70 KD
Oil tempered SiCr-alloyed clutch and transmission spring wire
70 KD is especially intended for the manufacture of clutch and transmission springs and similar moderately high fatigue stressed springs. 70 KD S is a shaved version of 70 KD intended for applications with higher surface requirements. The material has good relaxation properties. The wire is manufactured in sizes from Ø 0.50 to 7.00 mm. Sizes from Ø 7.00 to 15.00 mm is manufactured in unshaved version. Other wire sizes and shapes on request.
| C (%) | Si (%) | Mn (%) | P max. (%) | S max. (%) | Cr (%) |
|---|---|---|---|---|---|
| 0.50 - 0.60 | 1.20 - 1.60 | 0.50 - 0.80 | 0.025 | 0.020 | 0.50 - 0.80 |
Cleanliness in steel
Non-metallic inclusions:
Max. level 2 according to DIN 50602-M.
Corresponding standard: ASTM E-45-A.
1) Other wire sizes on request.
2) Ovality, i. e. the difference between the largest and smallest dimension of a cross section, is maximum half the tolerance range.
3) Conversion from tensile strength to hardness values can be calculated in standard ISO EN 18265. The tensile strength Rm within one coil does not vary more than 60 N/mm2.
4) Torsion test is carried out at ≤ 6.0 mm for assessing deformability. The fracture of the torsion test piece shall be smooth and perpendicular to the wire axis. The rupture shall show no longitudinal cracks.
For round wire
| Diameter (mm) | Tolerance (mm) | Tensile Strength (N/mm²) | Torsions (l=300 mm, min. revs) | Reduct. of area (min. %) |
|---|---|---|---|---|
| 0.50 - 0.80 | ±0.010 | 2080 - 2210 | 6 | |
| 0.81 - 1.30 | ±0.015 | 2080 - 2210 | 5 | 50 |
| 1.31 - 1.40 | ±0.015 | 2080 - 2210 | 5 | 50 |
| 1.41 - 1.60 | ±0.020 | 2080 - 2210 | 5 | 50 |
| 1.61 - 2.00 | ±0.020 | 2010 - 2160 | 5 | 50 |
| 2.01 - 2.50 | ±0.020 | 1960 - 2060 | 5 | 50 |
| 2.51 - 3.00 | ±0.020 | 1910 - 2010 | 4 | 50 |
| 3.01 - 3.20 | ±0.020 | 1910 - 2010 | 4 | 45 |
| 3.21 - 3.50 | ±0.025 | 1910 - 2010 | 4 | 45 |
| 3.51 - 4.50 | ±0.025 | 1860 - 1960 | 4 | 45 |
| 4.51 - 5.00 | ±0.025 | 1810 - 1910 | 3 | 45 |
| 5.01 - 5.60 | ±0.030 | 1810 - 1910 | 3 | 40 |
| 5.61 - 6.00 | ±0.035 | 1760 - 1860 | 3 | 40 |
| 6.01 - 6.50 | ±0.035 | 1760 - 1860 | 40 | |
| 6.51 - 7.00 | ±0.040 | 1710 - 1810 | 30 | |
| 7.01 - 8.00 | ±0.045 | 1710 - 1810 | 30 | |
| 8.01 - 9.00 | ±0.045 | 1660 - 1760 | 30 | |
| 9.01 - 10.00 | ±0.050 | 1660 - 1760 | 30 | |
| 10.01 - 12.00 | ±0.060 | 1610 - 1760 | 30 | |
| 12.01 - 15.00 | ±0.060 | 1610 - 1760 | 30 |
Yield point
The proof stress Rp0.2 is min. 0.9 x tensile strength of the wire.
Surface condition – non-destructive testing
In the standard size range 2.00 - 6.00 mm the wire is tested continuously in Eddy Current equipment ; for 70 KD a level of 60 microns and for 70 KD S of 40 microns. For 70 KDS diameter 6.60-8.60 mm, 60 microns. For size range 6.01-8.60 mm unshaved is tested continuously in Eddy Current equipment to a surface level of ≥ 80 microns. For diameter 6.60 - 8.60 unshaved 80 microns. For diameter 2.70-15.00 mm unshaved 100 microns.
Surface condition – end sample test
The wire is end sample tested by means of etch testing and binocular inspection as well as microscopical inspection of the material structure. Max. permissible depth of partial surface decarburization and surface defects, 1.3% x wire diameter. No complete decarburization allowed.
Surface condition
Surface condition – non-destructive testing
In the standard size range 2.00 - 6.00 mm the wire is tested continuously in Eddy Current equipment ; for 70 KD a level of 60 microns and for 70 KD S of 40 microns. For 70 KDS diameter 6.60-8.60 microns. For size range 6.01-8.60 mm unshaved is tested continuously in Eddy Current equipment to a surface level of ≥ 80 microns. For diameter 6.60 - 8.60 unshaved 80 microns. For diameter 2.70-15.00 mm unshaved 100 microns.
Surface condition – end sample test
The wire is end sample tested by means of etch testing and binocular inspection as well as microscopical inspection of the material structure. Max. permissible depth of partial surface decarburization and surface defects, 1.3% x wire diameter. No complete decarburization allowed.
E and G modulus of elasticity
206 kN/mm²
E and G modulus of shear
79.5 kN/mm²
Heat treatment
As soon as possible after coiling, the springs should be stress relieved.
Hot presetting
After shot peening, the springs should be hot preset or stress relieved. In order to reach optimum fatigue and relaxation properties, the springs must be preset at an appropriate stress.
Shot peening
In order to obtain optimum fatigue properties, the process time should be adjusted to get a complete treatment. Size of shots should be adapted to wire dimension, pitch and shot peening equipment. Shot peening of the inside of the spring coils is particularly critical.