INOX – Steel processing guide
WHAT ARE STAINLESS STEELS?
Stainless steels are iron alloys that are able to combine the typical mechanical properties of steels, the intrinsic characteristics of noble materials such as typically the remarkable qualities of resistance to corrosion.
In fact the term does not correspond to the true nature of these metals; in fact, they are “very oxidizable», that is to say that they have the possibility, thanks to the content of alloy elements, essentially the percentage of chromium, of “self-passivation” that is, to become covered with a layer of invisible oxides, molecular size, which protects the underlying metal from corrosion.
This phenomenon occurs whenever the environment is sufficiently oxidizing, such as the air we breathe, the water, various solutions, etc. The nature of this layer is such as to ensure the metal cover, even if locally occurring abrasion or removal of the film, provided always be sufficiently oxidizing conditions.
This concept is very important for the purposes of a good seal over time and in an appropriate manner against the various instances of corrosion. It is necessary in fact to enable the material, both during the processing of that mass in work, to be able to exchange with the environment that surrounds a sufficient amount of oxygen in order to be considered in the optimal conditions of passivation.
Of course this passive film can be more or less resistant and more or less anchored to the material depending on the chromium concentration present in the alloy and depending on the possible presence of other elements such as nickel, molybdenum, titanium, etc.
It is therefore clear that there are different degrees of rust resistance and corrosion resistance, therefore, exists, in the context of stainless, a scale of nobility depending on the content in the alloy of the above elements.
In addition to the corrosion resistance characteristics, there is a wide range of mechanical resistance which gives the possibility to choose between different types of performance, both at room temperature and at elevated temperatures.
The generic user is located accordingly in front of a remarkable performance series and the problem that often arises is precisely that of being able to choose the right material according to the uses, in a manner that does not “downsizing” nor “oversize” the choice and refer to the appropriate values of nobility and mechanical performance, suitable for a particular service.
It is necessary at this point to briefly illustrate the different types, by large aggregations, of these steels.