The benefits of heat treatment of metals

Heat treatment can make the final product more efficient in performing its tasks and more resistant to wear, and therefore more competitive. So below we list the benefits of heat treatment of metals.

1. Increase in strength and toughness

Heat treatment can change the microstructure of a metal, reduce grain size and increase grain number; under certain conditions, the crystal structure of the grains can also change (polymorphic transformation), which leads to changes in the mechanical properties of the metal.

For example, during quenching, a metal is heated to a high temperature and then rapidly cooled. This leads to crystal size and the formation of martensite, a microstructure with densely packed atoms that is the basis of hardened metal alloys. This structure provides greater hardness and strength of the metal.

Another way to increase metal strength is to temper it. After quenching, the metal is heated to a certain temperature and then cooled. This process reduces the excessive stiffness of the metal that can occur after quenching and preserves its strength.

There are also many other heat treatment methods that can affect the microstructure of the metal and its mechanical properties. For example, the heating and cooling cycle can be changed to achieve the desired result. The result of properly applied heat treatment processes can increase the tensile strength of steel by up to 50%.

2. Heat treatment can make steel softer

There is nothing paradoxical here. Changing the modes in the heating and cooling cycle can have a significant impact on the final result, so it is clear that levers of influence on the material structure can be applied in such a way as to achieve lower metal strength if this is the desired outcome. An example of this is hardening the surface of the metal while allowing the metal deeper in the product to remain soft. thus creating a thin layer of hard metal on the outside. This soft core makes the part resistant to breakage, absorbing stresses without cracking, while providing adequate wear resistance to the surface of the part.

3. Increased flexibility, reduced brittleness

One of the heat treatment methods for increasing the flexibility of metal is tempering. It is usually performed after metal hardening to reduce its rigidity and increase its flexibility. During quenching, the metal is heated to a high temperature and cooled rapidly to change its microstructure and increase its strength. However, this process can also make the metal brittle and easily breakable. Tempering is accomplished by heating the metal to a moderate temperature (typically 300 °C or 572 °F) and holding it at that temperature for a period of time. This process reduces the stiffness and increases the flexibility, ductility, and strength of the metal sample. Tempering is used in applications where it is important to have a metal that has a certain level of strength but is flexible and ductile enough to avoid tearing or brittleness during service. This procedure can also relieve stress and facilitate further machining.

4. Increased wear resistance

Gears, shafts, cutters, bearings, car body parts, tools, such as jackhammers, are just a short list of products where hardened metal adds extra strength and wear resistance, allowing them to operate under high stress without losing their functional properties. Heat treatment operations increase resistance to fatigue, allowing such steel components to work more efficiently over a longer period of time.

Extremely hard steels are often used as cutting tools that require sharp edges - heat treatment here is a critical operation to achieve long service life and shape retention. As noted, hard surfaces with ductile base materials can also be produced by heat treatment. Therefore, heat treatment returns a significant economic benefit due to the long service life of the resulting products.

5. Surface modification

In the process of heat treatment of metal, the surface may come into contact with air or other external gases and coolants at different temperatures. This inevitably leads to changes in its properties, which is also used in metalworking. In the case hardening process, metal is heated to high temperatures in an atmosphere of gas containing carbon (endothermic gas, natural gas, etc.) or nitrogen (ammonia), which react with the metal's surface to harden it. This process results in a hard, wear-resistant surface layer that also improves corrosion and abrasion resistance, while the core is relatively strong, allowing the steel to withstand impact loads.

6. Changes in thermal conductivity

The smaller the grain, the greater the thermal conductivity. An increase in the thermal conductivity of a metal is usually a side effect of heat treatment aimed at increasing the hardness of the metal. However, when thermal conductivity is a key property, quenching can be used to improve it in a targeted manner. For aluminum alloys used in the creation of radiators, the method of secondary phase hardening - planar hardening - is used. This method involves heat treatment of the alloy in such a way that secondary phases are formed in it, arranged in the form of flat dislocation walls. These walls provide excellent thermal conductivity of the material.

7. Changes in electrical conductivity

Reducing the grain size in general also improves electrical conductivity. Therefore, quenching and tempering methods are used in the creation of wires, contacts, soldering irons, electronic components, and other products where high electrical conductivity is important. Additionally, heat treatment processes are used in the production of electronic components to improve electrical and oxidation resistance or to produce thermocouples, where the accuracy of temperature measurement is important, which depends on the electrical conductivity of the metal.

8. Magnetic properties

Heat treatment can change the magnetic properties of metals. For the manufacture of permanent magnets, special materials are used that are heat-treated to improve their magnetic properties.

Heat treatment can also be used to reduce the magnetic permeability of metals, which is important in electrical devices where magnetic fields can cause undesirable effects such as inductance and magnetic losses.

9. Repair heat treatment

Heat treatment can be used to restore the structure of a metal after it has been worn or damaged. Metal wear is a complex process that results in a decrease in the strength and stability of parts due to external factors such as friction, corrosion, impacts, and others. In addition, during the operation of metal products made of hardened steel, a gradual destruction of the martensite structure can occur, which leads to a decrease in strength.

The process of restorative heat treatment may include quenching, normalizing, tempering, etc. It is used to restore metal products such as gears, shafts, pump wheels, and other complex parts that are subject to wear or damage due to operation. The rational use of this method can significantly increase the durability and reliability of long-term operation of metal products.

10. Variability of procedures and combinations of methods

Heat treatment of metals provides a variety of approaches that seem innumerable. However, they can be customized to achieve specific results. In addition, this process is well combined with other methods, such as mechanical or chemical processing. In some cases, a metal part may undergo several heat treatment procedures and other types of processing. The choice of the ideal method, however, really depends on the type of metal and the properties required, but in any case, it is necessary to test these properties to assess the effect of heat treatment on the mechanical properties of materials.