AISI 304 and AISI 316: what is the difference?

This is the question that many customers, who buy our seamless stainless steel tubes, asked us and it is the reason why we have decided to tackle the subject.

We all know that steel is resistant and versatile, excellent in various fields. For this reason, it is the most used material in the world. Although it is mainly composed of two elements, carbon and iron, there are multiple steel classes, divided into 4 categories:

• Carbon steel;
• Alloy steel;
• Tool steel;
• Stainless steel.

Inox steel

Stainless steel is an iron alloy containing a quantity of chromium between 11% and 30%. This element prevents deterioration due to time or the surrounding environment.

Depending on its composition, it is further divided into 4 categories: martensitic, ferritic, austenitic and austen-ferritic (or duplex).

The two grades we are talking about here fall within the austenitic steels’ category.

How to distinguish an AISI 304 from an AISI 316?

Although aesthetically identical, these two types of steels differ fundamentally in their chemical composition. AISI 316 stainless steel, compared to AISI 304, consists of the presence of molybdenum and a higher percentage of nickel.

But what, specifically, do these two elements entail?

By simplifying the concepts, molybdenum improves hot mechanical characteristics and resistance to localized corrosion, especially in the presence of chlorine and chloride.

Nickel also has a positive influence on corrosion resistance, mainly in the presence of sulfuric acid and in cases where the passive film is partially damaged or destroyed. In addition, it confers ductility and formability, making the austenite stable.

Where are AISI 304 seamless pipes used and where are AISI 316 ones used?

The customers to whom we sell these products, certainly make very varied uses of them.

There is no significant difference in use between the two grades, both are excellent and resistant in most situations.

In general, AISI 304 seamless pipes are more economically competitive and have greater hot workability, which in AISI 316 drops slightly due to the addition of molybdenum. But many of our customers prefer to spend a little more to play it safe and buy the top of the range: AISI 316 seamless pipes.

There are some particular cases in which AISI 316 pipes are necessary: in marine areas or in areas characterized by a strong presence of industrial pollution. In fact, for certain application sectors in which greater resistance to corrosion is essential, AISI 316 ensures that the pipes remain perfect for a long time.

As we said, in our seamless stainless steel tubes offering, you will find both grades we mentioned: AISI 304 and AISI 316. These are available from stock on our new e-commerce; we can send them to you, within 3- 5 days, or you can collect them directly in our warehouse in Bagnatica (BG). There is also a customized cutting service on 6-meter stainless steel tubing and piping, to meet every need or just to make delivery by express courier more convenient.

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For more information, details or requests, don’t hesitate to contact us at marketing@pipex.it.

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