Stainless Steel A2 and A4: Differences and Characteristics
Most stainless steel products, screws, and bolts on the market are manufactured in stainless steel A2 and A4. For this reason, we have decided to describe in this article, the world of stainless steel and its variations.
The main material used for the production of screws, bolts, and fastening elements, stainless steel is the material with which the hardware used in many industrial sectors is produced. Indeed, almost all hardware products are made of steel given the numerous advantages that this material offers. For this reason, it's important to know its characteristics, in order to fully utilize its potential.
What's the difference between steel and stainless steel?
The first important distinction to be made is between normal steel and stainless steel. Generally, steel is a ferrous alloy composed mainly of iron and carbon, produced in steel mills. This material also contains other elements that, depending on the percentages in which they appear, determine its chemical and structural composition. For example, stainless steel is composed of 50% iron and 12% chromium. It's precisely the presence of chromium that provides a particular resistance to corrosion of the material, the main advantage of its use.
Stainless steel also contains further amounts of carbon, silicon, and manganese. The ratio between these parts allows the material to be divided into 4 different types:
Ferritic stainless steels
Martensitic stainless steels
Austenitic-ferritic (or duplex) stainless steels
Austenitic stainless steels.
The last category is commonly known as stainless steel A2 and A4, materials whose characteristics and differences we will define in the next paragraph.
What is the difference between stainless steel A2 and A4?
As already anticipated in the previous paragraph, stainless steel A2 and stainless steel A4 products are used in all sectors given their numerous advantages: corrosion resistance, good polishability, and high hygiene coefficient. Such products are also widely used in internal processes because, for example, unlike galvanized steel products, they do not have a very high electrical potential and thus the risk of electrochemical corrosion (caused by contact with moisture) is very low.
The non-corrosive nature of A2 or A4 steel gives this material a very wide applicability: from the automotive sector, to the marine sector, to architecture, manufacturing industry, and DIY.
At this point, it seems natural to ask: what is the difference between stainless steel A2 and A4? The two materials have no visible difference, however, some characteristics make them different:
A2 is mainly used in the chemical and food industry;
A4, also known as marine stainless steel, is widely used in shipbuilding due to its resistance to salt fog.
Screws and bolts in stainless steel A2 and A4
In the previous section, we highlighted the various applications of A2 and A4 stainless steel products. Naturally, by "products," we're referring to A2 and A4 steel bolts and screws. With the wide array of sectors comes an equally wide range of opinions on which type of stainless steel to use in a practical manner.
Choosing the right type depends on the needs and final use of the product. An important point not to be overlooked is the certifications. Indeed, whether we're talking about threaded bars, self-locking nuts, washers, circlips, threaded inserts, taper or conical pins, or self-tapping screws, what matters is that they comply with UNI, DIN, and ISO standards.
Those faced with choosing between A2 or A4 hardware products will undoubtedly encounter the AISI 304 and AISI 316 designations. Indeed, one of the most frequent queries relates to the meaning of these acronyms. In the realm of stainless steel, AISI 304 and AISI 316 are the two most widespread and common types. Both are part of the austenitic steel family and are distinguished by the presence of Molybdenum, a chemical element from which corrosion resistance is derived.
AISI 316 contains a high concentration of Molybdenum and is characterized by its high corrosion resistance, even at high temperatures;
AISI 304 has a lower concentration of Molybdenum and is generally used at lower temperatures.
In the stainless steel hardware sector, products AISI 304 and AISI 316 are thus described using a parallel nomenclature: A2 and A4, respectively.
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