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Have you also wondered what the difference is between A2, A4 and A5?

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Have you also wondered what the difference is between A2, A4 and A5?

Are there corresponding names in EN standard? And what is AISI?

Here we will try to clarify the concepts a bit. In everyday speech, stainless steel is referred to as A2 and stainless acid-resistant steel as A4, so A2 stands for stainless and A4 for stainless acid-resistant steel. But unfortunately that does not say everything about what kind of steel we are dealing with. Nor can it be directly translated into an EN standard*.

An A designation can include several types of steel, that designation has a broader meaning. Below is a small table of different A designations:

A1 – chrome/ nickel steel with sulfur vs machine steel 

A2 – chrome/ nickel-steel plain stainless 

A3 – chrome/ nickel steel stabilized with titanium, niobium and tantalum 

A4 – chrome/ nickel-steel with molybdenum 

A5 – chrome/ nickel steel with molybdenum stabilized with titanium, niobium and tantalum

An A2 screw can be made of EN 1.4301 or EN 1.4306. An A5 screw can be made of EN 1.4571 or EN 1.4580 In EN ISO 3506, A stands for austenitic**.

We delve into the EN designations are taken up another blog post.

* EN standard=European standard from CEN or CENELEC

(CEN=European Committee for Standardization. Prepares European standards for areas not covered by CENELEC and ETSI.)

(CENLEC=European Committee for Electrotechnical Standardization. Develops European standards in the field of electricity.)

**Austenite, Is a metallurgical term for one of three crystal structures that form under atmospheric pressure between 912 - 1394 °C. Austenite named after a British metallurgist, W.C. Roberts-Austen.

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