Heat Treatment of Metals: Different Heat Treatment Methods and Its Benefits

heat treatment

Numerous processes can modify the working life of metal and can affect its physical and mechanical properties. These properties may include strength, hardness, toughness, machinability, ductility, formability, elasticity, etc. One of these processes is the heat treatment of metals.

This process changes metal’s productivity and the ways metals react to precision machining. During this procedure, the microstructure of different metals and alloys (such as steel and aluminum) are altered. In this way, we can get our required metal shape and properties that can fulfill the purpose.

The heat treatment process could find its roots centuries back. Where blacksmiths used to fabricate different objects by forging and tempering iron ores. To get the harder and less brittle part, it was cooled immediately after the application of extreme temperature. Heat treatment of metals has evolved magnificently over the years and is extensively used in the machining industry.

Ahead of this article, we will comprehensively demonstrate what is the heat treatment process and how it works, various benefits of heat treatment of metals, different types of heat treatment, etc. We hope if you read till the end, you will be able to learn all the necessary concepts about heat treatment of metals.

What is Heat Treatment?

In simple terms, the process of heating the metal until a required geometrical shape and properties are not achieved, and then cooling it back to make it harden is known as heat treatment of metals. In this process, the microstructure of the metal ensures the transitions in its mechanical, chemical, and physical characteristics. In this way, we alter the metal components into our required shape and properties. 

To obtain the requisite domifications in the properties of metals, specific predetermined heat treatment methods are used. These domifications help to improve the working life of the metal components. After the application of these methods, the properties like strength, hardness, toughness, machinability, ductility, formability, elasticity, etc., can improve significantly.

The common definition of heat treatment may be the heating and cooling of metals. But this process is not that simple. It has been evolved over the years and has advanced pretty much. As time passed on, numerous different methods have been developed. These methods help to attain the required changes in the microstructure of the metal and various other properties.

An accurate and carefully controlled heat treatment process can result in a superb outcome. Any mistake will lead to delays in project deadline, cost increment, and lowering of efficiency.

Importance of Heat Treatment of Metals in CNC Machining

Heat treatment is extremely important for parts to be manufactured applying CNC machining technology. Since these parts need to be high precision because they serve many paramount functions in the world’s most crucial industries. These industries include aerospace, defense, medical, automotive, and many other important industries.

For the better functioning of the metal parts, particularly steel, they are required to be heat treated. Otherwise, they will not function better or even not exist in the first place. The strength, hardness, toughness, and machinability of bronze, brass, aluminum, and titanium alloys, and non-ferrous metal’s workpieces are being enhanced with the application of the heat treatment process.

How Does Heat Treatment Work?

To obtain the required characteristics in metals or alloys, they are heated up to extreme predetermined temperatures. When these metals or alloys reside in that temperature for a specified period then they are being cold. These extreme temperatures sometimes reached 2400°F depending on the requirements. So, when these components are hot, their characteristics undergo mechanical, chemical, and physical transitions.

The period during which a particular component is heated is termed as soak time. The duration of soak time is pretty vital in producing the required metal characteristics. A metal component that undergoes a longer period of soak time will have different microstructure properties than the one with a shorter soak time.

The extent to which the metal component is cooled is of very significant importance. Faster or slower application of cooling will generate different outputs. It is the expert metallurgists who will evaluate whether the metal will be cooled faster or slower. So, careful practice and a good integration of soak temperature, soak time, cooling temperature, and cooling duration will result in spectacular microstructure changes of the metal.

Sometimes, a situation may occur where a metal or alloy will need to be heat processed many times. Because some properties would not change in the first round of the process. Again, an expert will be able to evaluate the number of the heat treatment process to be applied to get the required results.

Benefits of Heat Treatment of Metals

If metal parts are used without processing through heat treatment, then it will badly affect their performance. What will happen if we use the parts as it is? Well, they will not serve the purpose for what they were being installed. They will not cause only wastage of time, money, but might cause serious problems for many industries.

Using a properly heat treated metal part will make certain a superb functioning and excellent machine performance. Moreover, the part will have enhanced efficiency. The risk of any disaster due to ineffective metal parts will reduce largely.

Another great benefit of applying heat treatment to metals is that it helps in the reduction of internal stress and residue stress. These stresses are caused by external forces and they play a significant role in workpiece deformation. When we apply an external force that interacts with the internal crystalline structure of the workpiece and produces internal stress into it. This internal stress causes slack’s internal structure to rebalance its original state. Therefore, heat treatment will also be helpful in the stress reduction inside the workpiece.

Further benefits of heat treatment of metals are summarized below:

  • It helps to strengthen the metal, that interns, make it more flexible.
  • It creates wear-resistant properties to the metals.
  • It helps in brittleness improvement.
  • It helps in stress reduction that enables parts to be machined easier and reduces the chances of workpiece deformation.

Types of Heat Treatment and Their Purpose in CNC Machining

There are many types of heat treatment processes used to change the ways that determine how a metal will perform and react to CNC machining. Heat treatment can be applied to different metals before machining to make them easy to machine. Below, we elaborate on some important heat treatment process types and their effect on the parts during CNC machining.

  • Hardening

            In this type of heat treatment, as represented by its name, we use this method to hard the metals. The metal is heated to a specific temperature. Till a point is reached where all the elements present in the metal are converted into a solution. The crystal lattice structure of the metal may have defects that show a source for plasticity. Heat treatment helps to tackle these defects.

            This method brings the metal into a reliable solution with fine particles that strengthen the metal. Once the metal is thoroughly heated to the right temperature to produce a solid solution, it is immediately quenched to trap the particles into the solution. That results in its hardening. In some cases, few impurities may also be added to further harden the metal.

             Hardening of the metals enhances their strength that makes the metals more brittle and decreases the ductility. That will help in tempering the metals after the hardening process.

  • Annealing

            If it is required to increase the ductility of the metal then the annealing heat treatment method is applied. In this method, metal is heated to a specific temperature, being kept at that temperature for a certain period that allows transformation to occur, and then it is air-cooled. The metals that need to increase ductility include aluminum, copper, steel, silver, or brass.

            Once the ductility of the metal is increased that consequently decreases its hardness to make it more workable. Some metals are cooled quickly or slowly such as copper, silver, and brass whereas ferrous metals like steel must always be cooled gradually to allow annealing to occur.

            To improve the stability of a metal, it is being applied with an annealing heat treatment method before machining. It also makes the metal harder that reduces the chances to crack or fracture.

  • Normalizing

            Normalizing is an annealing process for steel to ductile. Here steel is heated 150-200°F higher than in annealing. Being kept in this condition for a longer period will be enough for the transformation to occur. Then it will be air-cooled and as discussed above, ferrous metals like steel must always be cooled gradually. During the normalization process, smaller austenitic grains will introduce to steel and slower air cooling will produce more refined ferritic grains.

           This process offers machinability, ductility, and strength improvement in the steel. Standardization is also useful to remove columnar grains and dendritic segregation that can occur during the casting of a part.

  • Tempering

             If we are required to increase the resilience of any iron-based alloys like steel then a tempering heat treatment method is used. Iron-based metals are usually very hard and therefore, they are often too brittle to be useful for most purposes. This is why, tempering is applied to alter their hardness, ductility, and strength. That makes performing the machining process on them easier.

             In this method, the metal is heated as usual. But here the temperature will be below the critical point because the lower temperatures cause a reduction in brittleness and help to maintain hardness. So, tempering helps to reduce the hardness caused by hardening.

Conclusion: In Shanghai Jinxi, we made lots of metal parts with heat treatment request, and we have the certified reliable suppliers to help us on it, firstly we do the rough machining and send to heat treating, and work on precision machining after the heating. If you have this demand to heat treat your metal parts, please feel free to leave us a message and we’ll get back within 12hours.

    Cora Feng
    Cora Feng

    Project Manager working on CNC Machining since 2010

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