Magnetic Stainless Steel, Austenitic, Ferritic, Martensitic

Stainless steel is often recognized for its corrosion resistance. But some grades also have varying magnetic abilities.


 Of the three stainless grades, austenitic steels have the least magnetic capability. Ferritic and martensitic steels, on other hand, have considerably stronger magnetic capabilities depending on how they are processed.

Austenitic

Austenitic steels are typically made up of 17 to 25 percent chromium. While austenitic metals are known for their strength and weldabilty, magnetic permeability among this family of stainless steels is weak.
 There is no presence of magnetic permeability among metals in the austenitic family when in the annealed condition; a state achieved when stainless steel is heat treated. This is due to the high nickel content present in austenitic steels.
 When heavily cold-worked, austenitic types 302 and 304 are slightly ferromagnetic, the strongest level of magnetism can be achieved. Cold-working has no effect on evoking magnetic abilities on austenitic metals such as 316 stainless due to its high nickel-to-chromium ratio.


Returning 302 and 304 stainless to a non-magnetic state can be accomplished through the heat treatment application of stress relieving. The ability to achieve magnetism can be eradicated completely with a full solution treatment at 1000 to 1150 degrees Celsius.

Ferritic

Ferritic steels are magnetically soft, which means they can be easily magnetized and demagnetized. Soft magnetic metals are used in the production of a wide array of products ranging from refrigerators to power electronic circuits.
 While other metals on the market are considered more effective for making soft magnetic components, ferritic steels are often used for applications which require corrosion resistance. Solenoid cores and pole pieces are among the products in which ferritic steels are used.


Compared to plated iron and silicon-iron, ferritic steel is considered a more cost effective material. Designed specifically for soft magnetic components, ferritic type 430FR is known for its high electrical resistivity.
 This high electrical resistivity makes 430FR an excellent performer in Alternating Current (AC) based applications. The magnetic ability of ferritic steels decreases when cold-worked. Conversely, these stainless metals retain a permanent level of weak magnetism if exposed to magnetic fields.

Martensitic

Like ferritic metals, martensitic steel is also ferromagnetic. In order to reach its full corrosive resistance potential, martensitic steel must be tempered, polished and hardened. If magnetized in the hardened condition, martensitic steel will exhibit permanent magnetic ability.