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Why some stainless steel can attract magnets, but some stainless steel cannot?

release time：

2025-06-03 18:18

1. Core reason: crystal structure difference

Austenitic stainless steel (non-magnetic or weakly magnetic)

Represented by 304 and 316, it contains high nickel (Ni) and chromium (Cr), and has a face-centered cubic structure at room temperature. The direction of the internal atomic magnetic moment is chaotic, and the magnetism cancels each other out.

Typical characteristics: magnets cannot attract (such as kitchen sinks and medical devices).

Ferritic/martensitic stainless steel (magnetic)

Represented by 430 and 410, it contains chromium (Cr) but less nickel (Ni), forming a body-centered cubic structure, and the direction of the atomic magnetic moment is consistent, showing ferromagnetism.
Typical characteristics: magnets can attract (such as knives, car exhaust pipes).
Key point: The difference in magnetism is essentially a different arrangement of atoms, which has nothing to do with whether it contains iron (all stainless steels contain iron).

2. Other influencing factors

Magnetic changes caused by cold working
Austenitic stainless steel (such as 304) may be partially transformed into martensite after bending and stamping, resulting in weak magnetism.
Example: 304 stainless steel straight tube is non-magnetic, but the corner can be attracted by magnet after bending.

‌Chemical composition deviation‌

Composition segregation during smelting (such as imbalance in chromium/nickel ratio) may cause austenitic steel to mix with ferrite, resulting in magnetism.