Steel 50SiCrMo6 +QT (Quenched and tempered)
Heat-treated state · default condition
EN 50SiCrMo6
Standard service condition for leaf springs, torsion bars and hot-coiled springs — highest elastic limit and fatigue strength.
Values for the +QT condition
Other 50SiCrMo6 tempers and conditions
50SiCrMo6 is listed in 7 conditions; see the grade overview at 50SiCrMo6.
Compare all 7 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
Spheroidize annealed | Softest, most ductile delivery state — chosen for cold heading, cold coiling or deep machining of bar/wire. | 450 | 710 | 18 | 210 HB | — |
Annealed | Pick for machining, straightening or cold work before final quench and temper. | 500 | 790 | 15 | 235 HB | 43 W/m·K |
Treated for high shearability | Order when leaf-spring or bar blanks are cold-sheared: microstructure/hardness set to shear cleanly without cracking. | 520 | 800 | 14 | 22 HRC | 8.1 % IACS |
Supplied with specified hardenability | Choose when the spring maker must guarantee through-hardening of thick leaves/bars; delivered hot-rolled or annealed with a Jominy band. | 570 | 950 | 11 | 29 HRC | 7.9 % IACS |
Restricted (narrowed) hardenability band | Same as +H but with a tightened Jominy scatter band for reproducible distortion and hardness in mass-produced springs. | 580 | 950 | 11 | 28 HRC | 8 % IACS |
Hot rolled | Cheapest mill condition for spring makers who hot-form and then quench and temper in-house. | 600 | 1,000 | 10 | 30 HRC | 7.9 % IACS |
+QTDefaultThis page Quenched and tempered | Standard service condition for leaf springs, torsion bars and hot-coiled springs — highest elastic limit and fatigue strength. | 1,550 | 1,750 | 7 | 49 HRC | — |
What is 50SiCrMo6 +QT?
50SiCrMo6 +QT is 50SiCrMo6 heat treated to +QT — standard service condition for leaf springs, torsion bars and hot-coiled springs — highest elastic limit and fatigue strength. 50SiCrMo6 +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 7% and the elastic modulus is 206 GPa (29.9 Msi). 50SiCrMo6 +QT has a density of 7.85 g/cm³ (0.284 lb/in³), heavier than 56% 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
- Polishes to a fine finish — 65/100, better than 78% of steel grades
Limitations
- Limited ductility — 7%, worse than 96% 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 — 45 MPa·√m (41 ksi·√in), worse than 90% of steel grades
50SiCrMo6 +QT properties
Typical room-temperature values for 50SiCrMo6 +QT; 15 are specific to this condition. Other listed values are 50SiCrMo6 reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
50SiCrMo6 +QT has a density of 7.85 g/cm³ (0.284 lb/in³), heavier than 56% of steel grades. It melts at 1,420°C (2,588 °F).
Mechanical15
50SiCrMo6 +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 7% and the elastic modulus is 206 GPa (29.9 Msi).
Thermal6
50SiCrMo6 +QT is rated for continuous service to 280°C (536 °F). It conducts heat at 40 W/m·K (23.1 BTU/hr·ft·°F), worse than 64% of steel grades. Thermal expansion is 12.3 µm/m·K (6.83 µin/in·°F).
Electrical3
50SiCrMo6 +QT conducts electricity at 7.8 % IACS, worse than 57% of steel grades.
Chemical & Environmental3
Corrosion resistance is not recommended (11/100), worse than 73% of steel grades.
Sustainability4
Producing a kilogram of 50SiCrMo6 +QT takes about 30 MJ of energy and emits 2.1 kg of CO₂ — more than 56% of steel grades. Typical recycled content is 25%.
Manufacturability6
50SiCrMo6 +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 50SiCrMo6 +QT
Is 50SiCrMo6 easy to machine?
Machine in +A/+AC condition with carbide tooling and rigid setups; at 46–52 HRC only grinding, hard turning with CBN, or EDM are practical.
Can 50SiCrMo6 be welded?
Not recommended for load-bearing spring joints (C ≈ 0.5 %, high Si/Cr); if unavoidable use 250–350 °C preheat, low-hydrogen consumables and immediate post-weld temper.
Can 50SiCrMo6 be formed, bent or molded?
Hot-form/coil at 850–950 °C then oil quench ~860 °C and temper 400–480 °C to target hardness; cold coiling only from +AC wire followed by full heat treatment.
What surface finishes work on 50SiCrMo6?
Shot-peen highly stressed surfaces to restore fatigue life, then phosphate + epoxy paint or zinc-flake coating; avoid acid pickling/electroplating without a hydrogen bake-out.
50SiCrMo6 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 |
|---|---|---|
| Chigher-carbon variant of 45SiCrMo6 | 0.46 – 0.54 | 0.5 |
| Siraises elastic limit and relaxation resistance | 1.2 – 1.5 | 1.35 |
| Mn | 0.5 – 0.9 | 0.7 |
| Cr | 0.6 – 0.9 | 0.75 |
| Mohardenability in thick sections, temper resistance | 0.15 – 0.3 | 0.22 |
| P | ≤ 0.03 | — |
| S | ≤ 0.03 | — |
| Fe | balance | — |
50SiCrMo6 +QT — frequently asked
What is 50SiCrMo6 +QT used for?
50SiCrMo6 +QT is typically used for leaf springs, heavy-duty coil springs and clutch springs. In short: heavy-duty leaf spring grade; higher carbon than 46SiCrMo6; grinding-only after hardening.
What is the yield strength of 50SiCrMo6 +QT?
50SiCrMo6 +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 50SiCrMo6 +QT easy to machine?
Not especially — machinability is rated poor (25/100, worse than 93% of steel grades). Machine in +A/+AC condition with carbide tooling and rigid setups; at 46–52 HRC only grinding, hard turning with CBN, or EDM are practical.
Can 50SiCrMo6 +QT be welded?
Not readily — weldability is rated poor (15/100). Not recommended for load-bearing spring joints (C ≈ 0.5 %, high Si/Cr); if unavoidable use 250–350 °C preheat, low-hydrogen consumables and immediate post-weld temper.
What surface finishes work on 50SiCrMo6 +QT?
Shot-peen highly stressed surfaces to restore fatigue life, then phosphate + epoxy paint or zinc-flake coating; avoid acid pickling/electroplating without a hydrogen bake-out.
Can 50SiCrMo6 +QT be formed, bent or molded?
Hot-form/coil at 850–950 °C then oil quench ~860 °C and temper 400–480 °C to target hardness; cold coiling only from +AC wire followed by full heat treatment.
What is the maximum service temperature of 50SiCrMo6 +QT?
50SiCrMo6 +QT 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 10083-1/-3 — Steels for quenching and tempering (delivery conditions +A, +AC, +S, +QT, +H, +CH) — CEN (2006)
- EN 10027-2 — Numerical designation system (material number 1.8063) — CEN (2015)
- 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 (spring steel fatigue data) — ASM International (1996)
- EN 13906-1 — Cylindrical helical springs, design and calculation — CEN (2013)
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.