Steel 61SiCr7 +QT (Quenched and tempered)
Heat-treated state · default condition
EN 61SiCr7
The service condition for suspension coil springs, torsion bars and leaf springs — peak strength with usable ductility.
Values for the +QT condition
Other 61SiCr7 tempers and conditions
61SiCr7 is listed in 7 conditions; see the grade overview at 61SiCr7.
Compare all 7 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
Spheroidize annealed | Choose when maximum cold formability/upsetting or easy machining of this high-carbon grade is required. | 440 | 740 | 20 | 210 HB | — |
Treated for high shearability | Mill condition with controlled soft, uniform structure so bar/coil can be cold sheared to length without cracking. | 470 | 780 | 17 | 20 HRC | 6 % IACS |
Annealed | Standard soft delivery condition for bar and wire that must be cold formed, coiled or machined before hardening. | 500 | 820 | 15 | 235 HB | — |
Supplied with specified (core) hardenability band | Order this when a guaranteed Jominy/hardenability band is needed so heavy bar sections harden through to core. | 520 | 850 | 14 | 23 HRC | 6 % IACS |
Hot rolled | Cheapest mill condition for bar/coil that will be fully re-heat-treated by the spring maker. | 700 | 1,100 | 12 | 31 HRC | 5.8 % IACS |
+QTDefaultThis page Quenched and tempered | The service condition for suspension coil springs, torsion bars and leaf springs — peak strength with usable ductility. | 1,550 | 1,750 | 8 | 48 HRC | — |
Hardened | As-quenched martensite — maximum hardness but brittle; an intermediate state that must be tempered before service. | 1,900 | 2,300 | 1 | 63 HRC | — |
What is 61SiCr7 +QT?
61SiCr7 +QT is 61SiCr7 heat treated to +QT — the service condition for suspension coil springs, torsion bars and leaf springs — peak strength with usable ductility. 61SiCr7 +QT has a yield strength of 1,550 MPa (225 ksi) and a tensile strength of 1,750 MPa (254 ksi) — stronger than 97% of steel grades. Elongation at break is 8% and the elastic modulus is 200 GPa (29 Msi). 61SiCr7 +QT 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).
Advantages
- High strength — 1,550 MPa (225 ksi), better than 97% of steel grades
Limitations
- Limited ductility — 8%, worse than 95% of steel grades
- Limited formability — 10/100, worse than 95% of steel grades
- Difficult to machine — 25/100, worse than 93% of steel grades
- Difficult to weld — 15/100, worse than 91% of steel grades
- Low fracture toughness — 48 MPa·√m (43.7 ksi·√in), worse than 88% of steel grades
61SiCr7 +QT properties
Typical room-temperature values for 61SiCr7 +QT; 16 are specific to this condition. Other listed values are 61SiCr7 reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
61SiCr7 +QT 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
61SiCr7 +QT has a yield strength of 1,550 MPa (225 ksi) and a tensile strength of 1,750 MPa (254 ksi) — stronger than 97% of steel grades. Elongation at break is 8% and the elastic modulus is 200 GPa (29 Msi).
Thermal6
61SiCr7 +QT is rated for continuous service to 250°C (482 °F). It conducts heat at 34 W/m·K (19.6 BTU/hr·ft·°F), worse than 77% of steel grades. Thermal expansion is 12 µm/m·K (6.67 µin/in·°F).
Electrical3
61SiCr7 +QT conducts electricity at 5.5 % 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 61SiCr7 +QT takes about 30 MJ of energy and emits 2.3 kg of CO₂ — more than 56% of steel grades. Typical recycled content is 30%.
Manufacturability7
61SiCr7 +QT's machinability is poor (25/100, worse than 93% of steel grades); weldability poor (15/100); formability not recommended (10/100).
Common Calculations5
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with 61SiCr7 +QT
Is 61SiCr7 easy to machine?
Machine only in the +A/+AC soft condition with sharp carbide or coated HSS tooling; at 45–52 HRC only grinding or hard turning with CBN is practical.
Can 61SiCr7 be welded?
Essentially not weldable in spring service — high carbon equivalent causes quench cracks; if unavoidable, preheat 300–400 °C and re-heat-treat the whole part.
Can 61SiCr7 be formed, bent or molded?
Hot coil at 850–950 °C or cold coil in annealed/oil-tempered condition, then quench from ~870 °C in oil and temper 400–480 °C for 45–52 HRC; protect against decarburization.
What surface finishes work on 61SiCr7?
Shot peen (often stress peen) to restore fatigue life after grinding, then phosphate + epoxy powder or zinc-flake coating; avoid acid pickling or electroplating due to hydrogen embrittlement.
61SiCr7 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 | 0.57 – 0.65 | 0.61 |
| Siraises elastic limit and relaxation resistance | 1.6 – 2 | 1.8 |
| Mn | 0.7 – 1 | 0.85 |
| Crhardenability and temper resistance | 0.2 – 0.4 | 0.3 |
| P | ≤ 0.03 | — |
| S | ≤ 0.03 | — |
| Fe | balance | — |
61SiCr7 +QT — frequently asked
What is 61SiCr7 +QT used for?
61SiCr7 +QT is typically used for suspension springs, valve springs and stabilizer bars. In short: high-carbon Si-Cr spring steel; very high fatigue life; form soft, harden after.
What is the yield strength of 61SiCr7 +QT?
61SiCr7 +QT has a typical yield strength of 1,550 MPa (225 ksi) and a tensile strength of 1,750 MPa (254 ksi) — stronger than 97% of steel grades. Strength varies by condition: see the 7 listed tempers.
Is 61SiCr7 +QT easy to machine?
Not especially — machinability is rated poor (25/100, worse than 93% of steel grades). Machine only in the +A/+AC soft condition with sharp carbide or coated HSS tooling; at 45–52 HRC only grinding or hard turning with CBN is practical.
Can 61SiCr7 +QT be welded?
Not readily — weldability is rated poor (15/100). Essentially not weldable in spring service — high carbon equivalent causes quench cracks; if unavoidable, preheat 300–400 °C and re-heat-treat the whole part.
What surface finishes work on 61SiCr7 +QT?
Shot peen (often stress peen) to restore fatigue life after grinding, then phosphate + epoxy powder or zinc-flake coating; avoid acid pickling or electroplating due to hydrogen embrittlement.
Can 61SiCr7 +QT be formed, bent or molded?
Hot coil at 850–950 °C or cold coil in annealed/oil-tempered condition, then quench from ~870 °C in oil and temper 400–480 °C for 45–52 HRC; protect against decarburization.
What is the maximum service temperature of 61SiCr7 +QT?
61SiCr7 +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.
Sources
- EN 10089 — Hot-rolled steels for quenched and tempered springs — CEN (2002)
- EN 10270-2 — Steel wire for mechanical springs, oil hardened and tempered — CEN (2011)
- EN 10132-4 / EN 10083 delivery-condition designations (+A, +AC, +S, +CH, +H, +QT) — CEN (2003)
- ASM Handbook Vol. 1 — Properties and Selection: Irons, Steels and High-Performance Alloys (spring steels) — ASM International (1990)
- ASM Handbook Vol. 19 — Fatigue and Fracture — ASM International (1996)
- GB/T 1222 (60Si2CrA / 61SiCr7 ) — SAC (2016)
- SMM / Mysteel (2025)
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.