Steel A401 OT-SR
Heat-treated state
ASTM A401
The normal finished-spring condition: coiling stresses removed, set resistance improved, small strength drop.
Values for the OT-SR condition
Other A401 tempers and conditions
A401 is listed in 4 conditions; see the grade overview at A401.
Compare all 4 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
OTDefault Oil tempered (quenched and tempered) wire, 2–6 mm | Standard as-supplied condition for general high-stress coil, torsion and clutch springs. | 1,700 | 1,900 | 7 | 53 HRC | 5 % IACS |
OT-SRThis page oil tempered, coiled and stress relieved (400–430 °C) | The normal finished-spring condition: coiling stresses removed, set resistance improved, small strength drop. | 1,720 | 1,870 | 7.5 | 52 HRC | 5 % IACS |
OT + SR + shot peened | Choose for maximum fatigue life in valve, clutch and suspension springs; compressive surface layer raises endurance ~20–35 %. | 1,720 | 1,870 | 7 | 53 HRC | 5 % IACS |
Valve spring quality | Specify when >10⁷-cycle life is required: tighter inclusion rating, eddy-current surface inspection and decarburisation limits. | 1,780 | 1,950 | 8 | 54 HRC | 5 % IACS |
What is A401 OT-SR?
A401 OT-SR is A401 heat treated to OT-SR — the normal finished-spring condition: coiling stresses removed, set resistance improved, small strength drop. A401 OT-SR has a yield strength of 1,720 MPa (249 ksi) and a tensile strength of 1,870 MPa (271 ksi) — stronger than 99% of steel grades. Elongation at break is 7.5% and the elastic modulus is 203 GPa (29.4 Msi). A401 OT-SR has a density of 7.8 g/cm³ (0.282 lb/in³), lighter than 87% of steel grades. It melts at 1,420°C (2,588 °F). OT is the default condition FabDigit quotes; OT-SR is available on request or by drawing note.
Advantages
- High strength — 1,720 MPa (249 ksi), better than 99% of steel grades
Limitations
- Difficult to weld — 10/100, worse than 99% of steel grades
- Low fracture toughness — 23 MPa·√m (20.9 ksi·√in), worse than 98% of steel grades
- Difficult to machine — 15/100, worse than 98% of steel grades
- Limited ductility — 7.5%, worse than 95% of steel grades
- Limited service temperature — 245°C (473 °F), worse than 88% of steel grades
A401 OT-SR properties
Typical room-temperature values for A401 OT-SR; 22 are specific to this condition. Other listed values are A401 reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
A401 OT-SR has a density of 7.8 g/cm³ (0.282 lb/in³), lighter than 87% of steel grades. It melts at 1,420°C (2,588 °F).
Mechanical16
A401 OT-SR has a yield strength of 1,720 MPa (249 ksi) and a tensile strength of 1,870 MPa (271 ksi) — stronger than 99% of steel grades. Elongation at break is 7.5% and the elastic modulus is 203 GPa (29.4 Msi).
Thermal6
A401 OT-SR is rated for continuous service to 245°C (473 °F). It conducts heat at 33 W/m·K (19.1 BTU/hr·ft·°F), worse than 80% of steel grades. Thermal expansion is 12.2 µm/m·K (6.78 µin/in·°F).
Electrical3
A401 OT-SR conducts electricity at 5 % IACS, worse than 82% of steel grades.
Chemical & Environmental3
Corrosion resistance is not recommended (13/100), better than 66% of steel grades.
Sustainability4
Producing a kilogram of A401 OT-SR takes about 30 MJ of energy and emits 2.3 kg of CO₂ — more than 56% of steel grades. Typical recycled content is 25%.
Manufacturability7
A401 OT-SR's machinability is poor (15/100, worse than 98% of steel grades); weldability not recommended (10/100); formability poor (27/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with A401 OT-SR
Is A401 easy to machine?
Supplied at ~50–55 HRC; effectively non-machinable — grind or wire-EDM ends, or machine only after full anneal followed by re-hardening.
Can A401 be welded?
Not recommended: 0.55 %C + Cr gives untempered martensite and cracking; use mechanical ends or resistance/laser welding with immediate local re-tempering.
Can A401 be formed, bent or molded?
Cold coil in the oil-tempered condition with generous index (C ≥ 4); always stress relieve 400–430 °C for 20–30 min after coiling to restore elastic limit.
What surface finishes work on A401?
Shot peen for fatigue, then zinc/zinc-nickel plate (bake 190–220 °C, 4–8 h against hydrogen embrittlement), zinc-phosphate + oil, or epoxy/powder coat; no anodizing.
A401 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 |
| Sigives high relaxation resistance | 1.2 – 1.6 | 1.4 |
| Mn | 0.5 – 0.8 | 0.65 |
| CrSWOSC-V allows 0.50–0.80 | 0.6 – 0.8 | 0.7 |
| P≤0.025 for valve spring quality | ≤ 0.04 | — |
| S≤0.025 for valve spring quality | ≤ 0.04 | — |
| Fe | balance | — |
A401 OT-SR — frequently asked
What is A401 OT-SR used for?
A401 OT-SR is typically used for high-stress automotive springs, shock absorber springs and heavy-duty coil springs. In short: strongest oil-tempered wire; highest relaxation resistance in class; handles service to 245 °C.
What is the yield strength of A401 OT-SR?
A401 OT-SR has a typical yield strength of 1,720 MPa (249 ksi) and a tensile strength of 1,870 MPa (271 ksi) — stronger than 99% of steel grades. Strength varies by condition: see the 4 listed tempers.
Is A401 OT-SR easy to machine?
Not especially — machinability is rated poor (15/100, worse than 98% of steel grades). Supplied at ~50–55 HRC; effectively non-machinable — grind or wire-EDM ends, or machine only after full anneal followed by re-hardening.
Can A401 OT-SR be welded?
Not readily — weldability is rated not recommended (10/100). Not recommended: 0.55 %C + Cr gives untempered martensite and cracking; use mechanical ends or resistance/laser welding with immediate local re-tempering.
What surface finishes work on A401 OT-SR?
Shot peen for fatigue, then zinc/zinc-nickel plate (bake 190–220 °C, 4–8 h against hydrogen embrittlement), zinc-phosphate + oil, or epoxy/powder coat; no anodizing.
Can A401 OT-SR be formed, bent or molded?
Cold coil in the oil-tempered condition with generous index (C ≥ 4); always stress relieve 400–430 °C for 20–30 min after coiling to restore elastic limit.
What is the maximum service temperature of A401 OT-SR?
A401 OT-SR is rated for continuous use to about 245°C (473 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between A401-OT and A401-VSQ?
OT is the default condition — standard as-supplied condition for general high-stress coil, torsion and clutch springs. VSQ: specify when >10⁷-cycle life is required: tighter inclusion rating, eddy-current surface inspection and decarburisation limits. Yield strength is 1,700 MPa in OT versus 1,780 MPa in VSQ.
Sources
- ASTM A401/A401M — Standard Specification for Steel Wire, Chromium-Silicon Alloy — ASTM International (2020)
- JIS G 3561 — Oil tempered chromium silicon alloy steel wires for valve springs (SWOSC-V) — JSA (2018)
- GB/T 18983 — - (55SiCrA / 55CrSiA) — SAC (2017)
- ASM Handbook Vol.1: Properties and Selection — Irons, Steels and High-Performance Alloys (Spring Steels) — ASM International (1990)
- Shigley's Mechanical Engineering Design, Table 10-4/10-5 (spring wire materials) — McGraw-Hill (2020)
- ASM Handbook Vol.19: Fatigue and Fracture — ASM International (1996)
- Oil-tempered Cr-Si spring wire product data (Suzuki Garphyttan / Kobe Steel class) — producer (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.