Due to the globalization of fasteners production, it’s important to understand the raw materials specifications. The ISO 898-1:2013, describes the raw materials for screws in steel. When analyzing different solutions, one of the key factors should be that steel quality. This difference will change the price levels, and can generate important issues on the final application. Bellow, we present the screw property class, the raw material used for each property and some characteristics.
ISO 898-1:2013 grade 8.8 Chemical Composition
Property class
Material and heat treatment
Chemical composition limit (cast analysis, %)a
Tempering temperature ⁰CMin.
C
P
S
Bb
min.
max.
max.
max.
max.
8.8
Carbon steel with additives (e.g. Boron or Mn or Cr) quenched and tempered
0,15e
0,40
0,025
0,025
0,003
425
Carbon steel quenched and tempered
0,25
0,55
0,025
0,025
Alloy steel quenched and temperedg
0,20
0,55
0,025
0,025
ISO 898-1:2013 Grade 8.8 Mechanical Properties
Mechanical or physical property
Tensile strength, Rm, MPa
Stress at 0,2 % non-proportional elongation, Rp0,2, MPa
Stress under proof load, Spf, MPa
Proof strength ratioSp,nom/ReL,min
Percentage elongation after fracture for machined test pieces, A, %
Percentage reduction of area after fracture for machined test pieces, Z, %
Height of non-decarburized thread zone, E, mm
Depth of complete decarburization in the thread, G, mm
