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Heat Treating Steel and Its Purpose in Precision Machining

Here’s everything you need to know about heat treating steel.

Heat Treating Steel and Its Purpose in Precision Machining - KB Delta

Heat treating is one of the methods used in altering the ways metals react to or perform when it comes to precision machining. Components can undergo machining before the final heating and hardening stages. Heat treating can also be applied to a specific part in order to make the material much more machinable.

Heat treating affects several aspects of steel, including:


  • Ductility
  • Elasticity
  • Strength
  • Formability
  • Hardness
  • Machinability
  • Toughness


Heat treating also affects the mechanical and physical properties of steel or any other metal such that it alters future work on it or changes its use.

Let’s check out the different types of heat treating as well as how they affect unique parts during precision machining.


Types of Heat Treating Steel Processes

  • Annealing

This is a heat treatment process in which a specific metal – such as aluminum, silver, steel, copper, brass, etc. – is heated steadily until it reaches a particular temperature. This temperature is maintained for a specific period in order to give room for transformation to take place.

The heated metal is then cooled by air. This heat treating process boosts the metal’s ductility and reduces its hardness, making it more workable for the manufacturer.

Some metals – such as brass, copper, and silver – can be cooled slowly or quickly, while ferrous metals such as steel require gradual cooling so that annealing can occur.

Annealing can be employed before a specific metal undergoes machining in order to enhance its stability. This makes much harder metals or materials far less likely to fracture or crack.


  • Case Hardening

This heat treating process involves hardening the external layer of the material while ensuring its interior remains soft. Some metals with low carbon content – like steel, iron, etc. – will require the infusion of additional carbon into their surfaces. High heat is then combined with some chemicals and other elements in order to produce a hardened outer layer.

Hardening metals make them more brittle. This is why case hardening is typically useful only for applications that require a durable wear layer and highly flexible metal.

Case hardening is generally used as the last step after the piece of metal or material has been successfully machined.


  • Hardening

It is important to note that defects within the crystal lattice structure are the major source of plasticity or ‘give.’ Therefore, to harden a metal, it is heated until the various elements that make up the metal turn to a solution.

This process readily addresses the defects mentioned earlier by turning the metal into a dependable solution with ultra-fine particles in order to strengthen the metal.

As soon as the metal is thoroughly heated and reaches the specified temperature to produce a solution, it is quenched quickly in order to trap the fine particles in the solution.

Precipitation hardening requires the introduction of impurity particles to the metal alloy. This helps to further increase the strength of the metal alloy.


  • Normalizing

This type of heat treatment is a form of annealing process but for steel. The steel is heated until it reaches up to 150 degrees to 200 degrees Fahrenheit higher than the temperature required for annealing.

This temperature is maintained at critical levels and long enough for transformation to take place. When steel undergoes this type of heat treatment, it must be air-cooled.

This heat treating process gives rise to austenitic grains, while air cooling brings forth more refined ferritic grains. Normalizing enhance ductility, machinability, as well as strength of the metal.

Standardization is also required to get rid of dendritic segregation and columnar grains that may occur due to casting a specific part.


  • Tempering

This is a heat treating method employed to enhance the resilience of an iron-based alloy such as steel, etc. All iron-based metals are incredibly hard, making them much too brittle and practically useless for many purposes.

But tempering can be employed as the ideal method for changing the ductility, hardness, as well as strength of iron-based alloys. This makes the final product much easier to machine.

Tempering involves heating the iron-based metal to a specific temperature below the critical point. Lower temperatures minimize brittleness but maintain hardness, which is still not too valuable. Higher temperatures are often required for less strength and hardness with increased plasticity.

Another excellent option is buying material and hardening it before machining or an already hardened metal. Although this type of metal is somewhat more difficult to machine, it eradicates the profound risk of changing part sizes, far unlike post-machining heat treatment processes.

It also assists in eliminating the need for a grinding shop in order to get the tolerances or tight finishes.


Why Heat Treating is Important in Manufacturing Quality Parts

Precision is key when it comes to manufacturing high-quality parts. Heat treating metal dramatically increases its strength, which is why it is one of the most popular choices in the aerospace and automotive industries.

Heat treating metal does the following:


  • Improves its workability and machinability
  • Enhances its strength and toughness
  • Boosts its wear resistance and durability
  • Improves its magnetic properties


Types of Furnaces for Heat Treating Metal

To successfully heat treat metal, there must be close control over every factor that affects the cooling and heating of the part. This is only possible using the ideal equipment for heat treating metal.

The equipment for the process must also fit appropriately into the specific requirement of the project, including the size and type of furnace employed. The atmospheric condition inside the furnace can easily affect the overall condition of the metal undergoing heat treatment. Therefore, it should also be taken care of for a satisfactory outcome.

The following are the types of furnaces required or used for heat treating metals:


  • Batch furnace
  • Box-type furnace
  • Pit furnace
  • Elevator-type furnace
  • Car-type furnace
  • Fluidized bed furnace
  • Salt bath furnace
  • Bell-type furnace



Heat treatment is a crucial part of precision machining processes in order to transform metals efficiently. It also ensures your parts or pieces perform effectively and efficiently as you desire or need them to.

Heat treating metals enables controlled heating and cooling techniques required to alter their physical properties with the primary goal of improving them for precision machining.

Knowing the types of heat treatment enables you to make the right choice whenever you need to work with some metals.



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