Steel SUP7
GB SUP7
SUP7 is a JIS silicon-manganese spring steel, equivalent to AISI 9260, supplied hot rolled, annealed, normalized, cold drawn or quenched and tempered to several hardness bands.
Reference datasheet — SUP7 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 QT condition
SUP7 tempers and conditions
SUP7 is supplied in 8 conditions, soft to hard. QT is the default FabDigit quotes; the values on this page are for it.
Compare all 8 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
Solution annealed | Softest condition for machining, cold forming and cold coiling before quench-and-temper. | 450 | 760 | 20 | 230 HB | — |
Normalized | Grain refinement and structure homogenization after hot forging, prior to hardening. | 610 | 1,000 | 13 | 31 HRC | 6 % IACS |
Hot rolled | Mill-supplied hot-rolled bar or flat for subsequent hot forming and heat treatment. | 620 | 1,030 | 12 | 29 HRC | — |
Cold drawn | Cold-drawn bar or wire with better size tolerance and surface, for cold-coiled parts that are hardened afterwards. | 720 | 900 | 10 | 26 HRC | 5.8 % IACS |
QT | Pick when toughness and impact resistance matter more than maximum elastic limit (heavy leaf springs, thick sections). | 1,180 | 1,330 | 12 | 41 HRC | — |
QTDefault Quenched and tempered | Standard delivered spring condition — best balance of elastic limit, fatigue life and sag resistance. | 1,370 | 1,550 | 9 | 46 HRC | — |
quenched & tempered plus shot peening | Standard production finish for automotive springs: compressive surface stress raises fatigue life substantially. | 1,370 | 1,550 | 9 | 46 HRC | 5.2 % IACS |
QT | Maximum elastic limit for small torsion bars and highly stressed springs; ductility and toughness are minimal. | 1,700 | 1,900 | 6 | 52 HRC | — |
What is SUP7?
SUP7 is a JIS silicon-manganese spring steel, equivalent to AISI 9260, supplied hot rolled, annealed, normalized, cold drawn or quenched and tempered to several hardness bands. It is used for automotive coil and leaf springs in the same applications as SUP6, reaching 1370 MPa yield, 1550 MPa tensile, 9 % elongation and about 440 HB (46 HRC) in the default QT condition. Service is limited to 250 °C because of temper softening, machinability is poor (score 22) and the steel is effectively unweldable once hardened. It also has no corrosion resistance and requires shot peening plus a protective coating. SUP7 has a density of 7.75 g/cm³ (0.28 lb/in³), lighter than 93% of steel grades. It melts at 1,400°C (2,552 °F). SUP7 has a yield strength of 1,370 MPa (199 ksi) and a tensile strength of 1,550 MPa (225 ksi) — stronger than 96% of steel grades. Elongation at break is 9% and the elastic modulus is 206 GPa (29.9 Msi).
What is SUP7 used for?
- Automotive coil springs
- Leaf springs
- Truck and trailer suspension springs
- Agricultural and off-highway machinery springs
- Heavy spring washers and clips
- Spring plates and brackets
Advantages
- High strength — 1,370 MPa (199 ksi), better than 96% of steel grades
Limitations
- Difficult to machine — 22/100, worse than 95% of steel grades
- Limited ductility — 9%, worse than 93% of steel grades
- Low fracture toughness — 40 MPa·√m (36.4 ksi·√in), worse than 92% of steel grades
- Difficult to weld — 15/100, worse than 91% of steel grades
- Limited service temperature — 250°C (482 °F), worse than 85% of steel grades
SUP7 properties
Typical room-temperature values for SUP7-QT; bars are the position among steel grades.
Physical3
SUP7 has a density of 7.75 g/cm³ (0.28 lb/in³), lighter than 93% of steel grades. It melts at 1,400°C (2,552 °F).
Mechanical16
SUP7 has a yield strength of 1,370 MPa (199 ksi) and a tensile strength of 1,550 MPa (225 ksi) — stronger than 96% of steel grades. Elongation at break is 9% and the elastic modulus is 206 GPa (29.9 Msi).
Thermal6
SUP7 is rated for continuous service to 250°C (482 °F). It conducts heat at 40 W/m·K (23.1 BTU/hr·ft·°F), worse than 64% of steel grades. Thermal expansion is 11.5 µm/m·K (6.39 µin/in·°F).
Electrical3
SUP7 conducts electricity at 5.2 % IACS, worse than 81% of steel grades.
Chemical & Environmental3
Corrosion resistance is not recommended (12/100), worse than 53% of steel grades.
Sustainability4
Producing a kilogram of SUP7 takes about 28 MJ of energy and emits 2.1 kg of CO₂ — less than 56% of steel grades. Typical recycled content is 25%.
Manufacturability8
SUP7's machinability is poor (22/100, worse than 95% of steel grades); weldability poor (15/100); formability poor (20/100).
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. SUP7 is highlighted; hover a dot for its name, or open the interactive family chart.
Working with SUP7
Is SUP7 easy to machine?
Machine in the annealed condition (≈230 HB) with sharp carbide tooling; at 45+ HRC only grinding, hard turning with CBN or EDM are practical.
Can SUP7 be welded?
Essentially not weldable in service condition (CE ≈ 0.9–1.0); if unavoidable use low-hydrogen consumables, 300–400 °C preheat and immediate full re-quench-and-temper.
Can SUP7 be formed, bent or molded?
Hot form leaf/coil springs at 850–950 °C, or cold coil in the annealed/cold-drawn state then oil quench 830–860 °C and temper 420–560 °C; protect against decarburization in a controlled atmosphere.
SUP7 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 | 0.55 – 0.65 | 0.6 |
| Sihighest Si of the SUP Si-Mn family | 1.8 – 2.2 | 2 |
| Mn | 0.7 – 1 | 0.85 |
| P | ≤ 0.03 | |
| S | ≤ 0.03 | |
| Curesidual max | ≤ 0.3 | |
| Niresidual max | ≤ 0.25 | |
| Crresidual max | ≤ 0.35 | |
| Fe | balance |
What surface finishes work on SUP7?
Shot peen after tempering for fatigue life, then phosphate + epoxy/powder coat or zinc-flake; avoid acid pickling and electroplating without a post-plating hydrogen bake.
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 SUP7 in FabDigit's catalog. Equivalence is nominal — check the exact specification when certification matters.
- Similar grades
- 9260
How much does SUP7 cost?
SUP7 is a budget-cost steel ($), cheaper than about 90% 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.
SUP7 — frequently asked
What is SUP7 used for?
SUP7 is typically used for automotive coil springs, leaf springs, truck and trailer suspension springs, agricultural and off-highway machinery springs, heavy spring washers and clips and spring plates and brackets. In short: high-silicon spring steel; AISI 9260 equivalent; economical leaf-spring grade.
What is the yield strength of SUP7?
SUP7 has a typical yield strength of 1,370 MPa (199 ksi) and a tensile strength of 1,550 MPa (225 ksi) — stronger than 96% of steel grades. Strength varies by condition: see the 8 listed tempers.
Is SUP7 easy to machine?
Not especially — machinability is rated poor (22/100, worse than 95% of steel grades). Machine in the annealed condition (≈230 HB) with sharp carbide tooling; at 45+ HRC only grinding, hard turning with CBN or EDM are practical.
Can SUP7 be welded?
Not readily — weldability is rated poor (15/100). Essentially not weldable in service condition (CE ≈ 0.9–1.0); if unavoidable use low-hydrogen consumables, 300–400 °C preheat and immediate full re-quench-and-temper.
What surface finishes work on SUP7?
Shot peen after tempering for fatigue life, then phosphate + epoxy/powder coat or zinc-flake; avoid acid pickling and electroplating without a post-plating hydrogen bake.
Can SUP7 be formed, bent or molded?
Hot form leaf/coil springs at 850–950 °C, or cold coil in the annealed/cold-drawn state then oil quench 830–860 °C and temper 420–560 °C; protect against decarburization in a controlled atmosphere.
What is the maximum service temperature of SUP7?
SUP7 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.
What is the difference between SUP7-QT and SUP7-A?
QT is the default condition — standard delivered spring condition — best balance of elastic limit, fatigue life and sag resistance. A: softest condition for machining, cold forming and cold coiling before quench-and-temper. Yield strength is 1,370 MPa in QT versus 450 MPa in A.
How much does SUP7 cost?
SUP7 is a budget-cost steel ($), cheaper than about 90% 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
- JIS G 4801 Spring steels — JSA (2021)
- GB/T 1222 (60Si2Mn / 60Si2MnA) — SAC (2016)
- SAE J404 / ASTM A29 (grade 9260) — SAE / ASTM (2020)
- ASM Handbook Vol.1 — Properties and Selection: Irons, Steels — ASM International (1990)
- ASM Handbook Vol.19 — Fatigue and Fracture — ASM International (1996)
- Machinery's Handbook (machinability ratings) — Industrial Press (2020)
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.