A comprehensive introduction to magnetic stainless steel

2025-06-30

1.What is magnetic stainless steel?

Definition: Magnetic stainless steel refers to stainless steel that can be attracted by a magnet at room temperature, and its magnetism mainly comes from ferrite or martensitic structure.
The difference from non-magnetic stainless steel: Common austenitic stainless steels (such as 304, 316) are usually non-magnetic (they may become weakly magnetic after cold working), while magnetic stainless steels are mainly martensitic, ferritic or precipitation-hardening stainless steels.

2. Types of magnetic stainless steel

(1) Martensitic stainless steel: It usually contains a relatively high amount of carbon and chromium, and has good strength and hardness. It is often used in cutting tools and tools.
Characteristics: High hardness, high strength, remarkable magnetism, medium corrosion resistance, requires heat treatment (quenching + tempering).
Typical grades:
410 (12% Cr) : Used for cutting tools and valves.
420 (with more carbon added) : Surgical instruments, bearings.
440C (High carbon and high chromium) : High-end cutting tools and bearings.
(2) Ferritic stainless steel: It has a relatively high chromium content, a low carbon content, and good corrosion resistance. It is suitable for kitchenware and industrial equipment.
Characteristics: Magnetic, with better corrosion resistance than martensitic (especially resistant to stress corrosion), but poor plasticity, and cannot be strengthened by heat treatment.
Typical grades:
430 (16-18% Cr) : Home appliances, architectural decoration.
434 (with molybdenum added) : Automotive exhaust system.
446 (High chromium and high temperature resistant) : Heat-resistant component.
(3) Precipitation-hardening stainless steel (PH steel
Characteristics: Through aging treatment, a hardened phase precipitates, featuring both high strength and magnetic properties.
Typical grades:
17-4PH (Cu/Nb precipitation) : Aerospace, turbine components.

3. Characteristics of magnetic stainless steel

Magnetism: Due to its iron content, magnetic stainless steel exhibits obvious magnetism in a magnetic field.
Corrosion resistance: Although not as good as austenitic stainless steel, ferritic and martensitic stainless steels still have a certain degree of corrosion resistance.
Strength and hardness: Martensitic stainless steel usually has high strength and hardness, making it suitable for manufacturing components that can withstand high pressure.

4. Application of Magnetic Stainless steel

Knives and tools: Due to its high strength and hardness, it is often used to make knives, scissors and other cutting tools.
Automobiles and aerospace: Used for manufacturing engine components and structural parts.
Architecture and decoration: Used for the frames, doors, Windows and decorative elements of buildings.

5. Advantages and disadvantages of magnetic stainless steel

Advantages
Lower cost: Compared with high-alloy stainless steel, magnetic stainless steel is usually more economical.
Good mechanical properties: Suitable for use in high-load environments.
Disadvantages
Poor corrosion resistance: In some environments, it may rust more easily than other types of stainless steel.
Processing difficulty: Martensitic stainless steel may be more difficult to handle during processing.

6. Processing and treatment

Heat treatment: Martensitic steel needs to be quenched and tempered. Ferritic steel is not heat-treatable.
Welding: Ferritic steel is prone to grain coarsening, and the heat input needs to be controlled. Martensitic steel needs to be preheated to prevent cracking.
Surface treatment: Passivation enhances corrosion resistance, and coating improves electrical conductivity (such as in electromagnetic shielding applications).

7. Selection suggestions

Corrosion resistance takes priority: Choose high-chromium or molybdenum-containing ferritic steel (such as 434).
Strength priority: Martensitic steel (such as 420) or 17-4PH.
Cost sensitive: 430 or 409 (low-chromium ferrite).

8. Common Questions

Will magnetism disappear? Martensitic steel has stable magnetic properties; Ferritic steel loses its magnetism above the Curie temperature (about 750℃).
How to identify? Test with a magnet, but note that cold-worked austenitic steel may show weak magnetism.

9. Market and Development

Trend: Develop high-corrosion-resistant ferritic steels (such as super ferritic 444) to replace some austenitic steels.
Environmental protection: Nickel-free ferritic steel is more in line with resource sustainability.