Types of Stainless Steel
In order to understand the different types of stainless steel, it is important to start with the basics.
“Steel” refers to an alloy of iron and carbon, where the carbon content does not exceed 2.06%: any higher and the material is classified as cast iron.
The stainless version of this alloy has proven to be one of the most suitable materials for manufacturing a wide range of objects and equipment used across many industrial sectors.
Its superiority is due to its outstanding chemical and physical properties, which give it unique and highly valued characteristics.
What distinguishes stainless steel from other metals and materials is its high chromium content, which makes it highly resistant to corrosion and oxidation. A thin passive film forms on its surface when exposed to oxygen, effectively protecting it from external agents.
In more practical terms, stainless steel does not rust.
In addition to corrosion resistance, this protective layer gives the material a uniform appearance and excellent hygienic performance. As mentioned earlier, stainless steel is one of the safest materials in terms of compliance with sanitary regulations.
It is 100% food-contact approved, making it an ideal choice for sectors such as food processing, healthcare and cleanrooms.
Although its key features are well known, fewer people realise that there are multiple types and classifications of stainless steel. Each variant has its own unique properties and is more or less suitable depending on its intended application.
The 4 Main Families of Stainless Steel
When elements other than chromium are added to steel, its structural properties change. This allows stainless steels to be classified into four main families:
- Martensitic (13% chromium)
- Ferritic (18% chromium)
- Austenitic (18% chromium + 10% nickel or
18% chromium + 12% nickel + 2% molybdenum) - Duplex (22% chromium + 5% nickel)
As the number of alloying elements increases, the corrosion resistance of the material also improves—although its workability tends to decrease.
This makes the steel more stainless and, consequently, more hygienic, which is especially valuable in industries requiring high sanitary standards.
Another widely recognised way of indicating the presence of these elements is through numerical labels attached to the steel name.
For example, “18/10 steel” refers to a stainless-steel alloy containing 18% chromium and 10% nickel.
A steel marked 18/8/3 contains 18% chromium, 8% nickel and 3% molybdenum.
Official AISI Classification
Another widely adopted system for classifying stainless steel types is the AISI (American Iron and Steel Institute) nomenclature, which also refers to the alloy’s chemical composition.
Among the main categories, we find:
- AISI 304 – The most commonly used type of stainless steel, highly resistant and widely employed in manufacturing everyday objects. It belongs to the austenitic family—among the most durable stainless steels.
- AISI 316 – Similar to AISI 304, but enriched with molybdenum, making it even more corrosion-resistant, especially in high-humidity or saline environments.
- AISI 430 – A less resistant type with a less uniform surface finish. It is a ferritic stainless steel, generally more economical and better suited for industrial processing.
- AISI 441 – A cost-effective alternative to AISI 304. It is durable and commonly used for cooking surfaces and structural elements of tables and chairs.
At Facilitas, we manufacture our products using AISI 304 and AISI 441 stainless steel, ensuring excellent resistance, maximum hygiene and a smooth, uniform surface finish.
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