For extension springs in Grade 12.9 Steel, the controlling selection factors are corrosion exposure, strength requirement and service temperature. The grade data for Grade 12.9 Steel (class 12.9) is summarized below together with every size supplied.
Why Choose Grade 12.9 Steel for Extension Springs
The highest common strength class, for high-load machine assembly. For extension springs, this matters when requires plating or black-oxide protection is the primary requirement.
Mechanical & Physical Properties
| Grade designation | class 12.9 |
|---|---|
| Magnetic response | Magnetic |
| Service temperature | up to approx. +300 °C |
| Corrosion characteristic | Requires plating or black-oxide 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.
Galvanic & Galling Considerations
For extension springs in steel, the dominant compatibility issue is hydrogen embrittlement at high property classes (10.9 and above) when electroplated. Plating must be followed by an appropriate baking treatment, or a non-electroplated finish (mechanical zinc, zinc flake) should be substituted.
Sizes of Extension Springs Available in Grade 12.9 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 |