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