Steel SUP9
GB SUP9
SUP9 is a JIS G 4801 hot-rolled Cr–Mn spring steel (≈0.55 C, 0.8 Mn, 0.8 Cr) essentially equivalent to AISI 5155/5160 and GB 55CrMnA.
Values for the Annealed condition
SUP9 tempers and conditions
SUP9 is supplied in 6 conditions, soft to hard. Annealed is the default FabDigit quotes; the values on this page are for it.
Compare all 6 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
softest condition for cold forming | Pick when severe cold bending, upsetting or deep machining is needed before hardening. | 400 | 680 | 26 | 10 HRC | 8 % IACS |
AnnealedDefault full anneal, soft condition | Default stock condition for machining, cold forming and subsequent heat treatment. | 440 | 760 | 22 | 217 HB | — |
air cooled from ~870 °C | Use to homogenise structure and refine grain before final quench and temper. | 530 | 960 | 17 | 27 HRC | 7.8 % IACS |
as-rolled bar / flat stock | Mill as-supplied condition for spring makers who will form then quench and temper themselves. | 570 | 950 | 13 | 28 HRC | — |
annealed then cold drawn bar/wire | Chosen for close dimensional tolerance and bright surface on small bar and wire prior to hardening. | 720 | 900 | 10 | 26 HRC | 7.8 % IACS |
oil quenched, low temper to ≈48–52 HRC | Pick for blades, agricultural tines, scrapers and wear parts where hardness matters more than toughness. | 1,500 | 1,700 | 6 | 50 HRC | — |
What is SUP9?
SUP9 is a JIS G 4801 hot-rolled Cr–Mn spring steel (≈0.55 C, 0.8 Mn, 0.8 Cr) essentially equivalent to AISI 5155/5160 and GB 55CrMnA. It is chosen for leaf springs, coil springs, torsion bars and stabiliser bars because oil quenching and tempering gives 1300–1600 MPa strength with good fatigue and set resistance at low cost. Limits are poor corrosion resistance (must be painted/coated), sensitivity to decarburisation and surface defects that cut fatigue life, and loss of spring temper above roughly 200 °C. SUP9 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). SUP9 has a yield strength of 440 MPa (63.8 ksi) and a tensile strength of 760 MPa (110 ksi) — stronger than 50% of steel grades. Elongation at break is 22% and the elastic modulus is 206 GPa (29.9 Msi).
What is SUP9 used for?
- Coil springs
- Leaf springs
- Springs
Limitations
- Limited service temperature — 250°C (482 °F), worse than 85% of steel grades
SUP9 properties
Typical room-temperature values for SUP9-Annealed; bars are the position among steel grades.
Physical3
SUP9 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
SUP9 has a yield strength of 440 MPa (63.8 ksi) and a tensile strength of 760 MPa (110 ksi) — stronger than 50% of steel grades. Elongation at break is 22% and the elastic modulus is 206 GPa (29.9 Msi).
Thermal6
SUP9 is rated for continuous service to 250°C (482 °F). It conducts heat at 46 W/m·K (26.6 BTU/hr·ft·°F), better than 71% of steel grades. Thermal expansion is 12.3 µm/m·K (6.83 µin/in·°F).
Electrical3
SUP9 conducts electricity at 7.8 % IACS, worse than 57% of steel grades.
Chemical & Environmental3
Corrosion resistance is not recommended (11/100), worse than 73% of steel grades.
Sustainability4
Producing a kilogram of SUP9 takes about 26 MJ of energy and emits 2 kg of CO₂ — less than 64% of steel grades. Typical recycled content is 30%.
Manufacturability7
SUP9's machinability is good (55/100, better than 62% of steel grades); weldability poor (30/100); formability fair (45/100).
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. SUP9 is highlighted; hover a dot for its name, or open the interactive family chart.
Working with SUP9
Is SUP9 easy to machine?
Machine in the annealed/spheroidised state (≈60 % of 1212); above ~40 HRC use carbide or grind, and expect rapid tool wear.
Can SUP9 be welded?
Poor weldability due to high carbon equivalent — preheat 250–350 °C, low-hydrogen consumables, immediate post-weld temper, and re-heat-treat if the joint is load bearing.
Can SUP9 be formed, bent or molded?
Hot form 850–1050 °C or cold bend only when soft-annealed; harden by oil quench from 830–860 °C and temper 400–500 °C for spring temper.
Manufacturability
The process limits FabDigit applies to SUP9. Every SUP9 part is priced by an engineer; design inside these and the quote comes back without a redesign loop.
CNC machining
| Machinability | Fair55 / 100 |
|---|---|
| ISO material group | P.2 |
| Cutting speed (rough / finish) | 180 / 210 m/min |
| Minimum wall | 0.8 mm |
| Minimum internal radius | 1 mm |
| Drill depth limit | 5× diameter |
| Best surface (machined / polished) | Ra 1.6 / — |
| Hardenable after machining | No |
Sheet metal
| Formability | Better45 / 100 |
|---|---|
| Weldability | Fair30 / 100 |
| Bendable | Yes |
SUP9 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 |
|---|---|---|
| CSUP9A: 0.56–0.64 | 0.52 – 0.6 | 0.56 |
| Si | 0.15 – 0.35 | 0.25 |
| Mn | 0.65 – 0.95 | 0.8 |
| CrSUP9A: 0.70–1.00 | 0.65 – 0.95 | 0.8 |
| P | ≤ 0.03 | |
| S | ≤ 0.03 | |
| Curesidual, max | ≤ 0.3 | |
| Niresidual, max | ≤ 0.25 | |
| Fe | balance |
What surface finishes work on SUP9?
No natural corrosion protection: shot peen for fatigue, then phosphate+oil, zinc/zinc-flake plating or epoxy paint; avoid hydrogen-embrittling plating without bake-out.
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).
Plating
CVD Coating
Black / Phosphate
Thermal Spray
How much does SUP9 cost?
SUP9 is a standard-cost steel ($$), cheaper than about 71% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
SUP9 — frequently asked
What is SUP9 used for?
SUP9 is typically used for coil springs, leaf springs and springs. In short: premium chromium spring bar.
What is the yield strength of SUP9?
SUP9 has a typical yield strength of 440 MPa (63.8 ksi) and a tensile strength of 760 MPa (110 ksi) — stronger than 50% of steel grades. Strength varies by condition: see the 6 listed tempers.
Is SUP9 easy to machine?
Reasonably — machinability is rated good (55/100, better than 62% of steel grades). Machine in the annealed/spheroidised state (≈60 % of 1212); above ~40 HRC use carbide or grind, and expect rapid tool wear.
Can SUP9 be welded?
Not readily — weldability is rated poor (30/100). Poor weldability due to high carbon equivalent — preheat 250–350 °C, low-hydrogen consumables, immediate post-weld temper, and re-heat-treat if the joint is load bearing.
What surface finishes work on SUP9?
No natural corrosion protection: shot peen for fatigue, then phosphate+oil, zinc/zinc-flake plating or epoxy paint; avoid hydrogen-embrittling plating without bake-out.
Can SUP9 be formed, bent or molded?
Hot form 850–1050 °C or cold bend only when soft-annealed; harden by oil quench from 830–860 °C and temper 400–500 °C for spring temper.
What is the maximum service temperature of SUP9?
SUP9 is rated for continuous use to about 250°C (482 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
How much does SUP9 cost?
SUP9 is a standard-cost steel ($$), 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.
Can FabDigit make parts in SUP9?
Yes — SUP9 is available for CNC machining and sheet metal; every part is priced by an engineer rather than instantly. Upload a STEP file to get a price and a DFM check.
Sources
- JIS G 4801 — Spring steels — JSA (2021)
- GB/T 1222 — (55CrMnA / 60CrMnA) — SAC (2016)
- ASTM A689 / SAE J404 (5160) — ASTM / SAE (2019)
- ASM Handbook Vol.1 — Properties and Selection: Irons, Steels, and High-Performance Alloys — ASM International (1990)
- ASM Handbook Vol.16 — Machining; Vol.19 — Fatigue and Fracture — ASM International (1996)
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.