BS EN ISO 3506-1

Mechanical properties of corrosion-resistant stainless steel fasteners
Part 1: Bolts, screws and studs

Steel grade

A

for austenitic steel

C

for martensitic steel

  • can be hardened to an excellent strength

F

for ferritic steel

  • Cannot normally be hardened and should not be even if possible in certain cases.
  • Are magnetic

A5

  • Similar to A4, but stabilised.
    Can thus be used in high temp. applications

A1

  • Designed for machining
  • Has higher sulphur content and therefore lower corrosion resistance

A4 or A4L

  • "Acid proof steel"
  • Molybdenum alloyed
  • Has better corrosion resistance. Is to a certain extent suitable in an environment with chloride content.

A3

  • Similar to A2, but stabilised.
    Can thus be used in high temp. applications

A2 or A2L

  • Most commonly used.
    Not suitable for use in non-oxidizing acid and agents with chloride content
    -L for low carbon steel

C1

  • Have limited corrosion resistance
  • Are used in turbines, pumps and knives

C3

  • Have slightly better corrosion resistance than C1
  • Used in pumps and valves

C3

-Similar to C1
-Intended for machining

F1

  • Are normally used for simpler equipment.
  • F1 can, if need be, replace steels of grade A2 and A3 and be used in an environment with a higher chloride content

FA

May be included later
Are duplex steels. Have better properties than A4 and A5, especially concerning strength. Exhibit superior resistance to pitting and crack corrosion

Property class

A

50

Soft

70

Cold worked

80

High-strength

C1

50

Soft

70

Hardened and tempered

110

Hardened and tempered

C3

80

Hardened and tempered

C4

50

Soft

70

Hardened and tempered

F1

45

Soft

60

Cold worked

Marking

  1. Manufacturer's identification mark
  2. Steel grade
  3. Property class

Fasteners that do not fulfill the tensile or torsional requirements because of the geometry may
be marked with the steel grade, but shall not be marked with the property class

Passivation

See ISO 16048
For maximum corrosion resistance, passivation is recommended. Fasteners may be marked with the symbol "P" after the symbols for steel grade and property class