Steel 40CrNiMoA
GB 40CrNiMoA · AISI/SAE 4340
40CrNiMoA is a Ni-Cr-Mo low-alloy steel equivalent to AISI 4340 (SNCM439, 34CrNiMo6/1.6582), heat-treatable to ultra-high strength with deep hardenability.
Values for the Q&T condition
40CrNiMoA tempers and conditions
40CrNiMoA is supplied in 10 conditions, soft to hard. Q&T is the default FabDigit quotes; the values on this page are for it.
Compare all 10 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
full anneal ~820–840 °C, slow cool | Softest condition for deep machining, cold forming or as a pre-heat-treat stock; hardness capped at 269 HB per GB/T 3077. | 470 | 745 | 22 | 217 HB | — |
Hot rolled | Cheapest mill condition, bought as forging or machining blank when the shop will heat treat afterwards; properties vary with section and cooling rate. | 620 | 950 | 14 | 30 HRC | 7 % IACS |
Cold drawn | Bright, close-tolerance bar for direct machining of moderately loaded parts without further heat treatment. | 720 | 860 | 12 | 24 HRC | 7 % IACS |
~860–880 °C, air cool | Uniform, refined structure for forgings before final Q&T; already strong but with limited ductility because of the air-hardened bainite/martensite. | 860 | 1,280 | 12 | 39 HRC | — |
High-temper condition | Pick when toughness and machinability matter more than strength, e.g. large forged shafts and pressure-containing parts. | 860 | 1,000 | 18 | 30 HRC | — |
Q&TDefault Quenched and tempered | Standard stocked condition: balanced ~1000–1100 MPa strength with high toughness for shafts, gears and high-strength fasteners. | 950 | 1,080 | 16 | 34 HRC | — |
Mid-temper condition | Most common ordered hardness band for gears, connecting rods and driveline shafts; good strength/toughness compromise. | 1,000 | 1,100 | 15 | 34 HRC | — |
Lower temper | Use for higher-strength ~1300 MPa parts such as aerospace fittings and heavy-duty bolts where some ductility is still needed. | 1,200 | 1,300 | 12 | 40 HRC | — |
Low temper | High-strength ~1500 MPa condition for torsion bars, landing-gear-type parts and tooling; toughness and machinability drop sharply. | 1,350 | 1,500 | 10 | 44 HRC | — |
Quench and stress-relief temper | Maximum strength (~1800 MPa) condition for wear parts and tooling; brittle, notch- and hydrogen-sensitive, so avoid stress concentrations and plate only with post-bake. | 1,600 | 1,800 | 8 | 50 HRC | — |
What is 40CrNiMoA?
40CrNiMoA is a Ni-Cr-Mo low-alloy steel equivalent to AISI 4340 (SNCM439, 34CrNiMo6/1.6582), heat-treatable to ultra-high strength with deep hardenability. It is used for critical aerospace and heavy-machinery shafts, and is stocked as bar and forging stock in annealed, normalized, HR, CD and Q&T tempers from 28-32 HRC to 48-52 HRC; the default Q&T condition gives 950 MPa yield, 1080 MPa tensile, 16% elongation and 320 HB (34 HRC), with service to 400 °C. The high carbon equivalent makes welding a preheat-and-re-temper operation, machinability is 42, and the steel has no inherent corrosion resistance. 4140 is the easier, cheaper alternative below this strength level. 40CrNiMoA 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). 40CrNiMoA has a yield strength of 950 MPa (138 ksi) and a tensile strength of 1,080 MPa (157 ksi) — stronger than 91% of steel grades. Elongation at break is 16% and the elastic modulus is 207 GPa (30 Msi).
What is 40CrNiMoA used for?
- Aircraft landing gear components
- Drive shafts
- Industrial axles
- Gearbox shafts and pinions
- Heavy-duty crankshafts
- High-strength bolts and studs
- Torsion bars
Advantages
- High strength — 950 MPa (138 ksi), better than 91% of steel grades
- Polishes to a fine finish — 65/100, better than 78% of steel grades
40CrNiMoA properties
Typical room-temperature values for 40CrNiMoA-Q&T; bars are the position among steel grades.
Physical3
40CrNiMoA 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
40CrNiMoA has a yield strength of 950 MPa (138 ksi) and a tensile strength of 1,080 MPa (157 ksi) — stronger than 91% of steel grades. Elongation at break is 16% and the elastic modulus is 207 GPa (30 Msi).
Thermal6
40CrNiMoA is rated for continuous service to 400°C (752 °F). It conducts heat at 44 W/m·K (25.4 BTU/hr·ft·°F), better than 57% of steel grades. Thermal expansion is 12.3 µm/m·K (6.83 µin/in·°F).
Electrical3
40CrNiMoA conducts electricity at 7 % IACS, worse than 74% of steel grades.
Chemical & Environmental3
Corrosion resistance is poor (15/100), better than 75% of steel grades.
Sustainability4
Producing a kilogram of 40CrNiMoA takes about 32 MJ of energy and emits 2.3 kg of CO₂ — more than 70% of steel grades. Typical recycled content is 30%.
Manufacturability8
40CrNiMoA's machinability is fair (42/100, worse than 73% of steel grades); weldability poor (30/100); formability poor (25/100).
Common Calculations5
Values are nominal handbook figures for design screening. Certified mill or lot data ships with every FabDigit order on request.
Strength versus weight in the steel family
Yield strength against density for every steel grade FabDigit runs. 40CrNiMoA is highlighted; hover a dot for its name, or open the interactive family chart.
Working with 40CrNiMoA
Is 40CrNiMoA easy to machine?
Machine in the annealed or ≤32 HRC condition with rigid setups, sharp carbide and generous coolant; above 40 HRC switch to CBN/ceramic turning or grinding, and rough before final temper where possible.
Can 40CrNiMoA be welded?
High carbon equivalent means preheat 250–350 °C, low-hydrogen filler (e.g. ER100S/ER110S or matching), interpass control and immediate PWHT/re-temper; avoid welding parts already at high hardness.
Can 40CrNiMoA be formed, bent or molded?
Hot forge 1100–1200 °C, finish above 900 °C and normalize afterwards; cold forming is limited to the annealed condition and mild bends only.
Manufacturability
The process limits FabDigit applies to 40CrNiMoA. Every 40CrNiMoA part is priced by an engineer; design inside these and the quote comes back without a redesign loop.
CNC machining
| Machinability | Better42 / 100 |
|---|---|
| ISO material group | P.2 |
| Cutting speed (rough / finish) | 180 / 210 m/min |
| Minimum wall | 0.8 mm |
| Minimum internal radius | 1 mm |
| Drill depth limit | 5× diameter |
| Best surface (machined / polished) | Ra 1.6 / — |
| Hardenable after machining | No |
Sheet metal
| Formability | Fair25 / 100 |
|---|---|
| Weldability | Better30 / 100 |
40CrNiMoA 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 | 0.5 – 0.8 | 0.65 |
| Cr | 0.6 – 0.9 | 0.75 |
| Ni | 1.25 – 1.65 | 1.45 |
| Mo | 0.15 – 0.25 | 0.2 |
| PA grade (high-quality) limit | ≤ 0.03 | |
| SA grade (high-quality) limit | ≤ 0.03 | |
| Curesidual | ≤ 0.3 | |
| Fe | balance |
What surface finishes work on 40CrNiMoA?
Not anodizable — protect with black oxide, phosphate + oil, Zn or Cd plating, hard chrome, or gas nitriding (surface 550–650 HV); bake 190–220 °C after electroplating high-hardness parts to relieve hydrogen.
Surface treatments FabDigit runs on steel parts — pick them in the quote configurator or call them out on the drawing. Each links to its datasheet in the surface-finish library (thickness, specs, call-out, material verdicts).
Plating
CVD Coating
Black / Phosphate
Thermal Spray
Equivalent designations
Standards and trade names that resolve to Steel 40CrNiMoA in FabDigit's catalog. Equivalence is nominal — check the exact specification when certification matters.
How much does 40CrNiMoA cost?
40CrNiMoA is a standard-cost steel ($$), cheaper than about 61% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
40CrNiMoA — frequently asked
What is 40CrNiMoA used for?
40CrNiMoA is typically used for aircraft landing gear components, drive shafts, industrial axles, gearbox shafts and pinions, heavy-duty crankshafts and high-strength bolts and studs. In short: premium Ni-Cr-Mo bar.
What is the yield strength of 40CrNiMoA?
40CrNiMoA has a typical yield strength of 950 MPa (138 ksi) and a tensile strength of 1,080 MPa (157 ksi) — stronger than 91% of steel grades. Strength varies by condition: see the 10 listed tempers.
Is 40CrNiMoA easy to machine?
Not especially — machinability is rated fair (42/100, worse than 73% of steel grades). Machine in the annealed or ≤32 HRC condition with rigid setups, sharp carbide and generous coolant; above 40 HRC switch to CBN/ceramic turning or grinding, and rough before final temper where possible.
Can 40CrNiMoA be welded?
Not readily — weldability is rated poor (30/100). High carbon equivalent means preheat 250–350 °C, low-hydrogen filler (e.g. ER100S/ER110S or matching), interpass control and immediate PWHT/re-temper; avoid welding parts already at high hardness.
What surface finishes work on 40CrNiMoA?
Not anodizable — protect with black oxide, phosphate + oil, Zn or Cd plating, hard chrome, or gas nitriding (surface 550–650 HV); bake 190–220 °C after electroplating high-hardness parts to relieve hydrogen.
Can 40CrNiMoA be formed, bent or molded?
Hot forge 1100–1200 °C, finish above 900 °C and normalize afterwards; cold forming is limited to the annealed condition and mild bends only.
What is the maximum service temperature of 40CrNiMoA?
40CrNiMoA is rated for continuous use to about 400°C (752 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between 40CrNiMoA Q&T and 40CrNiMoA-HR?
Q&T is the default condition — standard stocked condition: balanced ~1000–1100 MPa strength with high toughness for shafts, gears and high-strength fasteners. HR: cheapest mill condition, bought as forging or machining blank when the shop will heat treat afterwards; properties vary with section and cooling rate. Yield strength is 950 MPa in Q&T versus 620 MPa in HR.
How much does 40CrNiMoA cost?
40CrNiMoA is a standard-cost steel ($$), cheaper than about 61% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
Can FabDigit make parts in 40CrNiMoA?
Yes — 40CrNiMoA is available for CNC machining and sheet metal; every part is priced by an engineer rather than instantly. Upload a STEP file to get a price and a DFM check.
Sources
- GB/T 3077 Alloy structural steels (2015)
- ASTM A29/A29M and SAE J404 (4340) — ASTM / SAE (2020)
- ASM Handbook Vol.1 — Properties and Selection: Irons, Steels, and High-Performance Alloys — ASM International (1990)
- ASM Handbook Vol.19 — Fatigue and Fracture — ASM International (1996)
- MMPDS-2023 typical properties for 4340 steel — Battelle/FAA (2023)
- Machinery's Handbook, 31st ed. (machinability ratings) — Industrial Press (2020)
- (40CrNiMoA) — Mysteel / 1688 (2025)
Property data is compiled from published supplier and standards handbooks and normalised for comparison; hardness values on non-Brinell scales are converted approximately for charting only. Manufacturability limits are FabDigit quote-engine defaults and may be relaxed by engineering review. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.