Steel SUP7-QT (Quenched and tempered)
Heat-treated state · default condition
GB SUP7
Standard delivered spring condition — best balance of elastic limit, fatigue life and sag resistance.
Values for the QT condition
Other SUP7 tempers and conditions
SUP7 is listed in 8 conditions; see the grade overview at SUP7.
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 | — |
QTDefaultThis page 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-QT?
SUP7-QT is SUP7 heat treated to QT — standard delivered spring condition — best balance of elastic limit, fatigue life and sag resistance. SUP7-QT 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). SUP7-QT 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).
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-QT properties
Typical room-temperature values for SUP7-QT; 14 are specific to this condition. Other listed values are SUP7 reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
SUP7-QT 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-QT 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-QT 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-QT 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-QT 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-QT'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. Confirm any required mill or lot documentation when quoting.
Working with SUP7-QT
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.
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.
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 | — |
SUP7-QT — frequently asked
What is SUP7-QT used for?
SUP7-QT 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-QT?
SUP7-QT 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-QT 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-QT 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-QT?
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-QT 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-QT?
SUP7-QT 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.
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. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.