How Does Heat Treatment Affect the Properties of Metals?16 March 2020
Various properties of metals experience change when they go through a heat treatment. Some changes make the metals more resilient or resistant while others allow them to be reshaped. Even though modern technology has created new methods for this type of treatment, blacksmiths many years ago used to accomplish similar goals by heating and cooling metals for horseshoes, wagon parts and more. To learn additional facts about how heat treatments affect the characteristics of metals, read the following details.
The Effects of Heating Metals
1. Thermal Expansion
As metals are heated, their volume, surface and length will expand. The term for these actions is thermal expansion. Each metal will have a different rate of expansion when exposed to the heat.
2. Structural Alterations
Another effect that heat treatments have on metals is that the structure of them will go through a transformation. This is due to the fact that heat displaces the allotrope atoms in metals and causes them to reform in a different configuration. For this reason, this action is called the allotropic phase transformation. It not only can change the structural shape of the metal, but it also can alter its strength, ductility and hardness of it.
3. Makes the Metals Resistant to Electrical Current
A heat treatment can effectively make a metal have a certain level of electrical resistance. The reason that this happens is that when metals are heated, their electrons can absorb addition energy and makes them move faster than normal.
4. Reduces a Metal’s Magnetism
Magnetic metals such as nickel, cobalt and iron can lose some of their magnetism by undergoing a heat treatment. In some cases, they are no longer magnetic at all.
Types of Heat Treatments
All heat treatments involve heating and cooling metals to change them in some fashion. The most popular reasons for performing these treatments is to increase a metal’s toughness, hardness, strength, corrosion or electrical resistance, and ductility. The following are the most common methods for performing these treatments:
• Annealing softens the metal through heating to make it workable and to increase its ductility. The metal is heated to the appropriate temperature to alter its microstructure and then, it is slow-cooled. It also increases the metal’s electrical conductivity.
• Hardening improves the mechanical properties of steel and other alloys. During this process the metal is heated to a high enough temperature to dissolve a portion of the carbon in it, prior to the appropriate quenching medium being applied. Hardening can increase wear resistance and strength but can also increase brittleness at times, so it is not recommended for some engineering applications.
• Normalising is used on alloys to provide them with a uniform composition and grain.
• Tempering is used on steel to improve its ductility. Steel that does not undergo this process is extremely hard but too brittle to use in many applications.
While there are many other details to learn about how heat treatments affect the properties of metals, the above information gives you a start on your education about this topic. Ensure that your metals receive the appropriate heat method to achieve your purposes.
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