In the last lesson we learned what alloys are and that steel is a binary alloy of iron and carbon. But when was stainless steel born, and what are its characteristics?
Some important dates
The discovery of stainless steel is due to the British Woods and Clark, who in 1872 patented an iron alloy containing 35% by weight of chromium and acid-resistant.
The industrialization of this material, however, took place only in 1913. Harry Brearley of Sheffield, was experimenting with different types of steel for firearms barrels, when he discovered that a sample of his own steel with 13-14% chromium and a relatively low carbon content (0.25%) did not rust when exposed to the atmosphere.
Let us move on to some more technical aspects
As already mentioned, steel is a binary alloy, with iron and carbon elements. There are, however, different types of steel: alloy steels and non-alloy steels. Non-alloyed steel consists exclusively of iron and carbon. In alloy steel, however, there are other elements to improve its chemical and physical characteristics. In the specific case of stainless steel the element that allows a greater resistance to corrosion is the Chromium.
Chromium is able to passivate. It is covered by a layer of oxides, very thin, which protects the surface of the metal. In this way, this layer, makes the action of external chemical agents almost nothing, or however, less effective.
Stainless steels also have a carbon content generally of less than 1.2%. The minimum content of “free” chromium (not combined with carbon) is between 11-12%. This value allows the formation of the continuous “passive” oxide layer.
The chromium in the alloy, in fact, by combining with carbon, can form chromium carbides, which limit the availability of these alloying elements to form oxides and, therefore, to passivate.
What are the characteristics of stainless steel?
Stainless steel has these characteristics:
– high corrosion resistance
– heat resistance
– simple and not too expensive maintenance
– can be reused
– easy to clean
– excellent resistance
See you on next Expert Lesson.
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