The difference between stainless steel AWS 304, 308, 309 and 316

First of all, what is stainless steel? Stainless steel is the combination of iron and carbon and which is composed of at least 15% chromium. The chrome therefore gives the peculiarity of making it stainless, and therefore not subject to oxidations.
To speak, while normal steel without chrome, if left under the rain in the long run rusts, losing robustness, stainless steel does not rust, maintaining its intact properties.

However, there are different types of stainless steel.
The types are commonly called AWS 304, AWS 308, AWS 309 and AWS 316.
The wording a.w.s. It stands for American Welding Society, which is the non-profit American entity that gives impetus to changes and evolutions of American legislation concerning the welding world. A.w.s. It has a reputation so important that it is also considered by other countries in the world, like all those of the European Union, to adopt common parameters to facilitate technical understanding between operators in the sector.

Thus, the AWS has led to these types of stainless steel we take for good and we also use them for our nomenclature in Italy as well as in the rest of Europe.
The different numbers (304, 308, 309 and 316) simply identify the different percentages of chromium, nickel and other materials contained in the steel.

• Let's specifically go, and leave from theAWS 304: 304 contains the 18% chromium and 8% nickel. The chrome have already guessed what is needed, but nickel? The nickel has the property to increase the elasticity of the stainless steel, fundamental if we wanted to use it as a contribution material to facilitate the bond with the welded material. It is usually difficult to find AWS 304 welding material, because it is that with less "noble" characteristics among all. It will be much more likely to find a stainless steel sheet 304, and use a contribution material that has a higher nickel percentage.
• L'AWS 316 It has the same percentages, then 18% chromium and 8% nickel, but with theAdding 2-3% molybdenum. Molybdenum is necessary to allow this type of stainless steel not to be subjected to corrosion. It is no coincidence that the AWS 316 is also called "food steel", precisely because it is often used for the construction of tanks that are used in the food industry to contain gastronomic products. It is known that foodstuffs contain acids that can lead to corrosion of materials, then 316 lends itself very well for this type of application.
• L'AWS 308 it is always composed from 18% chromium and 9% nickelthen 1% more nickel, making it more elastic. When welders ask me for a stainless steel electrode to weld 304, they mean that they want an AWS 308 stainless steel electrode, precisely because greater elasticity allows it to bind themselves well with 304 and has no additional features (like 316 and 309) which They are superfluous for the work he will have to do.
• Finally, theAWS 309 It is composed of 22% chromium and 12% nickel. The largest percentage of chromium increases the robustness, but to this it is also necessary to add nickel to compensate with more elasticity. For structural works in which the use of stainless steel is needed then the ideal would be the use of AWS 309.

The identification of the type of stainless steel that I will have to weld is necessary to succeed in carrying out a correct processing.

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