temperatures also increase elasticity and plasticity in the metal. 

During this process, metal should be heated up gradually to prevent cracking. The metal is held at a fixed temperature for a period of time before it is air-cooled. This period is determined by the thickness of the metal, roughly one hour per inch of thickness. 


Annealing differs in that the metal is cooled at a slow and controlled rate. The process starts by heating the metal to a specific temperature. This treatment serves various purposes:

  • Restores ductility
  • Improve the metal’s machinability
  • Soften metal for cold working
  • Enhance the electrical conductivity of the metal

When machining or grinding metal, also known as cold working, there is a risk of the metal becoming more hardened and cracking. Annealing the metal before cold working releases the stresses and prevents cracking. 

Metal is heated in large ovens with sufficient air circulation to a specific temperature. The metal is held at a raised temperature for a specific period before it is cooled down in a controlled down to room temperature. In addition, any defects are repaired caused by the deformation of the metal. 

Softness is created during the cooldown period. Thus, cooling down should occur at a very slow pace. The cooldown is achieved by simply switching off the oven and allowing the metal to cool down with the oven or submerging the metal in low-heat conductivity materials such as sand or ash. 

Since 1980, J.F. Heat Treating Inc has been your local professional metallurgy and heat treatment company. We provide all types of heat-treating services to soften, harden, relieve stress, or remove contaminants from your metal parts and components. 

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