Properties
Physical propertiesedit
Electricity and magnetismedit
Like steel, stainless steels are relatively poor conductors of electricity, with significantly lower electrical conductivity than copper. In particular, the electrical contact resistance (ECR) of stainless steel arises as the result of the dense protective oxide layer, and limits its functionality in applications as electrical connectors . Copper alloys and nickel coated connectors tend to exhibit lower ECR values, and are preferred materials for such applications. Nevertheless stainless steel connectors are employed in situations with ECR poses a lower design criteria and corrosion resistance is required, for example in high temperatures and oxidizing environments .
Magnetic propertiesedit
Martensitic and ferritic stainless steels are magnetic.
Ferritic steel consists of ferrite crystals, a form of iron with up to 0.025% carbon. Due to its cubic crystalline structure, ferritic steel only absorbs a small amount of carbon, which consists of one iron in each corner and a central iron atom. The central atom is responsible for its magnetic properties.
Grades with low coercitive field Hc have been developed for electrovalves used in household appliances and for injection systems in internal combustion engines. Some applications require non-magnetic materials, such as magnetic resonance imaging.
Annealed austenitic stainless steels are usually non-magnetic, though work hardening can make cold-formed austenitic stainless steels slightly magnetic. Sometimes, if austenitic steel is bent or cut, magnetism occurs along the edge of the stainless steel because the crystal structure rearranges itself.
| EN grade | Magnetic permeability, μ |
|---|---|
| 1.4307 | 1.056 |
| 1.4301 | 1.011 |
| 1.4404 | 1.100 |
| 1.4435 | 1.000 |
Gallingedit
Galling, sometimes called cold welding, is a form of severe adhesive wear, which can occur when two metal surfaces are in relative motion to each other and under heavy pressure. Austenitic stainless steel fasteners are particularly susceptible to thread galling, though other alloys that self-generate a protective oxide surface film, such as aluminium and titanium, are also susceptible. Under high contact-force sliding, this oxide can be deformed, broken, and removed from parts of the component, exposing the bare reactive metal. When the two surfaces are of the same material, these exposed surfaces can easily fuse. Separation of the two surfaces can result in surface tearing and even complete seizure of metal components or fasteners.
Galling can be mitigated by the use of dissimilar materials (bronze against stainless steel) or using different stainless steels (martensitic against austenitic). Additionally, threaded joints may be lubricated to provide a film between the two parts and prevent galling. Nitronic 60, made by selective alloying with manganese, silicon, and nitrogen, has demonstrated a reduced tendency to gall.
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