Stainless steels for fasteners: A2, A4, 1.4571 and special austenitic grades

Stainless steels contain at least 10.5% chromium, which forms a protective oxide layer on the surface. For fasteners, they are standardised in ISO 3506: steel group A2 (e.g. 1.4301, 1.4307) for general applications, A4 (e.g. 1.4401, 1.4571) with molybdenum for chloride-containing media and seawater, plus property classes 50, 70 and 80, which are achieved by work hardening. RS Randack also manufactures from martensitic grades such as 1.4057, from special austenitic grades such as 1.3974 and 1.4980, and from the martensitic precipitation-hardening steel 1.4534 for aerospace, marine and high-temperature applications.

What the property class means for stainless steel

A4-80 stands for steel group A4 with a minimum tensile strength of 800 MPa. Unlike quenched and tempered steels, the strength is not achieved by hardening but by work hardening of the material; for large sizes, A4-80 can therefore only be achieved to a limited extent. Hot forming eliminates the work hardening; A4-70 and A4-80 are therefore not forged but made from suitably work-hardened raw material, and the strength is verified on the test bar.

Special considerations in production

At RS Randack, austenitic steels are processed separately: dedicated containers, a cleaned saw, a new saw blade and fresh coolant, so that no foreign iron contaminates the surface and later causes rust staining. They tend to work-harden during machining and cause high tool wear; threads are rolled, which further increases the strength of the flanks. Crack testing is carried out using the dye penetrant method, because the material is non-magnetic.

What you should specify

Steel group and property class to ISO 3506 or material number, medium and service temperature, requirements for magnetic properties and crack testing, type of certificate.