Steel 40MnB-Q (As-Quenched)
Heat-treated state
GB 40MnB
Intermediate state only — full martensite hardness but brittle; must be tempered before service.
Values for the Q condition
Other 40MnB tempers and conditions
40MnB is listed in 11 conditions; see the grade overview at 40MnB.
Compare all 11 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
Solution annealed | Softest state, per GB/T 3077 hardness delivery requirement; choose for deep machining or cold heading of bolt blanks. | 350 | 610 | 21 | 185 HB | — |
Hot rolled | Cheapest mill condition for stock that will be re-heat-treated after machining. | 420 | 700 | 16 | 220 HB | — |
Normalized | Uniform fine pearlitic structure for machining stock or as pre-treatment before quenching. | 480 | 780 | 16 | 21 HRC | 8 % IACS |
Cold drawn | Bright, close-tolerance bar for shafts and pins used without further heat treatment. | 620 | 760 | 10 | 225 HB | — |
Q&T | Pick when impact toughness and machinability matter more than peak strength (large shafts, dynamically loaded parts). | 730 | 900 | 15 | 27 HRC | — |
QTDefault Quenched and tempered | Standard specification condition and the usual stocked/supplied state for shafts, arms and grade 8.8–10.9 fasteners. | 850 | 1,030 | 12 | 31 HRC | — |
Induction hardened | Choose for shaft journals and spline flanks needing wear resistance with a tough Q&T core. | 850 | 1,030 | 11 | 55 HRC | 7.5 % IACS |
Q&T to 33–38 HRC | Higher-strength Q&T band for gear blanks, splined shafts and wear-loaded parts. | 980 | 1,150 | 11 | 35 HRC | — |
Q&T to 40–45 HRC | Use where wear and high yield are needed and section is thin; toughness begins to fall off. | 1,230 | 1,400 | 9 | 43 HRC | — |
Q&T | For high-hardness wear parts and small high-strength fasteners; low ductility, notch-sensitive. | 1,380 | 1,620 | 8 | 48 HRC | — |
QThis page As-Quenched | Intermediate state only — full martensite hardness but brittle; must be tempered before service. | 1,550 | 2,000 | 2 | 56 HRC | 6.6 % IACS |
What is 40MnB-Q?
40MnB-Q is 40MnB heat treated to Q — intermediate state only — full martensite hardness but brittle; must be tempered before service. 40MnB-Q has a yield strength of 1,550 MPa (225 ksi) and a tensile strength of 2,000 MPa (290 ksi) — stronger than 97% of steel grades. Elongation at break is 2% and the elastic modulus is 206 GPa (29.9 Msi). 40MnB-Q 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). QT is the default condition FabDigit quotes; Q is available on request or by drawing note.
Advantages
- High strength — 1,550 MPa (225 ksi), better than 97% of steel grades
Limitations
- Limited ductility — 2%, worse than 99% of steel grades
- Limited service temperature — 150°C (302 °F), worse than 99% of steel grades
- Difficult to machine — 12/100, worse than 99% of steel grades
- Difficult to weld — 8/100, worse than 99% of steel grades
- Limited formability — 3/100, worse than 99% of steel grades
40MnB-Q properties
Typical room-temperature values for 40MnB-Q; 22 are specific to this condition. Other listed values are 40MnB reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
40MnB-Q 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
40MnB-Q has a yield strength of 1,550 MPa (225 ksi) and a tensile strength of 2,000 MPa (290 ksi) — stronger than 97% of steel grades. Elongation at break is 2% and the elastic modulus is 206 GPa (29.9 Msi).
Thermal6
40MnB-Q is rated for continuous service to 150°C (302 °F). It conducts heat at 36 W/m·K (20.8 BTU/hr·ft·°F), worse than 73% of steel grades. Thermal expansion is 12.2 µm/m·K (6.78 µin/in·°F).
Electrical3
40MnB-Q conducts electricity at 6.6 % IACS, worse than 76% of steel grades.
Chemical & Environmental3
Corrosion resistance is not recommended (9/100), worse than 98% of steel grades.
Sustainability4
Producing a kilogram of 40MnB-Q takes about 26 MJ of energy and emits 2 kg of CO₂ — less than 64% of steel grades. Typical recycled content is 25%.
Manufacturability6
40MnB-Q's machinability is not recommended (12/100, worse than 99% of steel grades); weldability not recommended (8/100); formability not recommended (3/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with 40MnB-Q
Is 40MnB easy to machine?
Machine in annealed or normalized state (180–235 HB) with carbide tooling; at 300 HB Q&T expect ~55 % of 1212 rates, and finish-grind anything above 40 HRC.
Can 40MnB be welded?
Poor weldability at 0.40 %C with boron — preheat 200–300 °C, low-hydrogen consumables, slow cooling and temper at 550–600 °C after welding; avoid welding on Q&T parts near critical sections.
Can 40MnB be formed, bent or molded?
Hot forge 1150–850 °C then normalize; cold heading/upsetting of bolt blanks only after spheroidize annealing, and boron content makes it strongly quench-hardening in oil.
What surface finishes work on 40MnB?
No corrosion resistance — protect with black oxide, phosphate + oil, zinc electroplate (bake to avoid hydrogen embrittlement above 1000 MPa), Dacromet or paint; tempered martensite polishes and hard-chromes well.
40MnB 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 | 0.37 – 0.44 | 0.4 |
| Si | 0.17 – 0.37 | 0.27 |
| Mn | 1.1 – 1.4 | 1.25 |
| BAcid-soluble boron; provides hardenability in place of Cr | 5×10⁻⁴ – 0 | 0 |
| Crresidual | ≤ 0.3 | — |
| Niresidual | ≤ 0.3 | — |
| Curesidual | ≤ 0.25 | — |
| P | ≤ 0.03 | — |
| S | ≤ 0.03 | — |
| Fe | balance | — |
40MnB-Q — frequently asked
What is 40MnB-Q used for?
40MnB-Q is typically used for shafts, bolts and connecting rods. In short: direct 40Cr replacement; 1030 MPa Q&T strength; poor weldability, oil-hardening.
What is the yield strength of 40MnB-Q?
40MnB-Q has a typical yield strength of 1,550 MPa (225 ksi) and a tensile strength of 2,000 MPa (290 ksi) — stronger than 97% of steel grades. Strength varies by condition: see the 11 listed tempers.
Is 40MnB-Q easy to machine?
Not especially — machinability is rated not recommended (12/100, worse than 99% of steel grades). Machine in annealed or normalized state (180–235 HB) with carbide tooling; at 300 HB Q&T expect ~55 % of 1212 rates, and finish-grind anything above 40 HRC.
Can 40MnB-Q be welded?
Not readily — weldability is rated not recommended (8/100). Poor weldability at 0.40 %C with boron — preheat 200–300 °C, low-hydrogen consumables, slow cooling and temper at 550–600 °C after welding; avoid welding on Q&T parts near critical sections.
What surface finishes work on 40MnB-Q?
No corrosion resistance — protect with black oxide, phosphate + oil, zinc electroplate (bake to avoid hydrogen embrittlement above 1000 MPa), Dacromet or paint; tempered martensite polishes and hard-chromes well.
Can 40MnB-Q be formed, bent or molded?
Hot forge 1150–850 °C then normalize; cold heading/upsetting of bolt blanks only after spheroidize annealing, and boron content makes it strongly quench-hardening in oil.
What is the maximum service temperature of 40MnB-Q?
40MnB-Q is rated for continuous use to about 150°C (302 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between 40MnB-QT and 40MnB-Q?
QT is the default condition — standard specification condition and the usual stocked/supplied state for shafts, arms and grade 8.8–10.9 fasteners. Q: intermediate state only — full martensite hardness but brittle; must be tempered before service. Yield strength is 850 MPa in QT versus 1,550 MPa in Q.
Sources
- GB/T 3077 (Alloy structural steels) — SAC / (2015)
- GB/T 699 / GB/T 1172 — SAC (1999)
- (Mechanical Design Handbook) (2018)
- ASM Handbook Vol.1: Properties and Selection — Irons, Steels — 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.