Steel 826M40-X
Hardness band
BS 826M40
X = hardened and tempered, 1150–1300 MPa
High-strength aerospace/racing condition; machining is hard and toughness starts to fall.
Values for the X condition
Other 826M40 tempers and conditions
826M40 is listed in 9 conditions; see the grade overview at 826M40.
Compare all 9 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
Annealed (softened, ~ max 248 HB) | Softest condition for deep machining, forming or re-heat-treatment of forgings. | 480 | 750 | 22 | 225 HB | — |
Normalized (air cooled from ~870 °C) | Grain-refined intermediate condition for forgings before final Q&T. | 620 | 950 | 16 | 30 HRC | 7.4 % IACS |
TDefault Hardened and tempered, 850–1000 MPa | Most commonly stocked Q&T condition — best balance of strength, toughness and machinability for large shafts. | 730 | 930 | 17 | 29 HRC | — |
Q&T then gas nitrided case | Use when a wear- and fatigue-resistant surface (≈600–700 HV case) is needed on a tough Q&T core. | 810 | 1,000 | 12 | 57 HRC | 7.2 % IACS |
Hardened and tempered, 1000–1150 MPa | General high-duty gear and shaft condition with still-workable machinability. | 900 | 1,075 | 14 | 34 HRC | 7.2 % IACS |
Solution heat treated (unstable) | Choose for highly loaded transmission and landing-gear components needing >1075 MPa. | 985 | 1,150 | 13 | 37 HRC | 7.2 % IACS |
XThis page Hardened and tempered, 1150–1300 MPa | High-strength aerospace/racing condition; machining is hard and toughness starts to fall. | 1,060 | 1,225 | 12 | 40 HRC | — |
Hardened and tempered, 1225–1375 MPa | Very high strength; usually finish-ground after heat treatment, hydrogen control essential. | 1,140 | 1,300 | 11 | 42 HRC | — |
Hardened and tempered, 1550 MPa min | Maximum-strength condition for small, well-controlled sections; low ductility and notch sensitivity. | 1,400 | 1,620 | 9 | 49 HRC | — |
What is 826M40-X?
826M40-X is 826M40 heat treated to X — high-strength aerospace/racing condition; machining is hard and toughness starts to fall. 826M40-X has a yield strength of 1,060 MPa (154 ksi) and a tensile strength of 1,225 MPa (178 ksi) — stronger than 93% of steel grades. Elongation at break is 12% and the elastic modulus is 208 GPa (30.2 Msi). 826M40-X 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). T is the default condition FabDigit quotes; X is available on request or by drawing note.
Advantages
- High strength — 1,060 MPa (154 ksi), better than 93% of steel grades
- High service temperature — 450°C (842 °F), better than 86% of steel grades
- Polishes to a fine finish — 65/100, better than 78% of steel grades
Limitations
- Limited ductility — 12%, worse than 84% of steel grades
- High embodied carbon — 2.5 kg CO₂/kg, worse than 82% of steel grades
- Difficult to weld — 25/100, worse than 77% of steel grades
826M40-X properties
Typical room-temperature values for 826M40-X; 10 are specific to this condition. Other listed values are 826M40 reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
826M40-X 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
826M40-X has a yield strength of 1,060 MPa (154 ksi) and a tensile strength of 1,225 MPa (178 ksi) — stronger than 93% of steel grades. Elongation at break is 12% and the elastic modulus is 208 GPa (30.2 Msi).
Thermal6
826M40-X is rated for continuous service to 450°C (842 °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
826M40-X conducts electricity at 7.2 % IACS, worse than 71% of steel grades.
Chemical & Environmental3
Corrosion resistance is not recommended (13/100), better than 66% of steel grades.
Sustainability4
Producing a kilogram of 826M40-X takes about 33 MJ of energy and emits 2.5 kg of CO₂ — more than 76% of steel grades. Typical recycled content is 30%.
Manufacturability8
826M40-X's machinability is fair (45/100, worse than 65% of steel grades); weldability poor (25/100); formability poor (25/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with 826M40-X
Is 826M40 easy to machine?
Machine in annealed or T condition with rigid setups, carbide tooling and flood coolant; above ~340 HB use reduced speeds or grind, and rough before final Q&T where possible.
Can 826M40 be welded?
Poor weldability (CE ≈ 1.0) — if unavoidable, use low-hydrogen consumables, 250–350 °C preheat, controlled interpass and immediate post-weld temper/stress relief below the last tempering temperature.
Can 826M40 be formed, bent or molded?
Hot forge 1150–850 °C then slow cool/anneal; cold forming limited to annealed stock and generous bend radii.
What surface finishes work on 826M40?
No natural corrosion protection: phosphate + oil, paint, zinc or hard chrome plate; bake 190–200 °C for 4–24 h after plating on X/Y/Z conditions to avoid hydrogen embrittlement; nitriding gives a hard wear surface.
826M40 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 – 0.4 | 0.25 |
| Mn | 0.45 – 0.7 | 0.57 |
| P | ≤ 0.04 | — |
| S | ≤ 0.04 | — |
| Cr | 0.5 – 0.8 | 0.65 |
| Mo | 0.45 – 0.65 | 0.55 |
| Ni | 2.3 – 2.8 | 2.55 |
| Fe | balance | — |
826M40-X — frequently asked
What is 826M40-X used for?
826M40-X is typically used for heavy shafts, gears and structural components. In short: heavy-section 4340 variant; deepest hardenability in family; poor weldability, CE ≈ 1.0.
What is the yield strength of 826M40-X?
826M40-X has a typical yield strength of 1,060 MPa (154 ksi) and a tensile strength of 1,225 MPa (178 ksi) — stronger than 93% of steel grades. Strength varies by condition: see the 9 listed tempers.
Is 826M40-X easy to machine?
Reasonably — machinability is rated fair (45/100, worse than 65% of steel grades). Machine in annealed or T condition with rigid setups, carbide tooling and flood coolant; above ~340 HB use reduced speeds or grind, and rough before final Q&T where possible.
Can 826M40-X be welded?
Not readily — weldability is rated poor (25/100). Poor weldability (CE ≈ 1.0) — if unavoidable, use low-hydrogen consumables, 250–350 °C preheat, controlled interpass and immediate post-weld temper/stress relief below the last tempering temperature.
What surface finishes work on 826M40-X?
No natural corrosion protection: phosphate + oil, paint, zinc or hard chrome plate; bake 190–200 °C for 4–24 h after plating on X/Y/Z conditions to avoid hydrogen embrittlement; nitriding gives a hard wear surface.
Can 826M40-X be formed, bent or molded?
Hot forge 1150–850 °C then slow cool/anneal; cold forming limited to annealed stock and generous bend radii.
What is the maximum service temperature of 826M40-X?
826M40-X is rated for continuous use to about 450°C (842 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between 826M40-T and 826M40-Z?
T is the default condition — most commonly stocked Q&T condition — best balance of strength, toughness and machinability for large shafts. Z: maximum-strength condition for small, well-controlled sections; low ductility and notch sensitivity. Yield strength is 730 MPa in T versus 1,400 MPa in Z.
Sources
- BS 970-3: Wrought steels for mechanical and allied engineering purposes (826M40 / EN26) — BSI (1991)
- 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)
- EN26 / 826M40 Ni-Cr-Mo alloy steel bar datasheet — UK alloy steel stockists (West Yorkshire Steel / Smiths) (2023)
- Machinery's Handbook — machinability ratings for alloy steels — Industrial Press (2020)
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.