Steel SUP6-N (Normalized)
Heat-treated state
GB SUP6
Grain refinement and structure homogenisation after forging, before hardening.
Values for the N condition
Other SUP6 tempers and conditions
SUP6 is listed in 8 conditions; see the grade overview at SUP6.
Compare all 8 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
Solution annealed | Choose for cold coiling, bending, upsetting or heavy machining before the final quench and temper. | 450 | 750 | 20 | 217 HB | — |
Hot rolled | Mill delivery condition for bar and flat that will be formed and heat treated by the spring maker. | 600 | 1,000 | 14 | 29 HRC | — |
NThis page Normalized | Grain refinement and structure homogenisation after forging, before hardening. | 640 | 1,050 | 13 | 31 HRC | 7 % IACS |
Cold drawn | Close-tolerance bright bar for machined spring components and torsion-bar blanks prior to hardening. | 700 | 880 | 10 | 24 HRC | 7 % IACS |
Q&T | Lower-hardness quench-and-temper used for thick leaf springs and where toughness matters more than peak stress. | 1,180 | 1,350 | 13 | 42 HRC | — |
QT44-48Default Q&T 44–48 HRC | Default production condition for leaf and hot-coiled springs: best balance of elastic limit, relaxation resistance and fatigue life. | 1,450 | 1,620 | 11 | 46 HRC | — |
Q&T + shot peened | Standard finishing for automotive leaf/coil springs — compressive surface stress markedly raises fatigue life. | 1,450 | 1,620 | 11 | 46 HRC | 6.6 % IACS |
Q&T 48–52 HRC | For highly stressed small springs and clips where maximum elastic limit is needed and impact loading is limited. | 1,620 | 1,800 | 8 | 50 HRC | — |
What is SUP6-N?
SUP6-N is SUP6 heat treated to N — grain refinement and structure homogenisation after forging, before hardening. SUP6-N has a yield strength of 640 MPa (92.8 ksi) and a tensile strength of 1,050 MPa (152 ksi) — stronger than 79% of steel grades. Elongation at break is 13% and the elastic modulus is 206 GPa (29.9 Msi). SUP6-N has a density of 7.75 g/cm³ (0.28 lb/in³), lighter than 93% of steel grades. It melts at 1,420°C (2,588 °F). QT44-48 is the default condition FabDigit quotes; N is available on request or by drawing note.
Advantages
- Low embodied carbon — 1.9 kg CO₂/kg, better than 92% of steel grades
- High strength — 640 MPa (92.8 ksi), better than 79% of steel grades
- Polishes to a fine finish — 65/100, better than 78% of steel grades
Limitations
- Limited formability — 15/100, worse than 87% of steel grades
- Difficult to weld — 20/100, worse than 84% of steel grades
- Limited ductility — 13%, worse than 78% of steel grades
- Low fracture toughness — 60 MPa·√m (54.6 ksi·√in), worse than 78% of steel grades
- Limited service temperature — 300°C (572 °F), worse than 78% of steel grades
SUP6-N properties
Typical room-temperature values for SUP6-N; 22 are specific to this condition. Other listed values are SUP6 reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
SUP6-N has a density of 7.75 g/cm³ (0.28 lb/in³), lighter than 93% of steel grades. It melts at 1,420°C (2,588 °F).
Mechanical16
SUP6-N has a yield strength of 640 MPa (92.8 ksi) and a tensile strength of 1,050 MPa (152 ksi) — stronger than 79% of steel grades. Elongation at break is 13% and the elastic modulus is 206 GPa (29.9 Msi).
Thermal6
SUP6-N is rated for continuous service to 300°C (572 °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
SUP6-N conducts electricity at 7 % IACS, worse than 74% of steel grades.
Chemical & Environmental3
Corrosion resistance is not recommended (12/100), worse than 53% of steel grades.
Sustainability4
Producing a kilogram of SUP6-N takes about 25 MJ of energy and emits 1.9 kg of CO₂ — less than 82% of steel grades. Typical recycled content is 30%.
Manufacturability8
SUP6-N's machinability is fair (40/100, worse than 77% of steel grades); weldability poor (20/100); formability poor (15/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with SUP6-N
Is SUP6 easy to machine?
Machine in the spheroidize-annealed condition (≈60 % of 1212); at 44–48 HRC use rigid setups with coated carbide or CBN, low feed, and expect heavy tool wear.
Can SUP6 be welded?
Effectively non-weldable for service parts — high carbon plus 1.6 % Si gives severe hardening and cracking; if unavoidable, preheat 300–400 °C and temper immediately afterwards.
Can SUP6 be formed, bent or molded?
Hot form/coil at 900–1000 °C or cold form in the annealed state, then oil quench from 830–860 °C and temper 440–500 °C; control furnace atmosphere to limit decarburisation, which kills spring fatigue life.
What surface finishes work on SUP6?
Remove decarburised skin by grinding or shot blasting, shot peen for fatigue, then phosphate+oil, powder coat or zinc/zinc-nickel plate with a 190–220 °C de-embrittlement bake.
SUP6 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 |
|---|---|---|
| CJIS G4801 | 0.56 – 0.64 | 0.6 |
| Simain strengthening/relaxation-resisting element | 1.5 – 1.8 | 1.65 |
| 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 | — |
SUP6-N — frequently asked
What is SUP6-N used for?
SUP6-N is typically used for leaf springs, coil springs and clutch discs. In short: high set-resistance spring steel; SAE 9260 equivalent; heat-treat only, non-weldable.
What is the yield strength of SUP6-N?
SUP6-N has a typical yield strength of 640 MPa (92.8 ksi) and a tensile strength of 1,050 MPa (152 ksi) — stronger than 79% of steel grades. Strength varies by condition: see the 8 listed tempers.
Is SUP6-N easy to machine?
Not especially — machinability is rated fair (40/100, worse than 77% of steel grades). Machine in the spheroidize-annealed condition (≈60 % of 1212); at 44–48 HRC use rigid setups with coated carbide or CBN, low feed, and expect heavy tool wear.
Can SUP6-N be welded?
Not readily — weldability is rated poor (20/100). Effectively non-weldable for service parts — high carbon plus 1.6 % Si gives severe hardening and cracking; if unavoidable, preheat 300–400 °C and temper immediately afterwards.
What surface finishes work on SUP6-N?
Remove decarburised skin by grinding or shot blasting, shot peen for fatigue, then phosphate+oil, powder coat or zinc/zinc-nickel plate with a 190–220 °C de-embrittlement bake.
Can SUP6-N be formed, bent or molded?
Hot form/coil at 900–1000 °C or cold form in the annealed state, then oil quench from 830–860 °C and temper 440–500 °C; control furnace atmosphere to limit decarburisation, which kills spring fatigue life.
What is the maximum service temperature of SUP6-N?
SUP6-N is rated for continuous use to about 300°C (572 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between SUP6 QT44-48 and SUP6-A?
QT44-48 is the default condition — default production condition for leaf and hot-coiled springs: best balance of elastic limit, relaxation resistance and fatigue life. A: choose for cold coiling, bending, upsetting or heavy machining before the final quench and temper. Yield strength is 1,450 MPa in QT44-48 versus 450 MPa in A.
Sources
- JIS G 4801 — Spring steels — Japanese Standards Association (2021)
- SAE J404 / ASTM A29 (grade 9260) — SAE / ASTM (2020)
- GB/T 1222 — (60Si2Mn) — SAC (2016)
- ASM Handbook Vol.1 — Properties and Selection: Irons, Steels and High-Performance Alloys — ASM International (1990)
- SAE Spring Design Manual (HS-795) — SAE International (1996)
- Mysteel / SMM (2026)
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.