How Do You Remove Magnetism from Stainless Steel?

Type	Example Grades	Structure	Magnetism
Austenitic	304, 316, 310S	Face-Centered Cubic (FCC)	Non-magnetic in annealed condition
Ferritic	430, 446	Body-Centered Cubic (BCC)	Strongly magnetic
Martensitic	410, 420	Body-Centered Tetragonal (BCT)	Magnetic
Duplex	2205, 2507	Mixed (Austenite + Ferrite)	Partially magnetic

Austenitic stainless steels, which are the most common, are non-magnetic when properly heat treated. However, when they are cold worked, bent, rolled, or machined, some of the austenitic structure transforms into martensite, which is magnetic.

For example, Type 304 stainless steel can become slightly magnetic after forming or welding. This is not a defect—it’s simply a result of strain-induced phase transformation.

---

2. Why Is Magnetism Undesirable in Stainless Steel?

While magnetism does not affect corrosion resistance or mechanical strength, in some environments it can cause serious problems.

Here are a few examples of where magnetism must be eliminated:

• Medical industry: Surgical tools and MRI-compatible equipment must be completely non-magnetic.

• Electronics: Magnetic interference can distort signals and affect sensors.

• Aerospace and defense: Magnetic materials can interfere with navigation and detection systems.

• Scientific laboratories: Equipment must remain magnetically neutral to ensure precise measurements.

• Marine engineering: Magnetism can attract iron particles or influence compasses and instruments.

For these reasons, manufacturers often perform demagnetization (degaussing) after machining, welding, or heat treatment.

---

3. Methods to Remove Magnetism from Stainless Steel

There are two primary approaches to removing magnetism from stainless steel:

1. Thermal demagnetization (annealing)

2. Electromagnetic demagnetization (degaussing)

Each method has specific advantages and is suitable for different grades and applications.

---

3.1 Thermal Demagnetization (Annealing Process)

The most effective way to remove magnetism from austenitic stainless steel is through solution annealing.

How it works:
During cold working, strain causes the formation of martensite—a magnetic phase. Heating the material to high temperatures (typically 1050°C to 1100°C) allows the internal crystal structure to revert fully to austenite, restoring its non-magnetic state.

Process steps:

1. Heat the stainless steel uniformly to 1050–1100°C (1920–2010°F).

2. Hold at temperature for 10–30 minutes depending on thickness.

3. Rapidly cool (water quench or forced air) to avoid carbide precipitation.

Important note:

• This process is suitable only for austenitic grades such as 304, 316, 310S, and 321.

• Ferritic and martensitic steels cannot become non-magnetic through annealing because their crystal structures are inherently magnetic.

Example:
A 304 stainless steel bar that becomes magnetic after machining can be heated at 1080°C followed by rapid cooling. This treatment restores its full non-magnetic austenitic phase.

---

3.2 Electromagnetic Demagnetization (Degaussing)

When heat treatment is not practical—such as for finished assemblies, large structures, or temperature-sensitive components—electromagnetic demagnetization is used.

How it works:
A strong alternating magnetic field (AC current) is applied to the material. The field gradually decreases in intensity, randomizing the magnetic domains until they are neutralized.

Typical methods:

• AC Coil Demagnetization: The component is passed through or surrounded by an AC coil, and the current is gradually reduced.

• Portable Degaussers: Handheld devices that create alternating fields for on-site demagnetization of small parts.

• Permanent Magnet Sweeping: For simple cases, alternating north-south magnets can be used manually to reduce localized magnetism.

Advantages:

• Works at room temperature.

• Can be applied to complex or assembled parts.

• Non-destructive and repeatable.

Limitations:

• Less effective on heavily magnetized or large-thickness materials.

• Some residual magnetism may remain (typically less than 2 Gauss, acceptable for most applications).

---

4. Step-by-Step: Electromagnetic Demagnetization Procedure

Here’s how industrial facilities commonly remove magnetism from stainless steel parts using AC demagnetization:

1. Measure initial magnetism using a gaussmeter (record baseline).

2. Select appropriate demagnetizer (AC coil or portable unit).

3. Apply alternating magnetic field to the component while gradually reducing current amplitude.

4. Slowly withdraw or rotate the part to evenly expose all surfaces to the decaying field.

5. Recheck magnetism—the goal is less than 2 Gauss residual field.

6. Repeat if necessary for large or complex shapes.

This process is widely used for pumps, valves, shafts, fasteners, precision instruments, and heat exchanger parts where heat treatment is not feasible.

---

5. Demagnetizing Different Types of Stainless Steel

a. Austenitic Grades (304, 316, 310S)

• Can become slightly magnetic due to cold work.

• Heat treatment (annealing) at 1050–1100°C is most effective.

• Electromagnetic demagnetization can be used for minor magnetism.

b. Ferritic Grades (430, 446)

• Naturally magnetic because of their ferritic structure.

• Magnetism cannot be completely removed, only slightly reduced.

• Degaussing can minimize surface magnetism for sensitive uses.

c. Martensitic Grades (410, 420)

• Strongly magnetic due to high carbon and martensitic phase.

• Cannot be demagnetized completely.

• Demagnetization may slightly reduce residual magnetism after tempering.

d. Duplex Grades (2205, 2507)

• Partially magnetic (50% ferrite).

• Degaussing can lower magnetic permeability but not eliminate it.

---

6. Practical Tips for Reducing Magnetism During Fabrication

The best way to remove magnetism is to prevent it from forming in the first place. Industrial engineers can follow these guidelines:

1. Use fully austenitic grades (high nickel, nitrogen-stabilized) to minimize martensite formation.

2. Avoid excessive cold working—limit bending, stretching, or forming beyond necessary tolerances.

3. Perform solution annealing after heavy deformation or welding.

4. Use non-magnetic tools and fixtures during fabrication.

5. Conduct demagnetization after welding to eliminate residual magnetism near heat-affected zones.

Implementing these steps helps maintain non-magnetic properties throughout the product’s lifecycle.

---

7. How to Test for Magnetism Before and After Treatment

Checking magnetism is simple but essential to ensure process success. Common testing methods include:

• Handheld magnet test: Quick indication if attraction exists.

• Gaussmeter (Tesla meter): Quantitative measurement of magnetic field strength.

• Permeability meter: Measures magnetic permeability (µr).

  • µr ≈ 1.0: Non-magnetic

  • µr 1.02–1.2: Slightly magnetic

  • µr >2.0: Strongly magnetic

Regular testing before and after demagnetization confirms whether the desired result has been achieved.

---

8. Industrial Applications Requiring Demagnetized Stainless Steel

Non-magnetic stainless steel is essential in precision industries where even slight magnetism can interfere with function or safety. Common sectors include:

• Medical devices: MRI-compatible tools, implants, and surgical instruments.

• Aerospace: Components near navigation systems or magnetic sensors.

• Semiconductor and electronics: Vacuum chambers, measurement fixtures, and cleanroom tools.

• Petrochemical and power generation: Instruments and flow meters sensitive to magnetic fields.

• Marine industry: Equipment near compasses or sonar systems.

In these fields, manufacturers such as SAKYSTEEL provide certified non-magnetic stainless steels with verified low magnetic permeability and full 3.1 MTC documentation.

---

9. Common Misconceptions About Demagnetizing Stainless Steel

Myth 1: All stainless steels can be made non-magnetic

Not true. Only austenitic grades can become fully non-magnetic through annealing. Ferritic and martensitic steels remain magnetic by nature.

Myth 2: Magnetism means low-quality stainless steel

False. Magnetic behavior is structural, not a quality issue. A magnetic 430 steel can still have excellent corrosion resistance.

Myth 3: Degaussing permanently removes magnetism

It removes residual magnetism, but future machining or welding may reintroduce magnetism.

Myth 4: Heating with a torch can demagnetize

Localized heating cannot achieve uniform structural transformation; proper annealing in a controlled furnace is required.

---

10. The Role of Alloy Composition in Magnetism Removal

The ease of demagnetization depends heavily on the chemical composition of the steel. The nickel and nitrogen content play a critical role in stabilizing the austenitic structure, which is non-magnetic.

• High-nickel grades (e.g., 316L, 310S) are easier to keep non-magnetic.

• Low-nickel grades (e.g., 201, 202) are more prone to partial magnetism after fabrication.

When designing components that require strict magnetic neutrality, it’s best to choose high-nickel, low-ferrite alloys from the start.

---

11. Case Study: Removing Magnetism from 316L Stainless Steel Components

A manufacturer producing marine valves from 316L stainless steel noticed magnetic attraction after machining. The magnetism level was around 15 Gauss—too high for the intended application.

Solution:

• The parts were heated at 1070°C for 30 minutes in a vacuum furnace.

• Rapid water quenching followed to restore the full austenitic phase.

• Final residual magnetism measured less than 1.5 Gauss, meeting specification.

This example demonstrates that proper thermal demagnetization can restore true non-magnetic properties even after heavy mechanical processing.

---

12. Safety Considerations in Demagnetization

When performing demagnetization, always observe safety precautions:

• Ensure equipment is properly grounded when using high AC currents.

• Avoid exposure to strong electromagnetic fields if pacemakers are present.

• Maintain adequate ventilation during heat treatment.

• Handle quenched components carefully due to thermal shock.

Industrial demagnetization should always be carried out under controlled conditions by trained professionals.

---

13. Measuring Success: Acceptable Magnetism Levels

In industrial standards, acceptable magnetism levels depend on the application. For example:

• Medical and aerospace components: Below 2 Gauss.

• General mechanical parts: Below 10 Gauss.

• Heavy industrial equipment: Below 20 Gauss may be acceptable.

Precise measurement ensures compliance with customer and project specifications.

---

14. Emerging Technologies for Demagnetization

Modern innovations are improving the efficiency of magnetism removal:

• Pulse demagnetizers: Deliver rapid, high-frequency pulses for deep penetration.

• Cryogenic demagnetization: Used for precision instruments at extremely low temperatures.

• Robotic degaussing stations: Automate the process for consistent quality control.

These technologies allow faster, safer, and more consistent demagnetization for mass production environments.

---

15. Final Thoughts: Restoring Non-Magnetic Properties Effectively

Removing magnetism from stainless steel is not always simple—but with the right understanding of material structure, it can be done effectively.

To summarize:

• Austenitic stainless steels can be fully demagnetized by heat treatment or electromagnetic degaussing.

• Ferritic and martensitic steels are inherently magnetic and can only be partially demagnetized.

• Proper material selection, controlled processing, and precise testing ensure stable non-magnetic performance.

By combining metallurgical expertise with advanced production methods, manufacturers can supply stainless steel materials that meet the most demanding magnetic specifications.

For industries requiring high-quality non-magnetic stainless steel, SAKYSTEEL provides complete solutions—offering premium austenitic grades, professional heat treatment, and global support with EN 10204 3.1 certification.