A common misconception is that stainless steel is non-magnetic. There are five classes of stainless steel, and only one is non-magnetic. However, it just happens to be that the most widely used type (austenitic) is the one that is not magnetic.
| Class | Magnetic? | Common Types |
|---|---|---|
| Ferritic | Yes | 430,442 |
| Austenitic | No | 304,316 |
| Martensitic | Yes | 410,416 |
| Duplex | Yes | 2205, 2507 |
| Precipitation Hardening | Yes | 17-4, 17-7 |
Magnetism has more to do with the steel’s grain microstructure than with its chemical make-up, so whether or not your stainless will be magnetic will depend on not only its microstructure, but also how it was manufactured or processed. The most common stainless steels, 304 and 316, have an austenitic microstructure and start out life non-magnetic. However as they are manufactured from raw steel to fasteners, they go through several cold forming processes (drawing, roll threading, heading) which changes the microstructure from austenitic to martensitic, thereby making the material more magnetic. The more cold forming, the more its microstructure is changed to martensite, and subsequently the more magnetic the fastener is likely to be.
If magnetism in austenitic stainless is not wanted, steps can be taken to limit it. Manufacturing processes can be chosen that do not cold form, i.e. cut threading vs roll threading. Alternatively, the finished fastener can go through an annealing treatment which will restore the microstructure to its original austenitic state.
Sir
Looking at your discussion one question appears to mind that is how magnetic steels are machined for eg how magnetic sstainless steel are threaded?
@Rohi- Unless there is a strong magnetic concern, we thread stainless steel bolts one of two ways (roll or cut) depending on factors such as material availability, cost, time, machine availability. If the end user has a concern regarding magnetism, be are happy to discuss options.
Corrosion protection is due to chemical makeup and has nothing to do with magnetism and micro structure thus it will remain corrosion resistant.
@Khurram- that is not entirely true. Hot forged stainless, if not properly solution annealed after forging, will most definitely rust. Solution annealing restores the grain boundaries and therefore the corrosion protection.
Corrosion protection is due to tu chromium oxide protective layer on the surface of bolts or any other profile. What it has to do with grain boundry?
@Khurram- Yes, an self-generating oxide layer does help to protect stainless steels from corrosion. Exactly how the grain structure affects that oxide layer we are not certain. We do not have a metallurgist on staff, you might need to contact someone more well-versed in this subject.