How to choose a brand of stainless steel
The choice of stainless steel does not begin with the question "304 or 316", but with the conditions in which the product will work. Humidity, temperature, contact with salts and acids, mechanical stress, welding method, and even surface quality are important. In practice, metalworking and steelmaking show especially well that there is no universal stainless steel. A material that works well inside a dry room can quickly become pitted near the sea or in a process environment with chlorides.
Corrosion resistance to stainless steels is primarily due to chromium. With its sufficient content, a thin passive film forms on the surface, which separates the metal from the environment and is able to recover from minor damage under suitable conditions. But the word "stainless" does not mean "invulnerable." Aggressive chemical environment, high temperature, cracks, surface contamination and improper processing can destroy protection.
Stainless steel AISI 304
AISI 304 is one of the most common austenitic stainless steels. The European equivalent is usually designated EN 1.4301. The material has good corrosion resistance in a normal atmosphere and in many mildly aggressive environments, high ductility and good weldability. Therefore, 304 is widely used in food equipment, containers, kitchen appliances, architectural elements and a variety of industrial products.
For a dry room, an urban environment without heavy salt pollution and contact with food, 304 is often a reasonable choice. It makes no sense to overpay for more alloy steel where its additional properties are not used.
The weak point of 304 is media with a noticeable chloride content. Marine aerosol, salt water, and some process solutions and anti-icing reagents increase the risk of pitting and crevice corrosion. It is here that the usual rule "stainless steel does not rust" begins to give unpleasant failures.
When is it better to choose AISI 316
The main difference between AISI 316 and 304 is the presence of molybdenum. It increases resistance to local corrosion, especially in environments containing chlorides. The common low carbon 316L version conforms to EN 1.4404 and is often used in the chemical, food, pharmaceutical, medical equipment, pipe fittings, and tanks.
316 should be considered for outdoor structures near the sea, equipment that regularly comes into contact with salts, and technological installations with a more aggressive environment. But this brand is not an absolute protection either. At high concentrations
