How to Demagnetize Metal for Welding?

Written By: Liam Bryant

Reviewed By: Russell Egan

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To demagnetize metal, employ methods like heating beyond the Curie temperature, applying a powerful magnetic field, using alternating current, or striking the metal repeatedly. These techniques effectively realign magnetic domains, with efficiency varying based on material type, temperature, and specific conditions.

The first technique of demagnetizing metal for welding is to burn it directly with a torch, while the second approach involves using a product called a degaussing coil, which uses an electric current to weaken the magnetic fields of your metal.

There are several ways that you can demagnetize metal. This is important because when magnetized metal is heated during welding the heat will cause it to retain its magnetic properties. This causes distortion and in some cases cracking in the weld. It can also cause a loss in the quality of the metal which you are attempting to weld.

Let’s describe the process in more detail.

How to demagnetize metal for welding

How Can You Demagnetize Metal for Welding?

You have two options when it comes to demagnetizing metal for welding. The first involves a process called heat degaussing, by which you can remove the magnetism from your metal by heating it with a torch. The second option is using a degaussing coil, an electrical device that emits an electric current through your metal.

Let’s describe these options in greater detail.

Heat Degaussing

Heat degaussing can be done by heating up your metal with a blowtorch. The heat will weaken the magnetic properties of the metal. This process is very effective and can be done quickly.

If you are unable or do not have access to a blowtorch then you can leave your metal in direct sunlight for a few hours. This process is less effective than using the blowtorch but it will get the job done if you are in an area where blowtorches are not readily accessible.

Benefits and Drawbacks of Heat Degaussing?

The benefit of heat degaussing is that it can be done quickly and easily with minimal equipment while heating up your metal with a blowtorch. The downside is that you have to heat up metal evenly in order to ensure that the magnetic properties are removed.

NOTE: If your metal is not heated evenly it could result in a loss of strength and durability.

How long do you have to heat up metal before magnetic properties are removed?

The amount of time it takes for the magnetic properties in your metal will vary depending on the thickness of your metal. If you are smelting 20mm thick material then it should only take around 15 minutes to demagnetize, while if you are smelting 100mm thick material it will likely take close to an hour or even more.

NOTE: The thicker the metal is the more time is required for heat degaussing.

What happens when your metal loses its magnetic properties?

When you remove the magnetism from your metal then it will have little or no strength when in a magnetic field. This in turn increases ductility and malleability without significantly affecting tensile strength or elongation percentage.

Degaussing Coils

The second way of demagnetizing metal for welding is to use a product called a degaussing coil. This approach is an easier option but also more expensive.

How to Demagnetize Metal for Welding?

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A degaussing coil emits a triple-phased alternating current, which demagnetizes your metal by causing it to lose its magnetic charge.

How can you detect residual magnetism in metals?

The best way is to use a gaussmeter, which is a tool used for detecting and measuring magnetism in metal. You Can Buy either analog or advanced digital versions.

How to use Gaussmeter?

It’s pretty simple. All you have to do is place the sensor onto your metal and make sure that there are no gaps between the metal and the sensor.

When you turn on the Gaussmeter it will light up green or red based on whether or not your material has magnetic properties.

NOTE: Red means residual magnetism, while green means free of magnetism.

What magnetism levels are safe for welding?

Since it is highly unlikely that your metal will be completely free of magnetism you will need to make sure that the Gauss level is less than 1.5. Anything above that and your metal will have a greater chance of cracking when being welded.

NOTE: Keep in mind that this value differs based on who you ask, with some sources saying anything below 3 gauss is good enough for welding while others say it should be under 5 or even 7 gauss. If you are concerned about your metal cracking then I would suggest staying under 3.

What happens when you exceed magnetic levels for welding?

It’s not pretty. Even if just a small amount of magnetism is left in your material it can lead to cracking or tearing while being welded. This will result in excess work and a higher chance of failure.

This is why it’s so important to degauss your metal before welding and not avoid it altogether.

Example of welding on magnetized steel
Example of welding on magnetized steel, source: Sino Stone

What are some safety precautions to take when demagnetizing metal for welding?

When it comes to safety, there are a few things you have to consider.

Never use heat degaussing on ferromagnetic metals (Iron, nickel, cobalt, samarium-cobalt, gadolinium and terbium) because they can catch fire when heated unevenly which creates the possibility of combustion.

Another thing you have to consider is potential fire hazards, since heat degaussing uses a blowtorch. Make sure that there are no flammable objects nearby before heating metal.

What can you do to help prevent cracking?

There are a few things that you can do to help reduce the risk of cracking in your welds. First, make sure that you are heat treating your metal properly. This is done by heating your material up to around 1050 degrees Fahrenheit, cooling it down to room temperature, and then heating it back up again.

What happens if there is no residual magnetism in metal?

If there is no residual magnetism then your metal will not retain its magnetic properties, making it perfect for welding. This in turn increases ductility and malleability without significantly affecting tensile strength or elongation percentage.

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