Mechanical properties of fasteners made of carbon steel and alloy steel ISO 898
| Metric/SAE Bolt Class | US Bolt Grade | Marking | Bolt Mateial | Bolt Diameter Size | Proof Strength N/mm2 | Yeild Strength N/mm2 | Tensile Strength N/mm2 |
|---|---|---|---|---|---|---|---|
| 4.6 | 2 | US-no marking | Low Carbon Steel | M5 to M36 | 225 | 240 | 400 |
| 4.8 | Low Carbon Steel | M1.6 to M16 | 310 | 340 | 420 | ||
| 5.8 | Low Carbon Steel | M5 to M24 | 380 | 420 | 520 | ||
| 8.8 | 5 | US-3 redial lines Metric – 8.8 | Medium Carbon Steel, Quenched and tempered | M1.6 to <M16 | 580 | 640 | 800 |
| 8.8 | 5 | US-3 redial lines Metric – 8.8 | Medium Carbon Steel, Quenched and tempered | M16 to M36 | 600 | 660 | 830 |
| 9.8 | Medium Carbon Steel, Quenched and tempered | M1.6 to M16 | 650 | 720 | 900 | ||
| 10.9 | 8 | US-6 redial lines Metric – 10.9 | Alloy Steel, Quenched and tempered | M5 to M36 | 830 | 940 | 1040 |
| 12.9 | Alloy Steel, Quenched and tempered | M5 to M36 | 970 | 1100 | 1220 |
1MPa = 1N/mm2 = 145 psi (pounds/inch2)
What is Tensile Strength of Bolt?
The maximum load in tension which a Bolt can withstand before breaking or fracturing.
What is Yield Strength of Bolt ?
The maximum load at which a Bolt exhibits a specific permanent deformation.
What is Proof Load of Bolt ?
An axial tensile load which a Bolt must withstand without evidence of any permanent set.
What is the meaning of 8.8 Class Bolt ?
In Matric form, bolt Class is defined by two numbers separated by dot.
1st number, i.e before the dot, indicates ultimate Tensile Strength in 100 MPa.
2nd number, i.e after the dot, indicates Yield Strength, by Ratio between Yield strength and ultimate Strength.
eg. 8,8 class bolts,
Ultimate Tensile Strength is 8×100=800 Mpa
Yield Strength is : 800 x 0.8 = 640 MPa