Steel A401
ASTM A401
A401 (SWOSC-V) is chromium–silicon alloyed, oil-tempered spring wire — the strongest and most fatigue-resistant of the common oil-tempered wires.
Reference datasheet — A401 is not in the instant-quote catalog. Upload your part and an engineer will quote it in this grade or suggest the closest stocked equivalent.
Values for the OT condition
A401 tempers and conditions
A401 is supplied in 4 conditions, soft to hard. OT is the default FabDigit quotes; the values on this page are for it.
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 |
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 |
Supply forms, finishes and certifications
Ways A401 is supplied — form, process route, surface or paperwork — without a datasheet of their own. The property values above apply.
| Option | What it is | Type |
|---|---|---|
OT-FINE | OT | Supply option |
OT-HEAVY | OT | Supply option |
What is A401?
A401 (SWOSC-V) is chromium–silicon alloyed, oil-tempered spring wire — the strongest and most fatigue-resistant of the common oil-tempered wires. Typical properties are about 1700 MPa yield and 1900 MPa tensile at 53 HRC, with a service temperature to roughly 245 °C, supplied in oil-tempered fine, heavy, stress-relieved, shot-peened and valve-spring-quality (VSQ) conditions. It is used where A229 carbon wire relaxes or fails in fatigue, at higher wire cost and with essentially no machinability or weldability. For static or low-cycle springs, A229 remains the cheaper option. A401 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). A401 has a yield strength of 1,700 MPa (247 ksi) and a tensile strength of 1,900 MPa (276 ksi) — stronger than 99% of steel grades. Elongation at break is 7% and the elastic modulus is 203 GPa (29.4 Msi).
What is A401 used for?
- High-stress automotive springs
- Shock absorber springs
- Heavy-duty coil springs
Advantages
- High strength — 1,700 MPa (247 ksi), better than 99% of steel grades
Limitations
- Difficult to weld — 10/100, worse than 99% of steel grades
- Low fracture toughness — 22 MPa·√m (20 ksi·√in), worse than 98% of steel grades
- Difficult to machine — 15/100, worse than 98% of steel grades
- Limited ductility — 7%, worse than 96% of steel grades
- Limited service temperature — 245°C (473 °F), worse than 88% of steel grades
A401 properties
Typical room-temperature values for A401-OT; bars are the position among steel grades.
Physical3
A401 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 has a yield strength of 1,700 MPa (247 ksi) and a tensile strength of 1,900 MPa (276 ksi) — stronger than 99% of steel grades. Elongation at break is 7% and the elastic modulus is 203 GPa (29.4 Msi).
Thermal6
A401 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 conducts electricity at 5 % IACS, worse than 82% of steel grades.
Chemical & Environmental3
Corrosion resistance is not recommended (12/100), worse than 53% of steel grades.
Sustainability4
Producing a kilogram of A401 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's machinability is poor (15/100, worse than 98% of steel grades); weldability not recommended (10/100); formability poor (30/100).
Common Calculations5
Values are nominal handbook figures for design screening. Certified mill or lot data ships with every FabDigit order on request.
Strength versus weight in the steel family
Yield strength against density for every steel grade FabDigit runs. A401 is highlighted; hover a dot for its name, or open the interactive family chart.
Working with A401
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.
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 |
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.
Surface treatments FabDigit runs on steel parts — pick them in the quote configurator or call them out on the drawing. Each links to its datasheet in the surface-finish library (thickness, specs, call-out, material verdicts).
Organic Coating
Black / Phosphate
Thermal Spray
Equivalent designations
Standards and trade names that resolve to Steel A401 in FabDigit's catalog. Equivalence is nominal — check the exact specification when certification matters.
- Similar grades
- SWOSC-V
How much does A401 cost?
A401 is a standard-cost steel ($$), cheaper than about 71% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
A401 — frequently asked
What is A401 used for?
A401 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?
A401 has a typical yield strength of 1,700 MPa (247 ksi) and a tensile strength of 1,900 MPa (276 ksi) — stronger than 99% of steel grades. Strength varies by condition: see the 4 listed tempers.
Is A401 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 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?
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 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?
A401 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.
How much does A401 cost?
A401 is a standard-cost steel ($$), cheaper than about 71% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
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; hardness values on non-Brinell scales are converted approximately for charting only. Manufacturability limits are FabDigit quote-engine defaults and may be relaxed by engineering review. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.