Steel 6145 QT46-50
Heat-treated state
AISI/SAE 6145 · UNS G61450
QT46-50 = q&T 46–50 HRC
Classic spring/torsion-bar temper with maximum elastic limit at usable toughness.
Values for the QT46-50 condition
Other 6145 tempers and conditions
6145 is listed in 10 conditions; see the grade overview at 6145.
Compare all 10 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
ADefault Solution annealed | Softest, most machinable condition; the normal supply state for bar that will be machined then quenched and tempered. | 420 | 670 | 22 | 197 HB | — |
Hot rolled | As-rolled mill condition; cheapest stock for parts that will be re-heat-treated after machining. | 460 | 760 | 18 | 217 HB | — |
Normalized | Uniform fine pearlitic structure for forgings before machining or final hardening; higher strength than annealed. | 615 | 940 | 18 | 27 HRC | — |
Cold drawn | Tight-tolerance bright bar with raised yield strength; pick for as-machined parts not needing heat treatment. | 690 | 790 | 12 | 229 HB | — |
Q&T 28–32 HRC | Tough general-purpose machine condition for shafts and highly stressed structural parts. | 900 | 1,000 | 18 | 30 HRC | — |
Q&T 34–38 HRC | Balanced strength/toughness for torsion bars, gear blanks and heavy-duty fasteners. | 1,080 | 1,180 | 15 | 36 HRC | — |
Q&T 40–44 HRC | High-strength condition for leaf/coil springs, punches and heavily loaded shafts. | 1,280 | 1,400 | 12 | 42 HRC | — |
QT46-50This page Q&T 46–50 HRC | Classic spring/torsion-bar temper with maximum elastic limit at usable toughness. | 1,480 | 1,620 | 10 | 48 HRC | — |
Q&T 52–54 HRC | Maximum strength temper for hand tools and wear parts; notch-sensitive, avoid stress raisers. | 1,650 | 1,830 | 8 | 53 HRC | — |
As-quenched | Intermediate process state only — must be tempered promptly; brittle and prone to quench cracking. | 1,650 | 2,100 | 2 | 59 HRC | 6.6 % IACS |
What is 6145 QT46-50?
6145 QT46-50 is 6145 heat treated to QT46-50 — classic spring/torsion-bar temper with maximum elastic limit at usable toughness. 6145 QT46-50 has a yield strength of 1,480 MPa (215 ksi) and a tensile strength of 1,620 MPa (235 ksi) — stronger than 97% of steel grades. Elongation at break is 10% and the elastic modulus is 205 GPa (29.7 Msi). 6145 QT46-50 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). A is the default condition FabDigit quotes; QT46-50 is available on request or by drawing note.
Advantages
- High strength — 1,480 MPa (215 ksi), better than 97% of steel grades
Limitations
- Difficult to machine — 16/100, worse than 98% of steel grades
- Limited ductility — 10%, worse than 91% of steel grades
- Low fracture toughness — 52 MPa·√m (47.3 ksi·√in), worse than 84% of steel grades
- Limited service temperature — 280°C (536 °F), worse than 82% of steel grades
6145 QT46-50 properties
Typical room-temperature values for 6145 QT46-50; 14 are specific to this condition. Other listed values are 6145 reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
6145 QT46-50 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).
Mechanical16
6145 QT46-50 has a yield strength of 1,480 MPa (215 ksi) and a tensile strength of 1,620 MPa (235 ksi) — stronger than 97% of steel grades. Elongation at break is 10% and the elastic modulus is 205 GPa (29.7 Msi).
Thermal6
6145 QT46-50 is rated for continuous service to 280°C (536 °F). It conducts heat at 45 W/m·K (26 BTU/hr·ft·°F), better than 66% of steel grades. Thermal expansion is 12.2 µm/m·K (6.78 µin/in·°F).
Electrical3
6145 QT46-50 conducts electricity at 7.5 % IACS, worse than 67% of steel grades.
Chemical & Environmental3
Corrosion resistance is not recommended (12/100), worse than 53% of steel grades.
Sustainability4
Producing a kilogram of 6145 QT46-50 takes about 29 MJ of energy and emits 2.1 kg of CO₂ — less than 53% of steel grades. Typical recycled content is 30%.
Manufacturability7
6145 QT46-50's machinability is poor (16/100, worse than 98% of steel grades); weldability poor (30/100); formability fair (45/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with 6145 QT46-50
Is 6145 easy to machine?
Machine in the annealed or ≤32 HRC condition with rigid setups, carbide tooling and generous coolant; above 40 HRC switch to grinding or CBN.
Can 6145 be welded?
Poor weldability (CE ≈0.85): preheat 250–350 °C, use low-hydrogen consumables, and temper immediately after welding to avoid martensitic cracking.
Can 6145 be formed, bent or molded?
Cold-form or coil only in the annealed state; springs are usually hot-coiled or coiled from annealed bar then quenched and tempered, with stress relief after coiling.
What surface finishes work on 6145?
No anodizing — protect with black oxide, phosphate + oil, zinc or Zn-Ni plating (bake at 190–220 °C for hydrogen relief); shot peening markedly raises spring fatigue life.
6145 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 | 0.43 – 0.48 | 0.46 |
| Mn | 0.7 – 0.9 | 0.8 |
| Si | 0.15 – 0.35 | 0.25 |
| Cr | 0.8 – 1.1 | 0.95 |
| V0.15 % minimum per SAE J404 | ≥ 0.15 | 0.18 |
| P | ≤ 0.04 | — |
| S | ≤ 0.04 | — |
| Fe | balance | — |
6145 QT46-50 — frequently asked
What is 6145 QT46-50 used for?
6145 QT46-50 is typically used for springs, shafts and high-strength fasteners. In short: higher hardenability than 6120; cr-V spring and shaft steel; poor weldability.
What is the yield strength of 6145 QT46-50?
6145 QT46-50 has a typical yield strength of 1,480 MPa (215 ksi) and a tensile strength of 1,620 MPa (235 ksi) — stronger than 97% of steel grades. Strength varies by condition: see the 10 listed tempers.
Is 6145 QT46-50 easy to machine?
Not especially — machinability is rated poor (16/100, worse than 98% of steel grades). Machine in the annealed or ≤32 HRC condition with rigid setups, carbide tooling and generous coolant; above 40 HRC switch to grinding or CBN.
Can 6145 QT46-50 be welded?
Not readily — weldability is rated poor (30/100). Poor weldability (CE ≈0.85): preheat 250–350 °C, use low-hydrogen consumables, and temper immediately after welding to avoid martensitic cracking.
What surface finishes work on 6145 QT46-50?
No anodizing — protect with black oxide, phosphate + oil, zinc or Zn-Ni plating (bake at 190–220 °C for hydrogen relief); shot peening markedly raises spring fatigue life.
Can 6145 QT46-50 be formed, bent or molded?
Cold-form or coil only in the annealed state; springs are usually hot-coiled or coiled from annealed bar then quenched and tempered, with stress relief after coiling.
What is the maximum service temperature of 6145 QT46-50?
6145 QT46-50 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.
What is the difference between 6145-A and 6145 QT52-54?
A is the default condition — softest, most machinable condition; the normal supply state for bar that will be machined then quenched and tempered. QT52-54: maximum strength temper for hand tools and wear parts; notch-sensitive, avoid stress raisers. Yield strength is 420 MPa in A versus 1,650 MPa in QT52-54.
Sources
- SAE J404 — Chemical Compositions of SAE Alloy Steels — SAE International (2021)
- ASTM A29/A29M — Steel Bars, Carbon and Alloy, Hot-Wrought — ASTM (2020)
- ASM Handbook Vol.1 — Properties and Selection: Irons, Steels, and High-Performance Alloys — ASM International (1990)
- ASM Handbook Vol.4 — Heat Treating — ASM International (1991)
- Machinery's Handbook, 31st ed. — Industrial Press (2020)
- GB/T 1222 (50CrVA) — SAC (2016)
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.