Material Knowledge Stainless Steel
Durable metals with rustproof properties
The term stainless steel popularly understood to mean particularly durable metals with rustproof properties. Stainless steel is often used in clean rooms and hygienically demanding workplaces. Where these properties come from and how the various types of stainless steels differ, are explained on this page.
More Information about stainless steel:
- Stainless steel does not necessarily denote a rust-resistant steel
- The chromium content determines the corrosion resistance
- A rust-resistant steel contains more than 10.5 % chromium
- Use in foodstuff and pharmaceutical industries
Definition of stainless steel
The use of stainless steel in industry began with the patent application for “steels with high resistance to corrosion” in 1912. The term stainless steel is a collective term for over 160
different steel alloys. Synonyms such as V2A, V4A or Inox have become widespread in German linguistic usage and were initially used by manufacturers and fabricators. Stainless
steel is a collective term for the non-rusting steels. They contain at least 10.5 % chromium (Cr) and have significantly improved corrosion resistance compared to unalloyed steels.
Higher Cr contents and other alloying components, such as nickel (Ni) and molybdenum (Mo) further increase corrosion resistance. Furthermore, the addition of certain other elements can also positively influence other properties.
Properties of stainless steel
- corrosion resistant
- high strength
- wear-resistant
- weldable
- temperature resistant
- hygienic
- conductive
- economic
- durable
- low maintenance
Contrary to common belief, stainless steel is not always corrosion resistant. The decisive factors are the alloys used and the contact with steel surfaces. If ferrous, corrodible metals are in contact, stainless steel can also rust. So flash rust or even deep corrosion
cannot be ruled out.
Corrosion Resistant - Why is stainless steel rustproof?
The alloy elements in the steel cause a thin, transparent "passive layer" to form on the surface. Although it is only a few atoms thick, it protects the material even in the event of surface damage. This stainless steel therefore requires no additional finish or metallic coating
such as galvanising or painting to remain corrosion resistant.
Together with oxygen atoms, chromium atoms in the steel form a dense and inert oxide layer that prevents oxidation from progressing and thus prevents the steel from rusting.
Hygienic - why is stainless steel hygienic?
The chromium oxide on the surface of stainless steel remains very smooth even afer frequent cleaning.
Germs find no suitable breeding ground. The consistently smooth surface facilitates cleaning.
Stainless steel does not react with common cleaning agents or disinfectants. The surface remains undamaged.
This feature is caused by the passive layer of the stainless stee!, among other things. It prevents ions from
escaping from the material. These ions prevent germ formation by destroying the cells of bacteria.
Stainless steel does not release particles when subjected to stress. This means that food, liquids or other organic
substances are not contaminated when they come into contact with stainless steel. Containers or surfaces made
of stainless steel are therefore ideal when foodstuffs are processed or stored.
Stainliess steel overview
Application sectors for stainless steel
Due to its special properties, stainless steel finds use in many branches. It is used in special industries with high demands on hygiene, such as the pharmaceutical and foodstuff industries, or in areas with high demands on corrosion resistance, such as in the offshore sector. Stainless steel is also present in everyday life, e.g. 18/10 stainless steel (robust chrome-nickel steel with 18 percent chrome and 10 percent nickel) is used for cutlery.
Stainless steel in everyday life
The shiny stainless steel optic enables the material to be used in design objects in architecture and everyday objects such as refrigerators, panels for vacuum cleaners etc.
If products are used outdoors, coatings can make steels corrosion resistant. Stainless steel is often used if the products also have a decorative function. The combination of corrosion resistance and durability provides for this. This is why we find
stainless steel used for furniture, railings, letterboxes, etc.
Stainless steel for extreme condition
V4A stainless steel in the common stainless steel grades 1.4401, 1.4404, 1.4435 and 1.4571 is used in very special applications due to its good resistance to acids and particularly high corrosion resistance. The application range of V4A (1.4571) covers, amongst others, the offshore sector, containers and pipes for chemical tankers, the storage of chemicals, the food industry and the pharmaceutical and paper industries.
V4A is similar to V2A stainless steel, but has an additional alloy content of 2% molybdenum. This results in a higher resistance to corrosion, even in media containing chloride. These properties of A4 stainless stee! make it suitable for use in extreme conditions, e.g. in the immediate vicinity of salt water. Due to the high salt content in the water and air in these environments, the material V2A is unsuitable and the more expensive use of V4A is mandatory.
A4 alloy fasteners are replacing more and more hot-dip galvanised fasteners on European motorways. Many noise barriers and guardrail systems around bridges are anchored . with A4 stainless steel threaded rods. The support systems of the pipes for the bridge drainage are also secured with A4.
Stainless steel in hygienic areas
The preferred application of stainless steel in hygienic areas is because the smooth, protective and stable chromium oxide layer. This layer ensures the corrosion resistance of stainless steels. Corrosion-resistant means that the base material is not attacked when in contact with food (e.g. fruit acids) and other environmental influences (e.g. oxygen and cleaning agents).
Another positive aspect for the use of stainless steel in the hygiene sector is its effect on food. It leaves no harmful substances or particle residues behind and thus does not lead to any contamination or alteration of the foodstuff. In addition, stainless steel is very easy to clean, which means that germs and bacteria have no surface to attack and hygiene conditions are optimal.
For most applications in the food sector, the austenitic stainless steel grades (1.4301, 1.4404) are highly suitable.
Duplex steels must often be used where very high corrosion is expected (e.g. high salt content in production processes such as salt curing etc).