Steel 61SiCrV6 +QT45 (+QT)
Heat-treated state
EN 61SiCrV6
Tougher temper for heavy leaf/torsion springs and stabiliser bars where impact and shock matter more than peak stress.
Values for the +QT45 condition
Other 61SiCrV6 tempers and conditions
61SiCrV6 is listed in 7 conditions; see the grade overview at 61SiCrV6.
Compare all 7 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
Annealed | Pick for machining, cold drawing or cold forming of the blank before final hardening. | 500 | 800 | 15 | 230 HB | — |
Normalized | Uniform fine pearlitic structure for stock that will be re-austenitised; occasionally used for machining blanks. | 600 | 950 | 12 | 29 HRC | 5.9 % IACS |
Hot rolled | Mill supply condition for bar and rod destined for hot coiling and subsequent quench-and-temper. | 700 | 1,100 | 10 | 33 HRC | 5.8 % IACS |
Cold drawn | Bright close-tolerance bar or pre-drawn wire for spring coiling before hardening. | 800 | 950 | 8 | 30 HRC | 5.8 % IACS |
+QT45This page +QT | Tougher temper for heavy leaf/torsion springs and stabiliser bars where impact and shock matter more than peak stress. | 1,400 | 1,550 | 9 | 47 HRC | — |
+QT48Default +QT | Standard hardened-and-tempered spring condition — best balance of elastic limit, sag resistance and fatigue life. | 1,620 | 1,800 | 7 | 50 HRC | — |
+QT | Maximum-stress temper for small-section, shot-peened valve and clutch springs; low toughness, very defect-sensitive. | 1,780 | 1,950 | 5 | 54 HRC | — |
What is 61SiCrV6 +QT45?
61SiCrV6 +QT45 is 61SiCrV6 heat treated to +QT45 — tougher temper for heavy leaf/torsion springs and stabiliser bars where impact and shock matter more than peak stress. 61SiCrV6 +QT45 has a yield strength of 1,400 MPa (203 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 205 GPa (29.7 Msi). 61SiCrV6 +QT45 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). +QT48 is the default condition FabDigit quotes; +QT45 is available on request or by drawing note.
Advantages
- High strength — 1,400 MPa (203 ksi), better than 96% of steel grades
- Polishes to a fine finish — 65/100, better than 78% of steel grades
Limitations
- Difficult to machine — 16/100, worse than 98% of steel grades
- Limited formability — 8/100, worse than 97% of steel grades
- Difficult to weld — 12/100, worse than 96% of steel grades
- Limited ductility — 9%, worse than 93% of steel grades
- Low fracture toughness — 45 MPa·√m (41 ksi·√in), worse than 90% of steel grades
61SiCrV6 +QT45 properties
Typical room-temperature values for 61SiCrV6 +QT45; 12 are specific to this condition. Other listed values are 61SiCrV6 reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
61SiCrV6 +QT45 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
61SiCrV6 +QT45 has a yield strength of 1,400 MPa (203 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 205 GPa (29.7 Msi).
Thermal6
61SiCrV6 +QT45 is rated for continuous service to 280°C (536 °F). It conducts heat at 33 W/m·K (19.1 BTU/hr·ft·°F), worse than 80% of steel grades. Thermal expansion is 11.5 µm/m·K (6.39 µin/in·°F).
Electrical3
61SiCrV6 +QT45 conducts electricity at 5.7 % IACS, worse than 80% of steel grades.
Chemical & Environmental3
Corrosion resistance is not recommended (11/100), worse than 73% of steel grades.
Sustainability4
Producing a kilogram of 61SiCrV6 +QT45 takes about 27 MJ of energy and emits 2 kg of CO₂ — less than 59% of steel grades. Typical recycled content is 30%.
Manufacturability7
61SiCrV6 +QT45's machinability is poor (16/100, worse than 98% of steel grades); weldability not recommended (12/100); formability not recommended (8/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with 61SiCrV6 +QT45
Is 61SiCrV6 easy to machine?
Machine only in the soft-annealed state (≤248 HB) with carbide tooling; at 48–52 HRC finish by grinding, EDM or CBN turning.
Can 61SiCrV6 be welded?
Not recommended — ~0.6 %C gives hard, crack-prone HAZ and destroys the spring temper; if unavoidable, preheat 300–350 °C and re-heat-treat the whole part.
Can 61SiCrV6 be formed, bent or molded?
Cold coil in the annealed or oil-tempered condition, or hot coil at 850–950 °C; harden from 860–880 °C in oil and temper 400–480 °C to the target hardness, then stress-relieve after coiling.
What surface finishes work on 61SiCrV6?
Always shot-peen springs for fatigue life; protect with phosphate + oil, Zn-flake or epoxy coating, and avoid acid pickling/electroplating unless a hydrogen-relief bake follows immediately.
61SiCrV6 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≈0.61 % C per EN designation | 0.58 – 0.65 | 0.61 |
| Sihigh Si raises elastic limit and sag resistance | 1.3 – 1.6 | 1.45 |
| Mn | 0.5 – 0.8 | 0.65 |
| Cr | 0.5 – 0.8 | 0.65 |
| Vgrain refinement, temper resistance | 0.1 – 0.2 | 0.15 |
| P | ≤ 0.03 | — |
| Smax; ≤0.015 for valve-spring quality | ≤ 0.03 | — |
| Fe | balance | — |
61SiCrV6 +QT45 — frequently asked
What is 61SiCrV6 +QT45 used for?
61SiCrV6 +QT45 is typically used for high-performance valve springs, racing suspension springs and high-fatigue coil springs. In short: top-tier fatigue spring steel; vanadium-refined grain; high stress-relaxation resistance.
What is the yield strength of 61SiCrV6 +QT45?
61SiCrV6 +QT45 has a typical yield strength of 1,400 MPa (203 ksi) and a tensile strength of 1,550 MPa (225 ksi) — stronger than 96% of steel grades. Strength varies by condition: see the 7 listed tempers.
Is 61SiCrV6 +QT45 easy to machine?
Not especially — machinability is rated poor (16/100, worse than 98% of steel grades). Machine only in the soft-annealed state (≤248 HB) with carbide tooling; at 48–52 HRC finish by grinding, EDM or CBN turning.
Can 61SiCrV6 +QT45 be welded?
Not readily — weldability is rated not recommended (12/100). Not recommended — ~0.6 %C gives hard, crack-prone HAZ and destroys the spring temper; if unavoidable, preheat 300–350 °C and re-heat-treat the whole part.
What surface finishes work on 61SiCrV6 +QT45?
Always shot-peen springs for fatigue life; protect with phosphate + oil, Zn-flake or epoxy coating, and avoid acid pickling/electroplating unless a hydrogen-relief bake follows immediately.
Can 61SiCrV6 +QT45 be formed, bent or molded?
Cold coil in the annealed or oil-tempered condition, or hot coil at 850–950 °C; harden from 860–880 °C in oil and temper 400–480 °C to the target hardness, then stress-relieve after coiling.
What is the maximum service temperature of 61SiCrV6 +QT45?
61SiCrV6 +QT45 is rated for continuous use to about 280°C (536 °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 spring steel wire — CEN (2011)
- EN 13906-1 — Cylindrical helical springs, design and calculation — CEN (2013)
- ASM Handbook Vol.1 — Properties and Selection: Irons, Steels and High-Performance Alloys (spring steels) — ASM International (1990)
- Stahlschlüssel (Key to Steel) — Verlag Stahlschlüssel Wegst (2019)
- Si-Cr-V spring steel bar and oil-tempered valve spring wire datasheets — Ovako / Suzuki Garphyttan (2022)
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.