Steel 31CrMoV9 · finish state
Steel 31CrMoV9 Q&T+Nitrided
Properties of the Q&T+Nitrided condition, compared with the other 31CrMoV9 tempers.
Final service condition for gears, spindles and extruder screws: hard, wear- and scuff-resistant case on a tough Q&T core with minimal distortion.
What is 31CrMoV9 Q&T+Nitrided?
31CrMoV9 Q&T+Nitrided is 31CrMoV9 supplied in the Q&T+Nitrided condition — final service condition for gears, spindles and extruder screws: hard, wear- and scuff-resistant case on a tough Q&T core with minimal distortion. 31CrMoV9 Q&T+Nitrided has a yield strength of 880 MPa (128 ksi) and a tensile strength of 1,100 MPa (160 ksi) — stronger than 90% of steel grades. Elongation at break is 11% and the elastic modulus is 210 GPa (30.5 Msi). 31CrMoV9 Q&T+Nitrided 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). Q&T is the default condition FabDigit quotes; Q&T+Nitrided is available on request or by drawing note.
Advantages
- High strength — 880 MPa (128 ksi), better than 90% of steel grades
- High service temperature — 500°C (932 °F), better than 90% of steel grades
- Good corrosion resistance — 22/100, better than 89% of steel grades
- Polishes to a fine finish — 70/100, better than 87% of steel grades
Limitations
- Difficult to machine — 8/100, worse than 100% of steel grades
- Limited ductility — 11%, worse than 89% of steel grades
- Difficult to weld — 20/100, worse than 84% of steel grades
- Limited formability — 20/100, worse than 80% of steel grades
31CrMoV9 Q&T+Nitrided properties
Typical room-temperature values for 31CrMoV9 Q&T+Nitrided — 11 properties are specific to this condition; the rest are grade-level values shared by every 31CrMoV9 temper. Each bar shows where the value sits among the steel grades in FabDigit's library — further right is higher.
Physical3
31CrMoV9 Q&T+Nitrided 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
31CrMoV9 Q&T+Nitrided has a yield strength of 880 MPa (128 ksi) and a tensile strength of 1,100 MPa (160 ksi) — stronger than 90% of steel grades. Elongation at break is 11% and the elastic modulus is 210 GPa (30.5 Msi).
Thermal6
31CrMoV9 Q&T+Nitrided is rated for continuous service to 500°C (932 °F). It conducts heat at 36 W/m·K (20.8 BTU/hr·ft·°F), worse than 72% of steel grades. Thermal expansion is 11.8 µm/m·K (6.56 µin/in·°F).
Electrical2
31CrMoV9 Q&T+Nitrided has an electrical resistivity of 2.2×10⁻⁷ Ω·m.
Chemical & Environmental2
Corrosion resistance is poor (22/100), better than 89% of steel grades.
Sustainability4
Producing a kilogram of 31CrMoV9 Q&T+Nitrided takes about 30 MJ of energy and emits 2.3 kg of CO₂ — more than 55% of steel grades. Typical recycled content is 25%.
Manufacturability8
31CrMoV9 Q&T+Nitrided's machinability is not recommended (8/100, worse than 100% of steel grades); weldability poor (20/100); formability poor (20/100).
Values are nominal handbook figures for design screening. Certified mill or lot data ships with every FabDigit order on request.
Other 31CrMoV9 tempers and conditions
31CrMoV9 is also supplied in 7 other conditions. The full side-by-side table is on the 31CrMoV9 overview.
- Q&TDefaultStandard stocked condition: oil/polymer quenched and tempered ~600–680 °C, ready for finish machining and subsequent nitriding.880 MPa yield · 34 HRC
- Q&T d<=16Small-diameter bar fully hardened through section — highest core strength available in this grade.950 MPa yield · 38 HRC
- Q&T+NitridedFinal service condition for gears, spindles and extruder screws: hard, wear- and scuff-resistant case on a tough Q&T core with minimal distortion.880 MPa yield · 65 HRC
- Q&T 40-100Typical shaft/gear-blank section; slightly lower core strength due to reduced quench severity.780 MPa yield · 31 HRC
- Q&T 100-160Heavy forged sections for large screws/barrels where 800–1000 MPa core strength is sufficient.680 MPa yield · 27 HRC
- +APick for rough machining, deep hole drilling or forming before the final quench-and-temper cycle.550 MPa yield · 230 HB
Working with 31CrMoV9 Q&T+Nitrided
Is 31CrMoV9 easy to machine?
Finish machine in the Q&T state with coated carbide, ~80–140 m/min and rigid setups; leave 0.02–0.05 mm for post-nitride lapping/grinding since the nitrided case is essentially unmachinable.
Can 31CrMoV9 be welded?
Poor weldability — 0.3 %C with 2.5 %Cr; if unavoidable, preheat 300–350 °C, use matching low-hydrogen or austenitic filler and temper immediately after welding; never weld nitrided surfaces.
Can 31CrMoV9 be formed, bent or molded?
Hot forge 1050–850 °C with slow cooling, then soft anneal ~680–710 °C; cold forming is impractical above the annealed condition.
What surface finishes work on 31CrMoV9?
Gas or plasma nitride 500–530 °C for 0.25–0.6 mm case (≥800 HV); alternatives are oxide-black, phosphating, hard chrome or QPQ — no anodizing.
31CrMoV9 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 – 0.34 | 0.31 |
| Si | ≤ 0.4 | 0.25 |
| Mn | 0.4 – 0.7 | 0.55 |
| P | ≤ 0.03 | — |
| Smax; lower S for higher toughness/ESR grades | ≤ 0.04 | — |
| Cr | 2.3 – 2.7 | 2.5 |
| Mo | 0.15 – 0.25 | 0.2 |
| V | 0.1 – 0.2 | 0.15 |
| Fe | balance | — |
31CrMoV9 Q&T+Nitrided — frequently asked
What is 31CrMoV9 Q&T+Nitrided used for?
31CrMoV9 Q&T+Nitrided is typically used for nitrided industrial shafts, gear surfaces, extruder screws and barrels, hydraulic piston rods, machine tool spindles and cam and control shafts. In short: high-strength Q&T bar.
What is the yield strength of 31CrMoV9 Q&T+Nitrided?
31CrMoV9 Q&T+Nitrided has a typical yield strength of 880 MPa (128 ksi) and a tensile strength of 1,100 MPa (160 ksi) — stronger than 90% of steel grades. Strength varies by condition: see the 8 listed tempers.
Is 31CrMoV9 Q&T+Nitrided easy to machine?
Not especially — machinability is rated not recommended (8/100, worse than 100% of steel grades). Finish machine in the Q&T state with coated carbide, ~80–140 m/min and rigid setups; leave 0.02–0.05 mm for post-nitride lapping/grinding since the nitrided case is essentially unmachinable.
Can 31CrMoV9 Q&T+Nitrided be welded?
Not readily — weldability is rated poor (20/100). Poor weldability — 0.3 %C with 2.5 %Cr; if unavoidable, preheat 300–350 °C, use matching low-hydrogen or austenitic filler and temper immediately after welding; never weld nitrided surfaces.
What surface finishes work on 31CrMoV9 Q&T+Nitrided?
Gas or plasma nitride 500–530 °C for 0.25–0.6 mm case (≥800 HV); alternatives are oxide-black, phosphating, hard chrome or QPQ — no anodizing.
Can 31CrMoV9 Q&T+Nitrided be formed, bent or molded?
Hot forge 1050–850 °C with slow cooling, then soft anneal ~680–710 °C; cold forming is impractical above the annealed condition.
What is the maximum service temperature of 31CrMoV9 Q&T+Nitrided?
31CrMoV9 Q&T+Nitrided 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.
Can FabDigit make parts in 31CrMoV9 Q&T+Nitrided?
Yes — 31CrMoV9 Q&T+Nitrided is available for CNC machining and sheet metal with instant online pricing. Upload a STEP file to get a price and a DFM check.
Sources
- EN 10085 — Nitriding steels: technical delivery conditions — CEN (2001)
- DIN 17211 (superseded) — Nitriding steels — DIN (1987)
- ASM Handbook Vol. 1 — Properties and Selection: Irons, Steels and High-Performance Alloys — ASM International (1990)
- ASM Handbook Vol. 4A — Steel Heat Treating Fundamentals (nitriding) — ASM International (2013)
- 31CrMoV9 / 1.8519 nitriding steel datasheet — Lucefin / Böhler / Dörrenberg (2021)
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.