Steel VDC-SR (Stress relieved)
Heat-treated state
GB VDC
Condition of the finished spring after coiling and low-temperature stress relief — raises elastic limit and sets free length.
Values for the SR condition
Other VDC tempers and conditions
VDC is listed in 7 conditions; see the grade overview at VDC.
Compare all 7 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
OT, diameter > 6.00–10.00 mm | Largest VDC sizes; choose an alloyed grade (VDCrV/VDSiCr) if full through-hardening or higher stress is required. | 1,410 | 1,600 | 8 | 46 HRC | 8.6 % IACS |
OT, diameter > 4.00–6.00 mm | Medium-heavy wire; strength drops with section due to reduced hardenability of the plain-carbon grade. | 1,480 | 1,680 | 7 | 48 HRC | 8.6 % IACS |
OTDefault Oil hardened and tempered, as supplied | Standard stocked condition: quenched-and-tempered wire ready for cold coiling of medium-size valve/clutch springs. | 1,560 | 1,770 | 6 | 50 HRC | 8.6 % IACS |
SRThis page Stress relieved | Condition of the finished spring after coiling and low-temperature stress relief — raises elastic limit and sets free length. | 1,620 | 1,750 | 5 | 49 HRC | 8.6 % IACS |
Shot peened (+ stress relieved) spring | Pick for high-cycle valve springs: compressive surface stress lifts fatigue limit 20–35 % over unpeened wire. | 1,630 | 1,750 | 6 | 50 HRC | 8.6 % IACS |
OT, diameter > 1.00–2.00 mm | Common size band for small engine valve springs and control springs. | 1,640 | 1,860 | 5.5 | 52 HRC | 8.6 % IACS |
OT, diameter 0.50–1.00 mm | Fine wire for small precision valve springs; highest strength band of the VDC table. | 1,700 | 1,930 | 5 | 53 HRC | 8.6 % IACS |
What is VDC-SR?
VDC-SR is VDC heat treated to SR — condition of the finished spring after coiling and low-temperature stress relief — raises elastic limit and sets free length. VDC-SR has a yield strength of 1,620 MPa (235 ksi) and a tensile strength of 1,750 MPa (254 ksi) — stronger than 98% of steel grades. Elongation at break is 5% and the elastic modulus is 206 GPa (29.9 Msi). VDC-SR 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; SR is available on request or by drawing note.
Advantages
- High strength — 1,620 MPa (235 ksi), better than 98% of steel grades
Limitations
- Limited service temperature — 150°C (302 °F), worse than 99% of steel grades
- Difficult to weld — 10/100, worse than 99% of steel grades
- Limited ductility — 5%, worse than 98% of steel grades
- Difficult to machine — 15/100, worse than 98% of steel grades
- Low fracture toughness — 25 MPa·√m (22.8 ksi·√in), worse than 97% of steel grades
VDC-SR properties
Typical room-temperature values for VDC-SR; 22 are specific to this condition. Other listed values are VDC reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
VDC-SR 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).
Mechanical15
VDC-SR has a yield strength of 1,620 MPa (235 ksi) and a tensile strength of 1,750 MPa (254 ksi) — stronger than 98% of steel grades. Elongation at break is 5% and the elastic modulus is 206 GPa (29.9 Msi).
Thermal6
VDC-SR is rated for continuous service to 150°C (302 °F). It conducts heat at 46 W/m·K (26.6 BTU/hr·ft·°F), better than 71% of steel grades. Thermal expansion is 12 µm/m·K (6.67 µin/in·°F).
Electrical3
VDC-SR conducts electricity at 8.6 % IACS, better than 66% of steel grades.
Chemical & Environmental3
Corrosion resistance is not recommended (12/100), worse than 53% of steel grades.
Sustainability4
Producing a kilogram of VDC-SR takes about 30 MJ of energy and emits 2.2 kg of CO₂ — more than 56% of steel grades. Typical recycled content is 20%.
Manufacturability7
VDC-SR's machinability is poor (15/100, worse than 98% of steel grades); weldability not recommended (10/100); formability fair (35/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with VDC-SR
Is VDC easy to machine?
Supplied at ~50 HRC — not machined; ends are ground with CBN/alumina wheels and coolant to avoid grinding burns and re-hardened white layers.
Can VDC be welded?
Effectively unweldable: high carbon plus quenched martensite gives cracking and destroys the temper; use mechanical hooks or ground/closed ends instead.
Can VDC be formed, bent or molded?
Cold coiled directly from the OT coil on CNC coilers, then stress relieved at 250–400 °C; keep index above ~4 and avoid nicks, as surface defects control spring life.
What surface finishes work on VDC?
Shot peen and preset for fatigue, then phosphate + oil, zinc or zinc-nickel plating or epoxy paint; always bake at ~200 °C after acid pickling/plating to relieve hydrogen.
VDC 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 |
|---|---|---|
| Cunalloyed valve-spring quality | 0.6 – 0.75 | 0.68 |
| Si | 0.15 – 0.35 | 0.25 |
| Mn | 0.6 – 0.9 | 0.75 |
| Ptighter than FDC/TDC | ≤ 0.02 | — |
| Stighter than FDC/TDC | ≤ 0.02 | — |
| Crresidual | ≤ 0.1 | — |
| Curesidual | ≤ 0.12 | — |
| Niresidual | ≤ 0.12 | — |
| Fe | balance | — |
VDC-SR — frequently asked
What is VDC-SR used for?
VDC-SR is typically used for engine valve springs, precision compression springs and small mechanical springs. In short: entry-level valve-spring wire; unalloyed carbon OT grade; lowest-cost VD quality.
What is the yield strength of VDC-SR?
VDC-SR has a typical yield strength of 1,620 MPa (235 ksi) and a tensile strength of 1,750 MPa (254 ksi) — stronger than 98% of steel grades. Strength varies by condition: see the 7 listed tempers.
Is VDC-SR easy to machine?
Not especially — machinability is rated poor (15/100, worse than 98% of steel grades). Supplied at ~50 HRC — not machined; ends are ground with CBN/alumina wheels and coolant to avoid grinding burns and re-hardened white layers.
Can VDC-SR be welded?
Not readily — weldability is rated not recommended (10/100). Effectively unweldable: high carbon plus quenched martensite gives cracking and destroys the temper; use mechanical hooks or ground/closed ends instead.
What surface finishes work on VDC-SR?
Shot peen and preset for fatigue, then phosphate + oil, zinc or zinc-nickel plating or epoxy paint; always bake at ~200 °C after acid pickling/plating to relieve hydrogen.
Can VDC-SR be formed, bent or molded?
Cold coiled directly from the OT coil on CNC coilers, then stress relieved at 250–400 °C; keep index above ~4 and avoid nicks, as surface defects control spring life.
What is the maximum service temperature of VDC-SR?
VDC-SR is rated for continuous use to about 150°C (302 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between VDC-OT and VDC-SP?
OT is the default condition — standard stocked condition: quenched-and-tempered wire ready for cold coiling of medium-size valve/clutch springs. SP: pick for high-cycle valve springs: compressive surface stress lifts fatigue limit 20–35 % over unpeened wire. Yield strength is 1,560 MPa in OT versus 1,630 MPa in SP.
Sources
- EN 10270-2 — Steel wire for mechanical springs, Part 2: Oil hardened and tempered spring steel wire — CEN (2011)
- ASM Handbook Vol.1 — Properties and Selection: Irons, Steels and High-Performance Alloys (spring steels) — ASM International (1990)
- Oil tempered valve spring wire datasheets (Suzuki Garphyttan / Bekaert / Kiswire) — various producers (2023)
- SMI Handbook of Spring Design — Spring Manufacturers Institute (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.