Is stainless steel magnetic? The answer to this question is this, austenitic stainless steel is non-magnetic. However, ferritic stainless steel and martensitic stainless steel are generally magnetic. Moreover, processing technology and temperature can affect the magnetic properties of stainless steel.
Kinds of Stainless Steel
Stainless steel is a high-alloy steel material, containing a variety of alloying elements. According to the different structures, stainless steel can be divided into austenitic stainless steel, ferritic stainless steel, martensitic stainless steel, and other types. Generally speaking, austenitic stainless steel (represented by 304) is non-magnetic. While ferritic stainless steel (mainly 430, 409L, 439, and 445NF, etc.) and martensitic stainless steel (represented by 410) are generally magnetic.
Image Source: Quora
Is Stainless Steel Magnetic? Austenitic Stainless Steel Says No
Austenitic stainless steel is widely used on the market. There are many types of austenitic stainless steel, such as 304/321/316/310. The representative steel of austenitic stainless steel is SUS304 (18Cr-8Ni-0.05C), commonly known as 304. SUS304 is the most widely used austenitic stainless steel. Because the properties of processing, weldability, and corrosion resistance are excellent, SUS304 are widely used in common lives ad indtrustial applications, such as magnetic separators, which accounts for about 60% of the world’s whole consumption of stainless steel, and it is not magnetic.
Sometimes people test the authenticity of stainless steel by checking whether the stainless steel is magnetic. For them, non-magnetic stainless steel is really stainless steel, and magnetic stainless steel is false stainless steel. This is a wrong identification method, the main reason is that for a long time, austenitic stainless steel has accounted for a large proportion of the stainless steel market, so people have the misconception that stainless steel is not magnetic.
| Alloy Group | Magnetic Response | Work Hardening Rate | Corrosion Resistance | Hardenable | Ductility | High Temperature Resistance | Low Temperature Resistance | Weldability |
| Austenitic | Generally No | Very High | High | By Cold Work | Very High | Very High | Very High | Very High |
| Ferritic | Yes | Medium | Medium | No | Medium | High | L ow | L ow |
| Martensitic | Yes | Medium | Medium | Quench & Temper | L ow | L ow | L ow | L ow |
Table Source: Web
Is Stainless Steel Magnetic? Martensitic and Ferritic Stainless Steel Say Yes
Martensitic stainless steel and ferritic stainless steel also have many varieties, such as 430/420/410, etc. A representative ferritic stainless steel is SUS430 (16Cr-0.05C), which is a kind of magnetic stainless steel. Several varieties of ferritic stainless steel have been developed to improve corrosion resistance, processability, and weldability. Since this type of stainless steel is basically free of Ni, it is relatively inexpensive and is widely used as a general stainless steel.
In the alloy composition, chromium (Cr) is a component that causes stainless steel to be magnetic. And another component nickel (Ni) will inhibit the production of this magnetism. Austenitic stainless steel is non-magnetic or weakly magnetic because its main alloy components are chromium and nickel. Martensitic or ferritic stainless steel, on the other hand, has chromium as its main alloying component and no nickel component, and its crystal structure is similar to that of carbon steel, which makes it easily magnetized.
| Composition Ranges for Different Stainless Steel Categories | |||||||
| Steel Category | Composition (wt%) | Hardenable | Ferro- Magnetism | ||||
| C | Cr | Ni | Mo | Others | |||
| Martensitic | >0.10 | 11-14 | 0-1 | V | Hardenable | Magnetic | |
| Ferritic | <0.08 | 12-19 | 0-5 | <5 | Ti | Not Hardenable | Magnetic |
| Austenitic | <0.08 | 16-30 | 8-35 | 0-7 | N, Cu, Ti, Nb | Not Hardenable | Not Magnetic |
Table Source: Web
Other Influencing Factors
Processing and temperature can make the non-magnetic stainless steel to become magnetic.
Processing | 304 stainless steel after cold working, the organizational structure will also be transformed to martensite, the greater the degree of cold working deformation, the more martensite transformation, and the greater the magnetism of the steel.
During cold working operations such as stamping, forming, forging, and surface polishing, 304 stainless steel usually becomes magnetic and is more susceptible to corrosion, especially in the machining area, because during the process, the austenitic microstructure is restored to martensite, which is magnetic and not resistant to corrosion.
Temperature | At high temperatures, 316L austenitic stainless steel may become slightly magnetic. At low temperatures, austenite can also spontaneously revert to martensite. Martensite is also magnetic, so 304 or 316 stainless steel may also exhibit weak magnetism.
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