Which Types of Stainless Steel Are Magnetic?

 

Which Types of Stainless Steel Are Magnetic?

Stainless steel is known for its corrosion resistance and versatility, making it a staple in industries like construction, automotive, food processing, and medical equipment. One common question is whether stainless steel is magnetic. The answer depends on the specific grade and its internal structure.

1. Understanding Stainless Steel Microstructures

Stainless steels are categorized into five main families based on their microstructure:

Austenitic Stainless Steel (Generally Non-Magnetic)

  • Structure: Face-Centered Cubic (FCC)
  • Common Grades: 304, 316, 310, 321
  • Features: Excellent corrosion resistance, high ductility, not hardenable by heat treatment
  • Magnetic Behavior: Non-magnetic in annealed state; may become slightly magnetic after cold working

Ferritic Stainless Steel (Magnetic)

  • Structure: Body-Centered Cubic (BCC)
  • Common Grades: 409, 430, 439
  • Features: Good corrosion resistance, high thermal conductivity, low cost
  • Magnetic Behavior: Magnetic in all conditions

Martensitic Stainless Steel (Magnetic)

  • Structure: Body-Centered Tetragonal (BCT)
  • Common Grades: 410, 420, 440A, 440C
  • Features: High strength, heat treatable, moderate corrosion resistance
  • Magnetic Behavior: Strongly magnetic

Duplex Stainless Steel (Partially Magnetic)

  • Structure: Mixed FCC + BCC (Austenitic + Ferritic)
  • Common Grades: 2205, S31803, 2507
  • Features: Excellent strength, stress corrosion cracking resistance
  • Magnetic Behavior: Partially magnetic due to ferritic content

Precipitation Hardening (PH) Stainless Steel (Magnetic)

  • Common Grades: 17-4PH, 15-5PH
  • Features: High strength and hardness after aging treatment
  • Magnetic Behavior: Magnetic after heat treatment

2. Why Are Some Stainless Steels Magnetic?

The magnetic properties of stainless steel depend on its crystal structure. Austenitic steels (like 304 and 316) have a structure that doesn’t support magnetism, while ferritic and martensitic steels have structures that align with magnetic fields.

Even non-magnetic stainless steels can develop partial magnetism due to mechanical deformation such as bending, rolling, or machining (cold working).

3. Magnetic Properties by Grade

Grade Type Magnetic Notes
304 Austenitic No (Slight after cold work) Most common stainless steel grade
316 Austenitic No Marine applications, resistant to chlorides
430 Ferritic Yes Used in kitchen appliances and trims
410 Martensitic Yes Blade materials, pump shafts
17-4PH Precipitation Hardening Yes Strong after aging; used in aerospace
2205 Duplex Partially Excellent resistance to corrosion cracking

4. Where Magnetic Properties Matter

Understanding whether a stainless steel is magnetic is crucial in certain industries:

Applications Requiring Non-Magnetic Stainless Steel

  • Medical instruments (MRI compatibility)
  • Electronic enclosures and shielding
  • Food and pharmaceutical production

Applications Requiring Magnetic Stainless Steel

  • Motors and generators
  • Magnetic separators
  • Appliance components like oven doors

5. How to Test for Magnetism

There are simple ways to determine whether stainless steel is magnetic:

  • Magnet Test: Use a standard magnet to see if it sticks.
  • Hall Effect Sensor: Measures the strength of magnetic field.
  • Material Analyzer: Determines the alloy’s composition and structure.

6. Can Cold Working Cause Magnetism?

Yes. Cold working can distort the crystal structure of austenitic stainless steels and introduce a partial magnetic response. Annealing (heating then cooling slowly) may reduce this magnetism but may affect the strength or corrosion resistance.

7. Choosing the Right Grade for Magnetic Sensitivity

When choosing stainless steel:

  • Use 304 or 316 for non-magnetic needs
  • Use 430, 410, or 17-4PH where magnetic behavior is required
  • Choose duplex grades when high strength and moderate magnetism are acceptable

8. Summary Table: Magnetic Behavior of Stainless Steel Types

Type Examples Magnetic? Remarks
Austenitic 304, 316 No (Slight after cold work) Most corrosion resistant
Ferritic 430, 409 Yes Budget-friendly, magnetic
Martensitic 410, 420, 440C Yes High hardness and strength
Duplex 2205, 2507 Partially High strength and corrosion resistance
PH Steel 17-4PH Yes Used in aerospace and high-load components

9. Conclusion

Not all stainless steel grades are magnetic. Austenitic grades like 304 and 316 are typically non-magnetic and suited for applications requiring minimal magnetic interference. Ferritic and martensitic grades are magnetic and useful for mechanical and structural applications. Duplex and PH steels offer a balance of properties and moderate magnetism.

Understanding these differences allows you to choose the right material for your application—whether it demands magnetic properties or must avoid them.

Contact Sakysteel

If you’re unsure which stainless steel grade is right for your application, contact us for expert advice:

 

Post time: Jul-01-2025