Extension Springs manufactured in Grade 8.8 Steel (class 8.8) are dimensioned to DIN 2097. The sections below give the mechanical and physical properties of the grade, its behavior in corrosive and elevated-temperature service, and the full size table.
Why Choose Grade 8.8 Steel for Extension Springs
The workhorse medium-carbon alloy grade for structural joints. For extension springs, this matters when requires plating (zinc) for corrosion protection is the primary requirement.
Mechanical & Physical Properties
| Grade designation | class 8.8 |
|---|---|
| Magnetic response | Magnetic |
| Service temperature | up to approx. +300 °C |
| Corrosion characteristic | Requires plating (zinc) for corrosion protection |
Corrosion Behavior in Service
Carbon and alloy steel extension springs require a coating for corrosion protection. Zinc plating (with or without passivation) is the most common; hot-dip galvanizing is used for outdoor structural service; black-oxide is mainly a tarnish-prevention finish for tool-room use.
Comparable Grades
For Extension Springs, class 10.9 or 12.9 is the comparable strength step. Move up when the joint preload approaches the proof load of the current class; move down when the joint is over-specified. For corrosion-critical service, switch to stainless A2 or A4.
Sizes of Extension Springs Available in Grade 8.8 Steel
| Wire dia d (mm) | Inner diameter Di (mm) | Outer diameter De (mm) | Free length Lo (mm) | Active coils n | Initial tension Fi (N) | Rate k (N/mm) | Material | Reference standard |
|---|---|---|---|---|---|---|---|---|
| 0.5 | 3.5 | 4.5 | 20 | 12 | 10 | 0.7 | Spring steel | DIN 2097 / EN 15800 |
| 0.6 | 4.5 | 5.7 | 25 | 12 | 15 | 1.2 | Spring steel | DIN 2097 / EN 15800 |
| 0.8 | 5.5 | 7.1 | 30 | 12 | 30 | 2.5 | Spring steel | DIN 2097 / EN 15800 |
| 1.0 | 7.0 | 9.0 | 40 | 15 | 45 | 3.5 | Spring steel | DIN 2097 / EN 15800 |
| 1.2 | 8.5 | 10.9 | 50 | 15 | 70 | 6.0 | Spring steel | DIN 2097 / EN 15800 |
| 1.5 | 11.0 | 14.0 | 60 | 15 | 100 | 8.0 | Spring steel | DIN 2097 / EN 15800 |
| 2.0 | 13.0 | 17.0 | 80 | 15 | 200 | 16.0 | Spring steel | DIN 2097 / EN 15800 |
| 2.5 | 17.0 | 22.0 | 100 | 15 | 380 | 30.0 | Spring steel | DIN 2097 / EN 15800 |
| 3.0 | 22.0 | 28.0 | 120 | 15 | 680 | 55.0 | Spring steel | DIN 2097 / EN 15800 |
| 4.0 | 28.0 | 36.0 | 160 | 15 | 1500 | 120.0 | Spring steel | DIN 2097 / EN 15800 |
| 5.0 | 36.0 | 46.0 | 200 | 15 | 2900 | 210.0 | Spring steel | DIN 2097 / EN 15800 |
| 6.0 | 46.0 | 58.0 | 250 | 15 | 5200 | 380.0 | Spring steel | DIN 2097 / EN 15800 |