Non-magnetism in stainless steels
The demands on stainless steels can be traced in several directions:
- Non-magnetic (paramagnetic) steels - austenitic steels meet these properties
- Magnetic steels (with magnetic properties) - especially ferritic steels
- Duplex steels are the middle way, for comparison we also list selected martensitic steels
1. Non-magnetic steels
Non-magnetic steels are most often austenitic steels. For these steels, their permeability (a measure of the material's ability to be magnetized by the surrounding magnetic field) is monitored (in addition to their corrosion and mechanical properties). It is mainly monitored in the form of relative permeability (i.e. in relation to the permeability of the vacuum), i.e. a value of 1 is met by the vacuum, steels normally have higher values, but depending on the type of material.
Non-magnetic steels are close to the value 1 - i.e. the influence of the applied magnetic field is very low - in the state without cold hardening they are up to the value 1.02. Depending on the amount and intensity of cold working, they not only harden, but also form partial martensitic phases which already exhibit magneticity. The growth of permeability as a function of the degree of cold hardening is shown in the following table:
Tab. 1:
| Grade | Relative permeability for a given level of cold working (ua) | |||
|---|---|---|---|---|
| 0 | 10 | 20 | 30 | |
| 305 (1.4303) | 1,004 | 1,004 | 1,004 | 1,005 |
| 304Cu (1.4301Cu) | 1,005 | 1,005 | 1,012 | 1,082 |
| 304 (1.4301) | 1,012 | 1,046 | 1,626 | 3,090 |
| 303 (1.4305) | 1,003 | 1,05 | 1,62 | 3,42 |
2. Magnetic steels
Magnetic steels are mainly ferritic steels. The individual grades are then designed with the target properties in mind. In some cases, there is a trade-off between the individual properties, both with regard to the magnetic (or electrical) properties of each other and with regard to the mechanical and corrosion properties.
A comparison of the properties and standard applications of the main magnetic steels is summarized in the following table:
Tab.2:
| Grade | 1.4106Mod | 1.4105Si | P12FM | P17 | 1.4511 |
|---|---|---|---|---|---|
| Saturation (T) | 1,60 | 1,60 | 1,70 | 1,65 | 1,67 |
| Coercivity (A/m) | 150-200 | 130-200 | 100-125 | 150-200 | 100-150 |
| Max. relative permeability | 1100-2000 | 1200-2200 | 2000-3000 | 1000-2000 | 2000-3000 |
| Remanence (T) | 0,25-0,8 | 05-0,9 | 0,5-0,7 | 0,5-1 | 0,5-1 |
| Resistance (µΩ.cm) | 76 | 77 | 78 | 60 | 60 |
| Machinability | increased | increased | increased | standard | standard |
| Environment / other properties | mildly chlorinated aquatic environments | compromise between corrosion resistance and magnetic properties / 2 level magn. properties | gasoline, fuels / excellent permeability and coercivity | fuel / magn. properties comparable to 1.4105Si, lower resistance, better mech. properties | fuels, more aggressive environment / better weldability, mag. properties comparable to P12FM, excellent compromise between corrosion resistance and mag. properties |
| Usage | electric valves e.g. beverage machines | electric valves and injectors (automotive) | electro injectors electrovalves magnetic sensors magnetic brakes | automotive | electrovalves, automotive |
3. Martensitic and duplex steels
The magnetic properties of martensitic and duplex steels are summarised in the table below:
Tab. 3:
| Grade | 1.4005 | 1.4313 | 1.4418 | 1.4542 | 1.4362 | 1.4462 | 1.4507 |
|---|---|---|---|---|---|---|---|
| Saturation (T) | 1,75 | 1,6 | 1,3-1,5 | 1,3-1,5 | 0,55 | 0,55 | 0,50 |
| Coercivity (A/m) | 800-1000 | 1200-1500 | 1650-2600 | 1800-3400 | 600 | 700 | 750 |
| Max. relative permeability | 180-380 | 200-300 | 100-200 | 50-200 | 50 | 40 | 30 |
| Remanence (T) | 0,9-1,2 | 0,7 | 0,5-0,7 | 0,4-0,7 | 0,05 | 0,04 | 003 |
| Resistance (µΩ.cm) | 57 | 60 | 80 | 70-80 | 80 | 80 | 85 |
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