Steel 817M40-Y (Condition Y)
Hardness band
BS 817M40 · AISI/SAE 4340
Very high strength for compact highly loaded parts; toughness and notch tolerance are markedly reduced.
Values for the Y condition
Other 817M40 tempers and conditions
817M40 is listed in 10 conditions; see the grade overview at 817M40.
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 | — |
YThis page 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 | — |
What is 817M40-Y?
817M40-Y is 817M40 heat treated to Y — very high strength for compact highly loaded parts; toughness and notch tolerance are markedly reduced. 817M40-Y 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 205 GPa (29.7 Msi). 817M40-Y 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). T is the default condition FabDigit quotes; Y is available on request or by drawing note.
Advantages
- High strength — 1,150 MPa (167 ksi), better than 94% of steel grades
- Polishes to a fine finish — 68/100, better than 83% of steel grades
Limitations
- Difficult to machine — 22/100, worse than 95% of steel grades
- Limited ductility — 11%, worse than 89% of steel grades
- Limited service temperature — 300°C (572 °F), worse than 78% of steel grades
- Low fracture toughness — 62 MPa·√m (56.4 ksi·√in), worse than 76% of steel grades
817M40-Y properties
Typical room-temperature values for 817M40-Y; 12 are specific to this condition. Other listed values are 817M40 reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
817M40-Y 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-Y 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 205 GPa (29.7 Msi).
Thermal6
817M40-Y is rated for continuous service to 300°C (572 °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-Y 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-Y 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-Y's machinability is poor (22/100, worse than 95% of steel grades); weldability fair (35/100); formability poor (28/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with 817M40-Y
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.
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.
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 | — |
817M40-Y — frequently asked
What is 817M40-Y used for?
817M40-Y 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-Y?
817M40-Y 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 10 listed tempers.
Is 817M40-Y easy to machine?
Not especially — machinability is rated poor (22/100, worse than 95% 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-Y 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-Y?
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-Y 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-Y?
817M40-Y is rated for continuous use to about 300°C (572 °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.
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. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.