Steel En25-X (Q&T Condition X)
Hardness band
High-strength band for crankshafts, torsion bars and landing-gear-type components.
Values for the X condition
Other En25 tempers and conditions
En25 is listed in 10 conditions; see the grade overview at En25.
Compare all 10 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
softened for machining/forming | Softest condition; pick for heavy machining or cold work before final hardening and tempering. | 440 | 700 | 22 | 210 HB | — |
Hot rolled | Mill-condition stock bought for subsequent forging and full heat treatment by the customer. | 560 | 880 | 16 | 25 HRC | 7.2 % IACS |
air cooled from austenitizing temperature | Uniform grain structure for forgings and stock prior to final heat treatment. | 570 | 850 | 18 | 24 HRC | 7.2 % IACS |
TDefault Q&T Condition T | Most commonly stocked hardened-and-tempered band: best balance of strength, toughness and machinability. | 700 | 930 | 15 | 28 HRC | — |
Q&T + Gas Nitrided case | Choose when wear resistance and fatigue life at journals or gear flanks matter; core stays at the Q&T condition. | 820 | 1,000 | 12 | 58 HRC | 7.2 % IACS |
Q&T Condition V | Higher-strength band for gear blanks and heavily loaded axles. | 850 | 1,070 | 13 | 34 HRC | — |
Solution heat treated (unstable) | For high-duty transmission and aerospace parts where strength dominates over machinability. | 930 | 1,150 | 12 | 37 HRC | — |
XThis page Q&T Condition X | High-strength band for crankshafts, torsion bars and landing-gear-type components. | 1,010 | 1,230 | 11 | 40 HRC | — |
Q&T Condition Y | Near-maximum tempered strength; check notch sensitivity and hydrogen embrittlement risk if plated. | 1,090 | 1,300 | 10 | 42 HRC | — |
Q&T Condition Z | Maximum-strength low-temper condition for special high-stress parts; toughness and machinability are marginal. | 1,330 | 1,620 | 8 | 49 HRC | — |
What is En25-X?
En25-X is En25 heat treated to X — high-strength band for crankshafts, torsion bars and landing-gear-type components. En25-X has a yield strength of 1,010 MPa (146 ksi) and a tensile strength of 1,230 MPa (178 ksi) — stronger than 92% of steel grades. Elongation at break is 11% and the elastic modulus is 207 GPa (30 Msi). En25-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 — 1,010 MPa (146 ksi), better than 92% of steel grades
- Polishes to a fine finish — 70/100, better than 87% of steel grades
Limitations
- Limited ductility — 11%, worse than 89% of steel grades
- Limited formability — 20/100, worse than 80% of steel grades
- Difficult to weld — 25/100, worse than 77% of steel grades
En25-X properties
Typical room-temperature values for En25-X; 10 are specific to this condition. Other listed values are En25 reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
En25-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
En25-X has a yield strength of 1,010 MPa (146 ksi) and a tensile strength of 1,230 MPa (178 ksi) — stronger than 92% of steel grades. Elongation at break is 11% and the elastic modulus is 207 GPa (30 Msi).
Thermal6
En25-X is rated for continuous service to 400°C (752 °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
En25-X conducts electricity at 7.2 % IACS, worse than 71% of steel grades.
Chemical & Environmental3
Corrosion resistance is not recommended (14/100), better than 70% of steel grades.
Sustainability4
Producing a kilogram of En25-X takes about 34 MJ of energy and emits 2.4 kg of CO₂ — more than 82% of steel grades. Typical recycled content is 35%.
Manufacturability7
En25-X's machinability is fair (45/100, worse than 65% of steel grades); weldability poor (25/100); formability poor (20/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with En25-X
Is En25 easy to machine?
Machine in the annealed or condition-T state with rigid setups, sharp carbide and generous coolant; above ~340 HB expect reduced speeds and consider grinding for finish features.
Can En25 be welded?
Weldable only with care: preheat 250–350 °C, low-hydrogen consumables, and immediate post-weld temper below the last tempering temperature; avoid welding on finished Q&T parts.
Can En25 be formed, bent or molded?
Hot forge at 1050–1200 °C then normalize; cold forming is impractical except mild straightening in the annealed condition.
What surface finishes work on En25?
Not anodizable — protect with black oxide, phosphate + oil, hard chrome, zinc or cadmium plating (bake to relieve hydrogen at high strength), or nitride for wear surfaces.
En25 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 | 0.27 – 0.35 | 0.31 |
| Si | 0.1 – 0.35 | 0.25 |
| Mn | 0.45 – 0.7 | 0.58 |
| Ni | 2.3 – 2.8 | 2.55 |
| Cr | 0.5 – 0.8 | 0.65 |
| Mo | 0.45 – 0.65 | 0.55 |
| P | ≤ 0.04 | — |
| Smax; 826M31 typically 0.035 max, resulphurised variants excluded | ≤ 0.04 | — |
| Fe | balance | — |
En25-X — frequently asked
What is En25-X used for?
En25-X is typically used for heavy-duty shafts, gears, aircraft components and axles. In short: 4340-class Ni-Cr-Mo steel; high strength with core toughness; deep-hardening large sections.
What is the yield strength of En25-X?
En25-X has a typical yield strength of 1,010 MPa (146 ksi) and a tensile strength of 1,230 MPa (178 ksi) — stronger than 92% of steel grades. Strength varies by condition: see the 10 listed tempers.
Is En25-X easy to machine?
Reasonably — machinability is rated fair (45/100, worse than 65% of steel grades). Machine in the annealed or condition-T state with rigid setups, sharp carbide and generous coolant; above ~340 HB expect reduced speeds and consider grinding for finish features.
Can En25-X be welded?
Not readily — weldability is rated poor (25/100). Weldable only with care: preheat 250–350 °C, low-hydrogen consumables, and immediate post-weld temper below the last tempering temperature; avoid welding on finished Q&T parts.
What surface finishes work on En25-X?
Not anodizable — protect with black oxide, phosphate + oil, hard chrome, zinc or cadmium plating (bake to relieve hydrogen at high strength), or nitride for wear surfaces.
Can En25-X be formed, bent or molded?
Hot forge at 1050–1200 °C then normalize; cold forming is impractical except mild straightening in the annealed condition.
What is the maximum service temperature of En25-X?
En25-X 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 En25-T and En25-Z?
T is the default condition — most commonly stocked hardened-and-tempered band: best balance of strength, toughness and machinability. Z: maximum-strength low-temper condition for special high-stress parts; toughness and machinability are marginal. Yield strength is 700 MPa in T versus 1,330 MPa in Z.
Sources
- BS 970-1: Wrought steels for mechanical and allied engineering purposes (826M31 / En25) — BSI (1996)
- 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)
- 826M31 (En25) Ni-Cr-Mo through-hardening steel bar datasheet — European alloy-steel bar stockholders (2022)
- GB/T 3077 (40CrNiMoA comparable grade) — SAC (2015)
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.