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Technical Data

austenitic stainless steels; best for corrosion resistance and most commonly used for the production of standard fasteners.

The International Organisation for Standardisation (ISO) published in May 1979 a specification (Standard 3506) for stainless steel fasteners. This defines a four digit product designation.

The first digit indicates the general classification of the steel:

A = austenitic

The second digit indicates the type of alloying elements:

A2 = austenitic 18/8 type (not free machining types), (18% Chromium & 8% Nickel). Also known as 304 S15 (formerly EN 58E) to BS 970

A4 = austenitic 18/10/3 type (18% Chromium, 10% Nickel & 3% Molybdenum). Also known as 316 S31.

The third & fourth digits indicate the strength (mechanical property) class and represent one tenth of the tensile strength expressed in Newtons per millimetres squared (N/mm2):

50 = lowest strength class which is usually for products of softened steel & with machined (cut) threads.

70 = higher strength class resulting from cold drawing.

80 = highest strength attainable by multiple cold drawing.

Thus A2-70 = austenitic 18/8 class 70 cold drawn with a minimum tensile strength of 700 N/mm2.

A2 & A4 are the most common steel grades used for fasteners. Generally A4 has better corrosion resistance especially for marine applications, although it is advisable to be fully aware of the application when giving advice.

• Ferritic stainless steels; not as good as austenitic stainless steels for corrosion resistance but good strength properties.

• Martensitic stainless steels; high strength, not as good or as versatile as austenitic and ferritic stainless steels.

Tensile Testing
Tensile Testing
Tensile Testing