Steel 40CrMnMo-QT550
Heat-treated state
GB 40CrMnMo
Higher-strength temper for highly loaded medium-section parts where toughness can be traded for strength.
Values for the QT550 condition
Other 40CrMnMo tempers and conditions
40CrMnMo is listed in 11 conditions; see the grade overview at 40CrMnMo.
Compare all 11 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
Solution annealed | Softest condition for deep machining, cold shearing or before final quench-and-temper. | 390 | 660 | 22 | 197 HB | — |
Hot rolled | Cheapest mill condition for stock that will be re-heat-treated after rough machining. | 520 | 820 | 15 | 21 HRC | 8 % IACS |
Normalized | Grain-refining pre-treatment for large forgings; also a low-cost medium-strength delivery state. | 600 | 900 | 16 | 26 HRC | 8 % IACS |
Cold drawn | Bright, size-accurate small-diameter bar for shafts and pins machined without further heat treatment. | 720 | 860 | 10 | 25 HRC | 8 % IACS |
Q&T 28–32 HRC (≈269–302 HB) pre-hardened block | Pre-hardened plate/block for large plastic moulds and jig plates machined in the delivered state. | 820 | 980 | 15 | 30 HRC | 8 % IACS |
QT600Default oil quench 850 °C + temper 600 °C ( , ≥980 MPa) | Standard GB/T 3077 delivery condition — best strength/toughness balance for shafts, gears and heavy forgings. | 850 | 1,030 | 14 | 31 HRC | — |
Nitrided | Choose when a hard, fatigue-boosting 0.2–0.5 mm case is needed on a tough Q&T core with minimal distortion. | 850 | 1,030 | 13 | 56 HRC | 8 % IACS |
Induction hardened | For journal and spline wear surfaces on Q&T shafts needing a hard, compressively stressed skin. | 850 | 1,030 | 14 | 54 HRC | 7.5 % IACS |
Q&T 32–36 HRC (≈302–341 HB) | Higher-hardness Q&T for mill rolls, mandrels and wear-loaded shafts still machinable with carbide. | 970 | 1,120 | 12 | 34 HRC | 8 % IACS |
QT550This page oil quench + temper 550 °C (≈38–42 HRC) | Higher-strength temper for highly loaded medium-section parts where toughness can be traded for strength. | 1,150 | 1,300 | 11 | 40 HRC | — |
oil quench + temper 450 °C (≈45–48 HRC) | Maximum practical hardness temper for wear parts; low toughness and temper-brittleness risk, use only in small sections. | 1,350 | 1,500 | 9 | 46 HRC | 7.5 % IACS |
What is 40CrMnMo-QT550?
40CrMnMo-QT550 is 40CrMnMo heat treated to QT550 — higher-strength temper for highly loaded medium-section parts where toughness can be traded for strength. 40CrMnMo-QT550 has a yield strength of 1,150 MPa (167 ksi) and a tensile strength of 1,300 MPa (189 ksi) — stronger than 94% of steel grades. Elongation at break is 11% and the elastic modulus is 210 GPa (30.5 Msi). 40CrMnMo-QT550 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). QT600 is the default condition FabDigit quotes; QT550 is available on request or by drawing note.
Advantages
- High strength — 1,150 MPa (167 ksi), better than 94% of steel grades
Limitations
- Limited ductility — 11%, worse than 89% of steel grades
- Difficult to machine — 35/100, worse than 84% of steel grades
- Low fracture toughness — 65 MPa·√m (59.2 ksi·√in), worse than 75% of steel grades
40CrMnMo-QT550 properties
Typical room-temperature values for 40CrMnMo-QT550; 11 are specific to this condition. Other listed values are 40CrMnMo reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
40CrMnMo-QT550 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
40CrMnMo-QT550 has a yield strength of 1,150 MPa (167 ksi) and a tensile strength of 1,300 MPa (189 ksi) — stronger than 94% of steel grades. Elongation at break is 11% and the elastic modulus is 210 GPa (30.5 Msi).
Thermal6
40CrMnMo-QT550 is rated for continuous service to 350°C (662 °F). It conducts heat at 42 W/m·K (24.3 BTU/hr·ft·°F), worse than 56% of steel grades. Thermal expansion is 12.3 µm/m·K (6.83 µin/in·°F).
Electrical3
40CrMnMo-QT550 conducts electricity at 8 % IACS, better than 55% of steel grades.
Chemical & Environmental3
Corrosion resistance is not recommended (12/100), worse than 53% of steel grades.
Sustainability4
Producing a kilogram of 40CrMnMo-QT550 takes about 30 MJ of energy and emits 2.1 kg of CO₂ — more than 56% of steel grades. Typical recycled content is 30%.
Manufacturability6
40CrMnMo-QT550's machinability is fair (35/100, worse than 84% of steel grades); weldability fair (35/100); formability poor (25/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with 40CrMnMo-QT550
Is 40CrMnMo easy to machine?
Rough machine annealed (≈197 HB) then Q&T; at 300 HB use rigid setups, coated carbide at 90–140 m/min and positive rake to control work-hardening and built-up edge.
Can 40CrMnMo be welded?
CE ≈ 0.85 — preheat 250–350 °C, low-hydrogen consumables, interpass control and immediate post-weld temper at 30–50 °C below the part's tempering temperature; avoid welding above 40 HRC.
Can 40CrMnMo be formed, bent or molded?
Hot forge 1150–850 °C with slow cooling or immediate anneal to prevent flake/quench cracks; cold forming limited to the annealed state and gentle bends.
What surface finishes work on 40CrMnMo?
No corrosion resistance bare — protect with oil, phosphating, black oxide, paint, hard chrome or nitriding; VD-degassed heats polish to mould-grade SPI-B finishes.
40CrMnMo 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 |
|---|---|---|
| CGB/T 3077 | 0.37 – 0.45 | 0.41 |
| Si | 0.17 – 0.37 | 0.27 |
| Mnraised vs 42CrMo4 for hardenability | 0.9 – 1.2 | 1.05 |
| Cr | 0.9 – 1.2 | 1.05 |
| Mo | 0.2 – 0.3 | 0.25 |
| Niresidual | ≤ 0.3 | — |
| Curesidual | ≤ 0.25 | — |
| P0.025 max for high-grade quality | ≤ 0.03 | — |
| S0.025 max for high-grade quality | ≤ 0.03 | — |
| Fe | balance | — |
40CrMnMo-QT550 — frequently asked
What is 40CrMnMo-QT550 used for?
40CrMnMo-QT550 is typically used for large shafts, rolling mill parts and heavy forgings. In short: deep-hardening 42CrMo4 type; suits large forged sections; nitridable and induction-hardenable.
What is the yield strength of 40CrMnMo-QT550?
40CrMnMo-QT550 has a typical yield strength of 1,150 MPa (167 ksi) and a tensile strength of 1,300 MPa (189 ksi) — stronger than 94% of steel grades. Strength varies by condition: see the 11 listed tempers.
Is 40CrMnMo-QT550 easy to machine?
Not especially — machinability is rated fair (35/100, worse than 84% of steel grades). Rough machine annealed (≈197 HB) then Q&T; at 300 HB use rigid setups, coated carbide at 90–140 m/min and positive rake to control work-hardening and built-up edge.
Can 40CrMnMo-QT550 be welded?
With care — weldability is rated fair (35/100). CE ≈ 0.85 — preheat 250–350 °C, low-hydrogen consumables, interpass control and immediate post-weld temper at 30–50 °C below the part's tempering temperature; avoid welding above 40 HRC.
What surface finishes work on 40CrMnMo-QT550?
No corrosion resistance bare — protect with oil, phosphating, black oxide, paint, hard chrome or nitriding; VD-degassed heats polish to mould-grade SPI-B finishes.
Can 40CrMnMo-QT550 be formed, bent or molded?
Hot forge 1150–850 °C with slow cooling or immediate anneal to prevent flake/quench cracks; cold forming limited to the annealed state and gentle bends.
What is the maximum service temperature of 40CrMnMo-QT550?
40CrMnMo-QT550 is rated for continuous use to about 350°C (662 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between 40CrMnMo-QT600 and 40CrMnMo-QT450?
QT600 is the default condition — standard GB/T 3077 delivery condition — best strength/toughness balance for shafts, gears and heavy forgings. QT450: maximum practical hardness temper for wear parts; low toughness and temper-brittleness risk, use only in small sections. Yield strength is 850 MPa in QT600 versus 1,350 MPa in QT450.
Sources
- GB/T 3077 Alloy structural steels (2015)
- EN 10083-3 Steels for quenching and tempering — alloy steels (42CrMo4 comparison) — CEN (2006)
- 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)
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.