The steel stainlessalso known by the name of stainless steel or Stainless steelis a particular steel alloy with specific characteristics that guarantee effective protection against corrosion. It is widely used in various sectors, including the food sector, which is certainly closer to our daily use. Being an alloy, It has its own particular recipe which distinguishes it from other types of alloys, identifying it strengths and weaknessesIn this article we describe its main uses, the composition of the alloy and the differences with some of the most common alloys.
How Stainless Steel Alloy is Made: The Chemical Composition
So what changes compared to other steel alloys? It should be remembered that it is possible to talk about steel when we are dealing with an alloy of iron (Fe) and carbon (C), the latter with percentages not exceeding about 2%. In the case of stainless steels, in addition to these two essential components, we find further chemical elements present in the alloy, mainly the chrome (Cr) and the nickel (Ni). Usually, therefore, a stainless steel alloy is distinguished from other alloys by identifying it as an iron-chromium-carbon alloywith percentages of chromium (Cr) greater than 12% and relatively low carbon percentages. Other elements can then be added to give it additional properties, such as workability or better weldability.
The alloy thus formed has many similarities with the lesser-known Cor-Ten steel: this too is an Iron-Carbon alloy, with the addition of other elements such as copper (Cu), the chrome (Cr) and the phosphorus (P). This alloy has better mechanical characteristics than stainless steel, especially in terms of resistance, which makes it more attractive in the civil/mechanical sector in terms of applications. Both alloys demonstrate significant protection against spontaneous corrosion of steel in aggressive environments.
How the INOX alloy works and its properties
Let’s start from the name: a steel alloy is improperly call stainlessas there is no alloy to date that does not in some way manifest the triggering of an oxidation process in unfavourable environmental conditions (for example, in the presence of air). The oxidation process is represented by that chemical reaction which involves the loss of electrons by a chemical species. This process, unfortunately spontaneous in the presence of oxygen, is the main cause of degradation and ruin of the material over time, also and above all from a mechanical point of view. Therefore, even stainless steel oxidizesbut thanks to the percentage content of chromium in the alloy, this oxidation affects the chromium and practically translates into the formation of a protective patina firmly “anchored” to the starting materialwhich interrupts the propagation of oxidation to the deep layers, which would then involve the iron present in the alloy, generating rust! In these cases we speak of passivation process.
What are the types of stainless steel?
There are mainly three big families of stainless steels:
- Steel alloys containing mainly chromium (Cr), with percentages varying between 11% and 18%, also called martensitic stainless steelsTheir particularity is due to the fact that, thanks to some heat treatments, they are able to develop an increase in mechanical characteristics, such as resistance, compared to ordinary steels.
- If the percentage of chromium exceeds those previously indicated, up to 18%, then we are talking about stainless ferricites. Unlike the previous ones, in this case there are no thermal processes capable of improving the mechanical performance of the alloy. However, they are very workable at any temperature (therefore both hot and cold).
- Steel alloys that contain both chromium (Cr) in high percentages (between 17% and 26%), and nickel (Ni) in percentages between 7% and 22%, are called austenitic stainless steelsThese alloys cannot be mechanically improved by thermal processes, but the mechanical characteristics of the finished product can be locally increased following significant permanent deformations imposed: technically, in these cases we speak of good hardening characteristics of the alloy.
The uses of stainless steel
Although one might generally think of stainless steel as being confined to classic kitchen utensils, the areas of application for these alloys are varied:
- In building they are often used for the construction of windows or elevators, even to a lesser extent for structural elements;
- In the sector of infrastructure They are widely used for water purification or potabilization systems.
- In the sector of transportinstead, are widely used for the structural components of vehicles.
- The sector to feedas is known, is very useful for the creation of various types of tools.
For this last sector of employment, in fact, it is appropriate to mention the Hygienic properties of the materialwhich make it a preferable choice for all those uses that require appropriate protection from external contamination. The hygiene of a material is a combination of various aspects, among the most important we can mention the corrosion resistance, absence of crackable or deteriorating protective coatings, absence of porosity on the contact surface, high resistance to impacts and thermal shocks, low bacterial retentivity (low capacity to retain bacteria). There are several national and international standards that establish the suitability of stainless steel when in contact with drinking water and/or various types of food material, which is why it is widely used in the production of a whole series of objects used daily by each of us.
