Steel 34CrAlNi7-10 +QT-800 (+QT)
Heat-treated state
EN 34CrAlNi7-10 · also Nitralloy 135
Heavy-section bar and forgings where mass effect lowers the guaranteed core strength.
Values for the +QT-800 condition
Other 34CrAlNi7-10 tempers and conditions
34CrAlNi7-10 is listed in 8 conditions; see the grade overview at 34CrAlNi7-10.
Compare all 8 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
Annealed | Delivery condition for bar/forging stock that will be rough machined and then quenched, tempered and nitrided in-house. | 450 | 720 | 18 | 225 HB | — |
Cold drawn | Precision bar stock with close tolerance and clean surface for small nitrided pins, spindles and valve stems. | 600 | 800 | 11 | 24 HRC | 6.6 % IACS |
Normalized | Grain-refining condition after forging; rarely a final supply state because the alloy air-hardens to a fairly hard bainitic/martensitic structure. | 620 | 950 | 12 | 31 HRC | 6.6 % IACS |
+QT | Very large forged rolls, screws and cylinders where only the reduced strength class can be guaranteed at core. | 620 | 850 | 15 | 26 HRC | 6.6 % IACS |
+QT-800This page +QT | Heavy-section bar and forgings where mass effect lowers the guaranteed core strength. | 680 | 900 | 14 | 29 HRC | 6.6 % IACS |
+QT + nitrocarburized | Short-cycle ferritic nitrocarburizing for anti-scuffing/anti-galling surfaces where a thin, tough compound layer is enough. | 720 | 950 | 12 | 63 HRC | 6.6 % IACS |
+QTDefault Quenched and tempered | Standard stock condition: oil/water quenched and high-temperature tempered core, ready for finish machining and gas nitriding. | 780 | 1,000 | 13 | 33 HRC | — |
+QT + gas nitrided | Final functional condition: Q&T core plus 500–530 °C gas nitriding for maximum surface hardness, wear and bending-fatigue strength. | 780 | 1,000 | 11 | 68 HRC | — |
What is 34CrAlNi7-10 +QT-800?
34CrAlNi7-10 +QT-800 is 34CrAlNi7-10 heat treated to +QT-800 — heavy-section bar and forgings where mass effect lowers the guaranteed core strength. 34CrAlNi7-10 +QT-800 has a yield strength of 680 MPa (98.6 ksi) and a tensile strength of 900 MPa (131 ksi) — stronger than 80% of steel grades. Elongation at break is 14% and the elastic modulus is 210 GPa (30.5 Msi). 34CrAlNi7-10 +QT-800 has a density of 7.8 g/cm³ (0.282 lb/in³), lighter than 87% of steel grades. It melts at 1,400°C (2,552 °F). +QT is the default condition FabDigit quotes; +QT-800 is available on request or by drawing note.
Advantages
- High service temperature — 500°C (932 °F), better than 90% of steel grades
- Polishes to a fine finish — 70/100, better than 87% of steel grades
- High strength — 680 MPa (98.6 ksi), better than 80% of steel grades
Limitations
- Difficult to weld — 12/100, worse than 96% of steel grades
- Poor heat conductor — 33 W/m·K (19.1 BTU/hr·ft·°F), worse than 80% of steel grades
- Low electrical conductivity — 6.6 % IACS, worse than 76% of steel grades
- Limited formability — 24/100, worse than 76% of steel grades
- Limited ductility — 14%, worse than 75% of steel grades
34CrAlNi7-10 +QT-800 properties
Typical room-temperature values for 34CrAlNi7-10 +QT-800; 22 are specific to this condition. Other listed values are 34CrAlNi7-10 reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
34CrAlNi7-10 +QT-800 has a density of 7.8 g/cm³ (0.282 lb/in³), lighter than 87% of steel grades. It melts at 1,400°C (2,552 °F).
Mechanical16
34CrAlNi7-10 +QT-800 has a yield strength of 680 MPa (98.6 ksi) and a tensile strength of 900 MPa (131 ksi) — stronger than 80% of steel grades. Elongation at break is 14% and the elastic modulus is 210 GPa (30.5 Msi).
Thermal6
34CrAlNi7-10 +QT-800 is rated for continuous service to 500°C (932 °F). It conducts heat at 33 W/m·K (19.1 BTU/hr·ft·°F), worse than 80% of steel grades. Thermal expansion is 11.6 µm/m·K (6.44 µin/in·°F).
Electrical3
34CrAlNi7-10 +QT-800 conducts electricity at 6.6 % IACS, worse than 76% of steel grades.
Chemical & Environmental3
Corrosion resistance is poor (16/100), better than 79% of steel grades.
Sustainability4
Producing a kilogram of 34CrAlNi7-10 +QT-800 takes about 31 MJ of energy and emits 2.2 kg of CO₂ — more than 64% of steel grades. Typical recycled content is 25%.
Manufacturability7
34CrAlNi7-10 +QT-800's machinability is fair (48/100, worse than 57% of steel grades); weldability not recommended (12/100); formability poor (24/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with 34CrAlNi7-10 +QT-800
Is 34CrAlNi7-10 easy to machine?
Finish machine in the +QT condition with rigid setups and coated carbide (~90–140 m/min); leave 0.05–0.1 mm grinding stock since the nitrided case is essentially unmachinable except by grinding/lapping.
Can 34CrAlNi7-10 be welded?
Regard as non-weldable — high Al and high hardenability cause cracking and destroy the nitriding response; if unavoidable, use matching filler with 300–350 °C preheat plus full re-Q&T.
Can 34CrAlNi7-10 be formed, bent or molded?
Hot forge 1100→850 °C with slow cooling and mandatory soft anneal; cold forming limited to light straightening of annealed bar.
What surface finishes work on 34CrAlNi7-10?
Stress relieve at ~600–650 °C after rough machining, then gas nitride 500–530 °C for 0.3–0.6 mm case (≥900 HV); finish by grinding/superfinishing, and use oil, phosphate or black-oxide for corrosion protection (no anodizing).
34CrAlNi7-10 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 | 0.3 – 0.37 | 0.34 |
| Si | ≤ 0.4 | 0.25 |
| Mn | 0.4 – 0.7 | 0.55 |
| P | ≤ 0.03 | — |
| Smax; low-S variants for cleanliness | ≤ 0.04 | — |
| Cr | 1.5 – 1.8 | 1.65 |
| Mo | 0.15 – 0.25 | 0.2 |
| Niadded for core toughness/hardenability | 0.85 – 1.15 | 1 |
| Alforms hard AlN in nitrided case | 0.8 – 1.2 | 1 |
| Fe | balance | — |
34CrAlNi7-10 +QT-800 — frequently asked
What is 34CrAlNi7-10 +QT-800 used for?
34CrAlNi7-10 +QT-800 is typically used for gears, crankshafts and high-load pins and bushings. In short: nickel-toughened nitriding steel; best for shock-loaded parts; 500 °C service capability.
What is the yield strength of 34CrAlNi7-10 +QT-800?
34CrAlNi7-10 +QT-800 has a typical yield strength of 680 MPa (98.6 ksi) and a tensile strength of 900 MPa (131 ksi) — stronger than 80% of steel grades. Strength varies by condition: see the 8 listed tempers.
Is 34CrAlNi7-10 +QT-800 easy to machine?
Reasonably — machinability is rated fair (48/100, worse than 57% of steel grades). Finish machine in the +QT condition with rigid setups and coated carbide (~90–140 m/min); leave 0.05–0.1 mm grinding stock since the nitrided case is essentially unmachinable except by grinding/lapping.
Can 34CrAlNi7-10 +QT-800 be welded?
Not readily — weldability is rated not recommended (12/100). Regard as non-weldable — high Al and high hardenability cause cracking and destroy the nitriding response; if unavoidable, use matching filler with 300–350 °C preheat plus full re-Q&T.
What surface finishes work on 34CrAlNi7-10 +QT-800?
Stress relieve at ~600–650 °C after rough machining, then gas nitride 500–530 °C for 0.3–0.6 mm case (≥900 HV); finish by grinding/superfinishing, and use oil, phosphate or black-oxide for corrosion protection (no anodizing).
Can 34CrAlNi7-10 +QT-800 be formed, bent or molded?
Hot forge 1100→850 °C with slow cooling and mandatory soft anneal; cold forming limited to light straightening of annealed bar.
What is the maximum service temperature of 34CrAlNi7-10 +QT-800?
34CrAlNi7-10 +QT-800 is rated for continuous use to about 500°C (932 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
Sources
- EN 10085 — Nitriding steels: technical delivery conditions — CEN (2001)
- DIN 17211 (superseded) — Nitriding steels — DIN (1987)
- ASM Handbook Vol. 4A — Steel Heat Treating Fundamentals and Processes (Nitriding) — ASM International (2013)
- ASM Handbook Vol. 1 — Properties and Selection: Irons, Steels, and High-Performance Alloys — ASM International (1990)
- Nitriding steel bar datasheets (1.8550 / 1.8519 family) — Böhler / Ovako / Lucchini (2022)
- GB/T 3077 — Alloy structural steels (38CrMoAl comparison 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.