What Is Heat Treatment And How It Works

Although most people don’t know what heat treatment is, it’s actually an essential part of the manufacturing process. That’s because heat treating allows a metal piece to be improved in order for the material to better withstand wear and tear. Heat treatment involves heating a metal or alloy to a specific temperature and then cooling it to harden the material. 

What Is Heat Treatment?

Heat treatment can be used at different stages in the manufacturing process to change certain properties of that metal or alloy. For example, you might use heat treatment to make it stronger, harder, more durable, or more ductile, depending on what the material needs in order to perform properly. 

Some notable industries in which heat treatment plays an important role include aircraft, automobiles, hardware–such as saws and axes, computers, spacecraft, military, and the oil and gas industry.

How Does Heat Treatment Work?

In order to achieve the desired effect, the metal or alloy is heated up to a specified temperature, sometimes as hot as 2400°F, held at that temperature for a certain amount of time, and then cooled. While it’s hot, the metal’s physical structure, also called the microstructure, changes, ultimately resulting in its physical properties being changed.

The length of time the metal is heated for is called the ‘soak time.’ The length of soak time plays an important role in the characteristics of a metal, as metal soaked for a long amount of time will see different microstructure changes than metal soaked for a shorter period of time. 

The cooling process after the soak time also plays a part in the result of the metal. Metal may be cooled quickly, which is called quenching, or slowly in the furnace to make sure it achieves the desired result. The combination of the soak temperature, soak time, cooling temperature, and cooling duration all play a role in creating the desired properties in a metal or alloy.

When the metal is heat-treated during the manufacturing process also determines what properties are changed, and some metals may even be treated multiple times.

Knowing what temperatures to heat and cool metals at, as well as how long each step of the process should take for a specific metal or alloy is extremely complicated.

Because of that, material scientists known as metallurgists, study the effects of heat on metal and alloys and provide precise information on how to perform these processes correctly. Manufacturers rely on this information to ensure their metal pieces will have the correct properties at the end of the process.

Some Common Forms Of Heat Treatments

• Hardening: When a metal is hardened, it’s heated to a point where the elements in the material transform into a solution. Defects in the structure are then transformed by creating a reliable solution and strengthening the metal. This increases the hardness of the metal or alloy, making it less malleable.   
• Annealing: This process is used on metals like copper, aluminum, silver, steel, and brass. These materials are heated to a certain temperature, are held at that temperature until transformation occurs, and then are slowly air-dried.  This process softens the metal, making it more workable and less likely to fracture or crack. 
• Tempering: Some materials like iron-based alloys are very hard, making them brittle. Tempering can reduce brittleness and strengthen the metal. In the tempering process, the metal is heated to a temperature lower than the critical point to reduce brittleness and maintain hardness. 
• Case Hardening: The outside of the material is hardened while the inside remains soft. Since hardening can cause materials to become brittle, case hardening is used for materials that require flexibility while maintaining a durable wear layer. 
• Normalization: Similar to annealing, this process makes the steel more tough and ductile by heating the material to critical temperatures and keeping it at this temperature until transformation occurs. 

Why Is Heat Treatment Important?

Without heat treating metal, especially steel, metal parts for everything from airplanes to computers wouldn’t function properly, or might not even exist in the first place. Non-ferrous metal parts in particular would be much weaker. Aluminum and titanium alloys, as well as bronze and brass, are all strengthened through heat treatment. Many of these metals are used in the production of cars, airplanes, and other products that rely on strong metals not only for performance but for safety as well.

Because heat-treated metals are often stronger than non-heat treated metals, treating metal pieces upfront prevents corrosion, which won’t result in the replacement of expensive metal parts later on or as frequently. This causes machines to run more cheaply and efficiently and prevents problems.

Heat Treatment Process

Step 1: Check warehouse and goods

• Clean the entire factory and drying chamber. Prepare materials, burning materials and necessary equipment for the processing process.
• There are record books, survey records, diagrams, acceptance records and a list of implementers.
• Survey the surrounding scene to ensure fire safety and environmental sanitation.
• Origin of pallet, check the size, thickness and moisture of the pallet.
• Determine environmental temperature and humidity.

Step 2: Check the operation of the processing chamber, specifically

• Check the air circulation fan system.
• Check the heating system and radiator.
• Check whether the door system is closed or not?

Step 3: Place pallets into the processing chamber, specifically as follows

• Pallets are placed on wooden bars about 10-15cm high.
• Pallets are stacked on top of each other into a box-shaped block, spaced away from the wall to ensure ventilation and to move around to insert the probe.
• Pallets can hold a maximum of 80% of the processing chamber volume

Step 4: Drill and plug in the temperature sensor probes

• Drill a hole into the center of the wood core and insert the temperature sensor probe and cover the probe hole with glue.

Step 5: Seal the processing chamber

• Before sealing the door, you must check to see if there are any errors in the room and if there is anyone inside.
• Seal the treatment chamber by closing the main door (side door if any), to ensure that heat does not escape into the environment.

Step 6: Operate the boiler to provide heat to the processing chamber

• Prepare materials and light the furnace.
• Check the furnace and pipes before burning.
• Look after the boiler while working, pay attention to the exhaust valves.
• During operation, if you see any abnormal signs, you must know how to stop the furnace properly.

Step 7: Operate the processing chamber

• Open the air circulation fan.
• Open the valve to supply thermal steam to the processing chamber.
• Monitor the clock and record the temperature in a log
• When the temperature sensor at the center of the wood core reaches 560C, we maintain this temperature for at least 30 minutes, then stop providing heat to the drying chamber.
• During the 30-minute monitoring period, log 1 time every 5 minutes.

Step 8: End of heat treatment time

• Cool the pallet, then take it out of the processing chamber, move it to the quarantine warehouse and seal it according to regulations.
• Stamp the pallet product clearly and easily, with blue ink and 2 stamps facing each other.
• Issue fumigation certificate to the Customers

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