Steel TDC OT+SR
Heat-treated state
OT+SR = oQ&T + stress relieved after coiling
Standard post-coiling low-temperature bake to restore elastic limit and stabilise spring free length.
Values for the OT+SR condition
Other TDC tempers and conditions
TDC is listed in 2 conditions; see the grade overview at TDC.
- OT+SR
- OT+SP
Compare all 2 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
OT+SRThis page OQ&T + stress relieved after coiling | Standard post-coiling low-temperature bake to restore elastic limit and stabilise spring free length. | 1,650 | 1,790 | 7 | 51 HRC | 9 % IACS |
OQ&T + stress relieved + shot peened | Choose when cyclic life is the limiting factor: compressive surface stress lifts the fatigue limit by roughly 20–30 %. | 1,650 | 1,810 | 7 | 52 HRC | 9 % IACS |
What is TDC OT+SR?
TDC OT+SR is TDC heat treated to OT+SR — standard post-coiling low-temperature bake to restore elastic limit and stabilise spring free length. TDC OT+SR has a yield strength of 1,650 MPa (239 ksi) and a tensile strength of 1,790 MPa (260 ksi) — stronger than 99% of steel grades. Elongation at break is 7% and the elastic modulus is 206 GPa (29.9 Msi). TDC OT+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).
Advantages
- High strength — 1,650 MPa (239 ksi), better than 99% of steel grades
Limitations
- Limited service temperature — 150°C (302 °F), worse than 99% of steel grades
- Difficult to machine — 12/100, worse than 99% of steel grades
- Limited ductility — 7%, worse than 96% of steel grades
- Difficult to weld — 12/100, worse than 96% of steel grades
- Low fracture toughness — 32 MPa·√m (29.1 ksi·√in), worse than 95% of steel grades
TDC OT+SR properties
Typical room-temperature values for TDC OT+SR; 22 are specific to this condition. Other listed values are TDC reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
TDC OT+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).
Mechanical14
TDC OT+SR has a yield strength of 1,650 MPa (239 ksi) and a tensile strength of 1,790 MPa (260 ksi) — stronger than 99% of steel grades. Elongation at break is 7% and the elastic modulus is 206 GPa (29.9 Msi).
Thermal6
TDC OT+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 12.5 µm/m·K (6.94 µin/in·°F).
Electrical3
TDC OT+SR conducts electricity at 9 % IACS, better than 71% of steel grades.
Chemical & Environmental3
Corrosion resistance is not recommended (12/100), worse than 53% of steel grades.
Sustainability4
Producing a kilogram of TDC OT+SR takes about 30 MJ of energy and emits 2.1 kg of CO₂ — more than 56% of steel grades. Typical recycled content is 22%.
Manufacturability7
TDC OT+SR's machinability is not recommended (12/100, worse than 99% of steel grades); weldability not recommended (12/100); formability fair (40/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with TDC OT+SR
Is TDC easy to machine?
Supplied fully hardened at ~45–57 HRC — treat as a finished section: cut by abrasive wheel or carbide/CBN parting, grind ends, no conventional turning or drilling.
Can TDC be welded?
Effectively unweldable at 0.65–0.75 %C; any arc or resistance weld destroys the temper and cracks — use hooks, loops or mechanical joints instead.
Can TDC be formed, bent or molded?
Designed for cold coiling straight from the coil on CNC spring machines; keep the spring index above ~4, avoid sharp re-bends of coiled parts, and always bake 230–400 °C for 20–30 min after coiling.
What surface finishes work on TDC?
No corrosion resistance — phosphate + oil, mechanical zinc, or zinc/zinc-nickel plating with a 190–220 °C hydrogen-relief bake within 4 h; epoxy powder coat for exposed springs.
TDC 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 |
|---|---|---|
| Cplain-carbon spring chemistry, no deliberate alloying | 0.6 – 0.75 | 0.68 |
| Si | 0.15 – 0.35 | 0.25 |
| Mn | 0.6 – 0.9 | 0.75 |
| P | ≤ 0.03 | — |
| S | ≤ 0.03 | — |
| Crresidual | ≤ 0.15 | — |
| Niresidual | ≤ 0.15 | — |
| Curesidual | ≤ 0.12 | — |
| Fe | balance | — |
TDC OT+SR — frequently asked
What is TDC OT+SR used for?
TDC OT+SR is typically used for general-purpose compression and extension springs, mattress springs and mechanical fastening springs. In short: oil-tempered general spring wire; more uniform strength than FDC; 130 °C service ceiling.
What is the yield strength of TDC OT+SR?
TDC OT+SR has a typical yield strength of 1,650 MPa (239 ksi) and a tensile strength of 1,790 MPa (260 ksi) — stronger than 99% of steel grades. Strength varies by condition: see the 2 listed tempers.
Is TDC OT+SR easy to machine?
Not especially — machinability is rated not recommended (12/100, worse than 99% of steel grades). Supplied fully hardened at ~45–57 HRC — treat as a finished section: cut by abrasive wheel or carbide/CBN parting, grind ends, no conventional turning or drilling.
Can TDC OT+SR be welded?
Not readily — weldability is rated not recommended (12/100). Effectively unweldable at 0.65–0.75 %C; any arc or resistance weld destroys the temper and cracks — use hooks, loops or mechanical joints instead.
What surface finishes work on TDC OT+SR?
No corrosion resistance — phosphate + oil, mechanical zinc, or zinc/zinc-nickel plating with a 190–220 °C hydrogen-relief bake within 4 h; epoxy powder coat for exposed springs.
Can TDC OT+SR be formed, bent or molded?
Designed for cold coiling straight from the coil on CNC spring machines; keep the spring index above ~4, avoid sharp re-bends of coiled parts, and always bake 230–400 °C for 20–30 min after coiling.
What is the maximum service temperature of TDC OT+SR?
TDC OT+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.
Sources
- EN 10270-2 — Steel wire for mechanical springs, Part 2: Oil hardened and tempered spring steel wire — CEN (2011)
- ASTM A229/A229M — Steel Wire, Quenched and Tempered for Mechanical Springs — ASTM International (2017)
- JIS G 3560 — Oil tempered wire for mechanical springs — JSA (2019)
- ASM Handbook Vol.1 — Properties and Selection: Irons, Steels, and High-Performance Alloys (Spring Steels) — ASM International (1990)
- EN 13906-1 — Cylindrical helical springs, design and calculation — CEN (2013)
- Oil tempered spring wire product data (OQ&T carbon grades) — Suzuki Garphyttan / Kobe Steel (2023)
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.