Alloy, stainless, hardened steel and acid proof?
Here we explain a few basic concepts about steel.
What is steel?
Steel is a malleable material that consists mainly of iron, with carbon as the main alloying element.
Standard carbon steel has an iron content of at least 95% by weight and a carbon content of max. 2% by weight. Other commonly used elements include chromium, manganese, silicon, molybdenum and sulfur.
What is an alloy?
An alloy is a material consisting of at least two elements, one or more of which is typically metallic.
Alloy steel has one or more elements added to the basic material.
What is stainless steel?
Stainless steel refers to the types of steel that are alloyed primarily with chromium and nickel: the high content of chromium and nickel gives the steel properties that protect against corrosion (rust). Stainless steel has a chromium content of at least 10.5% by weight. A stainless steel used in fastening technology typically has a chromium content of 18% by weight and a nickel content of 8% by weight. Please note! Stainless steels also rust, but take much longer to do so than standard carbon steel.
What does it mean if a steel is acid proof?
Acid-proof steel refers to a stainless steel with a higher alloy content than traditional stainless steel.
An acid-proof steel typically contains molybdenum. The higher alloy content provides enhanced corrosion protection, which is why it is sometimes referred to as acid proof. ESSVE’s A4 steel is acid proof.
What do the terms C4, A2 and A4 mean?
As many of you may already know, these are designations for corrosion resistance classes: C4 is good, A2 better and A4 best
Our surface treated product is called CorrSeal and contains C4 class, meaning it withstands approx. 15 years of use outdoors, while A2 withstands up to 50 years in the same environment.
A4 is an acid-proof steel that is extremely resistant to rust. The more aggressive the environment, the better anti-corrosion protection you need. Aggressive environments include salt water, pools containing chlorine or detergents and chemicals. Flexibility is another factor influencing choice of screw and surface treatment. Flexibility is about how much the screw can be bent without breaking.
C4, CorrSeal, is made of hardened steel. The hardening makes the screw strong but not as flexible as our A2 and A4 stainless steel screws. Our A2 and A4 stainless steel screws are soft and able to absorb large movements without breaking. This is important when building structures that will be exposed to a lot of movement. Either when the timber moves a lot, due to the size of the structure, or at steps and railings that are subjected to a lot of stress.
What’s the difference between the stainless A2 and A4 alternatives?
The A4 steel is alloyed with molybdenum and the A2 steel is not; this gives A4 stronger corrosion protection than A2.
What does it mean if a steel is hardened?
Hardened steel has undergone heat treatment that transforms its surface from soft to hard. The process is designed to increase hardness, so the material can absorb more load on its surface and remain unaffected. Hardening does not affect core hardness. The purpose of a soft core structure is to allow the product to withstand a certain amount of movement without breaking, which is important for e.g. a decking screw.
Why are screws surface treated?
Surface treatments are mainly used on carbon steel, not stainless steel. Stainless steel is already sufficiently inert against corrosion. In addition to surface treatments providing protection against corrosion, this can also be done for aesthetic reasons, such as painted fastening. Standard carbon steel fastenings are often coated with zinc via processes such as electrogalvanisation or hot-dip galvanization. The surface layer of zinc protects the substrate (iron) against corrosion.
Zinc acts as a sacrificial anode to iron as it’s less noble.
What’s special about ESSVE’s CorrSeal surface treatment?
Our CorrSeal surface treatment consists of zinc and epoxy, which provide greater protection than ordinary electrogalvanisation or hot-dip galvanization.