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Does stainless steel rust?

Stainless steel is truly an extraordinary material. Greatly resistant to phenomena such as corrosion or wear, long durability over time and low bacterial retention (which makes it extremely hygienic), it is often considered to possess another important characteristic: stainless steel cannot rust.

But is it actually true? Certainly, compared to normal steel, the possibility of rusting is quite low, but this should not be excluded in all circumstances.

Let’s find out more together.

Stainless steel is truly an extraordinary material. Greatly resistant to phenomena such as corrosion or wear, long durability over time and low bacterial retention (which makes it extremely hygienic), it is often considered to possess another important characteristic: Stainless steel cannot rust. But is it actually true? Certainly, compared to normal steel, the possibility of rusting is quite low, but this should not be excluded in all circumstances. Let's find out more together.

How rust forms

The main “enemy” of steel, which can lead to the formation of rust, is oxygen. In ordinary steels, oxygen reacts with the iron molecules present in the steel and forms a porous surface which can help the progress of this reaction. This process, if prolonged, can lead to the formation of layers of rust.

Stainless steel, instead, is also composed of chromium atoms, present in different concentrations depending on the type of steel. The oxygen with which steel comes into contact, reacts with the atoms and forms a thick layer of oxide which instead prevents the progress of the reaction.

This layer is also called passive layer and thanks to this, stainless steel proves to be much more resistant and less susceptible to rusting. However, as anticipated, it is not impossible for rust to form.

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Corrosion of stainless steel

The reasons for the formation of rust in stainless steel are mainly two:

  1. 1. The passive layer could not form
  2. 2. The passive layer has been destroyed

Having said this, we remind you that it is possible to avoid the absence or destruction of the passive layer only by thoroughly cleaning all the stainless steel surfaces from any processing residue. Cleaning is therefore an important form of rust and corrosion prevention.

In any case, it all depends on the passive layer and its presence on the steel surface. Its absence causes different types of corrosion, let’s see some of them:

  • Surface corrosion: uniform erosion of the workpiece surface. It occurs when acids or highly alkaline solutions act on the surface.
  • Pitting corrosion: when the passive layer is penetrated This is caused by chloride ions which, in the presence of an electrolyte, remove the chromium atoms from stainless steel. These, as seen, are necessary for the formation of the passive layer and, if removed, lead to the formation of numerous filiform alveoli.
  • Contact corrosion: occurs if metallic materials of different types come into contact with each other and are wetted by an electrolyte. The less valuable material is affected and dissolves. Stainless steels are noble materials compared to most other metal materials, so it runs less of this risk.

Conclusions

As we have seen, stainless steel is not a perfect material, immune to any deterioration. However, compared to other materials it is certainly of a higher quality, able to withstand more time and more intense conditions of use.

This does not mean that it is not necessary to treat it with suitable products, carry out precise cleaning and regular maintenance: these remain fundamental activities for maintaining its quality.

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