ISO 898-1 & 898-2 do not specify an exact grade of steel. Rather, they define the mechanical property requirements, the allowable range of chemical composition, and whether or not the fasteners must be quenched and tempered. For 898-1, Property Class 8.8, the allowable composition is as follows:
C = 0.25-0.55
P = 0.035 max
S = 0.035 max
B = 0.003 max
The C range is allowed to be 0.15-0.40 if alloying elements such as Mn, B, or Cr are used. The minimum tempering temperature is 425 C.
For 898-2, Property Class 8, the allowable composition is as follows:
C = 0.58 max
Mn = 0.25 min
P = 0.060 max
S = 0.150 max
For sizes below M16, the nuts do not need to be quenched and tempered.
