Steel FDSiCr OT-HEAVY
Heat-treated state
Large suspension/clutch springs; strength drops with section but relaxation resistance is retained.
Values for the OT-HEAVY condition
Other FDSiCr tempers and conditions
FDSiCr is listed in 6 conditions; see the grade overview at FDSiCr.
Compare all 6 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
Annealed | Intermediate supply condition for cold heading, machining or hot coiling followed by full quench and temper. | 500 | 780 | 16 | 20 HRC | 8 % IACS |
OT-HEAVYThis page oil hardened and tempered, d 5.0–10.0 mm | Large suspension/clutch springs; strength drops with section but relaxation resistance is retained. | 1,520 | 1,720 | 8 | 50 HRC | 7 % IACS |
OTDefault Oil hardened and tempered, d 2.0–5.0 mm | Standard stocked condition: coil the spring directly from the wire, then low-temperature stress relieve. | 1,680 | 1,900 | 6 | 54 HRC | — |
Stress relieved | Mandatory post-coiling treatment: restores elastic limit, stabilises free length and improves set/relaxation resistance. | 1,750 | 1,880 | 6 | 53 HRC | 7 % IACS |
Stress relieved and shot peened spring | Pick when cyclic life governs: compressive surface stress from peening markedly raises the fatigue limit. | 1,750 | 1,880 | 6 | 54 HRC | 7 % IACS |
OT fine wire | Choose for small compression/torsion springs where the highest tensile level of the FDSiCr class is available. | 1,820 | 2,050 | 5 | 56 HRC | 7 % IACS |
What is FDSiCr OT-HEAVY?
FDSiCr OT-HEAVY is FDSiCr heat treated to OT-HEAVY — large suspension/clutch springs; strength drops with section but relaxation resistance is retained. FDSiCr OT-HEAVY has a yield strength of 1,520 MPa (220 ksi) and a tensile strength of 1,720 MPa (249 ksi) — stronger than 97% of steel grades. Elongation at break is 8% and the elastic modulus is 206 GPa (29.9 Msi). FDSiCr OT-HEAVY has a density of 7.85 g/cm³ (0.284 lb/in³), heavier than 56% of steel grades. It melts at 1,420°C (2,588 °F). OT is the default condition FabDigit quotes; OT-HEAVY is available on request or by drawing note.
Advantages
- High strength — 1,520 MPa (220 ksi), better than 97% of steel grades
Limitations
- Difficult to machine — 18/100, worse than 97% of steel grades
- Limited ductility — 8%, worse than 95% of steel grades
- Difficult to weld — 18/100, worse than 87% of steel grades
- Limited service temperature — 250°C (482 °F), worse than 85% of steel grades
FDSiCr OT-HEAVY properties
Typical room-temperature values for FDSiCr OT-HEAVY; 22 are specific to this condition. Other listed values are FDSiCr reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
FDSiCr OT-HEAVY has a density of 7.85 g/cm³ (0.284 lb/in³), heavier than 56% of steel grades. It melts at 1,420°C (2,588 °F).
Mechanical12
FDSiCr OT-HEAVY has a yield strength of 1,520 MPa (220 ksi) and a tensile strength of 1,720 MPa (249 ksi) — stronger than 97% of steel grades. Elongation at break is 8% and the elastic modulus is 206 GPa (29.9 Msi).
Thermal6
FDSiCr OT-HEAVY is rated for continuous service to 250°C (482 °F). It conducts heat at 42 W/m·K (24.3 BTU/hr·ft·°F), worse than 56% of steel grades. Thermal expansion is 12.2 µm/m·K (6.78 µin/in·°F).
Electrical3
FDSiCr OT-HEAVY conducts electricity at 7 % IACS, worse than 74% of steel grades.
Chemical & Environmental3
Corrosion resistance is not recommended (12/100), worse than 53% of steel grades.
Sustainability4
Producing a kilogram of FDSiCr OT-HEAVY takes about 30 MJ of energy and emits 2.3 kg of CO₂ — more than 56% of steel grades. Typical recycled content is 25%.
Manufacturability6
FDSiCr OT-HEAVY's machinability is poor (18/100, worse than 97% of steel grades); weldability poor (18/100); formability fair (45/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with FDSiCr OT-HEAVY
Is FDSiCr easy to machine?
Not a machining grade in the OT condition (~54 HRC) — grind or use in the annealed rod condition, then quench and temper.
Can FDSiCr be welded?
Essentially unweldable in service condition; only resistance/laser tack joints with immediate local re-temper, otherwise cracking in the HAZ.
Can FDSiCr be formed, bent or molded?
Cold coil at spring index ≥4, then stress relieve 350–420 °C for 20–40 min and preset; avoid sharp bends and tight hook radii.
What surface finishes work on FDSiCr?
Shot peen for fatigue duty; protect with zinc phosphate + oil, Zn or Zn-Ni plating with 190–220 °C hydrogen bake-out within 4 h, or epoxy/powder coating.
FDSiCr chemical composition (wt %)
Limits by weight percent from the governing specification, written the way the spec states them — a single maximum for impurities, a range for alloying elements, and the base element as balance. Nominal is the typical mid-range value.
| Element | Spec limit (wt %) | Nominal |
|---|---|---|
| C | 0.51 – 0.59 | 0.55 |
| Siraises elastic limit and relaxation resistance | 1.2 – 1.6 | 1.4 |
| Mn | 0.5 – 0.8 | 0.65 |
| Crhardenability, temper resistance | 0.5 – 0.8 | 0.65 |
| P | ≤ 0.03 | — |
| S | ≤ 0.03 | — |
| Cumax, residual | ≤ 0.12 | — |
| Fe | balance | — |
FDSiCr OT-HEAVY — frequently asked
What is FDSiCr OT-HEAVY used for?
FDSiCr OT-HEAVY is typically used for valve springs, high-fatigue mechanical springs and suspension-related small springs. In short: valve-spring grade wire; good relaxation resistance; 250 °C service capability.
What is the yield strength of FDSiCr OT-HEAVY?
FDSiCr OT-HEAVY has a typical yield strength of 1,520 MPa (220 ksi) and a tensile strength of 1,720 MPa (249 ksi) — stronger than 97% of steel grades. Strength varies by condition: see the 6 listed tempers.
Is FDSiCr OT-HEAVY easy to machine?
Not especially — machinability is rated poor (18/100, worse than 97% of steel grades). Not a machining grade in the OT condition (~54 HRC) — grind or use in the annealed rod condition, then quench and temper.
Can FDSiCr OT-HEAVY be welded?
Not readily — weldability is rated poor (18/100). Essentially unweldable in service condition; only resistance/laser tack joints with immediate local re-temper, otherwise cracking in the HAZ.
What surface finishes work on FDSiCr OT-HEAVY?
Shot peen for fatigue duty; protect with zinc phosphate + oil, Zn or Zn-Ni plating with 190–220 °C hydrogen bake-out within 4 h, or epoxy/powder coating.
Can FDSiCr OT-HEAVY be formed, bent or molded?
Cold coil at spring index ≥4, then stress relieve 350–420 °C for 20–40 min and preset; avoid sharp bends and tight hook radii.
What is the maximum service temperature of FDSiCr OT-HEAVY?
FDSiCr OT-HEAVY is rated for continuous use to about 250°C (482 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between FDSiCr-OT and FDSiCr-ANN?
OT is the default condition — standard stocked condition: coil the spring directly from the wire, then low-temperature stress relieve. ANN: intermediate supply condition for cold heading, machining or hot coiling followed by full quench and temper. Yield strength is 1,680 MPa in OT versus 500 MPa in ANN.
Sources
- EN 10270-2 Steel wire for mechanical springs — Part 2: Oil hardened and tempered spring steel wire — CEN (2012)
- ASTM A401 Standard Specification for Steel Wire, Chromium-Silicon Alloy — ASTM (2020)
- ASM Handbook Vol.1: Properties and Selection — Irons, Steels and High-Performance Alloys — ASM International (1990)
- EN 13906-1 Cylindrical helical springs — compression springs (design moduli) — CEN (2013)
Property data is compiled from published supplier and standards handbooks and normalised for comparison. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.