Stainless Steel: Properties and Application in Valves, Manifolds and Other Hydraulic Components
Stainless steel is the heart of Mondeo’s production: a material that is corrosion-resistant, hygienic, durable and 100% recyclable. Chosen for its high performance and its potentially infinite service life, it is perfectly consistent with Mondeo’s philosophy of sustainability and hydraulic efficiency. The use of austenitic stainless steels AISI 304 and AISI 316, combined with electropolishing treatment, guarantees high-quality surfaces, greater long-term resistance and reduced pressure drop, for more efficient and reliable systems.
The Properties of Stainless Steel, Starting with Corrosion Resistance
Stainless steel is the material that best embodies our concept of fluid handling.
It is an alloy composed of iron, carbon and a minimum chromium content of approximately 12%. The term “stainless” refers precisely to the presence of chromium and the chemical phenomenon of passivation. Chromium has a very strong affinity with oxygen and, on contact with air or water, forms an extremely thin chromium oxide layer on the surface of the material. In this way chromium turns oxidation from enemy to ally, creating an invisible, self-regenerating barrier that protects the steel over time, making it stainless.
Hence the main characteristic of stainless steel: its extremely high corrosion resistance, whether in acidic, alkaline or high-chloride environments.
From this corrosion resistance derive the other characteristic properties of stainless steel: long-term durability even under demanding conditions, which is why stainless steel components do not require maintenance or costly replacements; hygiene, since the smooth, non-porous surface not only inhibits bacterial accumulation but is also ideal for cleaning operations.
It is, finally, a perfectly inert material that releases no substances and does not alter in the slightest the fluid it contacts.
The corrosion resistance of stainless steel is a natural characteristic that can be further enhanced by electropolishing treatments that promote the formation and stabilisation of the passive surface layer.
Classification and Nomenclature of Stainless Steels
There are more than one hundred types of stainless steel and three main families:
- Austenitic chromium-nickel steels
- Austenitic chromium-manganese-nickel steels
- Ferritic and martensitic chromium-only steels
Austenitic steels are the most widespread, for their ability to combine multiple properties: excellent corrosion resistance, high ductility, excellent weldability and formability, and resistance to high and low temperatures.
Excellent ductility in particular is due to the face-centred cubic (FCC) crystal structure, thanks to the presence of nickel which stabilises the austenitic phase of the steel at room temperature.
The American Iron and Steel Institute (AISI) uses a three-digit numbering system for steel designation. According to this nomenclature, austenitic chromium-nickel steels belong to the 300 series, austenitic chromium-manganese-nickel steels to the 200 series, and ferritic and martensitic chromium-only steels to the 400 series.
In Europe, the reference standard is EN 10088, which defines chemical composition, physical characteristics and supply conditions.
The most corrosion-resistant steels are the austenitic chromium-nickel steels of the 300 series, in particular AISI 304 (EN 1.4301) and AISI 316 (EN 1.4401).
The 200 series has a lower nickel content, partly replaced with manganese. This chemical composition, however, requires a reduction in chromium content compared to the 18% typical of AISI 304 and 316. The consequence is that the corrosion resistance of 200 series steels is significantly lower than that of the 300 series.
| Designation according to AISI/EN 10088 |
C | Cr | Ni | Mo |
|---|---|---|---|---|
| AISI 304 (1.4301) |
≤0,07 | 17,00 - 19,50 | 8,00 - 10,50 | - |
| AISI 316 (1.4401) |
≤0,07 | 16,50 - 18,50 | 10,00 - 13,00 | 2,00 - 2,50 |
Frequently asked questions about stainless steel
What is the main difference between AISI 304 and AISI 316?
AISI 304 typically contains approximately 18% chromium and 8% nickel, a composition that makes it very versatile across various civil and industrial applications. It has high corrosion resistance and excellent mechanical properties, with an outstanding price-to-quality ratio. AISI 316 additionally contains approximately 2–3% molybdenum, an addition that increases its corrosion resistance, making it particularly suitable for marine environments and applications involving aggressive chemicals with high chloride concentrations.
Why is stainless steel sustainable?
Stainless steel fits perfectly with a circular economy model and the reduction of environmental impact. Not only is it 100% recyclable (in Europe it is produced almost exclusively from recycled material), but it can be reused an infinite number of times without losing any of its properties and while maintaining its performance unchanged. Its excellent durability, by extending the service life of the product, also translates into significant savings in resources and energy.