Mechanical Properties for Stainless Steel Fasteners

Three 'property classes' are assigned to each of the austenitic stainless steel fastener grades. Table 1 shows the 0.2% proof stress, tensile strength and elongation values for each of these property classes.

This latest revision has removed the restrictions on the size of fastener (M24) for which the properties in table 1 can be guaranteed. However, there is a general clause which says that the standard is only applicable up to 39 mm diameter. Above that, the standard can still be used provided all parties agree that the properties can be achieved. The effect of these changes is to increase the maximum diameter on which the class 70 and 80 properties can be specified without discussion from 24 to 39 mm. This reflects the conservative nature of the previous 24 mm limit. Indeed, class 70 and 80 properties are available above 39 mm but this must always be discussed with the supplier. 

Property class 50 represents the steel in the annealed condition.

The most common and readily available supply condition is property class 70, which represents a 'cold drawn' for the bar stock from which the fasteners are made.

Property class 80 is based on severely hard cold drawn bar.

Some fasteners, depending on size and grade, can be supplied in an "unofficial" class A100 condition, i.e. with a minimum tensile strength of 1000 MPa.

All tensile stress values are calculated and reported in terms of the nominal tensile stress area of the thread.

The elongation measurement is determined on the actual bolt or screw length and not on a prepared test piece. It is expressed in millimetres (mm) of extension and not as percentage elongation, i.e. A = (L2 - L1) 
(where L1 = original length and L2 = length after fracture) 
d = nominal diameter of bolt, screw or stud

Notes

1. The tensile stress is calculated on the stress area
2. To be determined on the actual screw length and not on a prepared test piece.

1. The tensile stress is calculated on the stress area
2. To be determined on the actual screw length and not on a prepared test piece
3. Hardened and tempered at a minimum tempering temperature of 275 °C
4. Nominal thread diameter d ≤ 24 mm

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