STATO 70

Oil tempered SiCr-alloyed spring wire

STATO 70 is especially intended for the manufacture of springs exposed to static or moderately high fatigue stresses. The material has good relaxation properties.

The wire is manufactured in sizes from Ø 0.50 mm to 7.00 mm. Other wire sizes on request.

Chemical composition

C (%) Si (%) Mn (%) P max. (%) S max. (%) Cr (%)
0.50 - 0.60 1.20 - 1.60 0.50 - 0.80 0.025 0.025 0.50 - 0.80

Mechanical properties

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 70 N/mm2.

For round wire

Diameter (mm) Tolerance (± mm) Tensile Strength (N/mm²) Reduct. of area (min. %)
0.50 - 0.80 0.010 2100 - 2300
0.81 - 1.00 0.015 2100 - 2300 50
1.01 - 1.40 0.020 2060 - 2260 50
1.41 - 1.60 0.020 2040 - 2220 50
1.61 - 2.00 0.025 2000 - 2180 40
2.01 - 2.50 0.025 1970 - 2140 50
2.51 - 2.70 0.025 1950 - 2100 50
2.71 - 3.00 0.030 1910 - 2100 50
3.01 - 3.50 0.030 1900 - 2060 45
3.51 - 4.00 0.030 1870 - 2030 45
4.01 - 4.50 0.035 1860 - 2020 45
4.51 - 5.00 0.035 1830 - 1980 45
5.01 - 5.60 0.035 1800 - 1950 40
5.61 - 6.50 0.040 1780 - 1930 40
6.51 - 7.00 0.040 1740 - 1890 35

Yield point

The proof stress Rp0.2 is min. 0.9 x tensile strength of the wire.

Surface conditions

Surface condition

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, 1.5% x wire diameter. No complete decarburization allowed.

Physical properties

E and G modulus of elasticity

206 kN/mm²

E and G modulus of shear

79.5 kN/mm²

Recommendations

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.