GARBA 177 Supreme

Precipitation hardenable stainless spring wire. Shaved and EC-tested*. For applications demanding superior fatigue properties

GARBA 177 Supreme® is a semi-austenitic precipitation-hardenable stain¬less steel, processed by ESR (Electro Slag Refining), which reduces the risk of harmful inclusions. The ESR process together with a shaved surface improves the fatigue resistance as compared to GARBA 177PH.

Chemical composition

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

Cleanliness in steel

The presence of non-metallic inclusions in the wire rod is
inspected for every heat in accordance with the Suzuki
Garphyttan method by the steel supplier.

For wire rod samples: Inclusion size max. 15 µm down to 1 mm below surface. Inspection area: 350 mm2.

Inclusion size, surface 5–10 > 10–15 >15 µm
Max. number of inclusions Max grade D3
acc. to JK scale*
20  0

* Method for assessment of the content of non-metallic inclusions. Swedish Standard SS 111116 – Microscopic methods – Jernkontoret’s inclusion chart II for the assessment of non-metallic inclusions.

Mechanical properties

For round wire

Diameter (mm) Tolerance (± mm) Tensile Strength (N/mm²) Tensile strength after heat treatment 480C 1h (N/mm²)
0.30 - 0.40 0.005 1885 - 2165 2205 - 2525
0.41 - 0.50 0.008 1860 - 2130 2180 - 2490
0.51 - 0.65 0.008 1810 - 2070 2130 - 2430
0.66 - 0.80 0.010 1810 - 2060 2130 - 2430
0.81 - 1.00 0.010 1780 - 2030 2100 - 2390
1.01 - 1.25 0.015 1720 - 1960 2040 - 2310
1.26 - 1.50 0.015 1670 - 1910 1990 - 2260
1.51 - 1.75 0.015 1610 - 1850 1910 - 2180
1.76 - 2.00 0.015 1570 - 1800 1900 - 2160
2.01 - 2.50 0.015 1540 - 1770 1860 - 2120
2.51 - 3.00 0.020 1500 - 1710 1820 - 2060
3.01 - 3.50 0.020 1400 - 1600 1660 - 1940
3.51 - 4.25 0.020 1350 - 1550 1620 - 1920
4.26 - 5.00 0.025 1310 - 1500 1580 - 1800
5.01 - 5.60 0.025 1300 - 1490 1550 - 1790

Surface conditions

Surface performance
AC-surface 0.30–5.60 mm Ø . The AC-coating can be removed before heat treatment by using a 10-20% nitric acid pickle at room temperature.

Surface condition

Surface condition – non-destructive testing
In the standard size range 2.00-5,60 mm the wire can be tested continuously in Eddy Current equipment to a surface level of >40 microns.

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.
Density: 7.90 kg/dm3.

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

Electro slag refining (ESR) process
For applications demanding superior fatigue properties


Electro Slag Refining (ESR) process
ESR process, see figure 1.
The ESR process gives a material with lower level of inclusions compared to a material not processed with ESR and in addition also a better segregation level.
Material properties achieved by ESR in combination with shaved wire surface and precipitation hardening result in superior fatigue resistance.

Shaved and Eddy Current tested

Suzuki Garphyttan uses the most advanced Eddy Current testing equip¬ment available on the market. Experience from many years of surface testing in efficient continuous testing lines is a guarantee for high quality spring wire.

Eddy Current testing is carried out on material with high demands on surface quality. EC-testing is performed with both rotating (R) and stationary (D) probe test equipment.

 Steel grade  Dimension, mm  ESR Shaved   Unshaved  RD40
 GARBA 177 Supreme®  0.30 – 1.99  x  -  -
 GARBA 177 Supreme®  2.00 – 5.60  x  x  -


Steel grade Dimension, mm ESR Shaved Unshaved RD40
GARBA 177 Supreme® 0.30 – 1.99 X X – –
GARBA 177 Supreme® 2.00 – 5.60 X X – X

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 Supreme® 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 177 Supreme® subjected to three different stress levels at different temperatures.