Heat Treating Process
In essence, heat treating is heating a metal up to a certain temperature before cooling it to achieve desired properties such as increased strength or ductility. This is due to the microstructure (how the atoms and crystalline structure are arranged) changing through the process. The changes made to the metal will depend on the temperature, time (both of heating and cooling), and chemical makeup of the material, so accuracy of gauges and controls are critical to quality control.
The process varies by application but consists of three basic steps. The first is to heat the metal to the specified temperature, which will depend on the purpose of this component or piece. Once it reaches the desired temperature, it’s held there for another period of time (this will also depend on the situation). For surface-level changes like case hardening, this time will be shorter, while applications that require uniform heating and cooling will take longer. Once the metal has been heated and held, it’s cooled. Not only can how quickly this happens impact the material and outcome, but also what is used to cool it. Water, oil, air, and more can be used to achieve this, and all have different purposes.
Heat Treating FAQs
- Annealing – used for copper, aluminum, brass, and more and uses air-cooling to make them softer
- Case hardening – used to harden the outside of the material, usually used for materials that need ductility as well as a durable outer layer
- Normalizing – similar to annealing, makes the material software and easier to work with
- Hardening – this strengthens and hardens the material by rearranging defects in the microstructure with heat
- Tempering – primarily for iron-based alloys that can be brittle, tempering lowers this and maintains hardness
Metal, in particular steel, would be much weaker and structurally unpredictable without heat treating. Things like planes, buildings, and more require strong, reliable steel to make up their structure. All of this would be impossible without the strength and other desirable properties such as corrosion-resistance that heat treating provides.
As with other aspects of heat treating, this will depend on the application and required specifications. However, the more important or safety-focused the material is used for (such as aerospace applications), more cycles will likely be necessary to get the optimal outcome. For most situations however, one heat treatment cycle is usually enough.