Steel P91 · heat-treated state
Steel P91 Q&T
Properties of the Q&T condition, compared with the other P91 tempers.
Used for heavy-wall forgings, valve bodies and thick headers where liquid quenching is needed to get full martensite through-thickness; properties and hardness limits match N&T.
What is P91 Q&T?
P91 Q&T is P91 heat treated to Q&T — used for heavy-wall forgings, valve bodies and thick headers where liquid quenching is needed to get full martensite through-thickness; properties and hardness limits match N&T. P91 Q&T has a yield strength of 520 MPa (75.4 ksi) and a tensile strength of 670 MPa (97.2 ksi) — stronger than 67% of steel grades. Elongation at break is 22% and the elastic modulus is 218 GPa (31.6 Msi). P91 Q&T has a density of 7.77 g/cm³ (0.281 lb/in³), lighter than 92% of steel grades. It melts at 1,450°C (2,642 °F). HR is the default condition FabDigit quotes; Q&T is available on request or by drawing note.
Advantages
- High service temperature — 600°C (1,112 °F), better than 98% of steel grades
- Good corrosion resistance — 30/100, better than 95% of steel grades
- Tough — resists crack growth — 120 MPa·√m (109.2 ksi·√in), better than 80% of steel grades
Limitations
- Poor heat conductor — 26 W/m·K (15 BTU/hr·ft·°F), worse than 86% of steel grades
- High embodied carbon — 2.5 kg CO₂/kg, worse than 82% of steel grades
- Difficult to machine — 38/100, worse than 80% of steel grades
- Limited formability — 20/100, worse than 80% of steel grades
P91 Q&T properties
Typical room-temperature values for P91 Q&T — 10 properties are specific to this condition; the rest are grade-level values shared by every P91 temper. Each bar shows where the value sits among the steel grades in FabDigit's library — further right is higher.
Physical3
P91 Q&T has a density of 7.77 g/cm³ (0.281 lb/in³), lighter than 92% of steel grades. It melts at 1,450°C (2,642 °F).
Mechanical17
P91 Q&T has a yield strength of 520 MPa (75.4 ksi) and a tensile strength of 670 MPa (97.2 ksi) — stronger than 67% of steel grades. Elongation at break is 22% and the elastic modulus is 218 GPa (31.6 Msi).
Thermal6
P91 Q&T is rated for continuous service to 600°C (1,112 °F). It conducts heat at 26 W/m·K (15 BTU/hr·ft·°F), worse than 86% of steel grades. Thermal expansion is 10.9 µm/m·K (6.06 µin/in·°F).
Electrical2
P91 Q&T has an electrical resistivity of 6×10⁻⁷ Ω·m.
Chemical & Environmental2
Corrosion resistance is poor (30/100), better than 95% of steel grades.
Sustainability4
Producing a kilogram of P91 Q&T takes about 34 MJ of energy and emits 2.5 kg of CO₂ — more than 82% of steel grades. Typical recycled content is 30%.
Manufacturability7
P91 Q&T's machinability is fair (38/100, worse than 80% of steel grades); weldability fair (35/100); 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 P91 tempers and conditions
P91 is also supplied in 4 other conditions. The full side-by-side table is on the P91 overview.
- HRDefaultMill intermediate stock only: air-cooled hot-worked material with mixed hard martensite; P91 must be normalized and tempered before it can be used or certified.750 MPa yield · 35 HRC
- NormalizedIntermediate mill/repair condition only — very hard untempered martensite; must be tempered before service or further fabrication.950 MPa yield · 45 HRC
- Q&TUsed for heavy-wall forgings, valve bodies and thick headers where liquid quenching is needed to get full martensite through-thickness; properties and hardness limits match N&T.520 MPa yield · 20 HRC
- N&TThe only ASME/ASTM-acceptable service condition for P91 pipe, tube, forgings and plate — tempered martensite with balanced creep strength, toughness and 190–250 HB hardness.500 MPa yield · 19 HRC
- AnnealedSoftening treatment for heavy machining, cold forming or before re-normalizing; creep strength is not certified in this state.350 MPa yield · 180 HB
Working with P91 Q&T
Is P91 easy to machine?
Machines like ~215 HB low-alloy steel: rigid setups, carbide tooling, moderate speeds and heavy coolant; work-hardens locally and any cold-worked surface should be considered in later heat treatment.
Can P91 be welded?
Requires 200–250 °C preheat, matched 9CrMoV filler, tight interpass control (≤300 °C), cool to below Ms (~80–100 °C) before PWHT, then mandatory 750–780 °C PWHT; type-IV HAZ softening limits long-term creep life.
Can P91 be formed, bent or molded?
Hot form at 950–1150 °C; any hot bending or significant cold work must be followed by full re-normalizing and tempering to restore creep properties.
What surface finishes work on P91?
Not corrosion resistant at ambient — shot blast plus high-temperature aluminium paint, aluminizing or chromizing; no anodizing.
P91 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 |
|---|---|---|
| Ccarbide/carbonitride former, creep strength | 0.08 – 0.12 | 0.1 |
| Si | 0.2 – 0.5 | 0.35 |
| Mn | 0.3 – 0.6 | 0.45 |
| P | ≤ 0.02 | — |
| S | ≤ 0.01 | — |
| Crsteam oxidation resistance | 8 – 9.5 | 8.75 |
| Mosolid-solution creep strength | 0.85 – 1.05 | 0.95 |
| VMX precipitation | 0.18 – 0.25 | 0.21 |
| NbMX precipitation, grain refinement | 0.06 – 0.1 | 0.08 |
| Nnitride strengthening | 0.03 – 0.07 | 0.05 |
| Nimax; limited to keep Ac1 high | ≤ 0.4 | — |
| Almax; excess Al ties up N | ≤ 0.02 | — |
| Ti | ≤ 0.01 | — |
| Zr | ≤ 0.01 | — |
| Fe | balance | — |
P91 Q&T — frequently asked
What is P91 Q&T used for?
P91 Q&T is typically used for main steam piping, boiler headers, superheater and reheater tubing, forged pipe fittings and elbows, thick-wall pressure vessel plate and high-temperature valve and pump bodies. In short: high-temp power-plant pipe.
What is the yield strength of P91 Q&T?
P91 Q&T has a typical yield strength of 520 MPa (75.4 ksi) and a tensile strength of 670 MPa (97.2 ksi) — stronger than 67% of steel grades. Strength varies by condition: see the 5 listed tempers.
Is P91 Q&T easy to machine?
Not especially — machinability is rated fair (38/100, worse than 80% of steel grades). Machines like ~215 HB low-alloy steel: rigid setups, carbide tooling, moderate speeds and heavy coolant; work-hardens locally and any cold-worked surface should be considered in later heat treatment.
Can P91 Q&T be welded?
With care — weldability is rated fair (35/100). Requires 200–250 °C preheat, matched 9CrMoV filler, tight interpass control (≤300 °C), cool to below Ms (~80–100 °C) before PWHT, then mandatory 750–780 °C PWHT; type-IV HAZ softening limits long-term creep life.
What surface finishes work on P91 Q&T?
Not corrosion resistant at ambient — shot blast plus high-temperature aluminium paint, aluminizing or chromizing; no anodizing.
Can P91 Q&T be formed, bent or molded?
Hot form at 950–1150 °C; any hot bending or significant cold work must be followed by full re-normalizing and tempering to restore creep properties.
What is the maximum service temperature of P91 Q&T?
P91 Q&T is rated for continuous use to about 600°C (1,112 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
Can FabDigit make parts in P91 Q&T?
Yes — P91 Q&T 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
- ASTM A335/A335M — Seamless Ferritic Alloy-Steel Pipe for High-Temperature Service (Grade P91) — ASTM (2023)
- ASTM A213/A213M (T91) and A182/A182M (F91) — ASTM (2022)
- EN 10216-2 — Seamless steel tubes for pressure purposes, X10CrMoVNb9-1 (1.4903) — CEN (2020)
- GB/T 5310 — (10Cr9Mo1VNbN) — SAC (2017)
- ASME BPVC Section II Part D — allowable stresses and physical properties — ASME (2023)
- The Grades 91 Steel Handbook / CSEF steel guidelines — EPRI (2015)
- ASM Handbook Vol. 1 — Properties and Selection: Irons, Steels — ASM International (1990)
- Seamless P91/T91 tube datasheets — Vallourec / Tenaris / Sandvik (2022)
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.