Stainless steel qualities

Different types of stainless steel, more or less commonly used at Alinco and their application, organised according to AISI code

AISI 301 stainless steel

Is an austenitic, chromium-nickel stainless steel with unusually high uniform elongation when correct composition balance and deformation conditions are achieved. In practice, it is usually marketed in the form of spring steel and is generally supplied in thin sheets. It is suitable for extreme cold deformation. As a result of moderate to extreme cold deformation, its tensile strength increases significantly while retaining reasonable toughness. 301 grade is essentially non-magnetic in the annealed state, but becomes magnetic by cold working.

This property is usually not available for thin sheets in the traditional AISI 304 or 316 stainless steel grades, and we offer AISI 301 as an alternative.

AISI 303 stainless steel

303 and 303Se are easily machineable stainless steel grades that are close to AISI 304. These grades are never used in sheet metal processing, but sometimes requested on plans. In such a case, we always offer standard 304 or 316 stainless steel grades.

AISI 304 and 304L stainless steel

The most widely used stainless steel grade at Alinco and in the sheet metal processing industry.  It offers sufficient corrosion resistance for most indoor and non-aggressive applications. This grade is essentially non-magnetic in the annealed state, but can be made slightly magnetic by cold working. It is used extensively in mechanical engineering, in the food and pharmaceutical industry and in building applications such as handrails. The difference between 304 and 304L stainless steel types lies in the carbon content (L stands for low-carbon content). Lower carbon content minimises the risk of corrosion as a result of welding. For Alinco, the distinction is less relevant since – especially in the case of sheet metal – it only purchases the L variant. Nowadays, most sheet alloys also bear a double certification (i.e. both 304 and 304L stainless steel). AISI 304 is easy to work into an aesthetically pleasing finish.

AISI 309 stainless steel

Is an austenitic, chromium-nickel stainless steel grade with high heat resistance and is listed under the heat-resistant stainless steel grades as a result. It is widely used for draw welding wire, but also in the form of plate material for furnaces and the like. 309 grade is the cheapest among the current heat-resistant stainless steel types. The plates have a stainless steel colour, in contrast to the other common heat-resistant alloys which have a brown mill scale colour.

AISI 310, 310S and 314 stainless steel

These are also heat-resistant stainless steel grades. They are austenitic, chromium-nickel stainless steel grades with high heat resistance and greater strength at high temperature than the 309 alloys. They are essentially non-magnetic in both the annealed and cold-deformed states. The plates have a brown colour, which sometimes leads laypersons to believe that there are made from ordinary steel.

AISI 316 and 316L stainless steel

These grades are the more corrosion-resistant variants of 304(L) stainless steel. Here, too, the L stands for Low Carbon and has the same function as with AISI 304. In this grade also, we only purchase the L variant in the case of sheet material, and only plates of European origin. This is an austenitic, chromium-nickel-molybdenum stainless and heat-resistant steel alloy with corrosion properties that are superior to those of most other chromium-nickel steel grades. It is suitable for aggressive environments and products, construction (outdoor applications) and is also regularly used in the pharmaceutical and chemical industries. It is 1/4th to 1/3rd more expensive than AISI 304; apart from a higher resistance to corrosion, this stainless steel is of similar quality as 304 grade; it is also easy to work into an aesthetically pleasing finish.

AISI 321 and 321H stainless steel

AISI 321 is an austenitic, chromium-nickel stainless steel, similar to AISI 304 but with the addition of titanium to stabilise the carbon content. Originally, it was developed as a counterpart to 304L stainless steel which targeted the same goal with the Low carbon. It is used rather rarely. This type is recommended for components that are exposed to certain corrosive environments, and which are manufactured using welding and cannot be subsequently annealed. Another advantage is that it is a bit more heat resistant than AISI 304 and, because of that, fits between the conventional types of stainless steel grades and the heat-resistant ones and can withstand temperatures ranging between 425 and 900˚C in certain corrosive environments. This type of stainless steel is not (or is less) suited for an aesthetically pleasing finish. AISI 321H is a variant of 321 stainless steel with a carbon content kept between 0.04 and 0.10 percent to improve strength at high temperature. Both 321 and 321H are more difficult to weld.

AISI 400 series stainless steel

The whole 400 series stainless steel belongs to the ferritic stainless steel grades, which are not or hardly ever used in the conventional sheet metal processing industry. They are magnetic as a result and, as a rule, are viewed in the sheet metalworking industry as being of somewhat lesser quality because they are closer to ordinary steel. For this reason, they are usually somewhat more sensitive to corrosion, but also cheaper. This does not mean, however, that they don’t have specific uses in certain sectors. The only type of stainless steel in the 400 series that we use is the 430 grade.

AISI 430 stainless steel

This type of stainless steel is sufficiently corrosion resistant for most home and kitchen applications and is widely used in standard appliances, such as dishwashers, fryers, ovens and similar because of the lower cost involved. Its poor weldability is a disadvantage. At Alinco, we only use this stainless steel because of its magnetic properties, i.e. if a customer explicitly requests magnetic stainless steel or if we need a strike plate in a magnetic door catch fitted in a stainless steel cabinet, we sometimes use the 430 grade since we find it hard to use another type.