OTEVA 101 SC

Oil tempered SiCrVMoW-alloyed ultra-high tensile clutch and transmission spring wire for surface nitriding.

OTEVA® 101 SC is a Super Clean steel, especially intended for the manufacture of clutch and transmission springs and other springs requiring high fatigue properties and good relaxation properties at increased working temperatures.

Manufactured as standard in shaved condition in sizes from Ø 2.00 mm to 5.00 mm or in egg or elliptical shape corresponding to round cross section 2.50 mm to 5.00 mm. Other wire sizes on request.

Chemical composition

C (%)	Si (%)	Mn (%)	P max. (%)	S max. (%)	Cr (%)	V (%)	Mo (%)	W (%)
0.50 - 0.70	2.10 - 2.40	0.30 - 0.70	0.020	0.030	1.10 - 1.40	0.05 - 0.25	0.05 - 0.25	0.05 - 0.25

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.

Before release for production, Suzuki Garphyttan performs non-metallic inclusion inspection for every fifth heat. The criteria for supplier inspection and releasing inspection are the following;

For wire rod samples: Inclusion size max. 15 µm down to 1 mm below surface. Inspection area 1 000 mm².

Inclusion size, surface	5–10	> 10–15	>15 µm
Max. number of inclusions	50	7	0

As stated by IVSWMA, International Valve Spring Wire Manufacturers Association, it is likely to find occasional inclusions in valve spring quality steel of a size larger than 30 µm.

Mechanical properties

For round wire

Diameter (mm)	Tolerance (mm)	Tensile Strength (N/mm²)	Torsions (l=300 mm, min. revs)	Reduct. of area (min. %)
2.00 - 2.50	±0.020	2100 - 2200	2	40
2.51 - 3.20	±0.020	2100 - 2200	2	40
3.21 - 4.00	±0.025	2100 - 2200	2	40
4.01 - 5.00	±0.025	2100 - 2200	2	40

Surface conditions

Surface condition

Surface condition – non-destructive testing
In the standard size range 2.00 - 5.00 mm the wire is tested continuously in Eddy Current equipment to a surface level of ≥ 40 microns. Other wire sizes on request.

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, 0.5% x wire diameter. No complete decarburization allowed.

Standards

Nearest equivalent standards

EN 10270-2

Recommendations

Heat treatment

As soon as possible after coiling, the springs should be stress relieved. Depending on nitriding temperature used later in the spring manufacturing process, this temperature may be decreased.

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.

Soft shot peening

Before the nitriding process a soft shot peening process shall be applied in order to remove the oxide layer on the spring wire surface.

Nitriding

Springs of OTEVA® 101 SC must be nitrided to obtain optimum fatigue and relaxation properties. Our recommendation is gas nitriding.

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.

For nitrided springs with an extremely hard surface zone, it is important to use a shot peening media with high hardness.

Shot peening of the inside of the spring coils is particularly critical.

Spring Conditions For Tests

Spring conditions for fatigue and relaxation tests (specially designed test spring) Diagram 1 and 2:
Wire diameter	Ø 3.85 mm
Diameter external	26.95
Spring length, I0	53.0
N active	4.15
Spring index	6.0
Stress relieving
Temperature	450°C (790 ±10 °F)
Time	30 minutes
Soft shot peened
Speed	20-30 m/s
Time	5 min
Shot size	0.8 mm
Nitriding	Gas nitriding
Temperature	450-470°C
Time	5-20 hours
Aim for surface hardness	Min. 850 Hv
Aim for core hardness	Min. 610 Hv
Compound (white) layer	Max. 1 µm.
Shot peening (triple shot peening for nitrided springs)
1st treatment	Pressure 0.3 MPa with RCW shoot size 0.6 mm (hardness 800 Hv) for 20 minutes.
2nd treatment	Pressure 0.3 MPa with RCW shoot size 0.25 mm (hardness 800 Hv) for 10 minutes.
3rd treatment	Pressure 0.2 MPa with fine shoot size (hardness 700 HV) for 10 minutes.
Aim for Almen arc-height	0.55 – 0.60 mm
Hot presetting	1500 N/mm2 (nitrided springs)
(theoretically set)	1300 N/mm2 (not nitrided springs)
Temperature	200°C (max. 250°C)
Time	10 minutes

Relaxation And Fatigue Properties

In diagram 1 the fatigue properties of this grade are illustrated in a Goodman-diagram, based on a special test spring design.

Diagram 2 shows the relaxation properties (loss of load) of nitrided springs made from OTEVA® 101 SC wire subjected to static compression at different temperatures, nitrided/not nitrided.

OTEVA 70 SC, OTEVA 70 SC PLUS

Oil tempered SiCr-alloyed valve spring wire

OTEVA® 70 SC is a Super Clean steel, especially intended for the manufacture of clutch/ transmission springs with extremely high fatigue properties and good relaxation properties at moderately increased working temperature. The wire is manufactured in shaved condition in sizes from Ø 0.50 mm to 10.0 mm, or in egg or elliptical shape corresponding to round cross section 2.50 mm to 6.50 mm Other wire sizes and shapes on request.

OTEVA® 70 SC PLUS is intended for manufacture of valve springs and other springs requiring extremely high fatigue properties and good relaxation properties at increased working temperatures. Further information about the approval process for OTEVA SC PLUS is found here.

Chemical composition

C (%)	Si (%)	Mn (%)	P max. (%)	S max. (%)	Cr (%)
0.50 - 0.60	1.20 - 1.60	0.50 - 0.80	0.025	0.020	0.50 - 0.80

Cleanliness in steel

The presence of non-metallic inclusions in the wire rod is inspected for every heat of OTEVA® 70 SCin accordance with the Suzuki Garphyttan method by the steel supplier.

Before release for production, Suzuki Garphyttan performs non-metallic inclusion inspection for every fifth heat. The criteria for supplier inspection and releasing inspection are the following;

For wire rod samples: Inclusion size max. 15 µm down to 1 mm below surface. Inspection area: 1 000 mm².

Inclusion size, surface	5-10 µm	>10-15 µm	>15 µm
Max. number of inclusions	50	7	0

For OTEVA 70 SC PLUS, every heat is inspected including a SEM-EDS analysis of inclusions > 10µm to verify a Super Clean composition.

As stated by IVSWMA, International Valve Spring Wire Manufacturers Association, it is likely to find occasional inclusions in valve spring quality steel of a size larger than 30 µm.

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 50 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		40
7.01 - 8.00	±0.045	1710 - 1810		40
8.01 - 9.00	±0.045	1660 - 1760		35
9.01 - 10.00	±0.050	1660 - 1760		35

Yield point

The proof stress R_p0.2 is min. 0.9 x tensile strength of the wire.

Surface conditions

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 to a surface level of ≥ 40 microns. For size range 6.01-8.60 mm is tested continuously in Eddy Current equipment to a surface level of ≥ 60 microns. Other wire sizes on request.

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 % x wire diameter. In shaved condition; for diameters <=2 .00 mm 10 µm, for diameters > 2.00 mm 0.5% x d. For diameters > 6.60-10.00 mm 0.7% x d.

Physical properties

E and G modulus of elasticity

206 kN/mm²

E and G modulus of shear

79.5 kN/mm²

Standards

Nearest equivalent steel grades

EN VDSiCr, SIS 142090-05

Nearest equivalent standards

EN 10270-2, ASTM A877 A, BS 2803 685A55HD, JIS G3561 SWOSC-V

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.

Spring Conditions For Tests

Spring conditions for fatigue and relaxation tests (specially designed test spring) Diagram 1 and 2:
Wire size	Ø 4.00 mm
Diameter external	28.00 mm
Spring length, l0	59.5 mm
N active	4.80
Spring index	6.0
Stress relieving
Temperature	420 ±5°C (790 ±10 °F)
Time	30 minutes
Shot peening	Speed 48 m/sec. for 20 minutes, size of shots 0.8 mm
Hardness of Shot-peening grit (shot):	610-670 Hv
Aim for Almen arc-height	Min. 0.40-0.45 mm
Hot presetting (theoretically set)	1200 N/mm2
Temperature	200°C (max. 250°C)
Time	10 minutes

Relaxation And Fatigue Properties

In diagram 1 the fatigue properties of this grade are illustrated in a Goodman-diagram, based on a special test spring design.

Diagram 2 shows the relaxation properties (loss of load) of springs made from OTEVA® 70 SC wire subjected to static compression at different temperatures.

Additional

Additional information

Delivery forms
See separate sheet.

OTEVA 75 SC, OTEVA 75 SC PLUS

Oil tempered SiCrV-alloyed high tensile valve spring wire

OTEVA® 75 SC is a Super Clean steel, especially intended for the manufacture of clutch/ transmission springs with extremely high fatigue properties and good relaxation properties at moderately increased working temperatures.

Manufactured as standard in shaved condition in sizes from Ø 1.60 mm to 10.0 mm, or in egg or elliptical shape corresponding to round cross section 2.50 mm to 6.50 mm. Other wire sizes and shapes on request.

OTEVA® 75 SC PLUS is intended for manufacture of valve springs and other springs requiring extremely high fatigue properties and good relaxation properties at increased working temperatures.

Further information about the approval process for OTEVA SC PLUS is found here.

Chemical composition

C (%)	Si (%)	Mn (%)	P max. (%)	S max. (%)	Cr (%)	V (%)
0.50 - 0.70	1.20 - 1.65	0.50 - 0.80	0.020	0.020	0.50 - 1.00	0.05 - 0.20

Cleanliness in steel

The presence of non-metallic inclusions in the wire rod is inspected for every heat of OTEVA® 75 SC in accordance with the Suzuki Garphyttan method by the steel supplier.

Before release for production, Suzuki Garphyttan performs non-metallic inclusion inspection for every fifth heat. The criteria for supplier inspection and releasing inspection are the following;

For wire rod samples: Inclusion size max. 15 µm down to 1 mm below surface. Inspection area: 1 000 mm².

Inclusion size, surface	5-10 µm	>10-15 µm	>15 µm
Max. number of inclusions	50	7	0

For OTEVA 75 SC PLUS, every heat is inspected including a SEM-EDS analysis of inclusions > 10µm to verify a Super Clean composition.

As stated by IVSWMA, International Valve Spring Wire Manufacturers Association, it is likely to find occasional inclusions in valve spring quality steel of a size larger than 30 µm.

Mechanical properties

For round wire

Diameter (mm)	Tolerance (mm)	Tensile Strength (N/mm²)	Torsions (l=300 mm, min. revs)	Reduct. of area (min. %)
1.60 - 2.00	±0.020	2160 - 2260	5	45
2.01 - 2.50	±0.020	2110 - 2210	5	45
2.51 - 3.20	±0.020	2060 - 2160	5	45
3.21 - 4.00	±0.025	2010 - 2110	4	45
4.01 - 5.00	±0.025	1960 - 2060	3	45
5.01 - 5.60	±0.030	1910 - 2010	3	40
5.61 - 6.00	±0.035	1910 - 2010	3	40
6.01 - 6.50	±0.035	1910 - 2010		35
6.51 - 7.00	±0.040	1910 - 2010		35
7.01 - 8.00	±0.045	1860 - 1960		35
8.01 - 9.00	±0.045	1860 - 1960		35
9.01 - 10.00	±0.050	1860 - 1960		35

Yield point

The proof stress R_p0.2 is min. 0.9 x tensile strength of the wire.

Surface conditions

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 to a surface level of ≥ 40 microns. For size range 6.01-8.60 mm is tested continuously in Eddy Current equipment to a surface level of ≥ 60 microns. Other wire sizes on request.

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 % x wire diameter. In shaved condi-tion; for diameters <=2 .00 mm 10 µm, for diameters > 2.00 mm 0.5% x d. For diameters > 6.60-10.00 mm 0.7% x d.

Physical properties

E and G modulus of elasticity

206 kN/mm²

E and G modulus of shear

79.5 kN/mm²

Standards

Nearest equivalent steel grades

EN VDSiCrV

Nearest equivalent standards

ASTM A877 B

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.

Spring Conditions For Tests

Spring conditions for fatigue and relaxation tests (specially designed test spring) Diagram 1 and 2:
Wire size	Ø 4.00 mm
Diameter external	28.00 mm
Spring length, l0	59.5 mm
N active	4.80
Spring index	6.0
Stress relieving
Temperature	420 ±5°C (790 ±10 °F)
Time	30 minutes
Shot peening (double shot peening)
1st treatment	Speed 56 m/sec. for 20 minutes, size of shots 0.8 mm
2nd treatment	Speed 30 m/sec. for 10 minutes, size of shots 0.8 mm
Hardness of Shot-peening grit (shot):	610-670 Hv
Aim for Almen arc-height	Min 0.45 mm
Hot presetting (theoretically set)	1300 N/mm²
Temperature	200°C (max. 250°C)
Time	10 minutes

Relaxation And Fatigue Properties

In diagram 1 the fatigue properties of this grade are illustrated in a Goodman-diagram, based on a special test spring design.

Diagram 2 shows the relaxation properties (loss of load) of springs made from OTEVA® 75 SC wire subjected to static compression at different temperatures.

OTEVA 90 SC, OTEVA 90 SC PLUS

Oil tempered SiCrVNi-alloyed ultra-high tensile valve spring wire for
surface nitriding

OTEVA® 90 SC is a Super Clean steel, especially intended for the manufacture of clutch/transmission springs with extremely high fatigue properties and good relaxation properties at increased working temperatures.

Manufactured as standard in shaved condition in sizes from Ø 2.00 mm to 6.00 mm, or in egg or elliptical shape corresponding to round cross section 2.50 mm to 6.00 mm. Other wire sizes on request.

OTEVA® 90 SC PLUS is intended for manufacture of valve springs and other springs requiring extremely high fatigue properties and good relaxation properties at increased working temperatures.

Further information about the approval process for OTEVA SC PLUS is found here.

Chemical composition

C (%)	Si (%)	Mn (%)	P max. (%)	S max. (%)	Cr (%)	V (%)	Ni (%)
0.50 - 0.70	1.80 - 2.20	0.70 - 1.00	0.020	0.020	0.85 - 1.05	0.05 - 0.15	0.20 - 0.40

Cleanliness in steel

The presence of non-metallic inclusions in the wire rod is inspected for every heat of OTEVA® 90 SC in accordance with the Suzuki Garphyttan method by the steel supplier.

Before release for production, Suzuki Garphyttan performs non-metallic inclusion inspection for every fifth heat. The criteria for supplier inspection and releasing inspection are the following;

For wire rod samples: Inclusion size max. 15 µm down to 1 mm below surface. Inspection area: 1 000 mm².

Inclusion size, surface	5-10 µm	>10-15 µm	>15 µm
Max. number of inclusions	50	7	0

For OTEVA 90 SC PLUS, every heat is inspected including a SEM-EDS analysis of inclusions > 10µm to verify a Super Clean composition.

As stated by IVSWMA, International Valve Spring Wire Manufacturers Association, it is likely to find occasional inclusions in valve spring quality steel of a size larger than 30 µm.

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 50 N/mm².
4) Torsion test is carried out 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. %)	Tensile strength after heat treatment 480C 1h (N/mm²)
2.00 - 2.50	±0.020	2180 - 2280	5	45	-
2.51 - 3.20	±0.020	2130 - 2230	5	45	5 -
3.21 - 4.00	±0.025	2080 - 2180	4	45	-
4.01 - 5.00	±0.025	2030 - 2130	3	45	-
5.01 - 5.60	±0.030	1980 - 2080	3	40	-
5.61 - 6.00	±0.035	1980 - 2080	3	40	-

Yield point

The proof stress R_p0.2 is min. 0.8 x tensile strength of the wire. The proof stress will rise above 0.9 x tensile strength after stress relieving the springs.

Surface conditions

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 to a surface level of ≥ 40 microns. Other wire sizes on request.

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 % x wire diameter. In shaved condi-tion; for diameters <=2 .00 mm 10 µm, for diameters > 2.00 mm 0.5% x d.

Physical properties

E and G modulus of elasticity

206 kN/mm²

E and G modulus of shear

79.5 kN/mm²

Standards

Nearest equivalent standards

ASTM A877 C

Recommendations

Heat treatment

As soon as possible after coiling, the springs should be stress relieved. Depending on nitriding temperature used later in the valve spring manufacturing process, this temperature may be decreased.

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.

Soft shot peening

Before the nitriding process a soft shot peening process shall be applied in order to remove the oxide layer on the spring wire surface.

Nitriding

Springs of OTEVA® 90 SC should be nitrided to obtain optimum fatigue and relaxation properties. Our recommendation is gas nitriding.

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.

For nitrided springs with an extremely hard surface zone, it is important to use a shot peening media with high hardness.

Shot peening of the inside of the spring coils is particularly critical.

Spring Conditions For Tests

Spring conditions for fatigue and relaxation tests (specially designed test spring) Diagram 1 and 2:
Wire size	Ø 3.85 mm
Diameter external	26.95 mm
Spring length, l0	53.0 mm
N active	4.15
Spring index	6.0
Stress relieving
Temperature	450 ±5 °C (840 ±10 °F) min. 420 °C (790 ±10 °F) for nitriding
Time	30 minutes
Soft shot peened
Speed	20-30 m/s
Time	5 min
Shot size	0.8 mm
Nitriding	Gas nitriding
Temperature	450-470°C
Time	5-20 hours
Aim for surface hardness	Min. 800 Hv
Aim for core hardness	Min. 560 Hv
Compound (white) layer	Max. 1 µm.
Shot peening (triple shot peening for nitrided springs)
1st treatment	Pressure 0.3 MPa (~60m/s)* with RCW shot size 0.6 mm (hardness 800 Hv) f or 20 minutes.
2nd treatment 3rd treatment Aim for Almen arc-height	Pressure 0.3 MPa (~60m/s)* with RCW shot size 0.25 mm (hardness 800 Hv) f or 10 minutes. Pressure 0.2 MPa (~40m/s)* with fine shot size (hardness 700 Hv) for 10 minutes. 0.55 – 0.60 mm
Hot presetting (theoretically set)	1500 N/mm² (nitrided springs) 1300 N/mm² (not nitrided springs)
Temperature	200°C (max. 250°C)
Time	10 minutes

* Pressure setting for an air blast system and the approximate corresponding shot speed for a centrifugal blast wheel (in brackets).

Relaxation And Fatigue Properties

In diagram 1 the fatigue properties of this grade are illustrated in a Goodman-diagram, based on a special test spring design.

Diagram 2 shows the relaxation properties (loss of load) of springs made from OTEVA® 90 SC wire subjected to static compression at different temperatures, nitrided/not nitrided.

OTEVA 91 SC

Oil tempered SiCrVMo-alloyed ultra-high tensile valve spring wire for surface nitriding

OTEVA® 91 SC is a Super Clean steel, especially intended for the manufacture of clutch/transmission springs with extremely high fatigue properties and good relaxation properties at increased working temperatures.
Manufactured as standard in shaved condition in sizes from Ø 2.00 mm to 10.0 mm, or in egg or elliptical shape corresponding to round cross section 2.50 mm to 6.00 mm. Other wire sizes on request.

OTEVA® 91 SC PLUS is intended for manufacture of valve springs and other springs requiring extremely high fatigue properties and good relaxation properties at increased working temperatures.

Further information about the approval process for OTEVA SC PLUS is found here.

Chemical composition

C (%)	Si (%)	Mn (%)	P max. (%)	S max. (%)	Cr (%)	V (%)	Mo (%)
0.50 - 0.70	1.80 - 2.20	0.30 - 0.60	0.020	0.025	0.80 - 1.00	0.05 - 0.15	0.05 - 0.15

Cleanliness in steel

The presence of non-metallic inclusions in the wire rod is inspected for every heat of OTEVA® 91 SC in accordance with the Suzuki Garphyttan method by the steel supplier.

Before release for production, Suzuki Garphyttan performs non-metallic inclusion inspection for every fifth heat. The criteria for supplier inspection and releasing inspection are the following;

For wire rod samples: Inclusion size max. 15 µm down to 1 mm below surface. Inspection area: 1 000 mm².

Inclusion size, surface	5-10 µm	>10-15 µm	>15 µm
Max. number of inclusions	50	7	0

For OTEVA 91 SC PLUS, every heat is inspected including a SEM-EDS analysis of inclusions > 10µm to verify a Super Clean composition.

As stated by IVSWMA, International Valve Spring Wire Manufacturers Association, it is likely to find occasional inclusions in valve spring quality steel of a size larger than 30 µm.

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 50 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. %)
2.00 - 2.50	±0.020	2180 - 2280	5	45
2.51 - 3.20	±0.020	2130 - 2230	5	45
3.21 - 4.00	±0.025	2080 - 2180	4	45
4.01 - 5.00	±0.025	2030 - 2130	3	45
5.01 - 5.60	±0.030	1980 - 2080	3	40
5.61 - 6.00	±0.035	1980 - 2080	3	40
6.01 - 7.00	±0.040	1910 - 2010		35
7.01 - 8.00	±0.045	1860 - 1960		35
8.01 - 9.00	±0.045	1860 - 1960		35
9.01 - 10.00	±0.050	1860 - 1960		35

Yield point

The proof stress R_p0.2 is min. 0.8 x tensile strength of the wire. The proof stress will rise above 0.9 x tensile strength after stress relieving the springs.

Surface conditions

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 to a surface level of ≥ 40 microns. For size range 6.01-8.60 mm is tested continuously in Eddy Current equipment to a surface level of ≥ 60 microns. Other wire sizes on request.

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 decarburiza-tion and surface defects, 1 % x wire diameter. In shaved condition; for diameters <=2 .00 mm 10 µm, for diameters > 2.00 mm 0.5% x d. For diameters > 6.60-10.00 mm 0.7% x d.

Physical properties

E and G modulus of elasticity

206 kN/mm²

E and G modulus of shear

79.5 kN/mm²

Standards

Nearest equivalent standards

ASTM A877 D

Recommendations

Oil tempered SiCrVMo-alloyed ultra-high tensile valve spring wire for surface nitriding

Heat treatment

As soon as possible after coiling, the springs should be stress relieved. Depending on nitriding temperature used later in the valve spring manufacturing process, this temperature may be decreased.

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.

Soft shot peening

Before the nitriding process a soft shot peening process shall be applied in order to remove the oxide layer on the spring wire surface.

Nitriding

Springs of OTEVA® 91 SC should be nitrided to obtain optimum fatigue and relaxation properties. Our recommendation is gas nitriding.

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.

For nitrided springs with an extremely hard surface zone, it is important to use a shot peening media with high hardness. Shot peening of the inside of the spring coils is particularly critical.

Spring Conditions For Tests

Spring conditions for fatigue and relaxation tests (specially designed test spring) Diagram 1 and 2:
Wire size	Ø 3.85 mm
Diameter external	26.95 mm
Spring length, l0	53.0 mm
N active	4.15
Spring index	6.0
Stress relieving
Temperature	450 ±5 °C (840 ±10 °F) min. 420 °C (790 ±10 °F) for nitriding
Time	30 minutes
Soft shot peened
Speed	20-30 m/s
Time	5 min
Shot size	0.8 mm
Nitriding	Gas nitriding
Temperature	450-470°C
Time	5-20 hours
Aim for surface hardness	Min. 800 Hv
Aim for core hardness	Min. 560 Hv
Compound (white) layer	Max. 1 µm.
Shot peening (triple shot peening for nitrided springs)
1st treatment	Pressure 0.3 MPa (~60m/s)* with RCW shot size 0.6 mm (hardness 800 Hv) for 20 minutes.
2nd treatment 3rd treatment Aim for Almen arc-height	Pressure 0.3 MPa (~60m/s)* with RCW shot size 0.25 mm (hardness 800 Hv) for 10 minutes. Pressure 0.2 MPa (~40m/s)* with fine shot size (hardness 700 Hv) for 10 minutes. 0.55 – 0.60 mm
Hot presetting (theoretically set)	1500 N/mm² (nitrided springs) 1300 N/mm² (not nitrided springs)
Temperature	200°C (max. 250°C)
Time	10 minutes

* Pressure setting for an air blast system and the approximate corresponding shot speed for a centrifugal blast wheel (in brackets).

Relaxation And Fatigue Properties

In diagram 1 the fatigue properties of this grade are illustrated in a Goodman-diagram, based on a special test spring design.

Diagram 2 shows the relaxation properties (loss of load) of springs made from OTEVA® 91 SC wire subjected to static compression at different temperatures, nitrided/not nitrided.

OTEVA 96 SC, OTEVA 96 SC PLUS

Oil tempered SiCrVMo-alloyed ultra-high tensile valve spring wire for
surface nitriding

OTEVA® 96 SC is a Super Clean steel, especially intended for the manufacture of clutch/transmission springs with extremely high fatigue properties and good relaxation properties at increased working temperatures.

Manufactured as standard in shaved condition in sizes from Ø 2.00 mm to 6.00 mm, or in egg or elliptical shape corresponding to round cross section 2.50 mm to 6.00 mm. Other wire sizes on request.

OTEVA® 96 SC PLUS is intended for manufacture of valve springs and other springs requiring extremely high fatigue properties and good relaxation properties at increased working temperatures.

Further information about the approval process for OTEVA SC PLUS is found here.

Chemical composition

C (%)	Si (%)	Mn (%)	P max. (%)	S max. (%)	Cr (%)	V (%)	Mo (%)
0.60 - 0.70	2.00 - 2.20	0.30 - 0.60	0.020	0.025	0.90 - 1.00	0.10 - 0.15	0.10 - 0.15

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.

Before release for production, Suzuki Garphyttan performs non-metallic inclusion inspection for every fifth heat. The criteria for supplier inspection and releasing inspection are the following;

For wire rod samples: Inclusion size max. 15 µm down to 1 mm below surface. Inspection area 1 000 mm².

Inclusion size, surface	5-10 µm	>10-15 µm	>15 µm
Max. number of inclusions	50	7	0

For OTEVA 96 SC PLUS, every heat is inspected including a SEM-EDS analysis of inclusions > 10µm to verify a Super Clean composition.

As stated by IVSWMA, International Valve Spring Wire Manufacturers Association, it is likely to find occasional inclusions in valve spring quality steel of a size larger than 30 µm.

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 50 N/mm².
4) Torsion test is carried out 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. %)
2.00 - 2.50	±0.020	2180 - 2280	5	45
2.51 - 3.20	±0.020	2130 - 2230	5	45
3.21 - 4.00	±0.025	2080 - 2180	4	45
4.01 - 5.00	±0.025	2030 - 2130	3	45
5.01 - 5.60	±0.030	1980 - 2080	3	40
5.61 - 6.00	±0.035	1980 - 2080	3	40

Yield point

The proof stress R_p0.2 is min. 0.8 x tensile strength of the wire. The proof stress will rise above 0.9 x tensile strength after stress relieving the springs.

Surface conditions

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 to a surface level of ≥ 40 microns. Other wire sizes on request.

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 % x wire diameter. In shaved condition; for diameters <=2 .00 mm 10 µm, for diameters > 2.00 mm 0.5% x d.

Physical properties

E and G modulus of elasticity

206 kN/mm²

E and G modulus of shear

79.5 kN/mm²

Standards

Nearest equivalent standards

EN 10270-2

Recommendations

Heat treatment

As soon as possible after coiling, the springs should be stress relieved. Depending on nitriding temperature used later in the valve spring manufacturing process, this tem-perature may be decreased.

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.

Soft shot peening

Before the nitriding process a soft shot peening process shall be applied in order to remove the oxide layer on the spring wire surface.

Nitriding

Springs of OTEVA® 96 SC should be nitrided to obtain optimum fatigue and relaxation properties. Our recommendation is gas nitriding.

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.
For nitrided springs with an extremely hard surface zone, it is important to use a shot peening media with high hardness.
Shot peening of the inside of the spring coils is particularly critical.

Spring Conditions For Tests

Spring conditions for fatigue and relaxation tests (specially designed test spring) Diagram 1 and 2:
Wire size Diameter external Spring length, l0 N active	Ø 3.85 mm 26.95 mm 53.0 mm 4.15
Spring index	6.0
Stress relieving
Temperature	450 ±5 °C (840 ±10 °F) min. 420 °C (790 ±10 °F) for nitriding
Time	30 minutes
Soft shot peened
Speed	20-30 m/s
Time	5 min
Shot size	0.8 mm
Nitriding	Gas nitriding
Temperature	450-470°C
Time	5-20 hours
Aim for surface hardness	Min. 800 Hv
Aim for core hardness	Min. 560 Hv
Compound (white) layer	Max. 1 µm.
Shot peening (triple shot peening for nitrided springs)
1st treatment	Pressure 0.3 MPa (~60m/s)* with RCW shot size 0.6 mm (hardness 800 Hv) for 20 minutes.
2nd treatment 3rd treatment Aim for Almen arc-height	Pressure 0.3 MPa (~60m/s)* with RCW shot size 0.25 mm (hardness 800 Hv) for 10 minutes. Pressure 0.2 MPa (~40m/s)* with fine shot size (hardness 700 Hv) for 10 minutes.. 0.55 – 0.60 mm
Hot presetting (theoretically set)	1500 N/mm² (nitrided springs) 1300 N/mm² (not nitrided springs)
Temperature	200°C (max. 250°C)
Time	10 minutes

* Pressure setting for an air blast system and the approximate corresponding shot speed for a centrifugal blast wheel (in brackets).

Relaxation And Fatigue Properties

In diagram 1 the fatigue properties of this grade are illustrated in a Goodman-diagram, based on a special test spring design.

Diagram 2 shows the relaxation properties (loss of load) of springs made from OTEVA® 96 SC wire subjected to static compression at different temperatures, nitrided/not nitrided.