Steel 817M40
BS 817M40 · AISI/SAE 4340
817M40 is the British Standard nickel-chromium-molybdenum engineering steel directly equivalent to AISI 4340, used quenched and tempered in the R–Z tensile classes.
Reference datasheet — 817M40 is not in the instant-quote catalog. Upload your part and an engineer will quote it in this grade or suggest the closest stocked equivalent.
Values for the T condition
817M40 tempers and conditions
817M40 is supplied in 10 conditions, soft to hard. 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 |
|---|---|---|---|---|---|---|
softened for machining/forming (max 248 HB) | Pick for heavy machining, deep-hole drilling or cold work before final quench and temper. | 470 | 745 | 22 | 217 HB | — |
Condition R | Lowest Q&T level; choose when maximum toughness and easy machining matter more than strength. | 600 | 775 | 20 | 20 HRC | — |
Condition S | General shafting condition with a good strength/toughness balance in large sections. | 660 | 850 | 18 | 25 HRC | — |
TDefault Condition T | The standard stocked En24T bar: strong, tough and still machinable — the default for shafts, gears and studs. | 760 | 930 | 16 | 29 HRC | — |
air cooled from ~870 °C | Grain-refining condition for forgings prior to hardening; not usually a delivery condition for finished parts. | 860 | 1,280 | 12 | 39 HRC | 7 % IACS |
Condition V | High-strength shaft/gear condition; machining now needs carbide tooling. | 900 | 1,075 | 14 | 34 HRC | — |
Solution heat treated (unstable) | For highly stressed bolts, torsion bars and drive components in moderate sections. | 1,000 | 1,150 | 13 | 37 HRC | — |
Condition X | Aerospace/motorsport strength level; grind rather than turn, and control hydrogen during plating. | 1,080 | 1,225 | 12 | 40 HRC | — |
Condition Y | Very high strength for compact highly loaded parts; toughness and notch tolerance are markedly reduced. | 1,150 | 1,300 | 11 | 42 HRC | — |
Condition Z | Maximum-strength condition (low-temperature temper) for landing gear and torsion members; brittle and highly hydrogen-sensitive. | 1,400 | 1,650 | 8 | 49 HRC | — |
Supply forms, finishes and certifications
Ways 817M40 is supplied — form, process route, surface or paperwork — without a datasheet of their own. The property values above apply.
| Option | What it is | Type |
|---|---|---|
U | Condition U | Coating |
What is 817M40?
817M40 is the British Standard nickel-chromium-molybdenum engineering steel directly equivalent to AISI 4340, used quenched and tempered in the R–Z tensile classes. Engineers specify it for critical structural parts where high strength must be combined with good through-thickness toughness and deep hardenability; it is supplied as hot-rolled and cold-drawn bar, heavy forgings and pre-tempered billet. Default-condition values are 760 MPa yield, 930 MPa tensile strength, 16% elongation and 285 HB (29 HRC), with service to 425 °C. Machinability is moderate (45/100), welding requires preheat and immediate temper, and there is no corrosion resistance; 708M40 (4140) is the cheaper option for lighter sections. 817M40 has a density of 7.85 g/cm³ (0.284 lb/in³), heavier than 56% of steel grades. It melts at 1,416°C (2,581 °F). 817M40 has a yield strength of 760 MPa (110 ksi) and a tensile strength of 930 MPa (135 ksi) — stronger than 85% of steel grades. Elongation at break is 16% and the elastic modulus is 205 GPa (29.7 Msi).
What is 817M40 used for?
- aircraft landing gear
- high-strength shafts
- gears
- fasteners
Advantages
- High strength — 760 MPa (110 ksi), better than 85% of steel grades
- Polishes to a fine finish — 68/100, better than 83% of steel grades
817M40 properties
Typical room-temperature values for 817M40-T; bars are the position among steel grades.
Physical3
817M40 has a density of 7.85 g/cm³ (0.284 lb/in³), heavier than 56% of steel grades. It melts at 1,416°C (2,581 °F).
Mechanical16
817M40 has a yield strength of 760 MPa (110 ksi) and a tensile strength of 930 MPa (135 ksi) — stronger than 85% of steel grades. Elongation at break is 16% and the elastic modulus is 205 GPa (29.7 Msi).
Thermal6
817M40 is rated for continuous service to 425°C (797 °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
817M40 conducts electricity at 7 % IACS, worse than 74% of steel grades.
Chemical & Environmental3
Corrosion resistance is not recommended (12/100), worse than 53% of steel grades.
Sustainability4
Producing a kilogram of 817M40 takes about 33 MJ of energy and emits 2.3 kg of CO₂ — more than 76% of steel grades. Typical recycled content is 35%.
Manufacturability7
817M40's machinability is fair (45/100, worse than 65% of steel grades); weldability fair (35/100); formability poor (28/100).
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. 817M40 is highlighted; hover a dot for its name, or open the interactive family chart.
Working with 817M40
Is 817M40 easy to machine?
Machine in the annealed or T condition with rigid setups and carbide tooling; above ~350 HB switch to grinding, and allow stock for distortion if heat treating after rough machining.
Can 817M40 be welded?
Weldable only with care — preheat 250–350 °C, low-hydrogen consumables, and immediate post-weld temper below the original tempering temperature to avoid hard, crack-prone HAZ.
Can 817M40 be formed, bent or molded?
Hot forge at 1050–1200 °C then normalize; cold forming and bending are limited to the annealed condition with generous radii.
817M40 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 | 0.36 – 0.44 | 0.4 |
| Si | 0.1 – 0.35 | 0.25 |
| Mn | 0.45 – 0.7 | 0.6 |
| Ni | 1.3 – 1.7 | 1.5 |
| Cr | 1 – 1.4 | 1.2 |
| Mo | 0.2 – 0.35 | 0.28 |
| S0.015–0.040 for free-machining 817M40 variants | ≤ 0.04 | 0.02 |
| P | ≤ 0.04 | 0.02 |
| Fe | balance |
What surface finishes work on 817M40?
No anodizing — protect with zinc/zinc-nickel or hard chrome plating (bake 190 °C after plating to relieve hydrogen), black oxide, phosphate, paint, or gas nitride for wear surfaces.
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).
Organic Coating
Black / Phosphate
Thermal Spray
Equivalent designations
Standards and trade names that resolve to Steel 817M40 in FabDigit's catalog. Equivalence is nominal — check the exact specification when certification matters.
- AISI / SAE
- 4340
How much does 817M40 cost?
817M40 is a budget-cost steel ($), cheaper than about 90% 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.
817M40 — frequently asked
What is 817M40 used for?
817M40 is typically used for aircraft landing gear, high-strength shafts, gears and fasteners. In short: deep-hardening 4340 equivalent; high strength with toughness; needs preheat to weld.
What is the yield strength of 817M40?
817M40 has a typical yield strength of 760 MPa (110 ksi) and a tensile strength of 930 MPa (135 ksi) — stronger than 85% of steel grades. Strength varies by condition: see the 10 listed tempers.
Is 817M40 easy to machine?
Reasonably — machinability is rated fair (45/100, worse than 65% of steel grades). Machine in the annealed or T condition with rigid setups and carbide tooling; above ~350 HB switch to grinding, and allow stock for distortion if heat treating after rough machining.
Can 817M40 be welded?
With care — weldability is rated fair (35/100). Weldable only with care — preheat 250–350 °C, low-hydrogen consumables, and immediate post-weld temper below the original tempering temperature to avoid hard, crack-prone HAZ.
What surface finishes work on 817M40?
No anodizing — protect with zinc/zinc-nickel or hard chrome plating (bake 190 °C after plating to relieve hydrogen), black oxide, phosphate, paint, or gas nitride for wear surfaces.
Can 817M40 be formed, bent or molded?
Hot forge at 1050–1200 °C then normalize; cold forming and bending are limited to the annealed condition with generous radii.
What is the maximum service temperature of 817M40?
817M40 is rated for continuous use to about 425°C (797 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between 817M40-T and 817M40-Z?
T is the default condition — the standard stocked En24T bar: strong, tough and still machinable — the default for shafts, gears and studs. Z: maximum-strength condition (low-temperature temper) for landing gear and torsion members; brittle and highly hydrogen-sensitive. Yield strength is 760 MPa in T versus 1,400 MPa in Z.
How much does 817M40 cost?
817M40 is a budget-cost steel ($), cheaper than about 90% 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.
Sources
- BS 970-1:1991 / BS 970 Part 3 — Wrought steels for mechanical and allied engineering purposes (817M40) — BSI (1991)
- ASTM A29/A29M and SAE J404 (AISI 4340 equivalent) — ASTM / SAE (2020)
- GB/T 3077 — (40CrNiMoA) — SAC (2015)
- ASM Handbook Vol.1 — Properties and Selection: Irons, Steels and High-Performance Alloys — ASM International (1990)
- ASM Handbook Vol.19 — Fatigue and Fracture (4340 K_IC and S-N data) — ASM International (1996)
- MMPDS-17 low-alloy steel allowables (4340) — Battelle/FAA (2022)
- En24 / 817M40 alloy steel bar datasheets — West Yorkshire Steel / Interlloy (2023)
- 40CrNiMo — Mysteel / 1688 (2026)
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.