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A2 and A4 – what are we talking about?

A2 and A4 – what are we talking about?

5341 Views 126 Liked Posted on: November 17th 2019
By: Gunnar Marinethings

What is the difference between stainless (A2) and stainless acid resistant (A4)? What do the designations mean?

A, F and C

Screws and nuts are usually divided into three different categories; austenitic (A), ferritic (F) and martensitic (C). They can each be classified with a number between 1 and 5 where 5 stands for the highest corrosion protection and 1 for the lowest. The most common variants are A2 and A4, i.e. austenitic with corrosion protection** class 2 or 4.

50, 70 and 80

Another classification that occur are property classes or breaking strength classes. There we find 3 different categories; 50, 70 and 80. They tell how much breaking strength a nut or screw has. The higher the number, the higher the breaking strength***. It can look like this: A2-50 or A2-80, i.e. austenitic* with corrosion protection class 2 with breaking strength 50 and 80 respectively (80 has the highest breaking strength).

The numbers that name the corrosion resistance work opposite to breaking strength, 50 stands for a higher corrosion resistance than 70 which in turn has a higher resistance than 80 even though the latter are very similar in that respect.

* See link for explanation of austenitic.

** Corrosion protection. A material's ability to resist degradation by substances such as e.g. way. air pollution, sea water, soil, galvanic voltages, etc.

***The breaking strength or tensile strength is the maximum tension load a material can handle when stretched or pulled before waisting occurs, which means that the cross-section of the material is significantly reduced.

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Tags : A2, A4, Aisi304, Aisi316
Posted in: Om rostfritt

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