GARBA 177 PH

Precipitation hardenable stainless spring wire.
For applications demanding medium fatigue properties.

GARBA 177PH is a semi-austenitic precipitation-hardenable stainless steel with high relaxation resistance at elevated temperatures and excellent fatigue properties. This material has good formability and good form stability during the precipitation hardening heat treatment and a moderate level of corrosion resistance.

Chemical composition

C (%) Si (%) Mn (%) P max. (%) S max. (%) Cr (%) Al (%) Ni (%)
0.09 0.70 1.00 0.040 0.015 16.00 - 18.00 0.70 - 1.50 6.50 - 7.80

Mechanical properties

For round wire

Diameter (mm) Tolerance (± mm) Tensile Strength (N/mm²) Tensile strength after heat treatment 480C 1h (N/mm²)
0.30 - 0.65 0.005 - -
0.66 - 1.01 0.008 - -
1.02 - 2.26 0.012 - -
2.27 - 4.01 0.015 - -
4.02 - 6.26 0.020 - -
6.27 - 8.00 0.025 - -
0.30 - 0.40 1925 - 2213 2225 - 2525
0.41 - 0.50 1900 - 2185 2200 - 2500
0.51 - 0.65 1850 - 2127 2150 - 2450
0.66 - 0.80 1825 - 2099 2125 - 2425
0.81 - 1.00 1800 - 2070 2100 - 2400
1.01 - 1.25 1750 - 2012 2050 - 2350
1.26 - 1.50 1700 - 1955 2000 - 2300
1.51 - 1.75 1650 - 1897 1950 - 2250
1.76 - 2.00 1600 - 1840 1900 - 2200
2.01 - 2.50 1550 - 1782 1850 - 2150
2.51 - 3.00 1500 - 1725 1800 - 2100
3.01 - 3.50 1450 - 1667 1750 - 2050
3.51 - 4.25 1400 - 1610 1700 - 2000
4.26 - 5.00 1350 - 1552 1650 - 1950
5.01 - 6.00 1300 - 1495 1550 - 1850
6.01 - 8.00 1250 - 1437 1500 - 1800

Surface conditions

Surface performance
AC-surface 0.30–8.00 mm Ø.
The AC-coating can be removed before heat treatment by using a 10-20% nitric acid pickle at room temperature.

Physical properties

E and G modulus of elasticity

Abt. 190 kN/mm2 in drawn condition.
Abt. 200 kN/mm2 after heat treatment.

E and G modulus of shear

Abt. 73 kN/mm2 in drawn condition.
Abt. 78 kN/mm2 after heat treatment.

Heat conductivity

Temperature oC 20 100 300
W/(m* oC) 15.0 15.5 19.0

Resistivity

Temperature oC 20 100 200 300
nΩm 900 950 1000 1050

Linear expansion

Pro oC <30-100 30-200 30-300
x10-6 13.0 13.5 14.0

Specific heat capactity

Temperature oC 100 200
J/(kg* oC) 480 520

Recommendations

Heat treatment

Normal procedure for precipitation hardening is heat treatment at 480oC (896oF) for 1 hour and then air cooling. This should be done as soon as possible after spring coiling.  The tensile strength of the wire before and after this treatment is given in the table in previous page.

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.

Relaxation And Fatigue Properties

In diagram 1 the fatigue properties of GARBA 177 PH is illustrated in a Goodman-diagram, based on a special test spring design.

Diagrams 2-3 show the relaxation properties (loss of load) of springs made from GARBA 177PH subjected to three differ-ent stress levels at different temperatures.